turbohatch96y7

iTrader: (15)

I'm looking for responses from people who have built more than one motor for accurate reply's.

Motor b18c1.
Bore 81.5mm using n50 rings.
I had the clearance at 0.0040.

Upon taking apart the motor from a burnt valve I noticed skirt wear on my cylinder walls.
So I figured ill re ring the motor and a light hone. Well upon inspecting further I noticed some wear spots were deeper. So I honed the motor till they went away. #4 cyliner and #1 had this wear that I was able to catch on my finger nail.

So I had to go to 0.0060 ptw to get these cylinders smooth. The other to are at about 0.0058
From research this gap is good for motors in the 700whp range. I'm at 400whp. Now I know this is way too big and is going to cause detonation and blow by.

I called a couple shops and I'm being told 0.0035 is where I want to be at for cp's.
I called cp and was told the same 0.0035 is the ptw I need and the skirt wear was because of being to loose at 0.0040 ptw.

I have a spare block I'm going to get bored and honed but I just want to make sure 0.0035 ptw is okay.

Question

Is 0.0035 going to make my skirts wear more than 0.0040?
What ptw is ideal for cp pistons?
If you build a motor for 700whp and have 0.0060 ptw how does it run when your not at your max power level? Lots of slap? Less miles before rebuild?

Spawne32

iTrader: (3)

It is not wayyy to big, this is fine for the type of pistons you are using, i said that before. Blow by and leak down is going to be determined by where you set your ring gaps. So dont go overly aggressive. Remember this is only the skirt you are measuring. While .0050 probably would have been more ideal for your power range, the 2618 alloy CP pistons are going to expand to fill most of that gap regardless. As ive found from research, CP's estimates for P2W are wayyyy too tight and have always resulted in horrible skirt wear.

turbohatch96y7

iTrader: (15)

Yeah I remember you saying that.
When I talked to cp they made it seem like 0.0040 was way too big. And 0.0060 was ridiculous

turbohatch96y7

iTrader: (15)

I'm on the fence to either run the motor as is and learn from there. I just don't want something horrible to happen and ruin the block

Spawne32

iTrader: (3)

Do a quick forum search about piston to wall clearance and skirt wear using CP pistons, you will find a common theme among all of the users. Hell i had what CP recommended on 4031 low expansion forged pistons on my supertech's and they STILL made contact with the bore after racing. Not nearly as much as your CP's did but still expanded out far enough.

familysedan2

I just learned the same thing with cp today actually lol. I'm using their 10.5:1 cr pistons in my b16 build. I already have the motor assembled so I'm gonna run it and see. But my builder assured me with the p2w I would not have slap or excessive wear beyond normal.. only time will tell but I have seen a lot of his work make great results so I am gonna take his word on it

EG1834

Would you consider coating the pistons? I did a set to restore piston to wall clearance from .006" down to .004", and it was only like $152 through PolyDyn, but that was for 8 pistons. It's nice because it still runs like it has .004" clearance, but if something bad happens, the coating wipes away before hurting the skirt of the piston.

turbohatch96y7

iTrader: (15)

What ptw are you at?

This is exactly what I started looking into. I forgot to ask laskey. About it when I had him on the phone.

What's the turn around time on that? Does the coating come in diffrent thickness? I know weisco coating has like 0.0005

mar778c

iTrader: (1)

OP,

Normally, with CP, I would go 0.004 for anything below 400 whp. Above that number, you need to start thinking about fuel, cams, manifold, etc. I think you are right about the clearance of 0.006 for 700 whp.

1st question, what does your set-up consist of?

turbohatch96y7

iTrader: (15)

my setup is pretty basic.
cp pistons
eagle rods
stock gsr cams.
running on 91 octane.
with a to4b turbo

mar778c

iTrader: (1)

I would do a couple of things in this case.

1 be a little conservative on the ring gaps.
2 make your setup a little laggy ie .82 exhaust housing
3 a bigger set of cams
4 let it warm up before you drive

blackeg

I think cp uses crack cocaine when the recommend ptw tolerences. They are really tight and have seen many issues including first hand when using their specs.

I like the advice that mar778c gave u. Just for the record there are/were lots of people using vitara pistons at those ptw specs and their motors ran fine. Just let it come up to temp a bit before u drive it and put load on the engine

rich7777

How about running a slightly higher viscosity oil ? Something like 10w50.

familysedan2

[QUOTE=turbohatch96y7;48478629]What ptw are you at?

To be honest I do not remember.. I can recheck with my builder if I see him in the next couple days

sleepencivic

What were the conditions when the motor failed? Do you run a wideband if so what are your AFR's in boost? Can you post your timing maps? For 400 hp with CP's you should of been good at .0040... you valve could of burt the valve from a poor tune or high timing. What did the spark plug look like on the cylinder wiht the burnt valve?

turbohatch96y7

iTrader: (15)

Yeah I remember your black cylinder walls lol. Im just confused why cp recommends that really tight clearance. I did find a good quote researching. " build it loose no one will know. Build it tight everybody knows"

Won't that mess with my bearing clearances at the same time?
I'm calling polydyn today and going to ask how long the coating process takes.

turbohatch96y7

iTrader: (15)

The motor was tuned at 11.0 afr.
Timing I'm unsure of ill post the map when I get my battery charged.
The spark plug porcelin was cracked on that cylinder when I pulled it. No sighn of detonation besides that.
I literally got the car tuned it made it off the dyno. I babied the car for the next two days, did one pull at 13psi and that's when the valve burnt. It happened so fast I didn't get a chance to glance at the a/f gauge.

rich7777

It depends how tight they are. Saying that though, I ran my old stock b16 on 10w 50 for ages.

mar778c

iTrader: (1)

turbohatchy96y7,

1. your ring gaps look good.
2. Yes, this will help to reduce back pressure
3. Not reduce back pressure but give you more overlap and reduce blowby.

turbohatch96y7

iTrader: (15)

Gotcha thanks.

So I called poly dyn and 19 bucks a piston for skirt coatings. And 40 bucks for skirt and top coating per piston.
I should get between 0010-0014 added on the pistons.
I'm most likely sending my rods in for the coating as well. 20 bucks per rod. 4 day turn around time.

rich7777

Sounds good.

sleepencivic

Why so rich on the afr's what octane gas do you run? Was the motor ever ran not tuned or was the motor broke in (rings seated) on the dyno? When the PTW measurment was taken did you take the piston measurment below the pin in the correct spot Cp reccomends?

turbohatch96y7

iTrader: (15)

Motor was broken in on my tune. I watched the af gauge and leaned it out. It idled always at 14.5 but did run sometimes really rich around 10.5 af. When the motor was put together the first time it all the measurements were taken by the nmachine shop I didn't have the tool then to double check them.

The motor is tuned now. What I'm wondering is if I should baby the car back to the dyno about 30 miles away. Or have it towed and broken in there.
I'm not sure yet.

Muckman

iTrader: (2)

Any peak EGT data to correlate with recommended p2w clearances?