355 w/ vortec heads

well this is the layout for my 355 build... im trying to figure out how much will it push roughly

355 block 010 nickel
new vortec heads 1.94/1.5
comp's 981 springs
comp's 1417 roller rockers
comp's sk12-238-2 lift@.050 218/224, lift .462/.469
speed pro 4.03, 5cc, coated
headers 1 1/2" primary tube
performer rpm intake edel
650cfm carb edel or 750cfm (i have both)

the car is a 1981 parisienne b-body coupe with a stock th250c and stock differential

any advice on parts is welcomed as well


Register now (free) or login to remove ads

Ditch the THM250 or it will ditch you

Otherwise it looks really nice.

i will and i know i will have to go easy with it... until i get a th350 in there

We did one a few years ago and we cut the Vortec heads for 10:5 comp. and used 6 inch rods and the engine dynoed 432 horse and 460 on the torque.

Make sure your not using the Mexican casting as they will hurt you on air flow.

With that small of cam a 750 will do nothing for you.

If you are not running a zero deck block or the heads have not been cut you may want to go with a cam that would be in the 226 @ .050 single pattern on a 108 to build some dynamic cylinder pressure which will help with torque and HP.

the heads are 062 don't know where they are made and don't think it has been decked (how would i check) but will a single pattern cam kick up the compression... i don't want more than ~10.5:1

You will be under 10:01 of the block has not been decked, Single pattern cams have less overlap and I don't know what your lobe sep. is but a tighter lobe sep. will make more dynamic pressure as well.

What is the ADV duration of your cam and Lobe sep, and what your duration at .200

ADV INT: 262
ADV EXH: 270
.050 INT: 218
.050 EXH: 224
LSA: 110
Factory rocker lift INT: 0.462in
Factory rocker lift EXH: 0.469in
RPM range: 1300-5600
Lobe lift: .308int/.313exh

i cant seem to find the duration more than the one advertised

Your cam is a little small for a true 10:1 compression. It will need to be tuned perfectly on pump premium. Going up a little on the cam or down a little on compression will give you a little more wiggle room if you just want to "set it and forget it" as far as tuning goes. And single pattern cams usually make more torque, but when you increase the intake duration you usually loose low end torque, so if that's what your after decrease the exhaust duration.

A 226 cam would be a good match for that compression though, and then maybe step up the stall a hair. Maybe better gears (depending on what you have).

Also, you MAY be over 10:1 depending on your actual deck clearance, gasket thickness, piston volume, and chamber volume. If the stars align right you may be as high as 10.5:1 you really need to measure it all.

Thats a small cam thats for sure.

low and mid torque i really want but i also want to run on 87 pump because it will be a daily not much for drag except maybe a couple guys on the street... so im not aiming for a high compression and dont want a stock compression either

If your block is not zero decked it going to be dam hard to get 10:01 if its a set of stock pistons they set down below the deck about .045

That is a Comp Extreme Energy 262. If you want to believe Chevy High Performance, they got 400 + HP and around 420 TQ with a Extreme 268 cam. Looking at the powerband graphs on Comps site, you would probably give up a little HP (maybe 5-10) and gain a little in TQ with the 262. Nice little motor for cruising.