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I think there is a reoccuring problem with....

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BurritaSVT

Veteran CEG'er
Joined
Feb 28, 2001
Messages
756
Location
houma, LA 70360
I am sorry to say first off the engine more than likely won't make it to SZ 2007 due to engine problems beyond my control. F

First off we all know I spun a rod due to thin oil and high heat on the oil side. When I tore the motor down I saw every journal in the motor was blueish meaning the oil was so thin and hot I had no protection on the motor journals.

I also had another crank redone I had a 2.5 liter crank (that will allow my motor to spin over a 3 liter crank) It will also give me faster accelration since the counter weights are closer to the center axis of rotation. Also will be less oil resistance going through the oil pool for less resistance. The crank had to have mallory plugs drill and welded in the crank to add the weight needed to balance the smaller crank to the 3 liter. The darn plugs were $75 a peice wow. but I am excited to rev this baby over 7500rpms.

Well the real reason I posted this info is because I noticed that various pistons were rubbing the block on the skirts. My engine builders builds more high performance motors than most shops do. The guy does viper motors that are in the 9 sec along with other top fuel cars. He is bery knowledgable too. And when I was boring the block I told him that diamond wanted to have th eblock between 0.0045 and .0005 over piston size for ring clearance he was shocked and said that was to tight. I listening to Diamond stayed with there specs but when I brought the pistons and block to him to show him the scars the skirts made on the cylinder walls he said I told you it was to tight.
So basically he saying that in a turbocharged car you want the pistons to have more clearnace than a NA motor due to the expansion of the pistons. I remember my 2.5 liter motor was the same and I blamed it on detonation but I really think I have a repeat here.

I like to know if anyone here has taken off some diamond pistons once ran with miles and noticed any similar rubbing of the skirts. I know it is somewhat normal to have small contact but not enough to scar the cylinders.

Well I have to rehone the block .001 over and buy new rings so I will build the motor next week and If I am not busy at work I may get lucky and have it built but I am not going to rush a $5k motor

I will bring my 2.5 liter stocker up to SZ and whip up some 3 liter...lol jk
 
BurritaSVT said:
So basically he saying that in a turbocharged car you want the pistons to have more clearnace than a NA motor due to the expansion of the pistons. I remember my 2.5 liter motor was the same and I blamed it on detonation but I really think I have a repeat here.
Click to expand...

Alot of the 03 Cobra guys complain about the tight piston to cylinder wall clearances...supposedly done that way so the motor doesn't make a racket and smoke at startup. Of course it has a downside as well...and that's the problem you're having. Terminator owners are nazi like when it comes to "cooling mods" to keep from frying their rear 2 cylinders (not "optimal" coolant flow there).

Anyway, why doesn't someone build a motor to the specs that guy gotapex has done?? isn't he making like 450-500hp with no problems??
 
Did you tell diamond what boost pressures you'd be running and all that? I'm assuming you did but in a turbo engine making lots of power (ie lots of boost) you usually end up with huge clearances that annoy normal people on cold start and stuff like that.

I would contact diamond with pics of the cylinder walls and see what they have to say as well.
 
In another post of his, I believe he said he was running 5w-30, which like he said is way thin for a turbo engine. I'm sure he has an air to oil cooler since svt's have them stock, but maybe a better question is does he have an upgraded one?

Sucks that you're having trouble joey but atleast you found the issue.
 
Kremithefrog said:
In another post of his, I believe he said he was running 5w-30, which like he said is way thin for a turbo engine. I'm sure he has an air to oil cooler since svt's have them stock, but maybe a better question is does he have an upgraded one?

Sucks that you're having trouble joey but atleast you found the issue.
Click to expand...

Ya 5w-30 is to thin. And svt's have a water to oil cooler.
 
