I found i had a blown head gasket on my 400 and thats why it wasnt firing on cylinders 4 and 6!!! There was water in the cylinder and im guessing thats why it wouldnt fire!!! About what kind of compression am i looking at if i switched from 76cc(882's) to some 64cc RHS vortecs??? The pistons have 4 small valve reliefs on them if that helps.

Im also thinking about swapping an ISKY 280 mega cam in there to replace the stock one thats currently in there. About how much power should i expect from this combo and will that cam be good for my setup???
400 .o30 over flattops 4-valve reliefs
RHS 64cc Vortecs
Air Gap intake
holley 750 Carb
1 3/4 supercomp headers
Stock 400 rods...im guessing...
stock 400 crank 3.75 stroke
2.5 dual exhaust to turn down flowmasters
I have 3:73 gears out back with 315/40r17's
muncie 4speed

Pleaase go over to the ROSS Racing Piston site and use their CR calculating program to see what CR. you have?

I aLWAYS INPUT A DOWN IN THE HOLE OF .025" FOR FLAT-TOP'S, -5 CC FOR VALVE NOTCH.

pdq67

Sorry, darn caps.

from 10.9:1 up (depending on decking, gasket and how much the pistons sit downt he hole) I used a 0.025 deck clearance, a 0.039" gasket and 6cc for valve reliefs for the 10.89:1. You make anything tighter and the ratio goes up QUICK.

the compression goes up when the quench height goes down but the motor will be more detonation prone with the larger quench (even though the compression is lower) if your motor is zero decked then it will be 11.3 or more unless those are big valve reliefs.

64cc heads with flat top pistons is what I have. You will have to get your exact measurements. You can't just say .025" down in the hole and expect any kind of accurate results.

Off hand, a ballpark guess is that you are between 10.5:1 and 11.5:1.

you'll have to put some cam in there to get the cyl pressure back down to acceptable. a stock cam with 10.5-11.0 compression just won't cut it. bye bye head gaskets. or lots of octane needed. check the block deck for flatness also,, when you check the heads for warp. look for cracks from the bolt holes in the block deck over into the center coolant steam holes also.

My buddy runs 64cc perf RPM heads with flattops zero decked a .041 gasket with herbert 280 cam runs consistant 7.20's on 93 oct

My buddy runs 64cc perf RPM heads with flattops zero decked a .041 gasket with herbert 280 cam runs consistant 7.20's on 93 oct

Is that on a 350? If so it is an apples to oranges comparison. 400s will build more compression with the same cc head, than their smaller cubed counterparts.

Right!!

That's why I said to go over to ROSS's Site!

pdq67

Is that on a 350? If so it is an apples to oranges comparison. 400s will build more compression with the same cc head, than their smaller cubed counterparts.

No a 400 but he also has 3.08 gears and 2500 stall it is a street sleeper very quite exhaust too.

So lets say i put a new set of 882's (supposidly they had some work done to them) in there that i have laying around, and put that 280 mega cam in with them... will the cam perform good in a 400 and about what would my compression be with these 76cc heads and flattops??? I have 3:73 gears with a 4speed if that matters.

there are lots of over 11 to 1 400 motors out there running on pump gas (premium 93/94) and some guys that know what they are doing run more than that . There is tons of info on here about that kind of stuff if you read some of the old posts. A cylinder head with a well designed combustion chamber will be a key ingrediant. those old factory heads are pretty bad chamber wise. The Vortec heads are the first really good factory gen1 heads(that have good chamber design) The 882 heads with the 76cc chambers would work for you but they wont set the world on fire performance wise. with them your compression will be a point or so lower than if you ran 64ish cc heads. which is probably for the best with those heads anyway.

good luck with your project

DJ

No a 400 but he also has 3.08 gears and 2500 stall it is a street sleeper very quite exhaust too.

My buddy runs 64cc perf RPM heads with flattops zero decked a .041 gasket with herbert 280 cam runs consistant 7.20's on 93 oct

7.20 = 11.30 in the 1/4. With a hyd 280* cam, 2500 stall and 3.08 gear.

Right. :rolleyes:

*cough* mwilson *cough*

7.20 = 11.30 in the 1/4. With a hyd 280* cam, 2500 stall and 3.08 gear.

Right. :rolleyes:

*cough* mwilson *cough*
Someone read my mind..............................:rolleyes:

So lets say i put a new set of 882's (supposidly they had some work done to them) in there that i have laying around, and put that 280 mega cam in with them... will the cam perform good in a 400 and about what would my compression be with these 76cc heads and flattops??? I have 3:73 gears with a 4speed if that matters.

Rough estimate would be 10 to 10.5:1. I did that no problem when I first built my engine. Same cam, but stocker iron heads for the 400.

My Sporstman II heads help because they have efficient combustion chambers. The KB piston help because they reflect the heat back into the chambers. I also removed all the sharp edges on my valve reliefs and chambers. That is how I get away with 11:1 no problem.

It will be interesting to see what happens when I add my new roller cam I had ground. Supposedly it will add a lot more cylinder pressure. I will keep everyone posted on the progress. I still need custom pushrods, to figure out what kind of timing cover I want to use, and finally decide if I want to switch my valvetrain over to 7/16". My studs, stud girdles, and rocker arms are 3/8". I am going to have a wicked ramp speed so I am a little nervous.