Why no gains after head install?
09-13-2011, 04:25 PM
#62
However a stall converter changes this by allowing the engine to get past that dead spot instantly, since the stall converter's job is to flash to the desired stall speed,, regardless of the gear ratio. lets say you have a 3600 stall and from a dig when you floor the car, the converter will "flash" to 3600rpm and instantly applies all the motors torque. The converter is basically slipping under 3600 rpm and the only real benifit to having the 3.73 gears is to "tighten" up that "loose" feel below stall speed.
Hope this helps... or did I make it more confusing lol?
Last edited by kinglt-1; 09-13-2011 at 04:48 PM.
09-13-2011, 04:59 PM
#64
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Ok how bout this. On my 99ss I had ARE stg2 heads (probably equal or slightly better than stock 243s), LS6intake, TR224 cam, Yank 3600SS stall 3.73 gears and ran 11.8@116-118 all day on a tune that shifted 1st-2nd and 2nd-3rd at 6000 rpms. Then I switched to 205cc AFRs and a FAST 78 but killed my 3.73s and had put 3.23s back in would run 11.9 and mph dropped to 114-115 only and never more, shifting closer to 6500. The 3.73 dropped me into the Powerband better on shifts and I was pulling above 6000rpms crossing the line. So even with more power the car ran a little slower with 3.23s.
Last edited by hardcore4sure; 09-13-2011 at 05:10 PM.
09-13-2011, 05:19 PM
#65
Ok how bout this. On my 99ss I had ARE stg2 heads (probably equal or slightly better than stock 243s), LS6intake, TR224 cam, Yank 3600SS stall 3.73 gears and ran 11.8@116-118 all day on a tune that shifted 1st-2nd and 2nd-3rd at 6000 rpms. Then I switched to 205cc AFRs and a FAST 78 but killed my 3.73s and had put 3.23s back in would run 11.9 and mph dropped to 114-115 only and never more, shifting closer to 6500. The 3.73 dropped me into the Powerband better on shifts and I was pulling above 6000rpms crossing the line. So even with more power the car ran a little slower with 3.23s.
09-13-2011, 07:25 PM
#70
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Old dyno # was 390rwhp with heavier Yank 3200 and ARE StgII (270cfm) heads, 3.23s 17X11 Grand Sport wheels and 315-35-17 Nitto DRs and a questionable mail order tune from TTS. I never dynoed with the AFR/FAST set up cuz I had the heads milled for 11.0 compression then sold the car. The new owner had it re-tuned (old tune sucked) and said it got 432 unlocked 450 locked. It had a Yank 3600SS was roughly 20lbs lighter and OEM Z06 wheels with 305-35-18 DRs. I usually ran on DRs but did ET streets once and ran 2 tenth & 2mph slower then the rear started whining. I worked at a dealership and got it replaced under warranty but had to use 3.23s. The new owner got it back to solid 11.8s @116 with new power but also ran ET Streets which were much taller. In the end had he went back to the 3.73s on the good tune shifting properly I honestly think it would have gone 11.4 or better.
09-13-2011, 07:30 PM
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It was mentioned earlier, but I don't know if you responded - how does your tune VE table compare now to when it was pre-heads? Your VE table should've increased all over, as the efficiency of the engine has been dramatically altered - the engine is receiving a lot more air now.
I reckon your tune is well worth dissecting, otherwise, you may have some mechanical factor which is contributing to it all.
Good luck.
I reckon your tune is well worth dissecting, otherwise, you may have some mechanical factor which is contributing to it all.
Good luck.
09-13-2011, 08:35 PM
#75
ok check my math. just did cyl1 intake PR. exhaust valve was starting its way down so I am on the base circle of the intake lobe. I measured 8.5 turns to 0 lash.
8.5 x .05=.425 + 6.8=7.225 + .080 preload=7.305.
So by that measurement if I am running a 7.325 PR then my preload would be at .100, correct? So could my valves be staying open? I checked this 3 times.
checking the exhaust valve now.
Just did the exhaust and came up with the exact same measurements. So to me it looks like my PRs are too long..??
8.5 x .05=.425 + 6.8=7.225 + .080 preload=7.305.
So by that measurement if I am running a 7.325 PR then my preload would be at .100, correct? So could my valves be staying open? I checked this 3 times.
checking the exhaust valve now.
Just did the exhaust and came up with the exact same measurements. So to me it looks like my PRs are too long..??
Last edited by LeftySS; 09-13-2011 at 09:01 PM.
09-13-2011, 08:41 PM
#76
Well that is what I am trying to figure out. Car does have 125K miles but I am the only owner and until the past year the car was never raced and always had the oil changed. Not saying it still isn't warn but that is why I am going to do a leak down and compression test to see though.
