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Old 01-08-2009, 07:30 PM
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cubic inches vs compression

at the local circle track there is a cubic inch rule that u cant be over 360 ci. another rule says u cant be over 155lbs compression which is very light for a 350ci eng.. as far as the carb it Must be a Single Holley 4412 two-barrel with stock venturi, metering blocks and boosters, horn stays on, and choke plate can be removed...... and now for my question

since the 350 block is kinda starving with the smaller carb and low compresion i was wondering if a smaller block (maybe 327) could make more power there is a gear rule in place so max revs would be around 6200..any ideas guys?

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Old 01-08-2009, 07:35 PM
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I have no comment except to say it is THIS situation that separates the men from the boys. When getting that little bit of an edge over your competitors in a purpose built engines. Where the smallest detail stands between winning and second, third, or fourth place.

Can't wait to see the responses.
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Old 01-08-2009, 07:59 PM
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Quote:
Originally Posted by notme76
at the local circle track there is a cubic inch rule that u cant be over 360 ci. another rule says u cant be over 155lbs compression which is very light for a 350ci eng.. as far as the carb it Must be a Single Holley 4412 two-barrel with stock venturi, metering blocks and boosters, horn stays on, and choke plate can be removed...... and now for my question

since the 350 block is kinda starving with the smaller carb and low compresion i was wondering if a smaller block (maybe 327) could make more power there is a gear rule in place so max revs would be around 6200..any ideas guys?
First Off, what length is the circle track, dirt or paved, banked or flat? How long are the straights? Are you allowed to use weight jacks, or not?

What are your weight restrictions, and the type of fuel allowed?

Are you currently racing, or just starting out, or thinking about it?
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Old 01-08-2009, 08:18 PM
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Is that you talon0713?
If not, I apologize and suggest you read this thread.....
is it pssible to make a 283 into a 327 stroker?

Last edited by johnnya; 01-08-2009 at 08:36 PM. Reason: spelling correction
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Old 01-08-2009, 08:25 PM
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Max cubes, max compression allowed...using a smaller engine is a waste of time.

I would borrow the compresssion gauge they use to check compression to be sure I am within 1 psi of the max according to them.

Running a slightly larger overlap cam will help with reducing compression at cranking speeds so you can run higher static compression.

Run a slightly smaller dia tire as wide as possible (cut them if you have too) to get the revs up, if you can afford it run a 30 series tire. I wouldn't worry about the carb, the engine will draw what it needs, just make sure it gets cold air from the hood in a high pressure area like the cowl.

Tune it right and kick some butt.
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Old 01-08-2009, 08:29 PM
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Length: 1/3 mile
Track Width Straightaway: 58 Feet
Track Width Corners: 50 Feet
Track Width Backstretch: 65 Feet


paved, slight banking... 2500lb weight 56% left weight max. open fuel rules
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Old 01-08-2009, 08:44 PM
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Okay, what's the gear ratio set forth by the track gods and are you limited to an automatic trans?



Larry
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Old 01-08-2009, 08:51 PM
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Quote:
Running a slightly larger overlap cam will help with reducing compression at cranking speeds so you can run higher static compression.
This is sound advice... what is your lift rule? .410? .450? Or do you have a vaccum rule in effect also?

I think we already debated this 327 vs. 350 myth a few posts ago, so no, I wouldn't go smaller on the cubic inches.

Good god man that's a small track what the heck are running for a gear? 5.36? or lower?
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Old 01-08-2009, 09:21 PM
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I would try...

4.155x3.25 358ci
6.20 rod
17:1 compression
cam duration at .260@.050
1.7 rockers
and the best carb you can afford to pay a pro.
turn it 9200 if you have the valvetrain.

As far as getting the crank compression legal, put a 4:1 gear driven starter on it with the 168 tooth flywheel and it'll turn slow enough to show it's legal. especially after the money race the battery will be low enough it won't crank well

You gotta a smart driver with this though. It will come apart at WOT at low rpm.
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Old 01-08-2009, 09:46 PM
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Quote:
Originally Posted by notme76
at the local circle track there is a cubic inch rule that u cant be over 360 ci. another rule says u cant be over 155lbs compression which is very light for a 350ci eng.. as far as the carb it Must be a Single Holley 4412 two-barrel with stock venturi, metering blocks and boosters, horn stays on, and choke plate can be removed...... and now for my question

since the 350 block is kinda starving with the smaller carb and low compresion i was wondering if a smaller block (maybe 327) could make more power there is a gear rule in place so max revs would be around 6200..any ideas guys?
You're in the game between the effects of static compression ratio against dynamic compression ratio.

