View Full Version : TBI 305 Build:


455 Formula
02-01-2011, 01:45:20 AM
Out here in Kalifornia, we are mandated to use TBI (if the car came with it) so we are planning a buildup on my buddy's 305 once the 331 goes in. He wants to keep the original engine and we have to keep the TBI, so that is what we have to work with.

His 1991 305 is a factory roller motor, so I wanted to ask, how much lift can we get away with on the 305 TBI heads????

I found quite a few spring sets that give a higher installed height, but I wanted to ask you guru's before we order ANYTHING.

The cam I am looking at is a Comp XFI Roller that is designed for the '87 up factory roller applications, buut its .560"/.555" lift seems like more than the stock retainer to guide clearance will allow.

We will likely do some tuning when this 305 is donw, so we have a little freedom on the cam.

Any advice from Chevy Guru's would be welcome!!!!!

80 camaro CJ
02-01-2011, 01:50:14 AM
ive heard vortec heads and LT1 cam but 99% of the time ppl say dont waste the time on the TBI its useless after 4500 unless you do some major moding to the TB itself

BondoSpecial
02-01-2011, 01:50:58 AM
That 305 has the swirl ramp heads (the 350 swirlies were '193, IIRC the 305 version is '191 casting #) that most people won't touch with a ten foot pole from what I've read over on third gen.org...the swirl ramp heads having better than average exhaust ports but very very poor intake flow, like 175 cfms...that build is another great candidate for 081 heads!! lol. I think you'd be the first person to run that much lift with TBI swirl ramp heads ever, I dont think those heads will benefit from that kind of lift

455 Formula
02-01-2011, 02:12:59 AM
I agree...I have read that too.

My buddy wants to keep the stock heads. Wouldn't '081' chambers be too large???? Do they have an exhaust crossover????

We are facing many restrictions from the smog man, so we have to use less than ideal stuff....:mad:

Kamikaze
02-01-2011, 02:25:33 AM
Steven beat me to the punch regarding the swirl ramp chamber heads.
Get rid of those and replace them with at least a set of S/R Torqers or Edelbrock Performer Centerbolts and the valve lift is no longer an issue!
Also adding the Edelbrock Performer TBI intake with the torque tubes will increase the mid to upper rpm torque range and allow the engine to pull as well as rev.

Get the TBI modded by Tom Miller's Turbo City and up the pressure regulator, install an injector spacer and also get a small throttle body spacer. Modify the stock air filter base with a short velocity stack and remove the silencer assembly on the inside. I can't remember who we got the device from but there is a TPS interface and a MAP sensor adjustment that gives you much more responsive throttle throughout the rpm range.

There are many reasonable hydraulic roller cams that will allow you to pass smog while increasing the performance of the little 305. Match them to your heads and gearing!

Exhaust is the single best thing you can do but you can also go too far! Believe it or not, most mildly modified TBI engines run well with small smog legal tube headers into a single 3" high flow cat with a good flowing muffler. You could run Flowtech's Terminator Muffler with a single 3" inlet and dual 2-1/2" outs and have a nice aggressive sound without to harsh resonance.

BondoSpecial
02-01-2011, 12:36:18 PM
Wouldn't '081' chambers be too large???? Do they have an exhaust crossover????


No, 081s are 58cc chambers. All of these heads have exhaust cross overs

retorq
02-01-2011, 02:18:28 PM
Simple solution: move.

Damon
02-01-2011, 07:32:11 PM
Plenty of guys have put a little extra umph in a TBI engine. The cam is the biggest restriction inside the engine. Outside the engine the biggest restriction is the entire factory exhaust system from the manifolds back.

You know how to fix the exhaust problem (shorties, good flowing exhaust behind them).

The cam is really in need of upgrading. It's called the "peanut cam" over on Thirdgen.org becuase of it's itsy-bitsy specs. 179/191* @ .050 with lift well below .400" on both valves. A stock factory TPI or later model LT1 cam is a popular upgrade and can get you quite a bit of power, even with the stock heads, while remaining computer-friendly. (Max lift on TBI heads is in the .450-.460" range before the retainers hit the guide seals.) This does not mean that tuning isn't required- it is, even on a dead-stock TBI engine to extract the most power.

