highest compression for 93 octane
12-07-2008, 06:00 PM
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depends on your dynamic compression, timing, block/head materials, quench, all sorts of interconnected head specs, etc. For example, my '89 XJS ran 11.5:1 and it called for (and I ran) 87 Octane. My '95 LT1 (reverse cooled, of course) Caprice ran 10.4:1, I believe, also on 87. The F/Y LT1 bodies needed 91 with Aluminum heads and a slightly different cam with slightly more compression. No way to make an accurate estimate of a totally safe (and nothing ever is totally safe) SCR without a lot more information and testing of similar set-ups.
12-08-2008, 08:28 AM
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AS stated above, there are alot of variables to deal with, and your cam of choice has alot to do with it as well. If you run a cam with alot of duration ( overlap), it will bleed off cylinder pressure at lower RPM's, and you can get by with a higher SCR. I am gonna be testing the waters on my own 414" L92 headed 12:1 here pretty soon. Cam is on teh "large"
side, in teh 260/270 range @ .050. I will prbaly have to tickle it with the Octane Boost or some race gas once the weather warms up come Summer time. BUt I think I may be good to go in teh cooler months. You do also have to look at your cooling system as well. You start running more compression, and your cooling system is not adequate, you can get into detonations problems even with 11:1 motors. So, again, alot more to look at.... Last edited by Gen414; 12-08-2008 at 08:29 AM. Reason: added
12-08-2008, 12:04 PM
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AS stated above, there are alot of variables to deal with, and your cam of choice has alot to do with it as well. If you run a cam with alot of duration ( overlap), it will bleed off cylinder pressure at lower RPM's, and you can get by with a higher SCR. I am gonna be testing the waters on my own 414" L92 headed 12:1 here pretty soon. Cam is on teh "large" side, in teh 260/270 range @ .050. I will prbaly have to tickle it with the Octane Boost or some race gas once the weather warms up come Summer time. BUt I think I may be good to go in teh cooler months. You do also have to look at your cooling system as well. You start running more compression, and your cooling system is not adequate, you can get into detonations problems even with 11:1 motors. So, again, alot more to look at....
side, in teh 260/270 range @ .050. I will prbaly have to tickle it with the Octane Boost or some race gas once the weather warms up come Summer time. BUt I think I may be good to go in teh cooler months. You do also have to look at your cooling system as well. You start running more compression, and your cooling system is not adequate, you can get into detonations problems even with 11:1 motors. So, again, alot more to look at....IF...I was to use 110 octane race gas all the time with the new 454ci, since it would be just a weekend/fun car, how high can the compression be then? There's literally 10 gas stations within 10 miles of my house since we have thousands of airboats in this area.
Also, whats the potential difference in HP with an 11.5:1 engine (pump gas) and a 13.xxxx engine (110 race gas), all else being equal?
Basically the goal here, is a max effort hydraulic cam 454ci engine, with a 300 shot. Hwy runs only, no track stuff.
12-08-2008, 04:48 PM
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Staying 93 pump gas is the goal, but had another question. Right now I have 11.3:1 in my 427ci and everything is fine even in 100* weather. My cooling system, for some good reason, works better than any LSx cooling system I've ever seen, its great and its stock.
IF...I was to use 110 octane race gas all the time with the new 454ci, since it would be just a weekend/fun car, how high can the compression be then? There's literally 10 gas stations within 10 miles of my house since we have thousands of airboats in this area.
Also, whats the potential difference in HP with an 11.5:1 engine (pump gas) and a 13.xxxx engine (110 race gas), all else being equal?
Basically the goal here, is a max effort hydraulic cam 454ci engine, with a 300 shot. Hwy runs only, no track stuff.
IF...I was to use 110 octane race gas all the time with the new 454ci, since it would be just a weekend/fun car, how high can the compression be then? There's literally 10 gas stations within 10 miles of my house since we have thousands of airboats in this area.
Also, whats the potential difference in HP with an 11.5:1 engine (pump gas) and a 13.xxxx engine (110 race gas), all else being equal?
Basically the goal here, is a max effort hydraulic cam 454ci engine, with a 300 shot. Hwy runs only, no track stuff.
For every point in compression, you can expect an increase in power by @ 4-8%. Give or take. Some say 7%. Some say 5%. But you can expect 4-8%. And if youa re running race gas all teh time, you can run whatever (for the most part) you want in compression. I mean I would not run say a 15:1 motor and spray it with 110 in the tank. But sure, 13:1 and 110 no problems at all. Now, 13:1 AND spraying a 300 shot it with 110. Uhhh, weather, tune, plug range, cam, load, will depend on what happens there.
Last edited by Gen414; 12-08-2008 at 04:48 PM. Reason: added
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12-08-2008, 04:59 PM
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For every point in compression, you can expect an increase in power by @ 4-8%. Give or take. Some say 7%. Some say 5%. But you can expect 4-8%. And if youa re running race gas all teh time, you can run whatever (for the most part) you want in compression. I mean I would not run say a 15:1 motor and spray it with 110 in the tank. But sure, 13:1 and 110 no problems at all. Now, 13:1 AND spraying a 300 shot it with 110. Uhhh, weather, tune, plug range, cam, load, will depend on what happens there.
12-08-2008, 07:58 PM
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Dedicated strip car I would say 12- 13:1 for a 300 shot. Thats alot of cylinder pressure, so head studs would be pretty much mandatory at that level as well, and of course a good set of head gaskets.
A steet car, I would say @ 11-11.5:1 and use the 110 for when you planned on spraying that much dope. It also depends onhow much trouble you want to go through in maintaining a vehicle with loads of cylinder pressure like high compression and lots of juice.
12-09-2008, 07:49 AM
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Well, there are motors out there with more compression than that and spraying it, but they are running higher than 110 I can tell you that. If someone is building a DEDICATED nitrous car, they are going to target anywhere from 11-13:1. AS they want to make the most power they can on motor (for the most part) and then introduce nitrous to the equation. Now, again, you are looking at variables...camshaft, plug heat range, timing retard, etc....
So, really there is no CONCRETE answer for your question. There is only going to be "if's" like, IF you have this or IF you have that, then you can do this....