I'm sure what they check is cranking pressure which is first the effect of static compression that being the division of total cylinder and combustion chamber volume by volume above the piston. Oh this leaves ever so much space to play. A cam with a lot of overlap and or late closing intake bleeds a ton of pressure while cranking. So if you've got (or the rules allow, a wild cam, you can bump the static ratio up quite a ways before you bang on 155 psi cranking.

Then there is that cam, it works with the heads and your carb limitations in strange and mysterious ways. That is a high overlap, late closing intake valve timing combined with a somewhat too small intake tract and a too small carb really jacks the port velocity up as the revs climb. This really begins to pack the cylinder with ram pressure from the port velocity. The effect is that the in-cylinder pressures, what's called the Dynamic Compression Ratio, goes way up with the revs, so the engine react's like it has a higher Static Compression Ratio.

Now the down side of insufficiently sized ports and carb is that the motor will run out of breath sooner than if it had some honkin' AFRs and a Dominator on it. So, if you can do porting, starting with a small port and doing a little cleaning so it flows more without getting big, a super valve job, and 5 angle if the rules allow any of this will help get mixture into the engine. Reversion cones in the headers, if permitted, will help keep the exhaust reversion from blowing mixture out during overlap.

I can't tell you how this temps me toward 305 heads with 350 valves and D dished pistons to dial the static compression in while developing a humongous swirl and keeping a real tight squish/quench. This just works the daylights out the mixture.

Long cam duration can be used to add time in which the too small ports and carb will have with which to fill the cylinder.

The Devil's in the details and rolling onto the track with the highest power engine isn't always the recipe.


Bogie
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Old 01-09-2009, 05:39 AM
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i've been told that cam overlap can only hide so much b4 it starts to steal more power then the extra compression is worth...lots of good advice here though...although a few guys arent reading my rules, i dont mind bending them but... gotta keep it looking legal!
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Old 01-09-2009, 06:11 AM
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a 327 crank in a 400 block would be the way to go, BUT its more expensive than going with a 350. a 350 will be better than a 327. And the DCR is the DCR regardless of displacement
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Old 01-09-2009, 08:12 AM
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here's a vacuum rules circle track motor build article:

http://www.circletrack.com/enginetec...les/index.html....

then do go back to the home page and read thru "ALL" the different tech sections articles in each...
(best lap time is how the "whole" car works)

you need to more closely study all the rest of the track motor rules to make a plan,,,
what you have posted so far is a kind of modified/outlaw type "no" restrictions race...
(350, 2V, 15Hg and then anything you want to do,,,which is not typical to pass tech inspection)
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Old 01-09-2009, 09:31 AM
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Quote:
Originally Posted by red65mustang
here's a vacuum rules circle track motor build article:

http://www.circletrack.com/enginetec...les/index.html....

then do go back to the home page and read thru "ALL" the different tech sections articles in each...
(best lap time is how the "whole" car works)

you need to more closely study all the rest of the track motor rules to make a plan,,,
what you have posted so far is a kind of modified/outlaw type "no" restrictions race...
(350, 2V, 15Hg and then anything you want to do,,,which is not typical to pass tech inspection)

it is for a modified class, and basicly that is all the rules within the engine....there are lots of dimensional / weight rules for the chassis but first im trying to come up with the "power Plant" that willl kick *****
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Old 01-09-2009, 10:12 AM
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my $.02:
"no rules"=
unless you have MEGA bucks, race at a different motor (rules) track or class....

not likely that track can offer purse's to cover a reasonable amount of your total operating cost every week and be competitive....

the track owner is 90%+ concerned about drawing a crowd for $$$$ in his pocket....

and who ever has the most to spend on his motor and car (repeatedly) will win....

Last edited by red65mustang; 01-09-2009 at 10:21 AM.
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