If you want to get fancy you can replace the factory intake with an Edelbrock TBI intake. Or use an entry-level dual plane carburetor intake with a home-built adapter plate on top. Either is worth some ponies.

Cam, exhaust and tuning is probably a good 40HP over stock. Just about anything you do to a TBI engine will make more power IF you tune to match it. The factory system is NOT forgiving of even modest changes in the engine's basic breathing characteristics, hence the need to stay on top of the tune.

455 Formula
02-01-2011, 08:33:28 PM
I appreciate the advice. We are looking at this from several different angles and the prospect replacement heads doesn't seem to bother my buddy like I thought it would. The Edelbrock TBI intake sounds like a good investment too.

I just penciled him out an exhaust system that features a 3.00" pipe right off the cat into a Magnaflow straight-through, curving outward and exiting right in front of the RR wheel with a flat section of 3.00" pipe with a stainless tip.

I have used the S/R Torquers on other people's 305's and felt they were really great heads.....

455 Formula
02-01-2011, 08:36:05 PM
On the bottom end we are planning on a set of KB Hupereutectic Flat Tops, Zero-Decked with Total Seal gapless Rings.

1972L
02-01-2011, 08:41:58 PM
Here's some info, that may be of some help. Many are quick to dis the swirlies, but my perspective is from a been there, done that angle.

If your friend in going to use his truck, like a truck, I recommend using the stock swirlies. Match it with a L98 or a Vortec roller to make great low end torque and get decent economy. I put together a 5.7 flattop motor with the 193 swirlies ported like the ones below with a GM L98 roller. (I ported one and then cut in half to get an idea of how much meat there was). I dropped this into TBI K1500 project truck last year and it runs much better than stock, while retaining the Fuel Milage of the stock engine. Lots of low end grunt to pull, and enough "go" to piss the F-250 diesel guys off.

Years ago I compared ported swirlies with Bowl ported Iron L98's and a set of Bowl ported World S/R's on a flat top 350 on a carbed C10. There wasn't much difference between all three. The swirlies pulled good till 5000+ given the same vehicle/weight/drivetrain/induction etc... The 193's do have better exhaust flow numbers than the others. There's plenty of documentation at TGO on these. http://www.thirdgen.org/techboard/tech-general-engine/450116-tpi-305-swirl-port.html

Sure there are better heads out there, but with a little elbow grease you can save some coin for other stuff.

The ported swirlies may not light the world on fire, but neither will the TBI, but it may be the most trouble free, reliable build you will ever do. On a side note, my buddy just put in a 5.7 flatop motor with a set of Iron L98's. His truck has 3.73's and is 2 wheel drive). He beats me by a truck length to 70 (mine is 4x4 with 32" tires and 3.42 gears).


http://i857.photobucket.com/albums/ab138/Billy-Biscayne/022.jpg
http://i857.photobucket.com/albums/ab138/Billy-Biscayne/007.jpg
http://i857.photobucket.com/albums/ab138/Billy-Biscayne/024.jpg

These headers will bolt to the factory "Y" pipe. You can get them for about $130 on eBay.
http://i.ebayimg.com/02/!CEC,0ygB2k~$(KGrHqN,!hME0fW2M36rBNQj!cM8ww~~0_12.JPG

455 Formula
02-01-2011, 09:26:42 PM
Man!!!!!

Those are California smog legal headers?????

455 Formula
02-01-2011, 09:28:35 PM
Here's some info, that may be of some help. Many are quick to dis the swirlies, but my perspective is from a been there, done that angle.

Yep, he tows with it...doubt it will ever see over 4400 rpm!!!!!

So, basically, you are knocking out the 'finger' hanging down from the roof of the port?????

GoldenOne7710
02-01-2011, 10:27:56 PM
Also adding the Edelbrock Performer TBI intake with the torque tubes will increase the mid to upper rpm torque range and allow the engine to pull as well as rev.

