More compression and less duration or less compression and more duration?
Thread Starter
Teching In
Joined: Jun 2015
Posts: 38
Likes: 0
More compression and less duration or less compression and more duration? I am trying to decide on a top end package and I am at the point where I need to figure out how much to mill my heads. The amount that I mill will negate which cam I can stick in there. I am new to this so these differences may not even make a difference.
The bottom end is a stock lm7 with stock CR of 9.5:1 (61.15cc with .051 gasket). The heads are going to be AI 243 cast 226cc (minus the chamber machining to keep stock chamber at 64cc). Assuming a .040 gasket, do I mill them way down to 58-60cc and bump compression up to around 10:1 or only mill them down to 62cc where I will be sitting at just a tad over stock at 9.6x:1
So obviously , with the concern of valves slapping the pistons, the more I mill the less duration cam I stick in there and the less I mill the more wild a cam i can put in there .
This is a DD 4500 lb vehicle - just looking for peoples opinions. This is my first 'aftermarket' powered vehicle so I have no idea how any of this will affect normal driving...
thanks
_Zblee
The bottom end is a stock lm7 with stock CR of 9.5:1 (61.15cc with .051 gasket). The heads are going to be AI 243 cast 226cc (minus the chamber machining to keep stock chamber at 64cc). Assuming a .040 gasket, do I mill them way down to 58-60cc and bump compression up to around 10:1 or only mill them down to 62cc where I will be sitting at just a tad over stock at 9.6x:1
So obviously , with the concern of valves slapping the pistons, the more I mill the less duration cam I stick in there and the less I mill the more wild a cam i can put in there .
This is a DD 4500 lb vehicle - just looking for peoples opinions. This is my first 'aftermarket' powered vehicle so I have no idea how any of this will affect normal driving...
thanks
_Zblee
Since it's a 4500 lb DD I would add more compression with a smaller cam in order to have better lower end torque to move all that weight. With less compression and more duration you will have a higher end power which it will take a little longer to take off but you will have more power up top. (This is just my opinion)
Are you planning on boost? 9.6 is roughly what many run in some pretty high hp cars(boosted). You want as much CR as you can but those dish pistons will make it hard.
I'd go as small as AI feels is safe. Probably 56-58cc. You'll be able to run pretty much any cam you want without DCR being a problem (smaller cams usually mean higher DCR, yes I know it's based on IVC events....). With your CR being lower a bigger cam will feel very weak down low. I suggest a smaller cam. 21x-22x in duration on a lower LSA like 112+4.
Just an opinion. Talk to any of the cam guru's on here and get detailed with them on what you want.
I'd go as small as AI feels is safe. Probably 56-58cc. You'll be able to run pretty much any cam you want without DCR being a problem (smaller cams usually mean higher DCR, yes I know it's based on IVC events....). With your CR being lower a bigger cam will feel very weak down low. I suggest a smaller cam. 21x-22x in duration on a lower LSA like 112+4.
Just an opinion. Talk to any of the cam guru's on here and get detailed with them on what you want.
Thread Starter
Teching In
Joined: Jun 2015
Posts: 38
Likes: 0
Are you planning on boost? 9.6 is roughly what many run in some pretty high hp cars(boosted). You want as much CR as you can but those dish pistons will make it hard.
I'd go as small as AI feels is safe. Probably 56-58cc. You'll be able to run pretty much any cam you want without DCR being a problem (smaller cams usually mean higher DCR, yes I know it's based on IVC events....). With your CR being lower a bigger cam will feel very weak down low. I suggest a smaller cam. 21x-22x in duration on a lower LSA like 112+4.
Just an opinion. Talk to any of the cam guru's on here and get detailed with them on what you want.
I'd go as small as AI feels is safe. Probably 56-58cc. You'll be able to run pretty much any cam you want without DCR being a problem (smaller cams usually mean higher DCR, yes I know it's based on IVC events....). With your CR being lower a bigger cam will feel very weak down low. I suggest a smaller cam. 21x-22x in duration on a lower LSA like 112+4.
Just an opinion. Talk to any of the cam guru's on here and get detailed with them on what you want.
Would a difference from 9.6 to 10.1 make a noticeable difference in low end (while driving)?
_Zblee
TECH Addict
Joined: Jul 2013
Posts: 2,189
Likes: 123
From: Portland, Oregon
Going from 9.6:1 up to 10:1 probably won't be noticeable on the butt dyno, however I would bet it is crisper and more responsive.
With those lame dished pistons, and no plans for boost, I would deck those heads to the smallest combustion chamber volume/highest compression ratio possible for your local fuel quality.
You can run 11:1 static compression with pump gas, assuming you have proper squish/quench, and a cam that keeps the dynamic compression under ~8.6 with the proper lift to not induce ptv clearance issues.