Well I recognized the oil was to thin after the fact but the sideskirts rubbing the bore is a clearance issue that most should be aware of the cobra and the lightnings come with more clearance I found out tonite than the stock mustang. Why because they have boosted application but the draw back is piston clatter when cold but once the psiton heat up they expand to stop the clatter but they never see tightness like my last two built motors saw. I beleive Daimond is using the stock clearance which are not sufficent for boost application but may be fine for NA. I will do some more research on what might be the best clearance for our application.
 
any chance you could have put the pistons in backwards?

I know that's kind of a DQ....but mine didn't even come with arrows on them.
 
My come with a F on them stating the piston side goes to the front of the engine so I did have them right but there were only 2 out of the 6 that were rubbing enough to cause damage but my builder said that the cylinders were more than likely running a little hotter than the others.
 
The piston to bore clearances are very tight on these engines stock but the factory prevents the skirts from scoring thecylinders by using a moly coating on the skirts.

Your engine didn't seize up from the pistons scoring the walls so that obviously wasn't too tight for high boost. I would think that you could send your pistons out to Swain coatings or something and have them coated on the skirts to prevent that next time, as well as coat the tops to prevent heat transfer.
Might be one of the better mods to do on your engine.

Also, yes the oil is too thin, we talked about this before and 10w40 is what I recommend for that engine.
 
I run 0W40 on a NA car because of the rpm I hit and heat it generates.
however on a different note. I have the stock pistons and rings. Aftermarket pistons and rings normally need cutom ring filing and fitting to make sure they are not too tight. When I tore apart my 35k mile 2.5L that spung to 8200rpm for a good portion of it's life the cylinders and rings looked great. That was on 5W30 Mobil 1.

On a related and more evil note. Funny how no turbo car to date (i.e. custom forged parts) has beat the power output of a stock 3L engine with a bare bone turbo kit??? What's up folks... Heck not like the platform could handle it EVER anyway.
 
my ring clearance were .026 on top ring and .024 on second ring and was filed and squared properly. I am saying the ring clearance for stock specs for forged piston (expand more than stocker) need mor clearances to avoid binding or overcocking on the piston. SVTcobras lighnings have forged pistons if I stand corrected and that is why they have more piston clearance than our stock pistons. So I am leaning towards saying that forged pistons need more clearance than stock correct me if I am wrong but the oil had nothing to do with my pistons. The bearings saw the to much wear and I was pushing over 500 ft/tq too so I will squeeze the oil more so I need more protection and oil thickeness to suport the loads plus I didn't have a aftermarket cooler too added to the wear too.
 
From what I know forged pistons need more clearance because they expand more under temperature. The Hypereutectic pistions actually have much better dimensional stability (change less due to temp)... too bad the compounds they add to do that make them more brittle.
 
Barge said:
From what I know forged pistons need more clearance because they expand more under temperature. The Hypereutectic pistions actually have much better dimensional stability (change less due to temp)... too bad the compounds they add to do that make them more brittle.
Click to expand...

Well said.
The answer to this one would be a beefier hyper-eutectic piston...especially since the stockers can take so much power with a good tune anyway.
I could imagine a cast hyper piston redesigned with thicker ring lands and thicker crown doing just great in this engine.
 
Really you would think a better design (for forced induction or whatever) hyper piston would actually be better than a forged. The forged are just a lot more forgiving for detonation since they tend to just kind of bend a little instead of breaking a ring land or whatever.

I guess the question then is... do manufacturers make small qty hyper pistons?

Also speaking about forged pistons, maybe people don't realize that even for a "forged" piston there can still be numerous material differences... so not every forged piston is the same as another. Unfortunately this type of information isn't always the easiest to find.
 
I would LOVE to have a company redesign a cast hyper piston with beefier parts for our cars!

Custom 9:1 pistons would be awesome as a start. Tighter tolerances for less blow-by and improved heat rejection would keep the heat in the combustion and not as much into the engine parts. Tighter tolerances also limit skirt slap making it quieter with less wear. Should be cheaper too.

Except for being brittle, they are a win win situation. :cry: Too bad it's like a snowballs chance in hell getting some made since it requires a large company to make them. Still, there are companies that might be "interested".
 
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