Get the TBI modded by Tom Miller's Turbo City and up the pressure regulator, install an injector spacer and also get a small throttle body spacer. Modify the stock air filter base with a short velocity stack and remove the silencer assembly on the inside. I can't remember who we got the device from but there is a TPS interface and a MAP sensor adjustment that gives you much more responsive throttle throughout the rpm range.


Agree 100% with this.....especially the intake upgrade. Take the stock intake off and throw it in the nearest lake. They flow air like a coffee straw. The Edelbrock is about the best you can do to stay within your emissions regulations.

Another good tip (if funds allow) is to upgrade the injectors. You can use injectors from a ~'91 Chevrolet 1500 SS (7.4L engine) that will help better supply anything producing more power than stock.

1972L
02-02-2011, 12:18:19 AM
The stock intake will run fine on a 305.
Bolt on the throttle body without a gasket and make sure the intake bores are machined to match the TB (mine needed some work) Radius the transition at the bottom of the bores as this makes an abrupt 90* turn. Make sure the ports are reasonably compatible with the heads. Clean the EGR passages, you may have to remove the plugs to get all the crud out. Use an Delco EGR valve, if you wish to retain MPG's on the Highway.

The 454 injecters run fat on a 383.....

As long as you don't go too wild the stock injectors will work fine, just bump up the fuel pressure. For every 1 psi increase is like 2 Lbs/hr per injector.

A low buck way to do the injector spacer is to get a TBI rebuild kit from Autozone (you will need the O-rings, gaskets and fuel screens anyway). It has two (2) injector pod gaskets. Adding a second one will raise the pod approx 1/8". Just enough as not to bind the fuel fitting entensions. The kit is about $28. I have the part # in the garage if you need it. Raisng the pod too much will cause bogging at tip in.

The "salad bowl" trick may not be needed on a 305 air cleaner housing. A Flat base 14" open element will work well with a TALL element. I eliminated the hot air stove flap and closed the hole in the snorkel (I live in Florida, it's probably 75 degress outside now) I have retained the stock housing and plumbing to the fender due to off road concerns (water) and to keep the engine from sucking hot azz South Florida underhood air in the Summertime.
The silencer on the fender is very restrictive. A Sawzall with a long blade did the trick to remove the "guts". (4 cuts, 90* apart, remove guts with long needlenose pliers). I do "flip the lid" for around town driving, just that is worth 10hp on a 5.7 or so it feels.

On the heads, all you want to do is smooth out the throat, don't shorten the vane, just clean it up from the edge to the wall. A 1/2 round nose carbide burr will do the trick. I had the seats cut in a Serdi, not ground with a cavemans rock. Add a 30* cut to the backside of the exhaust valves and you are good to go.
I think(?) I used the 943X valve springs on this build. I had New GM LT1 valves (1995 LT1) laying around so in they went. Don't forget the factory oil splash cups that go under the retainers. Your stock valves are about 20 years old, you might look at something like these. http://cgi.ebay.com/ebaymotors/Stainless-1-5-1-94-Valves-Z28-Springs-Chevy-sb-sbc-_W0QQcmdZViewItemQQhashZitem2eb26cf23dQQitemZ200561979965QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories


The L98 cam has a bit more duration than the Vortec cam, but not as much lift. I went with the L98 cam because I had it. Stock GM lifters and pushrods will do just fine. I did use an LT4 single roller timing chain (GM). Some of the aftermarket double rollers are or get noisy after 10,000 miles and that noise may be picked up by the knock sensor as detonation and retard timing so I have been told.

An S10 or Corvette converter with a higher stall will get you moving off the line and still retain lockup. Daaco Remans are about $90, depending on who you know. (you are going to have the engine out anyway). Make sure the flexplate holes align "before" you install the engine. A cooler is a must if you want the tranny to live.

I have the part number for the .431 mellonized distributor gear that must be run with a GM steel roller. The stock iron gear will disintigrate within 2000 miles. Slather it in Dow Corning GN Metal Assembly paste and do the Distributor gear on the cam also "before" installing the cam.

