Uh Oh, Too Much Compression?
TECH Fanatic
Joined: Feb 2004
Posts: 1,259
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From: Lexington, KY
I think your on the edge but if your not having any problems I would leave it alone. Do you have scanning capabilities to see if you are getting KR? If it is too high for the gas you are running it will show up with knock retard.
I don't have a scanning tool but I had the car tuned with this set-up, I will be switching to the GM MLS gasket and flycutting my pistons soon anyways so I should lose some compression there... But as for knocking, I'm not sure... After the tune my tuner said there was a little ping, so he took out timing? and it went right away
They start out at 66cc so 66 - 59 = 7cc of material removed. It takes about .007 milling to removed 1cc from a traditional LS1 head. So 7cc x .007 = .049.
Speed inc has this option for AFR heads on their website:
Flat mill cylinder heads .020" (66 cc to 62.5cc)
66 - 62.5 = 3.5cc and they say it's a .020 mill so:
.020 / 3.5cc = 0.0057142857142857142857142857142857 mill / cc
That's assuming their information is correct.
Take that info and:
0.0057142857142857142857142857142857 mill x 7cc of material removed = 0.04 mill exactly.
Or you could simply take their .020 number for -3.5cc of material and double that because 66 - 59 = 7cc. I just wanted to figure out how much material needed to be removed per cc.
.020 x 2 = .040
Finally someone said the right thing. Your static compression ratio aka the 11.x:1 number doesn't really mean **** when you're talking about gasoline limits. You have to use your DCR numbers for that. Here's a really nice DCR calculator Piano Prodigy did: https://ls1tech.com/forums/generation-iii-internal-engine/630637-my-dcr-calculator-if-you-have-comp-grind-doesn-t-get-any-easier-than.html
Useless!! You have a forged shortblock with vavle reliefs. Not an apple to apple comparison.
Speed inc has this option for AFR heads on their website:
Flat mill cylinder heads .020" (66 cc to 62.5cc)
66 - 62.5 = 3.5cc and they say it's a .020 mill so:
.020 / 3.5cc = 0.0057142857142857142857142857142857 mill / cc
That's assuming their information is correct.
Take that info and:
0.0057142857142857142857142857142857 mill x 7cc of material removed = 0.04 mill exactly.
Or you could simply take their .020 number for -3.5cc of material and double that because 66 - 59 = 7cc. I just wanted to figure out how much material needed to be removed per cc.
.020 x 2 = .040
Useless!! You have a forged shortblock with vavle reliefs. Not an apple to apple comparison.
^^ nice post ^^
The thing is that I am not going to run the cometic gasket, I will be running the thicker GM gasket and also I will be flycutting my pistons .080 only on the exhaust-- If what I have been reading is correct both of those things should drop some compression from my engine right?
ALSO, I have been running the same chamber heads with the cometic gasket and a 224 cam and I have had no problems... I don't understand why I have to worry? Will the new cam (X3) effect my compression
The thing is that I am not going to run the cometic gasket, I will be running the thicker GM gasket and also I will be flycutting my pistons .080 only on the exhaust-- If what I have been reading is correct both of those things should drop some compression from my engine right?
ALSO, I have been running the same chamber heads with the cometic gasket and a 224 cam and I have had no problems... I don't understand why I have to worry? Will the new cam (X3) effect my compression
Banned
Joined: Apr 2006
Posts: 1,875
Likes: 1
From: Naperville, IL
^^ nice post ^^
The thing is that I am not going to run the cometic gasket, I will be running the thicker GM gasket and also I will be flycutting my pistons .080 only on the exhaust-- If what I have been reading is correct both of those things should drop some compression from my engine right?
ALSO, I have been running the same chamber heads with the cometic gasket and a 224 cam and I have had no problems... I don't understand why I have to worry? Will the new cam (X3) effect my compression
The thing is that I am not going to run the cometic gasket, I will be running the thicker GM gasket and also I will be flycutting my pistons .080 only on the exhaust-- If what I have been reading is correct both of those things should drop some compression from my engine right?
