streetzlegend

iTrader: (2)

So, since the very first day of starting this motor, I get piston slap. It is gone once I let the car idle to operating temperatures. I have read that it is normal since unlike factory pistons, wisecos need to expand. Also a mistake I made was to not find out from the machine shop how much piston/wall clearance they provided but I did tell them I was planning for 15-20psi/500ish HP. (They must have left them pistons pretty loose)

My question is, is it really that common, does anyone else experience this slapping around at cold start?

GT-ER

iTrader: (4)

Some correct me if I'm wrong but I know this USED to be the norm on forged pistons, but don't newer forged pistons contain enough silicone to reduce the amount of expansion to the point of not needed excess amounts of play when cold?

streetzlegend

iTrader: (2)

I am not sure, I did remember calling Wiseco and they told me it was normal for cold start. This was last year so perhaps even the new stuff needs to expand.

binder

iTrader: (8)

The new materials shouldn't. I'm not sure what alloy and percentage of each your pistons have but i know that this isn't a problem with new technology.

I've never had a bit of piston slap with my arais ED pistons.

machining of the cylinders is based on the manufacturers specs, it has nothing to do with how much hp or boost you are running. They don't increase clearances for more boost. That actually would cause more problems.

I have seen a number of people complaining about piston slap with wiesco pistons, but i don't think it's "normal" by any means.

streetzlegend

iTrader: (2)

Dont you need more clearance for higher horsepower? the more power the more heat, therefore the more expansion from the pistons and the need for more clearance. Which is why Wiseco provides you with a sheet saying the clearances recommended for specific uses such as NA, FI, extreme racing, etc..

MR RIZK

iTrader: (7)

When I called wiseco the impression they gave the higher the boost the larger the clearance. First question that came out of their mouth was how much boost. If the pressure was not a concern why ask? For the Wiseco's they said 3 1/2 thou

westpak

iTrader: (19)

I have those and no piston slap, it sounds like the machine shop left a little too much wall clearance

streetzlegend

iTrader: (2)

Any possible issues with having too much wall clearance? As you saw on my oil report, my chrom is a little high, dont know if its related.

binder

iTrader: (8)

maybe they like to sound important??

I've only used 1 set of specs for any of the engines i've ever built. Granted these were high performance motorcycle engines, but they were revving to 17k and strung out. When i get my pistons they come with 1 clearance.

Arias has 1 clearance.

I'm sure it might make some difference but the heat thing isn't going to be key. You don't see people running around with 240* temps because they are boosted. My coolant and oil temps are the same as it was on a stock block so my engine is runnign the same temps. Might have a combustion chamber increase in temperature temporarily but how do they know you're not runnign meth or anything to cool the charge? they obviously didn't ask that question either did they?


You will have increased wear with piston slap. It will eventually wear the bore of the cylinder into an oval and you'll start losing compression. It will wear the crap out of the piston skirt too.

westpak

iTrader: (19)

I am not an expert in reading those reports but the chromium seems would be from piston ring wear, which depending on how bad the clearances are and the piston is allowed to rock too much the piston rings will wear quicker as they wont have the optimum seating surface with the walls, in addition to the other possible issues mentioned

MR RIZK

iTrader: (7)

binder you maybe right that they want to sound important but the interesting point is the the Wiseco spec sheet says 0.0025 where there tech support says 0.0035. So much for consistency

binder

iTrader: (8)

ya, i always have the machinists use the specs given with the set of pistons i order. I never alter them no matter what mods are going on the bike. Even for the bike that took a 150 shot of nitrous. Still used the clearances given. To this day it's still running strong as hell and fast on the strip.

so IDK what their deal is. 1 thousandth larger could make a difference between slap and no slap. I could see that if they said "this car runs 50* hotter than a stock engine all the time" but they never asked about temperatures.

MR RIZK

iTrader: (7)

In my lamens understanding is that builders will build with a larger p to b clearence as this will yield higher HP, lower break-in period but a side effect is shorter life span and "slapy" cold starts. With a tighter p to b clearence you will have a quiter engine but will require a longer controlled break-in period. This is just a general statement which I have heard from a few builders.

streetzlegend

iTrader: (2)

So now that I already have my engine running (8k miles old), anything I can do to somewhat reduce the piston slap on cold starts? Does oil viscosity affect it?

Nathan

Oil viscosity may well help. As you live in Florida with its very hot summers & mild winters there are a lot less negatives to using a higher viscosity oil.
I would try a 25w/60 & see how it goes.
@ 60F a 25w oil is likely to have a similar real feel viscosity to a 10w or 15w oil would have at sub zero temps, just as the 60 could also well be an asset in your FI motor in +100 deg summer temps

streetzlegend

iTrader: (2)

Thank you, I will look into this. I really like the Rotella t6, I wish they had a higher viscosity one, now I dont know what oil to trust that is much thicker.

HotRodG35

iTrader: (7)

I have the Forged Performance /Arias silicone free pistons. They run .005 wall clearance and sound like a diesel engine until warmed after driving 20 min. I was concerned with the piston slap and had Scharif check the motor out since I did the stage 1 short block swap myself. After driving 2 hours to Forged Performance Scharif said the motor was relatively quiet with solid motor mounts . Scharif recommended using straight 50w oil, so after switching to 50w oil engine ran little quiter.

streetzlegend

iTrader: (2)

Thank you for the information, how many miles do you have on the motor? Also what oil brand did you go with.

HotRodG35

iTrader: (7)

I have 3500 miles and currently running Napa 50w oil. After retune I'll swich to Motul. Scharif recommended the Napa oil for break in.

streetzlegend

iTrader: (2)

So to provide an update for anyone who may have experienced similar issue (cold start slapping), I switched from Rotella T6 5w40 to Rotella T 15W40. Piston slap is 95% gone!!!