These trucks are a breeze to work on. Make sure you have a power steering puller/installer before you get started. Other than the TBI, the rest is standard GM with the Metric/SAE bolts included for fun.

1972L
02-02-2011, 01:04:47 AM
While not the timing chain I used, here's an alternative that will work fine in a TBI truck. Summit has these for $56

From GM:

12371043 - Timing Chain Kit "Single Roller Design"





This special performance single roller design timing chain kit can be used on all 1987 and newer small block engines with roller lifter camshaft, except LT1, LT4, and 1997 and later LS1. This kit is quieter than the double roller chain. This kit includes the following components: camshaft sprocket P/N 12552129, crankshaft sprocket P/N 14088784, chain P/N 14088783, retainer P/N 10168501, retainer P/N 10088128, three bolts P/N 9424877, and two bolts P/N 14093637. Use these components for single service requirements. They will not work on flat tappet camshafts.





Copyright 2000 General Motors Corporation.

BondoSpecial
02-02-2011, 01:14:27 AM
Man!!!!!

Those are California smog legal headers?????

Hmmmm....will have to look into these. They have no smog tubes though so there is no way they are emissions legal.

1972L
02-02-2011, 01:35:11 AM
Hmmmm....will have to look into these. They have no smog tubes though so there is no way they are emissions legal.

They do come with a chickenpoop heat riser that clamps on to the front tube on the Pass side. My truck did not come with the A.I.R. pump or plumbing from the factory.

The trick here is that they will bolt to the stock "Y" pipe and can be removed/replaced if you have to go to the sniffer. The flanges are very thick but I had to do some elongating on the head side flange to get em to fit. Probably 45 minutes worth on the Pass side, and 30 minutes on the drivers side. These are Stainless Steel and a pain too grind. Test fit them to each head before getting the engine in the truck.

Spark plug access is a pain on #5 and #6 but plugs should last 25,000+ plus on these trucks. I used Remflex gaskets, and in doing so it moved the flanges outboard enough to where the stock Y would not fit. I could have spread them apart with the Porta-Power, but I opted to add a coupling to the drivers side crossover.

If you have ever seen the center pair of exhaust posts on a TBI exhaust manifold, you will appreciate these headers. (the center ports dump into one big hole on a TBI exhaust manifold, unlike a standard SBC exhaust manifold where you have a little bit of seperation)

BondoSpecial
02-02-2011, 01:41:16 AM
I don't have emissions inspections but I am keeping functional AIR just for the sake of clean running. I'd weld AIR trees onto a set of these but it would make them a lot uglier!! Something to think about though.

1972L
02-02-2011, 01:43:43 AM
I used GM cam #10066049
The factory 5.7 Vortec roller should work well in a 305

Here's a list of GM parts numbers and specs should you decide to go with a GM cam. Don't waste your $$$ on anything under .400" lift

http://www.gmtips.com/3rd-degree/dox/tips/cams/cams.htm

1972L
02-02-2011, 01:45:45 AM
I don't have emissions inspections but I am keeping functional AIR just for the sake of clean running. I'd weld AIR trees onto a set of these but it would make them a lot uglier!! Something to think about though.

Inject the A.I.R. into the "Y" for a clean look and clean burn

455 Formula
02-02-2011, 02:18:36 AM
Hmmmm....will have to look into these. They have no smog tubes though so there is no way they are emissions legal.

In California, the 1991 C1500 305 did not have an air pump.....

455 Formula
02-02-2011, 12:43:41 PM
Any idea where we could find some flow numbers for the 305 swirl port heads???? I would like to run it through my Dyno 2000 program......

455 Formula
02-02-2011, 12:45:30 PM
While not the timing chain I used, here's an alternative that will work fine in a TBI truck. Summit has these for $56

From GM:

12371043 - Timing Chain Kit "Single Roller Design"


Thanks!!!!

