Wiseco 8.8:1 Piston to Wall Clearance and Ring Gap

[lccynmbr13]

Motors burning a quart every 150mi now time to rebuild. I'm going with 8.8:1 Wisecos again but I'd like to hear some input on piston to wall clearance and ring gap. I previously made 514hp/484 tq on my current setup with what I believe was a .004 PTW and I have no way of finding out what the ring gaps were since I didn't build the motor. I'll be building this one and I have some specs of my own in mind. I don't plan on ever running nitrous but I will occasionally be hitting around 40psi boost pressures at the track and consistently high 20s on the street with water/meth on an FPT04Z88HTA (damn that takes too long to type). I really want to go less than .004 on the PTW as I'm tired of the constant oil burn. If I run a .0035 PTW with 0.19 top ring and 0.21 bottom ring will that be sufficient clearance for a 650-700hp build?

 

[lccynmbr13]

Come on I know you high horsepower guys want to keep your nasty little secrets in the dark but I'm just looking for a yes or no the setup you're pondering will be sufficient type deal not your specs!

 

[HIGHPSI4]

I feel 0.0035" is too tight for forged high boost applications. I run a 0.004" PTW clearence and have no oil burning issues.

 

[sb7775]

PTW =.004

Top ring .022
Second .026

 

[My1GLaser]

Wow! I run .003 PW clearance on my Wisecos, and that info was straight from Brian Nutter himself. I run 26-28 psi no oil burning and perfect compression. I went with .018 & .022 ring gap considering I would end up with a 500 hp turbo in the near future.

I don't think the ring gaps you mention will be sufficient for that boost. The PW clearance is probably fine in my book, but get a high hp guy to chime in.

Your oil burning issue is more ring end gap related IMO.

 

[lccynmbr13]

My1GLaser how long have you been running that set up? Oil burn isn't my only concern with the PTW I'm running an AEM EMS and with my PTW the engine is incredibly loud and it's hard to decipher the knock graph. My main concern is to quiet the engine with the PTW.

HIGHPSI4 do you know what your ring gaps are?

 

[My1GLaser]

6000 miles with about 50 track passes. Its my weekend car, so I drive it like I stole it every time I crank her up. I also change the oil every 500 miles. I do take care of her, so I can beat the piss out of it.

 

[kawboy]

My main concern is that the motor wasnt machined correctly

I have Wiseco 8.3:1's and with the PTW at .004 I have zero slap, very quiet, and no oil burn.

 

[lccynmbr13]

Thanks for the quality responses guys. All information considered I think I have a good game plan for my next build. .004 PTW with .021 top and .023 bottom and I'll definately be having the machine shop verify all measurements in front of me before I pay for the work. As for the comment about the motor potentially being mismachined it gave me about a year of daily driving untuned on a factory ecu with an extra .3 liters and a factory fuel pump/injectors AND super retarded timing on the CAS until I went with my final setup because I was a do do back in the day when first put the motor in but with new knowledge comes new achievements and hopefully I'll be seeing a potential 9 second street driven demon this summer pending purchase of the dog box

 

[awddsm95]

lccynmbr13,

Sounds like you have/will have a pretty nice setup.

Your Piston to Wall clearence really depends on a number of things. Wiesco's paperwork recomends .0025" for most applications but I would venture to say that clearence is more geared towards near stock power levels.

If you will be producing anything near 650hp you should really start to think about partially filling your block. Anything above this number without a filled block is playing with fire IMO. With a partially filled block and the power level you are targeting, I would shoot for .00375-.00425" PTW with Wiesco's pistons.

If you do not fill at all, and run a full water jacket, I would stay in the .00325-.00375" PTW range.

Full filled block, I would be up there in the .0045-.0055" range, but this would be for a dedicated track car.

These are numbers that I would reccomend for Wiesco's piston material.

As far as ring gap, I think your best bet is to run the gap calculations provide on the ring install sheet. These numbers .0021-.0022 Top and .0023-.0024 Bottom ring gaps are pretty standard, and I dont think that you will find much gain going higher or lower than those. A lot of V8 guys really preach ring gap and material and such. If you have the above mentioned gaps, and the gaps are square to each other, that will treat you well.

Good Luck!

 

[94awdcoupe]

From building mostly wiseco and JE and seeing the results of PTW from .0035-.013 I would say its piston suicide to run anything under .005 PTW

It will still be quiet and allows a little room for running lean and over expanding the piston. I have boxes and boxes of ruined pistons from running in the .0035-.004.

keep in mind most people dont get the opportunity to run a built motor and later get to see what the pistons look like. I personally run .0055-.006 and get near perfect leak down results. I run .020 top and .024 second. And you can add .004 to each and still get good results.

Mosty people think that small ring gaps lead to good ring seal. they would be wrong. The ring is sealed against wall from chamber pressure that gets behind ring and pushes it against wall. the second ring needs a little more as the pressure has to pass the first ring gap first.

