Ok so I've only ever built one engine in my life and it was a buick nailhead, but, I know a bit about them and here's my question:

I run an 85 C4 Z51 racecar that I brought in from Texas. It is an old school build (love it) with a carbed 355 mild build engine, no ecu, T10 tranny etc. It is dynoed at 335/375 at the wheels and is very reliable and strong. This puts the 2880 pound car right at the 9.1 power to weight ratio for its class in SCCA. I am racing here in Canada in a class where the power sky is the limit. At some point I will be looking for more power, so, to get it out of this engine or should I go with the 488HP crate motor. I'm looking to get between 425 an 500BHP.

I'm posting the build specs of my motor. I'd like opinions on where I'm at, what would it take to get that number out of this motor at what cost, or should I consider selling this motor and go to the crate as being better cost effective. Wish I could post pics, its really well done under the hood. The engine is pretty fresh.

1989 Silverado block, 1 piece main
Edelbrock Aluminum RPM heads
Victor JR intake, roller rockers 1.5,stud girdles,hydraulic flat tappets.
670 Holley with dual holley pumps
Lunati 292/292 cam .480..480 lift and 292 duration
Edelbrock aluminum water pump, Smiley underdrive pulley
HEI disributor, MSD wires, TR55 plugs
Canton 8 qt pan, melling pump
Hooker long tube headers,exhaust to the rear, no mufflers.
I do not know what the compression ratio is but I can use 91 octane (the former owner used 100). The block is stock internals I believe.

lots of other goodies that don't make power. I'm already told that I can make more power with an MSd 6AL system and maybe a 4150 750 carb
Anyway thats about it. I'll be running the car as is this season. Its pretty quick already.

 

I suppose it really has to do with how much do you want to spend? What RPM do you plan on shifting at? I assume the tires, brakes, suspension, and safety have all been taken care of?

 

Thats my point. which would be more cost effective to get my number which is between 425 and 500 BHP. Can I do it with the current motor with upgrades? Do I have to go into the bottom end? Am I at the top end of the heads and need other ones? Can I get it with a different cam and carburation? Ignition?

Or what could I get by selling the motor and going with the crate engine which is about 8k to my door. Would that be a better idea.

Don't worry about anything else. This car can handle GT2 laps with no problem from the clutch through to the bottom of the tires.

 

what are the rules for the engine ? stroke ? bore ?

 

A stock bottom end is not going to stand up to 500HP in a road race application.

Those heads and intake are capable of 500-550hp on a high compression, mech roller cam short block, so they will make the kind of power you want easily.

I don't know of a 670 Holley DP. A 650 DP is capable of about 450-500HP but if your shooting for over 450HP you really need to step up to a 750DP.

I would suggest you buy or build a better short block and reuse your top end (with proper valve springs and carb).
Will

 

start with a better block. i would not use a standard non bow tie gm block to produce 500whp in a road race environment. your best bet imo is an LSx swap which is both easier to make power with and a stronger overall design. crossbolted mains, better cylinder head angles etc.

if you stay SBC i would get a dart block and build up from there. you're also going to want more oil and water cooling capacity if you bring the hp up that much.

on top of that the c4 chassis starts really flexing when you go north of 800lb/in spring rates in the suspension

more power will require more cooling, more brake, more spring and more money, that's on top of the engine build.

i almost wonder if custom transmission gear ratios designed for the track you run on wouldn't be money better spent as 335/375 isn't a bad power combo albeit it a LOT for a stock bottom end. actually very surprised a stock bottom end is alive at that power level having been road raced. they usually come apart around 6000rpm

 

Eduardo we don't have rules here in Ontario. Its bracket racing like drags. You break out in the race you DQ and move up a class. Sky's the limit.

I'm not sure I have enough HP for GT2 here so I'll be running GT3. Almost all american cars that run GT2 put out 400 to 500 HP at the crank. Some of the smaller chassis like the jettas and hondas run about 370 turboed and they weigh only 22 to 2400 lbs so thats where I'm at.

Eventually I do want to run GT2 hence the thread. So it appears I could retain the heads, intake and cam and maybe and its the block that needs to change for one. Thanks. I know about all the other stuff. This car is very well built with coolers for trans and even the sweet PS pump. One could say its overbuilt. Everything on the car was built for reliability.

racebum funny enough the former owner says the engine is a mild build and very reliable. Guys no dummy either, he built the motor and has owned over 40 race cars. It doesn't make power over about 6000 and I shift it at about 5800. It pulls like a freight train. I do have plans to go to a TKO 500 trans also.

I ran the car hard last fall on track for over three hours. It ran flawlessly and handled like a miata on steroids which is how I describe all vettes to those who don't know what a truly amazing car they are. The Ram clutch and Dana44 hold up very nicely. I even liked the T10 although I could use another gear or different ratios.

 

Has anyone ever dealt with Patriot Performance? They have some really good looking engine combos.