Are these heads with casting number 3998997 worth using on a 355? They have been in she shop and freshly rebuilt. I know the information on the heads just not sure if I should use these or purchase some others.
what are you building? looks like you need a crank? What is the purpose of the engine?
I'm wanting to build a strong 355 to put in my truck. I would like to get 350-400hp out of the engine. I don't want to get the engine built and realize the heads are crap.
to build 400 horse power you need heads that flow over 200 CFM of air on the intake side.Ideally the exhaust side flows 75% ratio of the intake side. The most common heads used on 400 HP engines flow 240 cfm. Modified vortec heads/e tec aluminum heads/dart SHP and many others.If you have good suppliers in your area,then ask them what they sell.
It is very important to match your heads to your compression ration with proper placement of piston in the block and camshaft profile.
The size of engine is up to you.The bigger the engine the easier it is to make 400 hp.IE: a 400 cube engine is easier to make 400 hp than a 305.
Decide on an engine size you will use and almost everyone can help you decide on the parts.You might want to consider the budget when you post what you want.Quality parts enhance reliability and longevity.
example of what you could build;
shp heads(or equivalent)9.5 CR, 750 cfm carb,performer intake,Hydraulic roller cam with short duration,220 ish@ .050 and .500 ish lift, 1 5/8 inch long tube headers,3 inch exhaust.
There are cheaper ways to do this,just use this as my guide. Others will have ideas
Any stock head is going to be "crap" when compared to a decent aftermarket one. You can get to 400hp with Vortecs but with the cost to rebuild them and the price of some quality offshore heads I'd just go aftermarket.
That being said if a pair of Vortecs fall off a truck and all they need is springs and guide work then you'll do just fine using those- but since they're thin castings don't sink a hell of a lot of money into them.
Cheapo 400 hp build.....
350 SBC L31 heads
Flat tappet hydraulic cam, stock self aligning (SA) rockers, some head work for better springs.
In this build, a tight budget is called for. To that end, use stock self aligning rockers. Lift is under a half inch, so the SA rockers should be OK. Check to see if using a -0.050" lock will be needed to insure the valve tip sticks up far enough above the retainer so that the retainer top surface doesn't get loaded by the side rails of the rail rockers. More info on checking clearances, etc. under Resources.
Bore the block 0.030", use these or similar 12cc dished pistons w/5.7 rods.
Makes 9.6:1 static compression ratio. Cut block decks to zero and use a ~0.041" head gasket. The default gasket to use with aluminum heads is Fel-Pro 1003....
Fel-Pro Performance Head Gaskets Q1003 - SummitRacing.com
Makes a squish of 0.041".
Use XE274H Comp cam, installed straight up.
Comp p/n 981 valve springs, p/n 750-16 retainers, p/n 630-16 keepers and stock 1.5 rail rockers. 1.250" springs should be OK because the cam is a moderate grind, hydraulic flat tappet.
Machine the OD of the guide bosses to less than the I.D. of the damper spring and cut for PC-type positive seals.
Cut top of guide for 0.550" play from bottom of retainer to top of guide seal. Pin the pressed-in rocker studs with this kit.
Performance Distributors custom curved HEI distributor, p/n 12720, or build your own from a GM HEI.
Edelbrock RPM Vortec intake mounting a 750 vacuum secondary carb of your choice. Edelbrock, Rochester 5 psi max at the inlet, Holley 6 psi max at the inlet.
Performer RPM Vortec w/natural finish: p/n 7116, w/EnduraShine finish: p/n 71164, w/polished finish: p/n 71161, or look for a used manifold on craigslist to save a few shekels.
Long-tube 1-5/8" headers with X or H pipe right after the collectors, 2-1/2" to 3" pipes to the rear through mufflers of your choice.
Use 2500 stall converter, shorter rear gears.
RPM HP TQ
2000 138 364
2500 176 369
3000 224 392
3500 281 421
4000 331 435
4500 370 432
5000 402 422
5500 405 386
6000 375 328
Peak dynamic compression ratio 8.16:1 on KB's calculator.
Peak volumetric efficiency 97.2% @5000
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