mouseIX

Hello all,

I'm currently building my stock block 4g63 standard bore (3.36) with OEM bottom end paired with the Mahle power pak piston set. Plans are a 300-350hp track car. strictly track duty, 30min road course sessions. My question is what are appropiate ring gaps? Using the blown gas application specs with the gap card that came with the pistons.

Spec card with pistons:

top ring: 3.36x.0055"= .01848" gap
second ring: 3.36x.0065"= .02184" gap
oil ring: minimum .015" gap

Called Mahle personally and really quickly I was given these numbers, granted the guy was very hard to hear over the phone.

top ring: .015"-.018" gap
second ring: .012"-.014" gap
oil ring: minimum .015" gap

I know general rule of thumb the top gap should be larger than the second to help compensate for the extra heat the top ring is exposed to. And I've read people questioning the spec card with Mahle's rings because its backwards. Can that be because of different ring materials used between the top and second rings? They guy on the phone however told me gaps that are more "normal" with a larger top gap and smaller second. I started checking my gaps today with the ring installed one inch into the block (as per Mahle) and the base gap of the second rings are between .017-.018". Which is larger than what I was told to grind to over the phone. currently my top rings are all at .017". I haven't touched the oil rings yet. Can anyone chime in what sound normal? Should I go bigger based off my application? Engine modifications are. HKS 272's, full bolt ons, stock turbo and manifold, and I'm looking to tune for a very safe 21psi max. shooting for +300hp

If I left out any other helpful info let me know. I'm open to suggestions. Thanks for the help, I'm going to go drink a beer now.

Cheers

Craig

mouseIX

Bump

My wife wants this thing out of the house hahaha

okevolutionVIII

iTrader: (71)

.018-.022 for the top and .020-.026 for the 2nd are good numbers to aim for. I had an issue with my ring gaps being larger than what I wanted right out of the box after getting my p2w clearance to .004. I got .024 and .031, no problems with it at all. The difference in gap is extremely small and all a larger gap will do is burn a little oil and have a better safety margin when the engine is run hard, perfect for road racing.

mouseIX

Bump. Thanks for the input.

WRC-LVR

iTrader: (1)

Hi Craig,

Yes typically the end gap is bigger on the top ring due to the extra heat. Not sure about the material for the second ring.

You might pm TedB as he is very knowledgable about builds and blocks

Mahle is an excellent piston and crank maker both cast and forged ( VW and Porsche have used them for 60+ years )

Are the pistons forged or cast? What have you set the PTW clearance to ?

Milburn

okevolutionVIII

iTrader: (71)

To my knowledge, the 2nd ring gap should be larger to help release gasses trapped in between the 1st and 2nd rings and the 1st ring is tighter to keep more gasses out and compression up in the first place but yes, the top ring will see more heat and obviously expand more.

I'm sure there's a good reason to do it either way and as long as they aren't too tight which would cause the ring ends to touch and break/score cylinder walls when everything gets really hot, it will run hard perfectly fine.

WRC-LVR

iTrader: (1)

/\/\ True def makes a difference if the pistons are forged as they will need more clearance. A little tight and they could over compress the rings and cause what you are describing. Forged internals are built loose for this and other reasons. Cast pistons do not expand as much and can run tighter PTW and ring end gaps. But it also depends on the type of material the piston is made of as well as being forged, pressure cast or spun cast.

Oil rings are typically 3 piece and allow gases to flow easily so i dont beleive the #2 ring would need to be gapped wider. But i could be wrong.

Mahle should know the answer to all his questions if he talks to the right guys.

Craig will be running WOT most of the time, so 21 psi was the limit he settled on to help control heat and detonation. It will be tuned safely at that limit. IMHO we don't want oil getting in there as that raises cyl temp , creates hotspots and may lead to other bad things. He needs a good catch can system to minimize this issue.

mouseIX

Sorry for the delay. I finally received the tools needed to properly measure my piston to wall clearance. The Pistons are Forged.

Cylinder 1 PTW=0.0047"
Cylinder 2 PTW=0.0050"
Cylinder 3 PTW=0.0045"
Cylinder 4 PTW=0.0050"

Average PTW of 0.0048"

Thanks

Craig

WRC-LVR

iTrader: (1)

Craig,

The more i think about it the top ring needs to have more gap as it will have more heat directly on it. This is definitely in line with the blown engine info that Mahle gave you with the top gaps set to .015-.018 and the second ring to .012-.014 as you have posted up.

IMHO this will allow the top ring room for more expansion. The smaller second ring will trap blowby from the top ring. Im thinking that people who set the top ring to .018 and the second ring to .022 or more are the ones that post up about their oil consumption use. Excess crankcase pressure is my estimate..

What specs for the PTW did Mahle give you ? Are you in line with them ( .0045-.0050 as you posted) or do you need to have the block honed for more clearance?

If inline with the PTW specs, then set the ring end gap to the Mahle specs.

mouseIX

I need to contact Mahle again. The problem is the second ring gap out of the box is larger than the spec that Mahle on the phone told me... I believe the rings might have been packaged wrong (top and second rings swapped). i will talk with them tomorrow and let you know what I find.

WRC-LVR

iTrader: (1)

Yeah bad info or wrong parts kills cars....measure five times then grind once slowly :-)

See ya at C&O this weekend. Maybe I'll get a ride in the Porsche

mouseIX

So I just got off the phone with Mahle after a very informative discussion with one of there tech help guys named John. After crunching the numbers he settled on 0.018" for the TOP and SECOND rings. Suprisingly the Mustang Cobra Jet's use Mahle equipment and the piston diameters are a hair bigger than OEM 4g63 2.0L. Those engines also run the same .018" gap top and bottom.

Also we I picked up my seats and harness' from Ryan yesterday I spoke with him about building his motor. And general consensus from him and his discussions with Chad @ CBRD and AMS I've concluded that for the most part everyone gaps their rings too wide. Hence the countless threads of high horse power built motors with large amounts of blow by. On his 600hp+ AMS 2.3RR the gaps are similar to what I've posted above. A lot smaller than what I have read for a motor of that caliber. Funny that he has never had blow by issues hahaha.

Yes I will be at C&O on sunday around 7am in my fathers 911. See you then!

Cheers,

Craig

WRC-LVR

iTrader: (1)

Glad you had a good discussion with Mahle. I strongly suspected the gaps being touted by other people in the motorsports section were way wide....I still think it is going to be affected by the expansion of the piston. Personally .018 is pretty wide but blown motors with forged components need a decent gap. .005 sounds right for the PTW iMHO with forged pistons

.018 on both and .005 PTW ...go for it .

And general consensus from him and his discussions with Chad @ CBRD and AMS I've concluded that for the most part everyone gaps their rings too wide. Hence the countless threads of high horse power built motors with large amounts of blow by. On his 600hp+ AMS 2.3RR the gaps are similar to what I've posted above. A lot smaller than what I have read for a motor of that caliber. Funny that he has never had blow by issues hahaha.


Chad knows his stuff and AMS used to build solid 4g63's . Im thinking you have corroboration here.

Did you need a cylinder hone to match the bores exactly or do you have one ? LMK as I still have one in the tool box you can borrow if necessary

So when should we expect the assembly to get done? PM me when I need to do the base tune.

So maybe the mustang pistons would work with the correct rod and a minor bore ? 010 or .020 ? What is the pin height and are they gonna be tough enough for 30-40 psi of boost at 8-9K ?

Cya at C&O