BondoSpecial
02-02-2011, 02:29:09 PM
http://www.thirdgen.org/techboard/tbi/336750-tbi-tpi-heads-headflow.html

187 iron LO3 head: 165 intake; 140 exh (Fast355)
193 head: @0.500: 178.9 cfm intake 146.8 cfm exhast, stock heads from a 1995 Tahoe 350
081 iron head: 195 intake; 110 exh (ME Leigh)

http://www.thirdgen.org/techboard/tbi/177465-perfect-cam-swirl-port.html

What casting # does the 305 truck have, I thought the 305 truck was a 191? You should be somewhere in the mid 160s-low 170's intake @ .500" with a 305 swirl head based on the above....

455 Formula
02-02-2011, 03:10:45 PM
Steve,

It's still in the truck, so I have no ide what the casting numbers are. Thanks for the info!!!!!

BondoSpecial
02-03-2011, 01:40:11 AM
I just bought these on ebay tonight. I had a $10 ebay coupon so they came out to $129 to my door. For stainless headers that will bolt to the stock Y pipe (thanks for the tips 1972L I wouldn't have thought to look for these)...

I will just omit the AIR injection, the TPI setup I am running from a 1989 F-car has provisions for a 3 way selecter/diverter and I do have all the parts for those valves (purge/manifolds/cat are the 3 positions of the selecter/diverter, controlled by the ECM) but my truck has a new 2 way cat on it that does not have an AIR injection port, and I know the F car setup only injected air up to the manifolds for cold startup. So I think my non emissions but still multiport EFI and catted truck should run cleaner than most modified old v8s (and cleaner than the un tuned speed density TBI 327 ran with a small cam)

I'll take pics when I install these headers shortly

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=180619863266

1972L
02-03-2011, 01:35:49 PM
Here's a few more tips:

Test fit the headers to an old head, on your work bench.
The mounting holes on #5 and #6 may have to tweaked.

Get some Remflex gaskets, and throw the ones included in the box away. You may have to spread the "Y" or add a coupling, as I did. I suppose you have a favorite brand, as does everyone, but I'll use the Remflex's till something better comes along.

I opted for SAE collector bolts and doudle nutted em, I suppose you could get longer bolts and use the OEM springs if you wanted to. The included Stainless bolts seemed a little under size (diameter) for my preference.

An Autolite A6 spark plug fits in the Drivers side O2 sensor hole if you need to plug it. (cheap/quick/easy break off the porcelin and mig weld the remaining hole if you wish, now you have a "plug" that comes with a crush washer that will not leak for the low price of $1.99 and some elbow grease)

I gave the (included) 6 point header bolts away, they are stainless steel, but have a 10mm head. I opted for 12 point bolts with a 3/8" head. I have an assortment of bent/welded/tweaked wrenches that I use for headers.

The included spacer for the PS pump is thin, I was going to spin out another on the Lathe, but found that a Craftsman 9/16" short socket was the perfect length for my application, while using the OEM manifold bolt.

I was impressed with the thickness of the flanges on those headers, just what a truck header needs.

let me know what you think.

BondoSpecial
02-03-2011, 01:40:03 PM
Thanks for the tips. I actually have 2 o2 sensors, one for the NB o2 for the ECM and one for a wideband controller so the o2 port, I definitely need haha. My other o2 port is on the Y pipe. I am going to use springs and probably longer bolts like you said, for the y pipe ball and socket connections. For headers like this I might just use ultra copper around the port opening and no gaskets. If the flanges are nice and thick I will probably get away with it.

They have already sent me a Fedex tracking # for the headers so I should have them by early next week

How is it that I started reading someone else's truck build thread and that caused me to find good ideas and spend more money on my POS truck? It's dangerous coming on this board because I get so many ideas on here!

firechicken81
02-03-2011, 01:59:42 PM
Hey 1972L, I just put a set of headers on my 1992 chevy truck and the gaskets are crap. Do you have the part number for the Remflex gaskets on hand?

455 Formula
02-03-2011, 06:53:16 PM
Those headers are nice. Just confirming, they would fit my buddy's 1991 Truck????

Would the 305 TBI heads nbenefit from 2.02" x 1.60" valves like other SBC heads???? Or, does the small chamber limit your valve size?????

