Why no gains after head install?
09-14-2011, 08:02 AM
#101
(I was only referring to the M6 to: (a) demonstrate that neither M6s nor stalled autos actually operate at low rpm during the launch; and (b) the existence of a stall does not, in and of itself, explain why rear gears somehow don't count on autos.)
09-14-2011, 08:15 AM
#102
May be - I am not saying that M6 is quicker, or even equal to, an automatic in the initial launch. I am trying to understand how two equal automatic cars (identical horsepower, weight, stall, etc.) with different rear gears (e.g. 3.73 in one and 3.23 in the other) are dead even in the quarter mile.
Edit* thanks pred
Last edited by HTX; 09-14-2011 at 08:48 AM.
09-14-2011, 08:34 AM
#104
TECH Senior Member
09-14-2011, 09:11 AM
#106
So given what has been discussed is it safe to say that the gear change should have little to know effect on my actual MPH..?? I do appreciate the discussion and everyone’s thoughts, but I do need some help in figuring out if I have an engine problem, if not then I will equate the loss of power to the gears and/or the tune in which I will then have a pro clean it up. Not trying to be a jerk but can we put the converter/gears discussion on hold awhile. I need some questions answered so I can better determine my next course of action. Thanks!
So what in my setup could possibly be causing my power loss? I will be doing a compression check and leak down test hopefully tonight and I can give you guys the results to help me figure out if I have a bigger problem. That being said the time frame of being cam only and now heads and cam was less than 1500 miles so I can’t see excessive engine wear negating the head performance that I should’ve gained from the heads.
I did find some oil on the threads of the plugs on cylinders 7, 5, and 3. Bad valve seal?
Rechecking the preload on the lifters according to Shane’s write up from Thunder Racing, I would get 1.25-1.35 turns to 22ft lbs on four different valves. So to me that is telling me that my PRs (7.325) might be a little short and that a 7.35 or a 7.375 PR might be a better choice. What do you guys think?
So what in my setup could possibly be causing my power loss? I will be doing a compression check and leak down test hopefully tonight and I can give you guys the results to help me figure out if I have a bigger problem. That being said the time frame of being cam only and now heads and cam was less than 1500 miles so I can’t see excessive engine wear negating the head performance that I should’ve gained from the heads.
I did find some oil on the threads of the plugs on cylinders 7, 5, and 3. Bad valve seal?
Rechecking the preload on the lifters according to Shane’s write up from Thunder Racing, I would get 1.25-1.35 turns to 22ft lbs on four different valves. So to me that is telling me that my PRs (7.325) might be a little short and that a 7.35 or a 7.375 PR might be a better choice. What do you guys think?
09-14-2011, 12:41 PM
#110
Just make sure you are using the EO/IC method. I get a different reading on the intake/exhaust valves, about a .025 difference. I can get 1.5 turns on the intake and 1.25 on the exhaust. I asked Shane if it would be worth buying another set of pushrods so all of them would be 1.5 and he said no. He pretty much talked me out of buying another set of pushrods.
09-14-2011, 01:14 PM
#111
According to Shane@Thunder Racing 1 1/4-1 1/2 turns is about optimum. Stock lifters like .040-.080 preload. With the engine cold that's on the high side but when the engine warms up the block and heads grow decreasing the amount of preload on the lifter. Depending on who you ask will depend on how much preload 1 1/2 turns is.
Just make sure you are using the EO/IC method. I get a different reading on the intake/exhaust valves, about a .025 difference. I can get 1.5 turns on the intake and 1.25 on the exhaust. I asked Shane if it would be worth buying another set of pushrods so all of them would be 1.5 and he said no. He pretty much talked me out of buying another set of pushrods.
Just make sure you are using the EO/IC method. I get a different reading on the intake/exhaust valves, about a .025 difference. I can get 1.5 turns on the intake and 1.25 on the exhaust. I asked Shane if it would be worth buying another set of pushrods so all of them would be 1.5 and he said no. He pretty much talked me out of buying another set of pushrods.
09-14-2011, 01:50 PM
#112
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how well does a stock ls6 mani work with a cam and ported heads ? also doesnt a taller gear put more strain on an engine if the powerband is raised cause of the added airflow? good luck op with the diagnosis cant wait to see what the problem is ..
09-14-2011, 03:18 PM
#113
I've been biting my tongue on responding here but there has been so much discussion about the gear situation I felt it was worth chiming in.
