How much Compression on 93 otcane
07-14-2006, 07:08 AM
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How much Compression on 93 otcane My mods are in my sig. I'm running Patriot stage 2 heads 64cc. I can mill the heads and/or use a thinner gasket. What cc can I go down to and still be able to run the 93 octane gas? How much more horsepower and torque will I pick up? I'm probably at 10:5/1 at the moment give or take. The current head gaskets are stock LS6 gaskets. Id like to add around 30-40 hp and torque. Possible??
Thanks,
Matt
Thanks,
Matt
07-14-2006, 08:31 AM
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rule of thumb is 2-3% increase in power for a full point in compression increase, (ie: going from 10:1 to 11:1); so if you are making 400 crank hp at 10:1 and go to 11:1 you might see 8-12hp. again this is a rule of thumb only.
07-14-2006, 08:40 AM
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I am at 11 to 1 compression and have had no issues at all with Michigan fuels. I liked how she ran before they switched over to the Summer Blend. This fall the fuel changes back again. I only use Mobil 93 or BP's Amoco Ultimate 93. Runs bad on Sunoco 94 or 93. Horrible gas mileage, and reduced performance in my opinion.
07-14-2006, 11:12 AM
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It is mostly relative to DCR, not as much SCR.
Tight quench helps fight detonation.
I run 11.7x with 8.6x DCR on 94 with no issues. .040 quench and TR6 plugs (1 step colder gapped .040)
I run 26* advance timing, I saw no increase in power by going higher.
Tight quench helps fight detonation.
I run 11.7x with 8.6x DCR on 94 with no issues. .040 quench and TR6 plugs (1 step colder gapped .040)
I run 26* advance timing, I saw no increase in power by going higher.
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07-14-2006, 11:24 AM
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i did run 11:7 scr,around 9:0 dcr on 93 with gm mls gaskets but that was in the spring.i will have 11:9 scr now but i'm going to a bigger cam so dcr will be around 8:7 or so but dcr is where it's at.of course different motor combos will act differently also.
07-14-2006, 02:18 PM
#9
Like some of the others said, its DCR that matters, not SCR.
Bigger cube motors take a bigger cam which usually cuts down DCR. Thats why you can see strokers running 12:1 on pump gas.
While you may not pick up a ton of HP, the low end torque will definately be be bolstered a bit. It will really help eliminate any mushiness from down low.
Bigger cube motors take a bigger cam which usually cuts down DCR. Thats why you can see strokers running 12:1 on pump gas.
While you may not pick up a ton of HP, the low end torque will definately be be bolstered a bit. It will really help eliminate any mushiness from down low.
07-14-2006, 07:35 PM
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Originally Posted by allngn_c5
I am at 11 to 1 compression and have had no issues at all with Michigan fuels. I liked how she ran before they switched over to the Summer Blend. This fall the fuel changes back again. I only use Mobil 93 or BP's Amoco Ultimate 93. Runs bad on Sunoco 94 or 93. Horrible gas mileage, and reduced performance in my opinion.
07-14-2006, 09:28 PM
#12
I'm in the same boat and doing the same as you. I'm looking to pick up a little bit of low end throttle response / power. I've decided to take a three step approach to this:
1. I started to do custom, part throttle tuning since previously I had just WOT / dyno mailorder tuning. So I did notice a nice performance and drivability increase.
2. I have a couple header bolts stripped, so I'm pulling both heads and having them helicoiled, while they are off, I'm swapping the stock gaskets (0.056") with a thinner (0.040") cometic and increasing my dynamic compression, and decreasing my quench. This has been reported to help increase low end torque and actually reduce the tendency to detonate.
3. I'm still running a stock pulley, so I'll swap over to at least an underdrive pulley, and maybe a lighter one as well.
I figure doing these three things won't cost me too much money, since I can do the labor myself, and none of it will impact drivability but rather add more power where I drive the most, below 3500 rpm.
1. I started to do custom, part throttle tuning since previously I had just WOT / dyno mailorder tuning. So I did notice a nice performance and drivability increase.
2. I have a couple header bolts stripped, so I'm pulling both heads and having them helicoiled, while they are off, I'm swapping the stock gaskets (0.056") with a thinner (0.040") cometic and increasing my dynamic compression, and decreasing my quench. This has been reported to help increase low end torque and actually reduce the tendency to detonate.
3. I'm still running a stock pulley, so I'll swap over to at least an underdrive pulley, and maybe a lighter one as well.
I figure doing these three things won't cost me too much money, since I can do the labor myself, and none of it will impact drivability but rather add more power where I drive the most, below 3500 rpm.
07-14-2006, 09:34 PM
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Originally Posted by 408WS6
If I were you I would just stay at 10.5:1. The max you can go is 11.3:1 on 93 octane gas. I seriously doubt that you'll gain 30 hp going from 10.5 to 11.3:1.