BondoSpecial
02-03-2011, 07:02:26 PM
I don't think a 2.02 will clear the 305 bore honestly. But a 305 with 2.02 valves in a truck....why man, why!!! Being that it's just a 305 and it will still be TBI I don't think the 1.84/1.5 valve size is what's holding you back...look at the flow #s people got from the 081 TPI head still with 1.84/1.5 valves from thirdgen.org from one of the links I posted the other day. Also the mopar 360 heads usually came with 1.88 intake valves and guys made big power with those. I have no science or flow bench data to prove or disprove anything but I can't see putting big valves in a 305, TBI, truck. That thing will never be running at high rpms, these trucks lug around below 4,000 rpms most of the time unless you have messed with the governor or are running a manual trans and wailing on it.

455 Formula
02-03-2011, 08:12:12 PM
Sorry for all the questions.....I am just looking at making the 305 truck TBI motor the best I can do and since I can do the seats, and have the valves on the shelf, it's a low-dollar swap.

BondoSpecial
02-03-2011, 10:34:33 PM
I think 2.02s are out of the question, I think the biggest valves you can run in that 305 will be 1.94s (check me on that but I recall that being the case from reading on TGO)...but even so, if you take those 175 cfm heads and put bigger valves in but they are still swirl port truck heads, still on a 305 TBI heavy vehicle, I can't see that as added value. How about some 305 vortec heads just as a drop on with a fresh valve job?

1972L
02-03-2011, 10:35:25 PM
Hey 1972L, I just put a set of headers on my 1992 chevy truck and the gaskets are crap. Do you have the part number for the Remflex gaskets on hand?

You won't find remflex at Summit or Jegs.....


You can use the RF2006 for a stock TBI head
http://catalog.remflex.com/CHEVROLET_GM_CHEVY_Header_Exhaust_Manifold_Gasket_p/rf2006.htm

The RF2016 is a little thicker
http://catalog.remflex.com/CHEVROLET_GM_CHEVY_Header_Exhaust_Manifold_Gasket_p/rf2016.htm

Here's a list of off the shelf stuff
http://catalog.remflex.com/pindex.asp

Amazon has the best prices

Damon
02-03-2011, 10:48:05 PM
2.02 valves won't work. They hit the bore as soon as they clear the chamber (about .420" lift) and are badly shrouded all the way up to that point.

Stock 305 swirl port heads have 1.84" intakes and they're plenty big given the oddball swirl-type ports behind them. Basic pocket porting and a good performance valve job helps those heads considerably, just like older style heads. And given the unique ports that are behind the intake valves in swirlie heads I wouldn't risk ANY change in valves size. No telling what the real wrold results would be. Just as likely to make things worse as you are to make them better.

The GOOD news about swirl port heads is that they actually have a decent exhaust port. About the equal of factory Vortec heads (they flow in the ~150-160 range stock). With further improvements possible from a simple performace valve job, pocket porting and back-cutting the valve.

455 Formula
02-03-2011, 10:58:31 PM
Is it true that these heads prefer a single pattern camshaft????? We have used camshafts with less exhaust duration on BBC's, but that was due to a very different exhaust port.

Damon
02-03-2011, 11:09:06 PM
I don't know exactly how much "split" would be optimal based on my limited experience with those heads. However, traditional head/cam theory would suggest that a single pattern cam should be well suited to those kind of heads. I mean, you're pushing up against an 80% I/E flow ratio, it's just that you're getting there in a weird kinda way (being intake restricted rather than becuase of a phenomenal flowing exhaust port).

I don't think you're going to see much difference in power between a single pattern cam or one with 4* of split, 6* of split or maybe even a little more than that. I seriously doubt you would need anything like a factory ZZ4 cam that's got a huge 14* split, however.

455 Formula
02-03-2011, 11:10:32 PM
I really appreciate all the SBC knowledge!!!!!!

1972L
02-03-2011, 11:29:51 PM
Those headers are nice. Just confirming, they would fit my buddy's 1991 Truck????

Would the 305 TBI heads nbenefit from 2.02" x 1.60" valves like other SBC heads???? Or, does the small chamber limit your valve size?????

