S/C pressure VS. NA high compression?
Thread Starter
Burning Brakes
Joined: Jan 2005
Posts: 790
Likes: 9
From: Charleston SC
S/C pressure VS. NA high compression?
I just had a custom head/cam package done by one of our vendors and the compression from the head work bumped compression over 2 points (LS7). I didn't think much of it because I am tuning the car for meth and may even convert to E85.
Anyway, I talked to my tuner and he is concerned about the stock bottom end being able to survive at that pressure. So now he has me a bit concerned if maybe I should put a little thicker cometic gasket on it to lower it?!?!
However, I started thinking about guys running super chargers with 4-6 psi on stock bottom ends. I do understand that under light normal driving the SC isn't making boost and may not strain the bottom end but during some spirited driving the car would def see the extra 4-6 psi.
Am I worried for nothing?
Should I strongly consider a thicker cometic?
Will Meth or E help with my concerns?
I'm looking for factual information folks so please don't cloud this post by what you think or heard. I know there are some damn good engine builders here who can point me straight.
Thank you,
Jeff
Anyway, I talked to my tuner and he is concerned about the stock bottom end being able to survive at that pressure. So now he has me a bit concerned if maybe I should put a little thicker cometic gasket on it to lower it?!?!
However, I started thinking about guys running super chargers with 4-6 psi on stock bottom ends. I do understand that under light normal driving the SC isn't making boost and may not strain the bottom end but during some spirited driving the car would def see the extra 4-6 psi.
Am I worried for nothing?
Should I strongly consider a thicker cometic?
Will Meth or E help with my concerns?
I'm looking for factual information folks so please don't cloud this post by what you think or heard. I know there are some damn good engine builders here who can point me straight.
Thank you,
Jeff
Thread Starter
Burning Brakes
Joined: Jan 2005
Posts: 790
Likes: 9
From: Charleston SC
I'm not worried about his tuning skills, this guy is great. He knows his craft very well; he was just concerned about the stock pistons and bearings. I can appreciate his concern. I just thought I would bounce his concern off of some of the pro's who know what these rotating assemblies can and cannot take............................. and still live a healthy life.
Thanks for the input though, I hope to hear more.
Tech Contributor
Joined: Mar 2003
Posts: 12,094
Likes: 197
From: Colorado Springs, CO
St. Jude Donor '08-'09-'10-'11
I'm not worried about his tuning skills, this guy is great. He knows his craft very well; he was just concerned about the stock pistons and bearings. I can appreciate his concern. I just thought I would bounce his concern off of some of the pro's who know what these rotating assemblies can and cannot take............................. and still live a healthy life.
Thanks for the input though, I hope to hear more.
Thanks for the input though, I hope to hear more.
The stock pistons handle 700rwhp from forced induction. What will kill your pistons is detonation from compression that is well past what you can run on pump gas even with the biggest cams.
You always use the thinnest gaskets before you do any milling. Thinner gaskets help keep detonation under control because they reduce quench distance and milling hurts a heads flow. Increasing gasket thickness is wrong in all cases.
Replace the heads with ones that have no milling and use thinner gaskets for 11.5:1 to 11.8:1 compression.
Thread Starter
Burning Brakes
Joined: Jan 2005
Posts: 790
Likes: 9
From: Charleston SC
I have learned a bit more about static and dynamic compression and the affects overlap plays. I'm all about learning and if there is another good source you'd recommend, I'd be grateful.
Thread Starter
Burning Brakes
Joined: Jan 2005
Posts: 790
Likes: 9
From: Charleston SC
Not to cloud the reason for this post; the car was a LOW mileage cam/bolt-on car that made 561/524 to the tires. Before I dropped an exhaust valve, I decided to pull the heads and have them gone through (little port work, SS exhaust valves, guides, bump the compression a bit, and get a little more aggressive cam to match the cylinder heads, while I was at it). My plan all along was to tune for Meth right now and possibly go E85 this summer.
To answer your question, yes, this is a street car in my eyes (I'm sure not in others). I've had 10 and 9 second capable head/cam/nitrous cars most of my life so I am pretty tolerant of a little cam surge and all the little driveability quirks that go with them. My tuner made my last cam that made the aforementioned numbers drive darn near like stock, so that is what made me want to step it up 'a bit more'.
