These are the numbers I have so far. I want a street/strip engine that won't be driven everyday, but I want it to be reliable and handle a 150 shot of juice. The size of the combustion chamber (affecting dcr and scr) is pretty much my last variable besides valve size.(feel free to comment on that as well)

Stroke: 3.48
Rod: 5.7
ICA: 71
Bore: 4.03
Head gasket thickness: .039
Head gasket bore: 4.125
Piston to deck clearance: 0
Dish: 6

Any ideas/opinions are appreciated. Thanks.

 

Chamber size? What cylinder heads were you planning to use?

 

To give a GOOD answer there are a lot more variables.

Bret

 

I'm using stock ported aluminum heads. I knew you were going to say that, Bret, haha. I don't know my VE or I would have posted that up as well. It's going to be a newly built motor, so I'm hoping it's higher than stock. What other variables do you need?

 

using stock heads you don't have much of a choice...

 

Why not? If I'm getting them ported I can have almost anything larger than 54cc right? I'm thinking between 57-60cc, just wanted some opinions. (i.e. better to have larger chamber and thinner head gasket/milled head, or better to have smaller chamber with thicker head gasket/unmilled heads) Thanks.

 

Cylinder Head Volume 60 cc
Piston Head Volume 6cc
Gasket Thickness 0.039”
Gasket Bore 4.125”
Cylinder Bore Diameter 4.030”
Deck Clearance 0
Stroke 3.48”
Static compression ratio 10.75:1

I would play it safe with a 58-60cc chamber. Running on the edge can generate more power but demands constant attention to details expectedly when running a 150 shot.

Do you have an LT1, we stick with the stock valves except for all out applications.

 

Yes, I have an LT1. I probably don't really need larger valves, but for the price of a valve job and larger valves being around $300, I think it's worth it if I ever step up to a larger cam. For that compression, would my dcr be too low? I was shooting for a little over 8:1.

 

We are running mid to high 10s with the stock valve size and good porting >3000 lbs cars. I find with the 3.48 stroke and moderate RPM the 1.94" intake is all that’s needed.

Post all of your camshaft information

 

Thing is I can only afford moderate porting. What's more beneficial, more porting with stock valves or less porting with larger valves?

226/231 .560/.569 on 114+4

 

The unmodified port cannot adequately support the stock valve size, adding a larger valve to the stock port will do little to enhance performance.

On the other hand the stock valve size can support flow levels much higher than the stock port will flow.

 

If this is a moderately driven street car then you can go for more cam.

Here's a Lunati Hydraulic roller cam that we have good luck with:

Int = 301 @ .006 242 @.050 .376 times rocker
Exh= 311 252 .370
Put it on a 108 Sep Advanced 4

There's a bigger one

311 252 .370
319 260 370
Sep @ 108 advanced 4

As far as the deck clearance is concerned always try to keep the piston as close to the head as possible, and then adjust your chamber volume to achieve the C/R that you want. With a 52cc head .021 deck you're going to arrive at about 13 to 1 - this depends on how you arrive at the deck clearance, and how you have the piston configured.

I have to subscribe to what A.B. says - ported GM heads can make substantial power when done correctly, even with 1.94 & 1.5 valves, but you could go for the 1.57 Exh valve.

Denny

 

WOW, those are some big cams, especially for the street. I was looking at a larger cam:

Int = 286 @ .006 236 @.050 .580
Exh= 292 242 .585
111+4 LSA

13:1 also seems very high for pump gas. I was thinking more around 11:1, maybe a little more to get a 8.5:1 DCR. With a zero deck, I'll only need 58cc chambers to get there with .039 Felpro gaskets. Do you think I can do thinner gaskets with larger chambers to reduce quench? Piston is a 4-valve relief.

 

13:1 also seems very high for pump gas. I was thinking more around 11:1, maybe a little more to get a 8.5:1 DCR. With a zero deck, I'll only need 58cc chambers to get there with .039 Felpro gaskets. Do you think I can do thinner gaskets with larger chambers to reduce quench? Piston is a 4-valve relief.


Thats the point I was trying to make, but even 11 to 1 is to high for pump gas unless you have an "Engine Management System"

Therefore if you are using a carb you will have to rethink your set up, or plan on running racing gas. However there are some alternatives to the pump gas thing.

Get this book: High-Performance Automotive Fuels & Fluids By Jeff Hartman ISBN 0-7603-0054-2 - In this book he makes several suggestions to fixing the low octane problem, one of which is Toluene.

Just yesterday I talked with Jim Jones of Tra-Co Racing Engines about the pump gas thing and C/R's over 10 to 1. "The engines we used to do in california when I was in Culver City only had 9.5 and every time I tried to increase that to 10 it always rattled on the dyno and I had to cut a new chip to fix the problem, and wound up making less power because the lead had to be cut back."

Jim had special gaskets that allowed him to run very close head to deck clearances, but we had to cut the chambers out to 68cc's.

Denny@JDS Induction Products

 

I know about using Toluene to simulate higher octane. That's a lot of interesting stuff, but nothing really answered, or really even addressed my question.