I tight ring gap may restrict how much pressure gets behind the ring to make positive seal. worse than that the ring expands. if it expands too much the ends can touch and bore get scored from contact. rings do not contact wall during running. they ride on film of oil.

blowby does not come from tiny little ring gaps. it come from too much loss around whole circumference of the ring.

 

[lccynmbr13]

From building mostly wiseco and JE and seeing the results of PTW from .0035-.013 I would say its piston suicide to run anything under .005 PTW

It will still be quiet and allows a little room for running lean and over expanding the piston. I have boxes and boxes of ruined pistons from running in the .0035-.004.

keep in mind most people dont get the opportunity to run a built motor and later get to see what the pistons look like. I personally run .0055-.006 and get near perfect leak down results. I run .020 top and .024 second. And you can add .004 to each and still get good results.

Mosty people think that small ring gaps lead to good ring seal. they would be wrong. The ring is sealed against wall from chamber pressure that gets behind ring and pushes it against wall. the second ring needs a little more as the pressure has to pass the first ring gap first.

I tight ring gap may restrict how much pressure gets behind the ring to make positive seal. worse than that the ring expands. if it expands too much the ends can touch and bore get scored from contact. rings do not contact wall during running. they ride on film of oil.

blowby does not come from tiny little ring gaps. it come from too much loss around whole circumference of the ring.

Very good info I'll keep this in mind. If I go with as large of a PTW are you're saying to run I can still use my old pistons (they're in great shape).

 

[SlowSpyder]

Shoot an email to brian nutter from Wiseco. [email protected]

I would go with the manufacturers recommendations for the ptw clearance and ring clearances. I cant remember off the top of my head what my ring clearances were but i machined the bores to give me a .0028 ptw clearance. Brian told me that .0025 ptw is good to 550whp if you take it easy and no more than 15psi for the first 500 miles.

.0035 ptw for 550-650whp and .004 ptw for more or with a healthy shot of nitrous.

Ive got about 2000 miles on my build with Wiseco K548M87 9 to 1 pistons on my 4g64 and ive got no problems at all. Like i said before go with what the manufacturer suggests.

 

[Cesar]

I guess these engines have already been raced to death so I'm sure someone has the right formula. Wouldn't you base the specifications on past test results? Data logs should show the results needed. Other than power, force and temperature, what else can you measure? Speed and acceleration?

 

[diambo4life]

PTW =.004

Top ring .022
Second .026

That is too big.


Don't go anything bigger than 0.020" for the end gaps and keep your piston to wall clearance in the 0.0045"-0.0055" range.

 

[e85_4g63]

I know this is an old thread, but for future searches (how I came across this thread). I spoke with a tech from Wiseco today personally, and he told me the following:

stock to 400chp (crank horsepower) .035 PTW (piston to wall)
400 to 500chp .004 PTW
500 to 600chp .045 PTW
over 650chp (consult your engine builder)

As for ring gaps:

400chp to 550chp .020 to / .022 2nd
550chp to 650chp .022 top / .024 2nd
Over 650chp (again) consult your engine builder

 

[bastarddsm]

god even .005 sounds huge, but my pops tells me back in the day forged pistons used to be run at .010" or move. Not even making close to the power per hole were making.

I run mine at .00045, and feel that its too loose for my liking. I will be switching to a set of mahles when this motor is shot.

 

[JacksonAuto]

Mosty people think that small ring gaps lead to good ring seal. they would be wrong. The ring is sealed against wall from chamber pressure that gets behind ring and pushes it against wall. the second ring needs a little more as the pressure has to pass the first ring gap first.

I tight ring gap may restrict how much pressure gets behind the ring to make positive seal. worse than that the ring expands. if it expands too much the ends can touch and bore get scored from contact. rings do not contact wall during running. they ride on film of oil.

blowby does not come from tiny little ring gaps. it come from too much loss around whole circumference of the ring.

This

 

[kidtsi]

I run...

.004 PTW

Top ring .021
Second ring .025

Boosting 34psi 530 to 600 awhp.

 

[awdspyder98]

Ok guys.. Im fixing to put my motor back together and Im a bit confused on what size gaps to run. Ill be running around 30 psi at around 550whp... as per weisco sheet that came with the piston these are the calculatons:

1. This table is in inches. If you are measuring your bore in millimeters, you will need to convert to inches by dividing your bore size by 25.4.
2. Multiply your inch bore size by the "Bore x" column for your application to determine the end gap.
Example: For the top ring of an ATV with a 4.0" bore, multiply 4.0 X .004 = .016
Application
Top Ring
Bore x
2nd Ring
Bore x
Dirt / ATV / Snow / PWC
.0040"
.0050"
High-Performance Street / Strip
.0045"
.0055"
Street-Moderate Turbo / Nitrous
.0050"
.0055"
Late Model Stock
.0050"
.0055"
Circle Track/Drag Race
.0055"
.0060"
Blown Race Only
.0065"
.0070"
Nitrous Race Only
.0070"
.0075"

so by these calculations I come up with the following
Top ring....017
2nd ring.. .019

Would there be a reason why I should deviate from these calculations? Im running .20 over pistons. 85.5mm bores