IMO, the OP's gear swap has little to no impact when discussing trap speeds (not ET) which is what we should be focused on because as the sharper among you know, trap speed is always directly related to power output versus weight (with DA of course always directly effecting power output).
Guys, quarter mile trap speed is ALL about your power to weight ratio....when you look at that timeslip there can be a dozen variables that effect your ET (probably more), but the driving force behind your trap speed is the power your making and the weight of what your accelerating down the 1320 (aerodynamics next on the list more applicable in fast cars with big trapspeeds where the wall of air your pushing becomes a much larger issue)
A gear swap will have an impact on ET because the additional torque multiplication helps the car get out of the hole faster (assuming the traction is there), but trap speed is primarily a function of power to weight ratio will be very close regardless of the rear gears in question. Without increasing power or decreasing weight its difficult to change the trap speed but ET can vary a great deal with launch technique, converter, and gear ratio swaps. Look at the likes of Super stock and classes that really optimize track results without big horsepower involved....they have incredible ET's but very modest trap speeds because there not really making big power....just harnessing and optimizing what they have with deep gears and big stall speed converters and an incredible amount of time devoted to their suspension as well.
Ive seen some cars trap slightly higher with deader gears but of course lose a good deal of ET (which is mostly seen in the 60 foot times) and by the 330 mark the gear swap has zero effect on things assuming the car is shifted exactly the same to optimize its power curve.
Consider a few things here....
Higher gears (lower numerically) will almost always look better on the chassis dyno so technically there is more power available at the tire (and we know the weight of the car hasn't changed).
The OP has stated that the car 60 footed almost the same....thats where you would potentially see the greatest disadvantage in the gear swap and its not applicable here based on his documented results.
Some personal real world experience....I had a 71 Chevelle I used to race with a smallblock and a turbo 400 some 25 years ago....nothing exotic (tame by todays standards)....a high 12 second car. I had two complete rears that I used to swap from time to time because I was dating a girl that went to college 400 miles away (not a fun drive with the 4.11's in the car!!). Used to drop in a 336 rear before embarking on that journey (had the swap down to less than a couple of hours after a few cracks at it) and while the car always felt lazier with the highway gears (it didn't get to redline as quickly in any of the three gears), a buddies Nova who was fender to fender with me with the 4.11 rear installed, was still fender to fender with me from a roll with the 336 rear, all the way till one of us chickened out at 120+ or he ran out of gear....LOL.
And it makes sense because only horsepower dictates acceleration....not torque (and I understand the relation). In the case of my Chevelle, obviously my horsepower hadn't changed. Just for grins one weekend I decided to hit the local track with the 336 rear still installed in the car and while I was about 3 tenths slower (my 60 foot showing a good part of that loss), I ran within half a mile per hour of my best with the 4.11 rear in the car (on a warm fall day in decent air). At the time it was kind of an enlightening experience and it made sense based on racing my buddies Nova from a roll.
There are many speed calculators (online, sliderules, etc.) that can figure out your trap speed (and an ET assuming you can optimize the power required to run that trapspeed) and Im almost sure that not a single one of them asks you to input torque....only horsepower, weight, and aero in some of them (coefficient of drag for the car in question).
Getting this post back on topic I found it interesting that the OP's car ran the same 60 foot (with the deader gear) yet didn't pull any harder on the back half of the track which is what the trap speed is indicating....where is the back to back dyno curves of both of these combo's.....I suspect that would shed alot of light on what's going on here.
Anyway....sorry to derail with another post mainly related to gearing but I thought what I had to offer was worth the time reading and could be beneficial to the OP who is trying to sort things out. In the last 30 years I have been playing with hot rods and performance engines, I have never personally seen an increase in power that didnt show me a higher trap speed at the track....it simply always does. Its been my experience that when you have more available horsepower (be it engine mods, a lower density altitude, whatever) it will always show improvements in your trap speed regardless of gearing....ET however is an altogether different topic....much more complicated with a ton more variables.
-Tony
IMO, the OP's gear swap has little to no impact when discussing trap speeds (not ET) which is what we should be focused on because as the sharper among you know, trap speed is always directly related to power output versus weight (with DA of course always directly effecting power output).
