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Old 04-27-2010, 01:44 AM   #1
onefast68
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Default will to tight of a converter hurt pistons?

having a problem pinching rings from squashing the pistons...i have read some where that activating the kits at to low of a rpm will hurt pistons becuase the cylider fills up so quick at a low rpm.

my converter goes 3500rpm on motor,1st kit on off the brake,at .38 into the run i am at 4714rpm and the 2cd stage came on....at .50 i was at 5317rpm,1.0 at 6098rpm,1.31 at 6170rpm,shifted at 2.48 at 7292 rpm,rpms dropped to 6177at 2.75 into the run,crossed the 1/8 at 5.06 at 6553rpm's at 143mph..1/4 mile was 7.81 at 177 at 7400rpms..

this info is off my 7531 box..i just swapped to a 32inch tire from a 31inch and the car slowed from a 1.21 60ft to a 1.26..would you put more gear in or loosen the converter?car drives very straight with no tire spin at all,just lazy till the 2cd kit comes on,but still a little lazy with the taller tires...not scared of turning it a little higher on the topend...but if the lower rpms are hurting pistons then i want to stop that before anything else and i want it to 60ft close to 1.20.

went 4.98 on 31's but it spins sometimes on 31's ,so i put 32's on, but i want to get back to 4.90's on these tires and i do not want to spray it harder than i already am.

my first guess is to loosen the converter up about 800rpm on the launch and hope it will still hold on the big end.


3280lbs,big duke 632 with 2 32n pill foggers,1.80 glide,10inch ptc promod converter,4.10 gear,32x16slicks,tune is good and crisp,not to lean,and run 12degrees total on 2 kits.using no launch retard at all now as it doesnt need it right now..

opinions please.
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Old 04-27-2010, 08:17 AM   #2
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Default Re: will to tight of a converter hurt pistons?

IMHO....YES! You motor seems to be laboring WAY too much. Not knowing your exact combo, but in general, 12 degrees is quite soft for two 32 jet foggers which would make them lazy. I'll say again...in general! (so the keyboard nazi's don't have a cow)

Looks like a 4.30 rear gear might help both 1/8th and 1/4. You're trap rpm seems about 300 low on both (IMHO). The gear change should pick that up.
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Old 04-27-2010, 09:27 AM   #3
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Default Re: will to tight of a converter hurt pistons?

People told me I was crazy for thinking the low trans line pressure not charging the converter would hurt a piston, which would be the same as the converter tugging the motor down too far. I think it did, plus I kept trying to get after it harder and it never did pick up any or change e.t., so eventually I did hurt a couple.

I looked at it this way, when a diesel truck is pulling a load stick a pyrometer on it and put an 8 degree grade in front of it with 10,000 lbs behind it. Watch what happens to the temp in the cylinders. I don't see where it would be much different if the converter is tugging the motor down too far.

I'm taking out the converter I have in mine now, which still seems to be too aggresive and putting a smaller diameter different set up in the car, and I'll bet money it will be easier on the tuneup. (I won't have to pull as much timing or soften up cylinders as much)
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Old 04-27-2010, 09:39 AM   #4
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Default Re: will to tight of a converter hurt pistons?

The reason it hurts parts is the timing is too high at low rpm.
The curve on a stock truck is low at low rpm and high at high rpm...it is also load related...more load = less timing.
Even on our EFI Pro Stock engine...if the clutch is too tight by mistake..it will rattle all the pistons and rings...so we pull 10* out below normal rpm in timing map to stop breaking parts. The most timing you can run without "negative work" will make the most power...even if it is 10* total.
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Old 04-27-2010, 09:47 AM   #5
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Default Re: will to tight of a converter hurt pistons?

Quote:
Originally Posted by marc1166 View Post
IMHO....YES! You motor seems to be laboring WAY too much. Not knowing your exact combo, but in general, 12 degrees is quite soft for two 32 jet foggers which would make them lazy. I'll say again...in general! (so the keyboard nazi's don't have a cow)

Looks like a 4.30 rear gear might help both 1/8th and 1/4. You're trap rpm seems about 300 low on both (IMHO). The gear change should pick that up.
i agree with the soft timing..but at 14degrees it was lifting ringlands so i went to 12 and havent lifted one since..maybe it was lifting lands from the low rpm's and i cured it by softening the tune up with timing..the motor will be out today so its much easier to change the converter up than to swap gears .with my 31inch tires it was not lazy at all but i think it was slippin the tires enough to get the rpms up quicker and i was using then launch retard to help control it..there is no wheel spin on my 32's.

keep the opinions coming please
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Old 04-27-2010, 11:08 AM   #6
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Default Re: will to tight of a converter hurt pistons?

I think the converter is a bit too tight, but before I am convinced:

Titanium valves ? If so do you mind putting more rpm in the engine?
6100 is a bit low after the shift if you don't mind rpming the engine out the back door
Can you post a graph from the data logger?
Why such a low shift point?
What were your DSRPM's at the strip ?

There is no doubt that activating the nitrous at too low of rpms will hurt stuff. I had a buddy turn on 600 through a plate on a 632 on a chassis dyno at bout 3500, blew the shit out of it.
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Old 04-27-2010, 11:16 AM   #7
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Default Re: will to tight of a converter hurt pistons?