Chop those heads down to 57cc combustion chamber volume and stick a 224 single pattern cam in with some mild .600" lobes and the aforementioned 112+4 lsa, and enjoy it.
With those lame dished pistons, and no plans for boost, I would deck those heads to the smallest combustion chamber volume/highest compression ratio possible for your local fuel quality.
You can run 11:1 static compression with pump gas, assuming you have proper squish/quench, and a cam that keeps the dynamic compression under ~8.6 with the proper lift to not induce ptv clearance issues.
Chop those heads down to 57cc combustion chamber volume and stick a 224 single pattern cam in with some mild .600" lobes and the aforementioned 112+4 lsa, and enjoy it.
Thread Starter
Teching In
Joined: Jun 2015
Posts: 38
Likes: 0
Going from 9.6:1 up to 10:1 probably won't be noticeable on the butt dyno, however I would bet it is crisper and more responsive.
With those lame dished pistons, and no plans for boost, I would deck those heads to the smallest combustion chamber volume/highest compression ratio possible for your local fuel quality.
You can run 11:1 static compression with pump gas, assuming you have proper squish/quench, and a cam that keeps the dynamic compression under ~8.6 with the proper lift to not induce ptv clearance issues.
Chop those heads down to 57cc combustion chamber volume and stick a 224 single pattern cam in with some mild .600" lobes and the aforementioned 112+4 lsa, and enjoy it.
With those lame dished pistons, and no plans for boost, I would deck those heads to the smallest combustion chamber volume/highest compression ratio possible for your local fuel quality.
You can run 11:1 static compression with pump gas, assuming you have proper squish/quench, and a cam that keeps the dynamic compression under ~8.6 with the proper lift to not induce ptv clearance issues.
Chop those heads down to 57cc combustion chamber volume and stick a 224 single pattern cam in with some mild .600" lobes and the aforementioned 112+4 lsa, and enjoy it.
57cc would require a tad over .05" milling, isnt that quite a lot? seems to me that I rarely see people going over .03", but I will leave this to the professionals at AI to tell me how much is safe to mill off
Trending Topics
You have it the wrong way. More duration needs more compression, and the opposite is true for less duration. So out of those, neither.
I would probably do more duration and more compression, as those two seem to compliment eachother and help offset eachother's cons.
I would probably do more duration and more compression, as those two seem to compliment eachother and help offset eachother's cons.
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
Five Reasons the Camaro Was the Most Pivotal Player in the Pony Car Wars 2.0
Brett Foote
10 Reasons the LS7 Is GM's Most Extreme Naturally Aspirated V8 Engine Ever
Verdad Gallardo
Ask Phil about welding the chambers. It's a $200-300 option, and you could get the chamber size down to the low 50cc range and not need much more than a resurfacing. My 241 heads came in at 58.5cc. You would get a much more efficient chamber that won't get by leaving them as cast.
Compression is your friend; get as much as you safely can and keep the cam in the low 220's with a tighter LSA with that heavy of a car.
Jason
Compression is your friend; get as much as you safely can and keep the cam in the low 220's with a tighter LSA with that heavy of a car.
Jason
Thread Starter
Teching In
Joined: Jun 2015
Posts: 38
Likes: 0
Ask Phil about welding the chambers. It's a $200-300 option, and you could get the chamber size down to the low 50cc range and not need much more than a resurfacing. My 241 heads came in at 58.5cc. You would get a much more efficient chamber that won't get by leaving them as cast.
Compression is your friend; get as much as you safely can and keep the cam in the low 220's with a tighter LSA with that heavy of a car.
Jason
Compression is your friend; get as much as you safely can and keep the cam in the low 220's with a tighter LSA with that heavy of a car.
Jason
Aye, if you have no plans to swap our those dish pistons welding the chambers is a great option. Certainly get the highest CR you can and stick to around 8.5-8.6DCR. It's not easy to calculate but the guys that custom spec cams can give you all the number you need for the cam and chamber size you should want. Talk to Martin, Kip, EPS or Patrick G.
The only issue is that you'll never be able to get good quench with those pistons. That have almost no flat surface area so with 91OCT I'm thinking 11:1 might be a good spot. I am running 11.6:1 with 93OCT and a 225/227 114+4 cam. My DCR is pretty high but my quench is pretty much ideal.
The only issue is that you'll never be able to get good quench with those pistons. That have almost no flat surface area so with 91OCT I'm thinking 11:1 might be a good spot. I am running 11.6:1 with 93OCT and a 225/227 114+4 cam. My DCR is pretty high but my quench is pretty much ideal.
Did not even think of this - I have seen it for repairs but did not think about it for decreasing the chamber size. I will definitaley inquire about this. thanks for the suggestion
Thread Starter
Teching In
Joined: Jun 2015
Posts: 38
Likes: 0
I just shot the idea to Phil so we will see what he says about it