Guys, quarter mile trap speed is ALL about your power to weight ratio....when you look at that timeslip there can be a dozen variables that effect your ET (probably more), but the driving force behind your trap speed is the power your making and the weight of what your accelerating down the 1320 (aerodynamics next on the list more applicable in fast cars with big trapspeeds where the wall of air your pushing becomes a much larger issue)
A gear swap will have an impact on ET because the additional torque multiplication helps the car get out of the hole faster (assuming the traction is there), but trap speed is primarily a function of power to weight ratio will be very close regardless of the rear gears in question. Without increasing power or decreasing weight its difficult to change the trap speed but ET can vary a great deal with launch technique, converter, and gear ratio swaps. Look at the likes of Super stock and classes that really optimize track results without big horsepower involved....they have incredible ET's but very modest trap speeds because there not really making big power....just harnessing and optimizing what they have with deep gears and big stall speed converters and an incredible amount of time devoted to their suspension as well.
Ive seen some cars trap slightly higher with deader gears but of course lose a good deal of ET (which is mostly seen in the 60 foot times) and by the 330 mark the gear swap has zero effect on things assuming the car is shifted exactly the same to optimize its power curve.
Consider a few things here....
Higher gears (lower numerically) will almost always look better on the chassis dyno so technically there is more power available at the tire (and we know the weight of the car hasn't changed).
The OP has stated that the car 60 footed almost the same....thats where you would potentially see the greatest disadvantage in the gear swap and its not applicable here based on his documented results.
Some personal real world experience....I had a 71 Chevelle I used to race with a smallblock and a turbo 400 some 25 years ago....nothing exotic (tame by todays standards)....a high 12 second car. I had two complete rears that I used to swap from time to time because I was dating a girl that went to college 400 miles away (not a fun drive with the 4.11's in the car!!). Used to drop in a 336 rear before embarking on that journey (had the swap down to less than a couple of hours after a few cracks at it) and while the car always felt lazier with the highway gears (it didn't get to redline as quickly in any of the three gears), a buddies Nova who was fender to fender with me with the 4.11 rear installed, was still fender to fender with me from a roll with the 336 rear, all the way till one of us chickened out at 120+ or he ran out of gear....LOL.
And it makes sense because only horsepower dictates acceleration....not torque (and I understand the relation). In the case of my Chevelle, obviously my horsepower hadn't changed. Just for grins one weekend I decided to hit the local track with the 336 rear still installed in the car and while I was about 3 tenths slower (my 60 foot showing a good part of that loss), I ran within half a mile per hour of my best with the 4.11 rear in the car (on a warm fall day in decent air). At the time it was kind of an enlightening experience and it made sense based on racing my buddies Nova from a roll.
There are many speed calculators (online, sliderules, etc.) that can figure out your trap speed (and an ET assuming you can optimize the power required to run that trapspeed) and Im almost sure that not a single one of them asks you to input torque....only horsepower, weight, and aero in some of them (coefficient of drag for the car in question).
Getting this post back on topic I found it interesting that the OP's car ran the same 60 foot (with the deader gear) yet didn't pull any harder on the back half of the track which is what the trap speed is indicating....where is the back to back dyno curves of both of these combo's.....I suspect that would shed alot of light on what's going on here.
Anyway....sorry to derail with another post mainly related to gearing but I thought what I had to offer was worth the time reading and could be beneficial to the OP who is trying to sort things out. In the last 30 years I have been playing with hot rods and performance engines, I have never personally seen an increase in power that didnt show me a higher trap speed at the track....it simply always does. Its been my experience that when you have more available horsepower (be it engine mods, a lower density altitude, whatever) it will always show improvements in your trap speed regardless of gearing....ET however is an altogether different topic....much more complicated with a ton more variables.
-Tony
Last edited by Tony Mamo @ AFR; 09-14-2011 at 03:29 PM.
09-14-2011, 03:34 PM
#114
I've been biting my tongue on responding here but there has been so much discussion about the gear situation I felt it was worth chiming in.
IMO, the OP's gear swap has little to no impact when discussing trap speeds (not ET) which is what we should be focused on because as the sharper among you know, trap speed is always directly related to power output versus weight (with DA of course always directly effecting power output).
Guys, quarter mile trap speed is ALL about your power to weight ratio....when you look at that timeslip there can be a dozen variables that effect your ET (probably more), but the driving force behind your trap speed is the power your making and the weight of what your accelerating down the 1320 (aerodynamics next on the list more applicable in fast cars with big trapspeeds where the wall of air your pushing becomes a much larger issue)
A gear swap will have an impact on ET because the additional torque multiplication helps the car get out of the hole faster (assuming the traction is there), but trap speed is primarily a function of power to weight ratio will be very close regardless of the rear gears in question. Without increasing power or decreasing weight its difficult to change the trap speed but ET can vary a great deal with launch technique, converter, and gear ratio swaps. Look at the likes of Super stock and classes that really optimize track results without big horsepower involved....they have incredible ET's but very modest trap speeds because there not really making big power....just harnessing and optimizing what they have with deep gears and big stall speed converters and an incredible amount of time devoted to their suspension as well.