ALSO, I have been running the same chamber heads with the cometic gasket and a 224 cam and I have had no problems... I don't understand why I have to worry? Will the new cam (X3) effect my compression
The thing is that I am not going to run the cometic gasket, I will be running the thicker GM gasket and also I will be flycutting my pistons .080 only on the exhaust-- If what I have been reading is correct both of those things should drop some compression from my engine right?
ALSO, I have been running the same chamber heads with the cometic gasket and a 224 cam and I have had no problems... I don't understand why I have to worry? Will the new cam (X3) effect my compression
ALSO, I have been running the same chamber heads with the cometic gasket and a 224 cam and I have had no problems... I don't understand why I have to worry? Will the new cam (X3) effect my compression
Post # 23 explains why you may not need to flycut with the G5X3 cam (but you still need to check!). Also, if you haven't had detonation problems to date with your smaller 224 cam, then you shouldn't have any problems with the X3, due to its later Intake Valve Closing. As a matter of fact, thicker head gaskets reduce the activity (known as squish) in the chamber, and can increase the risk of detonation. If the are sealing well, leave them on and check clearance with cheacking springs and a dial indicator to see if it clears.
After all, Louis himself says it will.
Hi guys, there is 220 thou of valve drop with a milled, 59cc AFR and .040 cometics.
There is 200 thou of valve drop on a stock motor.
Any X series( G5, X1, X2, X3, X4, 111/112/114 excluding the xX ( which in most cases, thats install only here at the shop) will fit on a stock engine, 112 or 114. The X3 110 will not clear stock heads, but it will be close on the AFRs. You gain quite a bit of PTV with AFRs. If you are not sure, and want to know what your setup came in at, check it.
There is 200 thou of valve drop on a stock motor.
Any X series( G5, X1, X2, X3, X4, 111/112/114 excluding the xX ( which in most cases, thats install only here at the shop) will fit on a stock engine, 112 or 114. The X3 110 will not clear stock heads, but it will be close on the AFRs. You gain quite a bit of PTV with AFRs. If you are not sure, and want to know what your setup came in at, check it.
Good Luck!
Please do your self a favor and look for the G5x3 vs. MS3 Thread.
Post # 23 explains why you may not need to flycut with the G5X3 cam (but you still need to check!). Also, if you haven't had detonation problems to date with your smaller 224 cam, then you shouldn't have any problems with the X3, due to its later Intake Valve Closing. As a matter of fact, thicker head gaskets reduce the activity (known as squish) in the chamber, and can increase the risk of detonation. If the are sealing well, leave them on and check clearance with cheacking springs and a dial indicator to see if it clears.
After all, Louis himself says it will.
I wish that thread had been stickied, 'cause I know I've directed a dozen people to it since I've been here.
Good Luck!
Post # 23 explains why you may not need to flycut with the G5X3 cam (but you still need to check!). Also, if you haven't had detonation problems to date with your smaller 224 cam, then you shouldn't have any problems with the X3, due to its later Intake Valve Closing. As a matter of fact, thicker head gaskets reduce the activity (known as squish) in the chamber, and can increase the risk of detonation. If the are sealing well, leave them on and check clearance with cheacking springs and a dial indicator to see if it clears.
After all, Louis himself says it will.
I wish that thread had been stickied, 'cause I know I've directed a dozen people to it since I've been here.
Good Luck!
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^^ nice post ^^
The thing is that I am not going to run the cometic gasket, I will be running the thicker GM gasket and also I will be flycutting my pistons .080 only on the exhaust-- If what I have been reading is correct both of those things should drop some compression from my engine right?
ALSO, I have been running the same chamber heads with the cometic gasket and a 224 cam and I have had no problems... I don't understand why I have to worry? Will the new cam (X3) effect my compression
The thing is that I am not going to run the cometic gasket, I will be running the thicker GM gasket and also I will be flycutting my pistons .080 only on the exhaust-- If what I have been reading is correct both of those things should drop some compression from my engine right?
