Need Help With A Chevy 355 Engine We Had Built
Posted in Internal Engine Parts | Asked on May 26, 2010
First I went with aspeed shop recomendation on parts and all we wanted was to get 400hp from a sb chevy 355. The parts used 350 block bored 30 over, cast pistons flat top 4 vr, comp magnum cam 270 duration 470 lift intake/Exhaust lobe sep 110, Gear drive, Pro comp Aluminum 64cc/190cc 2.02/1.60 heads,aluminum 1.5 race roller rockers, Elderbrock preformer Intake, Elderbrock 1406-600cfm carb,Msd street fire distributer,Hooker long tube headers, Holey fuel pump with Reg set at 6psi. all parts are new except the block and crank. this engine was put in a 86 monte ss. The engine does not even feel close to making the 400 hp I wanted I am thinking of upping the cam but not sure what to go with. The trans is a new 200-4r with stock converter. I have no Idea what compression I have now. any help would be great. I have many pice during build if someone emails me at kahlua1836@msn.com I will show you all the pics during build. HELP
There are 3 Answers
Now you know the problem with “400 hp” small blocks. They may make that but it is at one rpm level. Fall off 100 rpm and the hp falls off like a rock off a cliff. Build a big engine. Take a 454 and build it lightly to 400 hp and you will have the same peak hp but double the hp at any level other than the peak rkpm. You will be able to tell it also. As far as your current engine, the only thing I see about it that seems a little weak is the .470 lift. I think probably .490 lift would be more normal. That Monte is just heavy for a small motor and 355 is small. Sorry.
Sounds like the right parts, maybe you just need to dial it in. The one thing that you did not mention was ‘porting & matching’ being done. If you have not machined the ports to match you will lose 15% to 25% HP at top rev’s. Also, just as important, the electronics. Computer chip upgrade, distributor cure re-timing & high output alternator to keep your plugs firing at top end. Let me know if problem persists after the above updates.
That guy at that performance shop needs to be slapped.
He talked you into buying his un wanted stock from what it seems.
I don’t know any true performance engine builders that would recommend a gear drive (they cause un wanted harmonics to be transfered from crank to valvetrain)
Flat top 4 vr in a 4.030″ x 3.48″ (355) engine will give you between 9.34:1 to 9.95:1 compression with 64cc heads depending on head gasket thickness, bore, and deck height.
The pro comp heads aint all that great. They are a poor designed alum head that gets people due to their low cost. As far as flow, the last ones I flowed didnt flow as much as stock vortec heads.
That cam is a single pattern, 224@.050″ duration and in fact alittle big for that compression.
Those heads with even many better heads makes more power with a dual pattern cam that has 8 to 12* more duration on the exhaust side that the intake, and more lift on exhaust side.
With 9.5:1 compression, you really need a cam around 218/228@.050″
With the cam you have, the stock stall torque converter is really holdng you back.
Your combo needs a 2600 min. stall speed and min 3.42 rear gears.
To me, that combo sounds more like a 340 HP @ 5500 RPM, 380 ft lbs torque @ 4000 RPM combo
Ohh and just to point out to that one person.. The 80′s monte carlo’s aint a heavy car. They are lighter than the camaros
86 monte SS weighs 3,387 lbs