My 408 was built to 11.3:1 and I get problems w/ predetonation and subsequent knock retard w/ the crappy gas I get around here.
Especially when its hot
If I were to do it all over again, I'd bump it back to 10.5:1 and not worry.
My 408 was built to 11.3:1 and I get problems w/ predetonation and subsequent knock retard w/ the crappy gas I get around here.
Especially when its hot If I were to do it all over again, I'd bump it back to 10.5:1 and not worry.
Wow thats complete BS! Many cars come from the factory with similar SCR. FROM THE FACTORY!
07-15-2006, 11:53 AM
#15
Well, I think the point that is trying to be made is that you can't make a general statement about what a car can/can't run based on one particular setup that is having issues. The bottom line is that DCR, heat, quench, cam specs, etc all play a role in what you can run without getting detonation. Right now, I'm running 11.6:1 SCR with a DCR of around 8.0:1, a quench of .032, and a lazy *** cam that bleeds off a good amount of compression, and I'm getting knock retard from possible detonation on 93 pump gas. Many people run higher SCR and DCR on 93 octane with no issues at all, so it's a case by case basis.
07-15-2006, 12:08 PM
#16
It really depends on the whole combination as to what octane you can/cannot run on.
FWIW. On my 408... with 11.3:1 SCR, my car will run on 87 octane with no knock retard anywhere with timing at 38ish when cruising and 27-28 at WOT. This is due entirely to the 248/254 114lsa cam having a TON of overlap and bleeding off craploads of compression (DCR is down at about 7.7:1) Car still makes 475+ through exhaust on 87 octane gas... in the Texas summer heat/humidity.
07-15-2006, 08:51 PM
#17
Originally Posted by 408WS6
Agreed. But the point that I am trying to make is that why go from 10.5 to 11.3 when all your going to gain is maybe 10 hp. Your not going to gain much. And as you pointed out, it comes down to DCR which you can easily (and more cheaply) change by simply changing out camshafts. Changing out pistons is much more expensive and much more work. Again, if it where me I would do exactly what I stated before and change out cams to get the DCR where my motor likes it. If you disagree, thats ok. Just go do what you think is best.
I wouldn't be so quick to discount the benefits of a higher dcr/scr with our style heads. I guess that's why some guys have better results than others based on how much they mill their heads and how tight they get their quench.
07-15-2006, 08:56 PM
#18
Originally Posted by The Alchemist
Actually I thought I read where Brian Tooley did a bunch of testing on heads and found that a stock set of heads that had been milled to produce a full point higher compression ratio actually made as much power as a high end ported set of heads that were at 10.1:1 compression ratio. I'll find the post later, but with all his testing, a higher compression always yeilded better results while using the same cam, headers, intake manifold etc.
I wouldn't be so quick to discount the benefits of a higher dcr/scr with our style heads. I guess that's why some guys have better results than others based on how much they mill their heads and how tight they get their quench.
I wouldn't be so quick to discount the benefits of a higher dcr/scr with our style heads. I guess that's why some guys have better results than others based on how much they mill their heads and how tight they get their quench.
07-15-2006, 10:19 PM
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Originally Posted by 408WS6
Hey fucktard,
1st [fact] - My car is predetonating. How can you call BS on that when you don't even know me or my car.
2nd [fact] - I doubt that many *factory* cars don't have the cam specs that mine does therefore does not have the DCR that my car has. That is contributing to why my car is predetonating.
What is stated is my opinion only. What you do is up to you. I would keep my cam or go with even more overlap and bump down the compression.
Have a nice day ********.
1st [fact] - My car is predetonating. How can you call BS on that when you don't even know me or my car.
2nd [fact] - I doubt that many *factory* cars don't have the cam specs that mine does therefore does not have the DCR that my car has. That is contributing to why my car is predetonating.
What is stated is my opinion only. What you do is up to you. I would keep my cam or go with even more overlap and bump down the compression.
Have a nice day ********.
Ahhhh....
When you are wrong result to name calling... very mature.
I never said your car was not detonating... I said nothing about you or your car. Please re-read my response.
It is funny you mention DCR now... when you said nothing about it in your first response. Sounds like you made a "oh ****, I made a fool of my self, let me search the forums so I can actually figure out what I am talking about."
You said "The max you can go is 11.3:1 on 93 octane gas." Which is WRONG!
How can you say that is an opinion... You stated the above as a fact... which it is not.
I run 12.33:1 SCR and 8.75:1 DCR on 93 octane with OUT detenation...
So isn't that prrof you are wrong? As already said DCR plays a bigger role than SCR
So your statment of "The max you can go is 11.3:1 on 93 octane gas." IS BS!
And everyone on these forums will back me up on that.
