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Discussion Starter #1
I just recently forged my 392 over the summer upped the boost everything went well. Car runs great. I bought the mmx rod piston pack with a few other things. Iam in Wisconsin and it's starting to get a bit cold here. I didn't drive my car for about 2 weeks, was 55 degrees f. Out side and that motor ran like crap for 15 min after everything got to operating temp she was money. Now today it was 40. I start it up runs ok for 30 seconds then it feels like it's missing check the exhaust no smoke no nothing looked clear as can be no codes no dash lights. Let it sit for 5 min take it out drive slow till warmed up after 15 min of driving sounds and runs great !! Not sure if this is normal for forged motors do they hate temps under 60 degree or I got a problem. During summer and early fall did ot have this problem
 

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If the pistons are 3618 they do need to get temp in them before they start to work well. This is normal for forged internals from what I’ve read.


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I just recently forged my 392 over the summer upped the boost everything went well. Car runs great. I bought the mmx rod piston pack with a few other things. Iam in Wisconsin and it's starting to get a bit cold here. I didn't drive my car for about 2 weeks, was 55 degrees f. Out side and that motor ran like crap for 15 min after everything got to operating temp she was money. Now today it was 40. I start it up runs ok for 30 seconds then it feels like it's missing check the exhaust no smoke no nothing looked clear as can be no codes no dash lights. Let it sit for 5 min take it out drive slow till warmed up after 15 min of driving sounds and runs great !! Not sure if this is normal for forged motors do they hate temps under 60 degree or I got a problem. During summer and early fall did ot have this problem

Sounds like there is a problem with your Tune. (Is it Tuned?) Contact Jay Greene and he will have her running like new money.
 

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Discussion Starter #5
It is tuned well cant rule that out but tunes dont just go bad as far as I know I think ism going to run a torpedo heater in garage today for a half hr start it see what happens if it is cold weather
 

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Well today I ran my torpedo heater for 40 min got my garage to 85 f car and outside of motor was 72. I started it up and barley any shaking no funny sounds normal piston slap. Took it for a spin did not die ran great. So iam not sure if it is tune related or motor but I cant see 40 degrees have that much of an effect on 2618 mahle pistons. Gonna suck losing my car for 2 more months due to outside temperatures.
 

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They are 2618 mahle I think u posted a type o possibly but I cant say there is not a 3618
Yes that was a typo 2618 is correct


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Well today I ran my torpedo heater for 40 min got my garage to 85 f car and outside of motor was 72. I started it up and barley any shaking no funny sounds normal piston slap. Took it for a spin did not die ran great. So iam not sure if it is tune related or motor but I cant see 40 degrees have that much of an effect on 2618 mahle pistons. Gonna suck losing my car for 2 more months due to outside temperatures.
A colder Motor requires more fuel to run (richer mixture). Since the motor is struggling with cold temps....there may be a vacuum leak with the recent motor work that is leaning out the mixture causing the problem. The intake manifold may be suspect. If your Tune was good before.....and you did not make MAJOR changes....it should not cause this problem. A vacuum leak makes sense to me. I normally take WD-40 and spray a touch in suspected areas to help find the leak. The motor will increase rpm's when you find the leak. Be mindful that WD-40 is combustible and be very careful around the exhaust headers.
 

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Well today I ran my torpedo heater for 40 min got my garage to 85 f car and outside of motor was 72. I started it up and barley any shaking no funny sounds normal piston slap. Took it for a spin did not die ran great. So iam not sure if it is tune related or motor but I cant see 40 degrees have that much of an effect on 2618 mahle pistons. Gonna suck losing my car for 2 more months due to outside temperatures.
The coefficient of expansion of aluminum is 0.000013 inches per degree of F, with a 40F degree change the pistons' were nearly 0.0005" larger. While that doesn't seem like much it is a good fraction of the total clearance between the piston and cylinder wall.

That and I suspect a tune that is not geared towards "real" cold is what is going on.

Added: In a hurry and forgot to mention this expansion is per inch so a 3.5" piston while it might not expand 3.5 * that 0.0005" it will expand at least that much probably more.

Might as well add a link:

 

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Discussion Starter #11
Guys thanks so much for the replies. I checked the gaskets they good used those comatic thick head gaskets and factory intake gasket and we triple checked tourqe numbers on full assembly. Iam feeling it's just cold weather at least fingers crossed dont feel like taking it apart. On a side note I wish i got the 4032 mahle pistons since iam not planning on making this chally a 1000 horse power drag car heard those are more forgiving on cold starts and so on.
 

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Guys thanks so much for the replies. I checked the gaskets they good used those comatic thick head gaskets and factory intake gasket and we triple checked tourqe numbers on full assembly. Iam feeling it's just cold weather at least fingers crossed dont feel like taking it apart. On a side note I wish i got the 4032 mahle pistons since iam not planning on making this chally a 1000 horse power drag car heard those are more forgiving on cold starts and so on.

Makes ZERO sense for a fuel injected motor to have a problem starting with 40 or 50 degree weather. A computer controlled, fuel injected motor should fire instantly and run well. If you went with a big cam or large throttle body the Tune needs to be tweaked. You could possibly have a fuel injector problem. A vacuum leak makes the most sense to me.
 

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Curious what plugs do you have in them and what are they gapped at

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Discussion Starter #14
It's not like me to forget these types of things but forgot what plugs I bought and the gap on them but I did buy the ones that mmx recommend and gapped them to there spec. And solid man I hear ya on that looks like they mic and build those pistons at 68 degrees f any cooler they shrink warmer they expand I know iam having trouble with it to its metal 20 degrees gimme a break
 

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Discussion Starter #15
Oh and ran the torpedo heater test again today ran great had to make sure it was not a fluke. Man the wife said dont upgrade it any more am I ever going to listen...
 

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Discussion Starter #17
For sure next year probably fore fuel system custom crank pulley port the blower maybe 850 900 to the ground why not motor can handle a 1000 but how to convince her ( babe car wont run unless i do this ;) )
 

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If you have to have a heater i would say something is off. Did you do rods and bearings? New crank bearings?
Just curious. It almost sounds like clearance is to tight.. i have pistons rods cam ect mine is not like yours and i used to live in iowa and would periodically start mine in the winter.



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It's not like me to forget these types of things but forgot what plugs I bought and the gap on them but I did buy the ones that mmx recommend and gapped them to there spec. And solid man I hear ya on that looks like they mic and build those pistons at 68 degrees f any cooler they shrink warmer they expand I know iam having trouble with it to its metal 20 degrees gimme a break

A bad / dirty Air Temp Sensor will cause the same problem. Part of it's job is to add fuel in cold temps. Makes sense and I had forgotten about that little rascal. Replace that and let us know if that solves the problem. I'm not buying piston clearance causing a rough cold start.
 

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Discussion Starter #20
Uschsmp ya I got all that. Cant say you are wrong but if it was a issue where it was to tight would have been worse in summer and was completely fine then will check that sensor out got some maf cleaner none the less but this car only has 16 k on it 1 k on motor thanks for advice.
 
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