But again, my concern is/was, can the bottom end take that kind of thump from the compression and live? I think the answer is going to be in the tune and good fuel to avoid detonation as Spin pointed out.
Fellas, I appreciate the input/feedback; I think I'm just going to move forward with the install and plan for E85 as my primary fuel.
-jeff
EDIT: Found this. Appears this is not un-charted territory.
http://forums.corvetteforum.com/c6-z...eo-inside.html
Last edited by FRDnemesis; Apr 22, 2013 at 11:38 AM.
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Former Vendor
Joined: Nov 2006
Posts: 187
Likes: 3
Stock MLS gaskets.
Not to cloud the reason for this post; the car was a LOW mileage cam/bolt-on car that made 561/524 to the tires. Before I dropped an exhaust valve, I decided to pull the heads and have them gone through (little port work, SS exhaust valves, guides, bump the compression a bit, and get a little more aggressive cam to match the cylinder heads, while I was at it). My plan all along was to tune for Meth right now and possibly go E85 this summer.
To answer your question, yes, this is a street car in my eyes (I'm sure not in others). I've had 10 and 9 second capable head/cam/nitrous cars most of my life so I am pretty tolerant of a little cam surge and all the little driveability quirks that go with them. My tuner made my last cam that made the aforementioned numbers drive darn near like stock, so that is what made me want to step it up 'a bit more'.
But again, my concern is/was, can the bottom end take that kind of thump from the compression and live? I think the answer is going to be in the tune and good fuel to avoid detonation as Spin pointed out.
Fellas, I appreciate the input/feedback; I think I'm just going to move forward with the install and plan for E85 as my primary fuel.
-jeff
EDIT: Found this. Appears this is not un-charted territory.
http://forums.corvetteforum.com/c6-z...eo-inside.html
Not to cloud the reason for this post; the car was a LOW mileage cam/bolt-on car that made 561/524 to the tires. Before I dropped an exhaust valve, I decided to pull the heads and have them gone through (little port work, SS exhaust valves, guides, bump the compression a bit, and get a little more aggressive cam to match the cylinder heads, while I was at it). My plan all along was to tune for Meth right now and possibly go E85 this summer.
To answer your question, yes, this is a street car in my eyes (I'm sure not in others). I've had 10 and 9 second capable head/cam/nitrous cars most of my life so I am pretty tolerant of a little cam surge and all the little driveability quirks that go with them. My tuner made my last cam that made the aforementioned numbers drive darn near like stock, so that is what made me want to step it up 'a bit more'.
But again, my concern is/was, can the bottom end take that kind of thump from the compression and live? I think the answer is going to be in the tune and good fuel to avoid detonation as Spin pointed out.
Fellas, I appreciate the input/feedback; I think I'm just going to move forward with the install and plan for E85 as my primary fuel.
-jeff
EDIT: Found this. Appears this is not un-charted territory.
http://forums.corvetteforum.com/c6-z...eo-inside.html
Thread Starter
Burning Brakes
Joined: Jan 2005
Posts: 790
Likes: 9
From: Charleston SC
They'd have had to take a slab of meat off the bottom of those heads in order to bring the compression up 2 points with stock pistons and stock head gaskets. You'd have to take so much off the heads that the intake alignment would likely be off. Somebody's math has to be off. You sure it didn't go up by .2?
Le Mans Master
Joined: Dec 2005
Posts: 6,999
Likes: 1,685
From: Southeast TX
[QUOTE=FRDnemesis;1583698963]Anyway, I talked to my tuner and he is concerned about the stock bottom end being able to survive at that pressure.
By "pressure", I'm assuming cylinder pressure?? That's influenced not only by compression ratio, but also by cam timing and ignition timing. It all has to work together. With heads cut that hard, you might also need to look closely at PTV clearances.
By "pressure", I'm assuming cylinder pressure?? That's influenced not only by compression ratio, but also by cam timing and ignition timing. It all has to work together. With heads cut that hard, you might also need to look closely at PTV clearances.