Quote:
Originally Posted by onefast68 View Post
i agree with the soft timing..but at 14degrees it was lifting ringlands so i went to 12 and havent lifted one since..maybe it was lifting lands from the low rpm's and i cured it by softening the tune up with timing..the motor will be out today so its much easier to change the converter up than to swap gears .with my 31inch tires it was not lazy at all but i think it was slippin the tires enough to get the rpms up quicker and i was using then launch retard to help control it..there is no wheel spin on my 32's.

keep the opinions coming please

That's what I'm saying, that with too tight of a converter you have to take out more timing than you normally would with the "right" converter. So it being too tight really isn't hurting any parts, as much as it is making it way more finicky on the tuneup. As far as the rpm drop on the gear change, how does the amount of nitrous change that? On mine with a small pill (.082) in the plate it drops 1460 rpm. If I pill it up (.110) that changes to 1000 rpm. A dramatic difference, but when I had this converter built there were no jet restrictions. So it kinda makes sense that it would do that with a smaller shot. Even spinning the motor higher, the rpm drop stays the same on mine anyway.
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Old 04-27-2010, 11:21 AM   #8
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Default Re: will to tight of a converter hurt pistons?

Quote:
Originally Posted by 63 NS Vette View Post
I think the converter is a bit too tight, but before I am convinced:

Titanium valves ? If so do you mind putting more rpm in the engine?
6100 is a bit low after the shift if you don't mind rpming the engine out the back door
Can you post a graph from the data logger?
Why such a low shift point?
What were your DSRPM's at the strip ?

There is no doubt that activating the nitrous at too low of rpms will hurt stuff. I had a buddy turn on 600 through a plate on a 632 on a chassis dyno at bout 3500, blew the shit out of it.
yes it has tit valves..the motor seems to pull good to about 7400,turning it higher at the shift point does not make it go faster..i would like to see it fall to maybe 6600 at the shift..can a converter be loosened on the stall without making it be to loose on the big end?

no logger on the car..just a 7531 box.
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Old 04-27-2010, 11:27 AM   #9
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Default Re: will to tight of a converter hurt pistons?

Quote:
Originally Posted by z289sec View Post
That's what I'm saying, that with too tight of a converter you have to take out more timing than you normally would with the "right" converter. So it being too tight really isn't hurting any parts, as much as it is making it way more finicky on the tuneup. As far as the rpm drop on the gear change, how does the amount of nitrous change that? On mine with a small pill (.082) in the plate it drops 1460 rpm. If I pill it up (.110) that changes to 1000 rpm. A dramatic difference, but when I had this converter built there were no jet restrictions. So it kinda makes sense that it would do that with a smaller shot. Even spinning the motor higher, the rpm drop stays the same on mine anyway.

mine drops 2400 on motor,1700 on 1 kit,1115 on both kits..the more power the more slip you get(stall) is what i have been told.
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Old 04-27-2010, 11:32 AM   #10
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Default Re: will to tight of a converter hurt pistons?

What is you slip % on the big end? My converter guy says he can adjust stall without effecting top end. I have never had to have this done so his word is all I have on that subject.

Without seeing a data logger graph it sounds like what may be happening is after the shift the engine is getting pulled down to an rpm that is close enough to peak tq that cylinder pressure is high, couple this with a converter that is too tight and the engine is not accelerating away from the situation. I am not sure how much info you can get from a 7531 box but if you can look at the engine rpms after the shift and they do not immediatly start to go up there is an issue there you need to fix with more power, more gear, looser converter, etc, otherwise the engine sits there at a too low of rpm, builds a bunch of heat, and cooks itself
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Old 04-27-2010, 11:45 AM   #11
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Default Re: will to tight of a converter hurt pistons?

Quote:
Originally Posted by 63 NS Vette View Post
What is you slip % on the big end? My converter guy says he can adjust stall without effecting top end. I have never had to have this done so his word is all I have on that subject.
using an online slip calculator(wallace racing)
mph 177
rpm 7400
gear 4.10
tire 101 rollout(32inch)

-2.487% converter slippage
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Old 04-27-2010, 11:45 AM   #12
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Default Re: will to tight of a converter hurt pistons?

Yes, they can loosen them up and still have them lockup good on top end. I don't know exactly which parts they change in them, but I know it can be done.

Wow 2.487%??? That bitch is tight. I thought mine at 6% was tight...lol
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Old 04-27-2010, 12:14 PM   #13
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Default Re: will to tight of a converter hurt pistons?

Quote:
Originally Posted by z289sec View Post
Yes, they can loosen them up and still have them lockup good on top end. I don't know exactly which parts they change in them, but I know it can be done.

Wow 2.487%??? That bitch is tight. I thought mine at 6% was tight...lol
that was (minus) -2.48....using my 1/8 mile numbers it shows 6.49 slippage(more beleivable for sure)
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Old 04-27-2010, 02:12 PM   #14
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Default Re: will to tight of a converter hurt pistons?

Quote:
Originally Posted by onefast68 View Post
that was (minus) -2.48....using my 1/8 mile numbers it shows 6.49 slippage(more beleivable for sure)

You probably need to use more rollout for the calculation. Slicks grow alot at 180

As someone else stated, there are a lot more adjustments to convertors these days than simply loose or tight. Also stall speed is pretty open as well these days with all the power management that people are doing changing your power setting at launch will affect what your convertor is doing during that portion of the run.

Convertors don't hurt parts alone, they need a little help from the tune-up to break things.
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Old 04-27-2010, 02:40 PM   #15
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Default Re: will to tight of a converter hurt pistons?

I think a converter change will help tons. I have 2 diff converters I use when I go from tt5 to a w it will save money in the long run and keep u out the engine shop
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