09-13-2011, 10:43 PM
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Exactly, very little. I didn't believe it myself except: I had a bolt on car vs. car (stock converters) only difference being 2.73 to 3.23 and neither one of us pulled. Not one inch. I have seen my car with 3.23s and 3.73s at the track with little to no effect on ET or traps. Nothing else matters when you see back to back proof. Gears in autos do give a seat of the pants feeling though....
09-13-2011, 10:46 PM
#79
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Use this: you find 0 lash then count the turns to get to 22 ft/pounds. From Shane at Thunder Racing
FWIW, EVERY cam install I have done using the LS7 lifter with a cam with greater than .600" lift (read smaller base circle) AND stock heads w/GM MLS gaskets has taken 7.425" pushrods for ~.050"-.060" preload. We measure lifter preload on each and every cam install we do. I have never had a lifter failure nor do we end up with the dreaded "sewing machine" noise.
Its very simple, If you change ANY of the following:
valve sizes, valve job, head milling, thinner/thicker head gaskets, decked block, cam with an altered base circle, etc... YOU MUST CHECK FOR PROPER PUSHROD LENGTH.
I have helped countless numbers of individuals with this process over the phone, via email, and PM's. I've posted the process on at least 3 occasions.
Here it is again in a nutshell:
1. Using the EO/IC method, get the lifter to the base circle of the cam.
2. Using a known length pushrod (7.400" is a good start with stock rockers) run the rocker arm bolt down to zero lash. This is easily done with your fingers "wiggling" the rocker, the point at which the "slack" is just gone is zero lash.
3. Set your torque wrench to 22 lb./ft. Tighten the rocker to full torque and count the number of turns it takes to get there. 1 full turn wtih a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface.
4. I normally shoot for 1 1/4 to 1 3/4 turns with stock type lifters like Comp 850's, LS1, LS7 etc.
For an example, if you use a 7.400" pushrod and come up with 3/4 of a turn, you will need at least .025" longer pushrod to get into range. If you end up with 2 1/4 turns, you will need one .025" shorter...
I might not know everything but I will tell you that this method has worked for me year after year cam swap after cam swap. We average 3 cam swaps a week here so you can do the math.
If you are not familiar with the EO/IC method for determining valve events in a 4 stroke engine, its very simple:
For a given cylinder as the Exhaust valve is Opening, the intake lifter will be on the base circle of the cam and lash/preload should be checked for that intake valve.
For a given cylinder as the Intake valve is Closing, the exhaust lifter will be on the base circle of the cam and lash/preload should be checked for that exhaust valve.
THIS METHOD ALWAYS WORKS!!!
I hope this helps someone. I have explained it so many times I think I do it in my sleep!!!
Shane
Its very simple, If you change ANY of the following:
valve sizes, valve job, head milling, thinner/thicker head gaskets, decked block, cam with an altered base circle, etc... YOU MUST CHECK FOR PROPER PUSHROD LENGTH.
I have helped countless numbers of individuals with this process over the phone, via email, and PM's. I've posted the process on at least 3 occasions.
Here it is again in a nutshell:
1. Using the EO/IC method, get the lifter to the base circle of the cam.
2. Using a known length pushrod (7.400" is a good start with stock rockers) run the rocker arm bolt down to zero lash. This is easily done with your fingers "wiggling" the rocker, the point at which the "slack" is just gone is zero lash.
3. Set your torque wrench to 22 lb./ft. Tighten the rocker to full torque and count the number of turns it takes to get there. 1 full turn wtih a stock 8mm X 1.25 bolt is ~.047" preload as measured at the pushrod/rocker interface.
4. I normally shoot for 1 1/4 to 1 3/4 turns with stock type lifters like Comp 850's, LS1, LS7 etc.
For an example, if you use a 7.400" pushrod and come up with 3/4 of a turn, you will need at least .025" longer pushrod to get into range. If you end up with 2 1/4 turns, you will need one .025" shorter...
I might not know everything but I will tell you that this method has worked for me year after year cam swap after cam swap. We average 3 cam swaps a week here so you can do the math.
If you are not familiar with the EO/IC method for determining valve events in a 4 stroke engine, its very simple:
For a given cylinder as the Exhaust valve is Opening, the intake lifter will be on the base circle of the cam and lash/preload should be checked for that intake valve.
For a given cylinder as the Intake valve is Closing, the exhaust lifter will be on the base circle of the cam and lash/preload should be checked for that exhaust valve.
THIS METHOD ALWAYS WORKS!!!
I hope this helps someone. I have explained it so many times I think I do it in my sleep!!!
Shane
09-13-2011, 10:48 PM
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Lol, makes sense as to why there's a handful of stock 2.73 cars that barely break in to the 13's, yet almost all 3.23 cars (I've seen) run 13.5-13.6 area?
Gear isn't everything in the slushbox world. But it's definately a noticeable gain.
Watched a friend's LT1 car go from 12.50's to 12.0's when he switched from a 3.23 to a 3.73. Yet it had small converter in it too?