Thread: Building torque

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Hello there,
My engine is a stock SBC, .060 overbored, dished pistons (only small dish with eyebrows) and 041 heads. Now I've just done a compression calculation and have found out this:
- the displacement is 737,9cc (because it's .060 over)
- total cylinder volume is 761cc
- gasket is 1,6cc
- chamber is 68cc
That would make a compressed volume of 92,7cc and a total volume of 830,6cc, giving my engine a static CR of 9:1 pretty exactly.

Now my car is a 5000 lbs van and I would like to put some torque into that small block. I'm not concerned about top speed, but would like a smooth idle, good mileage and big fat low end torque, eventually I'm planning on putting a different rear axle ratio in, but to do that I need TORQUE
I have planned on 1 5/8" headers, going into a 2" dual exhaust, and I already have an Edelbrock Performer (not Performer RPM) Manifold and a 600 cfm carb (also Edlebrock Performer)

To achieve that, should I go higher or lower in the CR? I'm going to get new heads anyway and I'm looking at a pair of 624 castings, they have 76cc chambers and would drop the CR to 8,3. Would that help torque? I haven't heard of anyone dropping the CR so far...
Should I get heads with a bigger Exhaust valve?
Go 1.6 exhaust rocker Ratio?
Or will I need a new cam?
The 041s had 160cc runners, does anyone know what runners the 624s have?

The total cylinder vomlume was measured with an accurate burrette and the method of filling the whole cylinder with water when it's at BDC under a lexan cover with a vent hole at the very top, so possibly I'm 2 or 3cc wrong on the total volume, but I measured twice and got the same result, so I guess it's correct enough.

First what are you using this for towing or what?
If you want good gas milage I would'nt go putting bigger valves in.


~ Vegas ~

No, I don't need it for towing. But it weighs 5,000 lbs empty and is used as a tour-bus for my band. Loaded with amps and stuff and people it goes up to almost 7,000 lbs. It doesn't have to travel fast, but it should travel far and have a reliable setup. Just thinking what changes should I make to get the powercurve high in low RPMs...

Your method of pouring the chambers and runners sounds correct and your computations for the cylinder volume looks good, but your results for the head gasket volume are flawed and I don't see where you've included the deck height (top of piston to top of block deck) unless that's what the 761 represents, which would mean you've added 23,1 cc's for deck.

Assuming the head gasket is a composition example, the compressed thickness would be somewhere around 0.040". Assuming the bore of the gasket is around 4.100", the computation would be as follows: .7854 x 4.1 x 4.1 x .04 x 16.387 = 8,65 cc's. Even if you were using a shim gasket of ....say....around 0.015" thickness, the volume would be 3,24 cc's.

As far as deck height, unless you specifically specified to your machine shop to zero deck the block the last time you had the block bored, I can assure you that the piston is down in the bore by at least 0.030" at top dead center. So, here we go: .7854 x 4.06 x 4.06 x .03 x 16.387 = 6,36 cc's.

I'm assuming flat-top pistons which would have about 7 cc's of valve relief volume.

cylinder 738,28
chamber 68
gasket 8,65
deck height 6,36
pistons 7
total 828,29

compressed (chamber, gasket, deck height, reliefs) 90,01

828,29 / 90,01 = 9.202:1

Anyway, back to your needs.
More cubic inches and/or longer stroke will give you more torque. You're limited on changing the compression ratio to make the motor more efficient by the quality of available pump gas, so you will have to do it with displacement/stroke/camshaft.

Hi Tech and Denny,
I didn't measure the deck height extra. I did the measuring like this:
First I smeared about 3cc of grease round the outer edge of the piston, so as to get a water tight seal (the first measurement went wrong here because water escaped past the rings).
Then I screwed a lexan plate with a vent hole onto the block, sealed with grease.
Then I filled the cylinder with water from a 100cc burrette til I was at the vent hole, which was at the highest point.
Surely that would already include the deck height then?
So it's 761cc including deck. The gasket I calculated like this: it has 1mm, so 0.1 cm of height (that is about .04"). The radius is 5.2 cm. And radius squared times Pi times height is the volume. so I get 0.1*5.2*5.2*3.14=8,5. OK, Sorry about that (Woops!) my mistake, didn't think I'd make a mistake that stupid, after all, I'm studying math
That would drop me to 8.4:1 CR ???????
Can only be a measuring error in the 761...
I'll get back to you as soon as I find out my mistkae, but it's getting a bit too trial-and-error like for me here

PS: Of course i can alwas go wrong here: I filled the 100cc burrette 8 times in the process. And if I can only fill it to let's say 2 or 3 cc exact (or the burrette's measurings include the snout) I'll be doing the same mistake EIGHT times. If that's 2 cc's every time I'll be looking at a error of 16cc :-(