The headers fit my 89 4x4
the same headers fit my buddies 94 4x2

I went with a Thorley/Jardine (single) cat back for the 93/94 due to the two bolt flange to the "Y" pipe for ease of installation/removal should I have any tranny/transfer case issues. This guy still has the dual exhaust for cheap (I had to call for the single)
http://cgi.ebay.com/ebaymotors/Chevy-sc-sbed-94-95-5-7-exhaust-Doug-Thorley-_W0QQcmdZViewItemQQhashZitem19bbd0de16QQitemZ110525210134QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

http://i.ebayimg.com/14/!B2Z0Bsw!2k~$(KGrHqJ,!iQE)qsnVFu8BMiVBKN3Fg~~_12.JPG

I did have to fab some hangers out of 1/2" steel rod and some 1/4" steel plate. The OEM 93/94 cat backs use steel rods welded to the tubes to hang the pipes unlike the 88-92's The rubber hangers make installation/removal a breeze. Note the steel hanger rods and the two bolt flange that bolt to the "y" in the above pic.

http://i.ebayimg.com/18/!B+8ZGEg!Wk~$(KGrHqJ,!g4Ezd9iqNZ4BNBREihcgw~~_12.JPG

The "Y" is a high flow unit from Magnaflow
It has the 02 bung before the cat if you need a place for a wideband O2 or to install a heated 02 sensor like the 93/94's. While purportedly not for sale in California, I got mine from Pac Audio (in California) cheaper than Amazon. (amazon has the pic showing the 2 bolt outlet flange/ the same unit fits the 2wd)
http://www.amazon.com/MagnaFlow-23256-Catalytic-Converter-compliant/dp/B000JKLEGA

Just get OEM size valves,
Tight guides and a good valve seat are the manditory.
There are plenty of pics of the porting work that needs to be done on the web
No need to go overboard, it's a 305 that ain't gonna spin 7000 rpm.

BondoSpecial
02-07-2011, 02:53:44 AM
I pulled the 350 TBI manifolds tonight and noticed that they do have a divided center trunk, it is not one open center trunk like was posted above. Here is a pic comparing the 350 TBI manifold to a 1989 Firebird 305 GTA exhaust manifold. Both have divided center trunks for the 2 middle ports. Headers should be here weds...I just took a pic showing the manifolds b/c of mention that the center would be wide open. These are 88 TBI manifolds, not sure if the non AIR injection trucks had different manifolds (being GM i would think it's the same manifold just not tapped for that front AIR injector but I don't know)

http://bondospecial.smugmug.com/1988-Chevy-K1500/More-TPI-work/sunday-feb-7-TPI-013/1179993430_fhx9W-XL.jpg

1972L
02-07-2011, 01:23:36 PM
The center exhaust ports have a divider, but it only extends about 3/4" to 1" into the TBI manifolds. How far down does it extend on those?

BondoSpecial
02-07-2011, 02:49:49 PM
Ah I misunderstood I was expecting a wide open center port. Both the TPI and TBI manifolds have that splitter like you said, 3/4" to 1" in. Not that I would ever use them but it looks like the TPI manifold is even worse than the TBI one from my pic...it's even more of a log with no runners at all for each individual cylinder.

1972L
02-07-2011, 08:54:41 PM
This will be my next project. This will replace the spacer ring between the throttle body and the air cleaner and be welded to the oem air cleaner housing. It will take a little work but it's much easier than using a salad bowl.

http://i.ebayimg.com/19/!CE,9I+w!mk~$(KGrHqV,!g0E0eoM+HssBNRz1bbJ8Q~~_12.JPG

I suppose I could have spent $50 and got a powercharger from summit, but it would still take just as much work.
http://www.summitracing.com/parts/HYP-4001

f-body
02-10-2011, 03:18:13 AM
This will be my next project. This will replace the spacer ring between the throttle body and the air cleaner and be welded to the oem air cleaner housing. It will take a little work but it's much easier than using a salad bowl.

http://i.ebayimg.com/19/!CE,9I+w!mk~$(KGrHqV,!g0E0eoM+HssBNRz1bbJ8Q~~_12.JPG

I suppose I could have spent $50 and got a powercharger from summit, but it would still take just as much work.
http://www.summitracing.com/parts/HYP-4001


Where did you find the bowl. I looked for a salad bowl and could not find the right size. A couple of xmass's ago i got a gift certificate to Orileys for $50 and bought the powercharger soup bowl.

f-body
02-10-2011, 03:21:02 AM
Out here in Kalifornia, we are mandated to use TBI (if the car came with it) so we are planning a buildup on my buddy's 305 once the 331 goes in. He wants to keep the original engine and we have to keep the TBI, so that is what we have to work with.