Ive seen some cars trap slightly higher with deader gears but of course lose a good deal of ET (which is mostly seen in the 60 foot times) and by the 330 mark the gear swap has zero effect on things assuming the car is shifted exactly the same to optimize its power curve.
Consider a few things here....
Higher gears (lower numerically) will almost always look better on the chassis dyno so technically there is more power available at the tire (and we know the weight of the car hasn't changed).
The OP has stated that the car 60 footed almost the same....thats where you would potentially see the greatest disadvantage in the gear swap and its not applicable here based on his documented results.
Some personal real world experience....I had a 71 Chevelle I used to race with a smallblock and a turbo 400 some 25 years ago....nothing exotic (tame by todays standards)....a high 12 second car. I had two complete rears that I used to swap from time to time because I was dating a girl that went to college 400 miles away (not a fun drive with the 4.11's in the car!!). Used to drop in a 336 rear before embarking on that journey (had the swap down to less than a couple of hours after a few cracks at it) and while the car always felt lazier with the highway gears (it didn't get to redline as quickly in any of the three gears), a buddies Nova who was fender to fender with me with the 4.11 rear installed, was still fender to fender with me from a roll with the 336 rear, all the way till one of us chickened out at 120+ or he ran out of gear....LOL.
And it makes sense because only horsepower dictates acceleration....not torque (and I understand the relation). In the case of my Chevelle, obviously my horsepower hadn't changed. Just for grins one weekend I decided to hit the local track with the 336 rear still installed in the car and while I was about 3 tenths slower (my 60 foot showing a good part of that loss), I ran within half a mile per hour of my best with the 4.11 rear in the car (on a warm fall day in decent air). At the time it was kind of an enlightening experience and it made sense based on racing my buddies Nova from a roll.
There are many speed calculators (online, sliderules, etc.) that can figure out your trap speed (and an ET assuming you can optimize the power required to run that trapspeed) and Im almost sure that not a single one of them asks you to input torque....only horsepower, weight, and aero in some of them (coefficient of drag for the car in question).
Getting this post back on topic I found it interesting that the OP's car ran the same 60 foot (with the deader gear) yet didn't pull any harder on the back half of the track which is what the trap speed is indicating....where is the back to back dyno curves of both of these combo's.....I suspect that would shed alot of light on what's going on here.
Anyway....sorry to derail with another post mainly related to gearing but I thought what I had to offer was worth the time reading and could be beneficial to the OP who is trying to sort things out. In the last 30 years I have been playing with hot rods and performance engines, I have never personally seen an increase in power that didnt show me a higher trap speed at the track....it simply always does. Its been my experience that when you have more available horsepower (be it engine mods, a lower density altitude, whatever) it will always show improvements in your trap speed regardless of gearing....ET however is an altogether different topic....much more complicated with a ton more variables.
-Tony
IMO, the OP's gear swap has little to no impact when discussing trap speeds (not ET) which is what we should be focused on because as the sharper among you know, trap speed is always directly related to power output versus weight (with DA of course always directly effecting power output).
Guys, quarter mile trap speed is ALL about your power to weight ratio....when you look at that timeslip there can be a dozen variables that effect your ET (probably more), but the driving force behind your trap speed is the power your making and the weight of what your accelerating down the 1320 (aerodynamics next on the list more applicable in fast cars with big trapspeeds where the wall of air your pushing becomes a much larger issue)
A gear swap will have an impact on ET because the additional torque multiplication helps the car get out of the hole faster (assuming the traction is there), but trap speed is primarily a function of power to weight ratio will be very close regardless of the rear gears in question. Without increasing power or decreasing weight its difficult to change the trap speed but ET can vary a great deal with launch technique, converter, and gear ratio swaps. Look at the likes of Super stock and classes that really optimize track results without big horsepower involved....they have incredible ET's but very modest trap speeds because there not really making big power....just harnessing and optimizing what they have with deep gears and big stall speed converters and an incredible amount of time devoted to their suspension as well.
Ive seen some cars trap slightly higher with deader gears but of course lose a good deal of ET (which is mostly seen in the 60 foot times) and by the 330 mark the gear swap has zero effect on things assuming the car is shifted exactly the same to optimize its power curve.
