I'm having one bult right now. It's being set up for a blower. I was talking to a guy at the local speed shop and he said these motors have a bad rod angle? That putting a blower on this would be a bad idea? He's got me a little flusterd. Was wondering if i could get some input from any of you.

They have a low "rod ratio". That is not something I'd worry about though. If you do the calculations on the additional force into the cylinder wall it is very, very small. There is a blancing issue with big small blocks, rod ratio (which I call mental masturbation) and pin height. Too high of a pin height is a real issue especially with the heat you can produce into the piston top with a blown or in my case nitrous motor. I will tell you this as a fact, given the two options, F the rod ratio and keep the pin height down.

Yup you wont be able to use a long rod......you need to get a good size dish with forced induction.

When i bought my Little M block, i wanted to maximize the cubes right away but JE, Ross & Wiseco wouldnt make me a piston for a 6" rod.....they said drop the rod length down & then we'll talk.

-Carm

Rick pretty much nailed it.
Although there is also the factor of ring stability. When the piston pin moves upwards with a long rod it compromises the ring lands. With a long rod 434 the pin moves WAY up there so durability becomes a major issue with cylinder pressures a supercharger can produce. With a really long stroke you can also run into issues were the compression ratio is so inherrently hi that it is a PITA to find a piston/cylinder head combo to get it back down to usable levels.
In general I don't like ultra-strokers for boosted applications for these reasons, but in this case you have already begun.
My best reccomendations:
Keep the rods short (5.7 or 5.65")
Use hi-pressure style piston rings; not conventional molly rings
Use a thermal Coat the piston tops, combustion chambers, and valves to minimize the heat soak into the piston.

what block are you using? Hopefully not a stock 400 block.

Jody

I figure a 434" with an 80 cc head on it if it has -5 cc flat-tops, a .028" thick headgasket and a stock, piston down-in-the-hole of about .025" should only be right at 10.18 to 1 CR...

And some 400's had 80 cc heads on them stock too..

Talk about an unshrouded SB wedge head!!!

A 434" engine is 4.155" b x 4.00" s isn't it??

Is this any help here???

pdq67

Yes it is a worked over stock 400 blk. with forged crank, rods, pistons. I cant aford the motor and blower at the same time. but the motor is being set up for a blower. it will have a 8.5 to 1 CR. I want to put a roots 671 on it later this year. with 7 to 10lbs. of boost.

TopGun, you're playing with fire with regards to a STOCK BLOCK 434" motor & a power adder.

I wouldnt chance it, good luck & take a look at DynoFlo shortblocks they have a good reputation going for them & come with an aftermarket block, fairly inexpensive: http://cgi.ebay.com/ebaymotors/SBC-421-434-shortblock-new-assembled-Small-Block-Chevy_W0QQcmdZViewItemQQcategoryZ33620QQihZ020QQitemZ300081675785QQtcZphoto

Contact these guys & they'll make the necessary changes for your low-compression motor.

I think a better choice all together would be less stroke, a longer rod & a lighter piston.....but thats just my $0.02

-Carm

Ya, save money on the blower and just throw a grenade down the chambers:screwup:

TopGun, you're playing with fire with regards to a STOCK BLOCK 434" motor & a power adder.

I wouldnt chance it, good luck & take a look at DynoFlo shortblocks they have a good reputation going for them & come with an aftermarket block, fairly inexpensive: http://cgi.ebay.com/ebaymotors/SBC-421-434-shortblock-new-assembled-Small-Block-Chevy_W0QQcmdZViewItemQQcategoryZ33620QQihZ020QQitemZ300081675785QQtcZphoto

Contact these guys & they'll make the necessary changes for your low-compression motor.

I think a better choice all together would be less stroke, a longer rod & a lighter piston.....but thats just my $0.02

-Carm

heck, most good engine shops won't do a n/a 434 with the stock block. I think it will be short-lived with a power adder.

Jody

..you are going down the wrong road on several points ,Top Gun.. you need an aftermarket block, shorter rods and a shorter stroke. A blown 434 is not really feasible. I know a shop that specializes in blown big inch small blocks and went down to watch them assemble one a few weeks ago and learn a little on the subject. They refuse to build 420, 427 and 434 and bigger SBC combos. They will not go bigger than 415ci, and even then they are forced to use a 5.7 rod, a custom -33cc dish piston with the pin right up on the bottom ring land, and even with larger chamber 72cc heads, still end up with a compression ratio of 8.35:1. Using the new 76cc AFR heads would get you to 7.99:1. You say you are on a budget, but what you want to build is not a budget motor. You can build a blown BBC with cast iron heads far cheaper and easier and make more power than you will know what to do with.

My advice is if you need to do a big inch blkown SBC is you NEED;
-aftermarket block: Dart or Motown
-keep the bore to 4.125" and use the expensive Cometic MLS gaskets to guarantee a good seal as you wont have a lot of cylinder wall between the bores.
-don't exceed a 3.875 stroke and a 5.7" rod length
-expect to buy expensive custom made forged pistons with a big dish so you can get the compression low enough for a roots blower (roots need lower compression than a centrifugal). The wrist pin will be as high as you want to go for a blower piston.
-all this means that you should keep the build to 415" and expect to pay a lot of money to do it.

A 383 is as big as I would go on a budget blown SBC. I have seen a couple of stock block 400ci blower motors, but that is not recommended either for a couple of reasons. These were very low boost budget motors for street rods.

I can give you the name of the shop that has the big inch blown SBC all scienced out with the custom pistons on the shelf. A short block will run about $7,500 with all the right parts. It will need very good heads to breath. He runs 230cc Dart Pro 1's.

Also, a 6-71 will be a bit small for this motor. You are talking big block territory and an 8-71 is recommended, here

A roots motor build is not the type where you build NA now and add the blower when you get the money. You need such low compression, she will be a dog without the blower. You need to build it right now. My advice if you are on a budget is either build a nice NA 406 or 415, or sell the 400 block and build a proper budget 383 (much cheaper than trying to build the stroker) with adequate parts.