68bigblock

I’m wanting to get 500 plus hp from my 427/390hp engine.
I will bore the engine to .60 over and replace stock cam with a roller cam. I don’t know the best fit for my 500 plus horsepower application.

I have stock heads 103cc oval port that I will put larger valves to boost HP.
Considering putting TRW L2268 Pistons. I thinking the compression will be near 11.5 with the 103cc heads.
I’m wanting to use pump gas. Any suggestions? Will this setup produce 550hp?

MelWff

how are you going to use pump gas with that compression? I dont see how your combo will produce 550HP gross with those stock heads and the few changes you have listed

stacka

427Hotrod

You can get past 500 HP pretty easily. First....need to actually measure the heads. Most of the time they are a lot larger than you think due to differing valvejobs and castings. I've seen some that were supposed to be under 100cc actually measure 115cc.

You can push the compression..but it will depend on your cam and tuning ability as well as cooling system, trans, gears etc etc. Probably better off to get under 11.0...and even then you need to make sure things are really right.

Just putting in larger valves is part of the battle. The important part is to have someone work the ports that knows what they are doing. GM iron oval ports can make well over 700 HP if done well. Little valves with good ports is better than big valves and poor ports.

Tell us the rest of the combo and what you want to do with the car. Solid roller...hyd roller?? Intake...carb....headers....exhaust....

JIM

68bigblock

Casting numbers on the heads are 3917215. They are original 103cc oval port heads.
Hyd roller is desired. I currently have the original aluminum intake and quadrajet card. I'm going to upgrade carb to either a 750 or 850 Holley. Have not yet made a decision on the intake.

68bigblock

I forgot to mention headers and side exhaust.

garygnu

look for a flat top piston to keep your static compression pump gas friendly .pick the cam last to get the desired dynamic compression .you mite need a single plane intake .I bet you could make 500 crank hp with a dual plane .I made 499 hp with a blueprinted ls6 with stock heads and a ls6 intake .it had a small 278 duration solid lifter crane cam.

Kacyc3

I am surprised no one has mentioned swapping to aftermarket heads.

454 with huge hy roller cam edel heads and through a 4k stall 442 to the ground

StraubTech

Set of ZZ502 take rovals.
Hyd roller camshaft
Morel lifters
550HP

ajrothm

Tomorrow I am dynoing my dads '65 396/425hp engine we just built....Its a stock appearing build that we are shooting for 500 crank hp through stock manifolds.

I'll report back tomorrow, if it hits mark, here is the combo"

Its a 408"(.060 396), 10.0-1 comp(ACTUAL), 65' rec port heads that have been milled, 2.25" intake valves, good valve job.
Scat 4340 rods, Racetec custom pistons, oem steel crank, CStraub hyd roller, Crane gold roller rockers. Stock corvette side pipe manifolds and 396/425hp Winters intake. Only thing not stock appearing is the 750 DP.

We'll see...

StraubTech

I guess I am on the HOTSEAT again!!!

68bigblock

This stuff is more sophisticated than I first thought! I just got off the phone with a man that builds vette engines in Oshkosh WI, and he said go back with 400hp 427 crank and do some head work to get more air through my heads along with bigger valves. Suggest no more that 10.5:1 pistons if i want to use pump gas.

ajrothm

Yes it is.... Way more science in this stuff then most think. Even when you do your homework it doesn't always work out as planned..>Something always bites you in the a$$


We dynoed our 396" yesterday, turns out our carb was only a 650 cfm as opposed to a 750 like we thought, we had an ignition misfire that would develop after 6300, and a couple other small gremlins that hurt us.... we ended up at 441hp/436tq.. We think that with a 780 cfm carb and the ignition misfire resolved, it will make 460-470hp through stock exhaust manifolds... No doubt 1 7/8"x3" headers would put us close to 500hp but... We'll never know, as we are about to put it back in the car.

Good luck on your build, do your research, remember that todays 93 octane sucks so anything more the 10.0-1 compression with iron heads is not a good idea...Especially if you want to keep atleast 34* of timing in it.

Jamess411

just remember one simple thing…it costs about 15 bucks per hp. So, 500 hp is 7500 and 1000 hp is around 15 grand ) OH, of course that does not include any rest of the car upgrading that will be needed.

lurch59

How about nitrous? Big blocks are pretty stout and handle it well.