Consider a few things here....
Higher gears (lower numerically) will almost always look better on the chassis dyno so technically there is more power available at the tire (and we know the weight of the car hasn't changed).
The OP has stated that the car 60 footed almost the same....thats where you would potentially see the greatest disadvantage in the gear swap and its not applicable here based on his documented results.
Some personal real world experience....I had a 71 Chevelle I used to race with a smallblock and a turbo 400 some 25 years ago....nothing exotic (tame by todays standards)....a high 12 second car. I had two complete rears that I used to swap from time to time because I was dating a girl that went to college 400 miles away (not a fun drive with the 4.11's in the car!!). Used to drop in a 336 rear before embarking on that journey (had the swap down to less than a couple of hours after a few cracks at it) and while the car always felt lazier with the highway gears (it didn't get to redline as quickly in any of the three gears), a buddies Nova who was fender to fender with me with the 4.11 rear installed, was still fender to fender with me from a roll with the 336 rear, all the way till one of us chickened out at 120+ or he ran out of gear....LOL.
And it makes sense because only horsepower dictates acceleration....not torque (and I understand the relation). In the case of my Chevelle, obviously my horsepower hadn't changed. Just for grins one weekend I decided to hit the local track with the 336 rear still installed in the car and while I was about 3 tenths slower (my 60 foot showing a good part of that loss), I ran within half a mile per hour of my best with the 4.11 rear in the car (on a warm fall day in decent air). At the time it was kind of an enlightening experience and it made sense based on racing my buddies Nova from a roll.
There are many speed calculators (online, sliderules, etc.) that can figure out your trap speed (and an ET assuming you can optimize the power required to run that trapspeed) and Im almost sure that not a single one of them asks you to input torque....only horsepower, weight, and aero in some of them (coefficient of drag for the car in question).
Getting this post back on topic I found it interesting that the OP's car ran the same 60 foot (with the deader gear) yet didn't pull any harder on the back half of the track which is what the trap speed is indicating....where is the back to back dyno curves of both of these combo's.....I suspect that would shed alot of light on what's going on here.
Anyway....sorry to derail with another post mainly related to gearing but I thought what I had to offer was worth the time reading and could be beneficial to the OP who is trying to sort things out. In the last 30 years I have been playing with hot rods and performance engines, I have never personally seen an increase in power that didnt show me a higher trap speed at the track....it simply always does. Its been my experience that when you have more available horsepower (be it engine mods, a lower density altitude, whatever) it will always show improvements in your trap speed regardless of gearing....ET however is an altogether different topic....much more complicated with a ton more variables.
-Tony
Thank you for the post!
That is always the way I understood it to. That is why I am not too concerned with my e.t. just the MPH. Another thing I need to mention is that I only ran the car with just the cam and stock heads for maybe 1500 miles. So having said that I should still see some gain from heads regardless of whether the engine is worn or not. Unless the increased compression is making a cylinder sealing problem worse because of the increased pressure in the cylinder..?? Could this be a true statement?
09-14-2011, 03:56 PM
#115
First and foremost, you really need to take your slips and use the date/time on them and enter them here:
http://www.dragtimes.com/da-density-...calculator.php
It would be really nice to rule out the weather 100%.
http://www.dragtimes.com/da-density-...calculator.php
It would be really nice to rule out the weather 100%.
09-14-2011, 05:26 PM
#120
Regarding the drive it was brutal with 4.11's....dont forget no overdrive.....this is kickin it old school....LOL
3200 RPM's for barely 60 MPH was agonizing but I did that on the way there....the way home I said screw it and drove almost 4K the entire painful ride home (many looks from passing cars with guys thinking "shift man....shift!")
Anyway....it was during that painful ride home I realized I wouldn't do this again until I bought another rear (I picked up an inexpensive 10 bolt posi versus the 4.11 12 bolt I normally ran). Worked out great....kept it behind my shed and broke it out a few times a year for the drive to Syracuse (from Long island).
Not long after the track outing though and realizing the car wasn't really any slower I kept it in for quite awhile but I always missed how quickly the car would seem to accelerate and get to redline with the 4.11's in the back!
A good percentage of the gains from gear swaps is the perception of how fast you car is because of the quicker rush to redline....what you have to realize is your covering less ground with less speed at the same RPM now....like a 10 speed bike in first gear instead of say third to overemphasize in an attempt to make a point.
-Tony