ALSO, I have been running the same chamber heads with the cometic gasket and a 224 cam and I have had no problems... I don't understand why I have to worry? Will the new cam (X3) effect my compression
Like said above running the cometics reduces squish and helps quench aka good things. What thickness are yours now? If they are still in good condition reuse them and save some money over buying new GM MLS ones.
Do you already have the cam you plan on running? If not I'd talk to Patrick G or Predator Z about designing a custom cam for your application. I also wouldn't be scared of flycutting. Yes, it's more work, but it'll be worth the extra power. With flycutting you can run a larger cam with a tighter LSA. You can also run thinner headgaskets that will help control detonation.
So let me get this straight... Louis from LGM is saying that we do not have to flycut when using a AFR 205 59cc head with the G5X3 on a 112 or a 114 LSA. I would like to know because i will be helping Rob (00formula00) install this cam and it would make life a little easier not having to fly cut. Before we cut should we clay the pistons and check PTV first. Or is it a deffinite fact that we have to flycut?????
Banned
Joined: Apr 2006
Posts: 1,875
Likes: 1
From: Naperville, IL
So let me get this straight... Louis from LGM is saying that we do not have to flycut when using a AFR 205 59cc head with the G5X3 on a 112 or a 114 LSA. I would like to know because i will be helping Rob (00formula00) install this cam and it would make life a little easier not having to fly cut. Before we cut should we clay the pistons and check PTV first. Or is it a deffinite fact that we have to flycut?????
That said, it is too easy to check & ensure it clears. Every engine is different, and a stock bottom end does not always push the pistons .007 out of the hole. Instead of pulling the heads to clay the valves, which can sometimes give a false reading, use a checking spring. This way, if you have clearance, you don't need to R&R the heads, clean the head bolt holes, etc. Here is what I suggest - take it for what it's worth:
- get the X3 cam if that's what you want
- pull the valve covers, remove the rockers and pushrods
- remove front engine dress and pull the cam
- install X3 cam, timing set & a degree wheel
- install checking springs (low tension coils) on the #1 intake and exhaust valves
- install adjustable length pushrod adjusted to the proper length - lifter preload (0.060" - 0.100")
- install a rocker arm on the intake valve and place a dial indicator on valve side of the rocker arm
- slowly turn the engine over to about 90* before TDC on the exhaust stroke (not compression)
Someone please correct the above if I've missed anything or made any errors.
Last edited by hammertime; Nov 2, 2007 at 02:59 PM.
59cc + .040 gasket, minus 1cc missing from my pistons = 11.67 SCR.
Without piston reliefs, ~11.8 sounds about right.
As I recall it, Tony's favorite formula always took the heads down to 61cc for ideal compression.
LG started taking them to 59cc, mainly to compensate for the 2cc they were flycutting out of the pistons for use with their bigger cams.
I have the X4 cam, so my DCR is a little lower than what it would be with the X3. At 11.67 SCR, and 8.77 DCR , I'm fine on 93 octane. Have not tried 91.
The DCR will be a little higher though for an X3 cam, so yeah I think that setup is probably too much for 91.
So, I am running a thicker fel pro gasket right now and everything fine, I run California91 and there is no ping/knock so what I don't understand is how if everything is of now, why would it change if I run the same gasket and flycut?
Assuming you are running .053 thick head gaskets, 59cc chambers, no valve reliefs, and a 224 duration cam on 110 ICL (IDK Thunders Lobes specs, but I used an XE-R to approximate them). It gives a SCR of 11.43, an IVC of 42* ABDC, and a scary high 8.96 DCR that should rattle that thing to death on 91 octane.
If you change nothing but the cam, the X3 grind has a 234* intake lobe on a 112 LSA and a 108 ICL. That moves your IVC to 45* ABDC, and drops the DCR to a more reasonable 8.73 - without any valve reliefs. While it may be marginal for 91 octane, it should be less likely to detonate with the larger cam than the smaller one.
I would be curious what your heads CC at for you to not have detonation issues with the TR224 cam you are running now.