His 1991 305 is a factory roller motor, so I wanted to ask, how much lift can we get away with on the 305 TBI heads????

I found quite a few spring sets that give a higher installed height, but I wanted to ask you guru's before we order ANYTHING.

The cam I am looking at is a Comp XFI Roller that is designed for the '87 up factory roller applications, buut its .560"/.555" lift seems like more than the stock retainer to guide clearance will allow.

We will likely do some tuning when this 305 is donw, so we have a little freedom on the cam.

Any advice from Chevy Guru's would be welcome!!!!!


You could look at http://www.dynamicefi.com/ for ecm upgrades. They sell modded GM ecm's that are fully programable. You could have an emissions tune to pass and a max tune for full power. This would wake up your TBI setup. Just a suggestion.

1972L
02-10-2011, 09:52:19 AM
I got the bowl from ebay, it's for some sort of handheld food processer. I'll post some pics when I proceed with that project.

The EBL is the way to fly if you have the $$$ and time.It's been on my wish ist for a while now. I was on track to do this but I've suffered a few minor (medical) setbacks.

The truck runs fine now, but I know it could run better with some ECM tweaking. I may get one of Harris's off the shelf TBI chips and call it a day. I have way too much other stuff going on to spend too much time on this project. I do need to get data logging though.

BondoSpecial
02-10-2011, 11:24:42 AM
I got the $99 special C/K 1500 stainless headers last night and installed them. They actually are made and fit pretty well for no name parts, and the flanges are SUPER thick which was good to see. The port size is oval and huge which I have been seeing on a lot of headers lately for SBC and it annoys me because no SBC has an exh. port anywhere near this shape or size....and that leaves almost no gasket surface area actually sealing against a stock head if you use oval gaskets provided with the headers. I used 1.5" round header gaskets I had instead and I'm still not a big fan of the oval header flanges. One out of the 8 ports on the headers was so large that it was close to breaking into the bolt hole and didn't leave much room for the gasket so I ran a weld bead around it to build it up and then filed it back down, you can see that in my pics. Other than that little tweak, they fit the stock Y pipe fine and the headers look super nice, too nice for my truck actually. If they end up leaking at the flanges these headers were so easy to install I will take them back out and run a fat weld bead around the inside of every port opening such that I have 1 5/8" round holes on center with the head ports, and run the flanges on a belt sander to knock them back down perfectly flat. Oh I also did have to clean up the port match on the headers with some carbides, you can see in my pics where I marked them up compared to their own oval gaskets that I ended up not using, how bad the mismatch was on one of the middle ports for each header. The mismatch wasn't quite that bad using the smaller 1.5" round gasket as a template so I didn't take as much off as you'd think but some was necessary.

Me photo album:

http://bondospecial.smugmug.com/1988-Chevy-K1500/Headers-and-serpentine/15777991_qhoLY#1183359074_dzads


Ignore the TBI unit loosely sitting on top of the TPI intake, I left that there so I don't have to leave the fuel lines open and fumigating my garage until I'm ready to hook up the new AN lines I'm trying to figure out.

1972L
02-10-2011, 08:44:21 PM
I'm glad to see the headers worked out for you.
I told you they were gonna need a little tweaking, but I think that's a given with 99.9% of exhaust related components.
After a year they'll turn a grayish color, but mine don't have any signs of rust or corrosion depite the Mud and water they've been through.

I can actually get to the wires on my starter solenoid, from the Top. Anyone that's worked on these trucks, knows that's a Plus.