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Cp Stocking Pistons Has Major flaw!!

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keltalon

Supporting VIP
3,474
959
Jun 29, 2003
Luthersville Ga, Atlanta, Georgia
In a recently cam test that I was doing my oil pump failed and ruined my bottom end. This forced me to have to rebuild it. While I was in the process of tested I decided to give a set of cp pistons a shot in my new build.

I read a lot of good things about cp pistons from how they are used in NASCAR and the professional drag circuit to specific techniques that set cp pistons above the rest. Like everybody here we are always trying to use the best components in our engines so that we are as close to bullet proof as we can get.

I ended up going with a set. The first thing I notice about the pistons , that was different from the ross ones that was currently in the engine, was that the valve relief was cut very deep and that there were little material left at the edge of the piston. I thought this might be a concern in that it might create a hot spot in the cylinder but since nobody has had any issues with them in the dsm community I didn't linger on my concern I just went ahead with the installation of the piston.

Here are some other differences of the ross and cp piston. Ross was 8.5to1 compression the cp was 9.0to1. the cp pistons was a little lighter than the ross I can't recall the exact weight in grams but cp was lighter. But the main reason for my giving them a try was the advertisement of the low tension oil ring. Once I got the pistons I did notice that the cp oil ring had a significant less tension than the ross units. These are just some of the few physical differences in the two. The other differences was advertisement of the pistons. Cp advertisement concerning the benefits of their piston influenced had the greatest influence on my gut feeling that they were a better piston and this is was caused me to give them a try verses going with another set of ross. Don't get me wrong the only forged piston I have every used in all my engine build was ross and have yet to have any issues out of them:thumb:

I guess sometimes we can't leave well enough alone. I put the engine back together and to make a long story short properly broke in the engine. Dialed in my tuned and the car was ready for some wide open pulls. Car pulled very hard and I was please with performance. I did notice a issue with coolant being pushed not much but enough to go into the reservoir in the upper rmp range so I turned the boost down and figured I would replace the head gasket when I got a chance.

After about 3000 miles I finally pulled the head. I could see where the boost was making its way into the coolant passages so I sent the head to the machine shop to be decked and ordered a new hks stopper head gasket. But I couldn't put the car back together because my concern about the way the pistons looked around the valve relief area the thin metal was being affected by the heat in thd cylinder. Here something to note , my car never saw any knock on dsm link. I never saw over 1450 degrees on my egt gauge and I run full e85. In fact all my tuned was the same as with the ross slugs.

I went ahead and pull the engine and broke it down. I did notice that the cp rings sealed like a charm the cylinder walls was nice and polished with no vertical piston ring lines and this is why I have faith in a custom set not to mention I had absolutely zero blow by . I have been working with cp on making me a set of custom pistons where the valve pocket is not as large as what comes on their stocking units they took note of all of my concerns and appreciated all of my feedback and recommendations and agreed to make a custom set that will soot my needs. It has been 5 weeks and still waiting on them to be completed. I agree with the thread below, Cp customer service stinks badly! I called cp sports compact manager 4 times he finally returned my call 3 weeks later.

JE or CP Pistons

I think custom cp piston will be awesome but the shelf units are a rebuild waiting to happen. here's a similar issue within the honda community reagarding cp thin valve pocket
Piston damage question - Club RSX Message Board

cp pistons not good? - Honda-Tech


bmw forum same issue Piston/Engine Pics - Worried About Valve Relief Cut - Need Help - Bimmerforums - The Ultimate BMW Forum

I need a new dyno and a new tune - Bimmerforums - The Ultimate BMW Forum

Before you decide to use cp 4g63 stocking pistons do your research.:thumb: This information is solely provided to inform the dsm community so that a wise decision can be made by each and everyone of you when it comes to chosing a set of pistons for you build nothing more nothing less.

here are some pictures of my cp pistons:boring: If I had not caught the problem when I did I would have ended up like some of those honda guys LOL>
 

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I could have told you that CP pistons are junk

At the shop im working at, I tore down a Prelude engine with those in it. Exact same thing happend. All four pistons, right where the valve release is, had chunks missing. Except the pistons I saw had way more damage then yours. Chunks were missing that were so big, you could almost see an inch or so of the first piston ring. Your exactly right, they are very poorly designed. Stay away from CP :)
 
Frack!

EDIT: Mine are .020" over, and despite that, it looks like the valve reliefs are cut beyond the edge of the piston. I'm afraid to see what's going on in there.
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good to kno that....ive heard sum good and bad reviews about cp pistons but now after seeing the pics and reading the thread....cp pistons arnt an option for me anymore :thumb:
 
good to kno that....ive heard sum good and bad reviews about cp pistons but now after seeing the pics and reading the thread....cp pistons arnt an option for me anymore :thumb:

Don't get me wrong I think the piston itself is a work of art they just need to redesign the valve pocket. Yeah stay away from the current stocking ones by all means! I just got word that they have my custom unit ready. I sent them a ross piston and told them that I would like them to duplicate it, valve pocket and all. I also had them to drop the compression ratio to 8:5 to 1 They did. like I said before their ring design is awesome this is the only reason I am willing to give them another try.
 
I worked for Lennox and we have two small logos on Kurt Busch's car. We had the good fortune to have a couple of sales meetings at Mr Penske's facility in North Carolina. Talking to the people there, I was told that their pistons were proprietary but were built by Manley and Mahle for a lot of the teams. My friend Eldon works for a Porche race team and he told me they also have Mahle build pistons for them.

Regards
Greg
 
I worked for Lennox and we have two small logos on Kurt Busch's car. We had the good fortune to have a couple of sales meetings at Mr Penske's facility in North Carolina. Talking to the people there, I was told that their pistons were proprietary but were built by Manley and Mahle for a lot of the teams. My friend Eldon works for a Porche race team and he told me they also have Mahle build pistons for them.

Regards
Greg
so you are saying that mahle build cp pistons?
 
No. Not at all. I believe a previous post stated that CP Pistons were used a lot in
nascar and that was not my understanding. I only heard Manley and Mahle mentioned as being the most popular manufacturers of pistons for the race teams. I am sure there are others.

Regards
Greg
 
No. Not at all. I believe a previous post stated that CP Pistons were used a lot in
nascar and that was not my understanding. I only heard Manley and Mahle mentioned as being the most popular manufacturers of pistons for the race teams. I am sure there are others.

Regards
Greg

Well I put that in a post because cp told me that their pistons was used in nascar maybe they told me a little white lie:shhh:
 
I could have told you that CP pistons are junk
THIS ^

At the shop im working at, I tore down a Prelude engine with those in it. Exact same thing happend. All four pistons, right where the valve release is, had chunks missing. Except the pistons I saw had way more damage then yours. Chunks were missing that were so big, you could almost see an inch or so of the first piston ring. Your exactly right, they are very poorly designed. Stay away from CP :)
I have good frined that had a built Turbo Hatch have almost the same exact thing happen....
I remember talking to him years ago, An CP pistons got brought up in Convo. I don't think I had ever seen him that pissed ever before about any parts an he's gone through many Parts/Platforms...:notgood:
 
Wiseco standard or HD if you are making alot of power.
 
So far I've been lucky with numerous track & dyno pulls, but this may explain why my car is knock happy. Will be inspecting mine asap. Thanks for the heads up!

Mine knocks too, and always towards the far end of the 1/4 mile (mostly 4th gear). I've tried everything but meth and E85 to get rid of it, and I can't help buy think my setup should be capable of a more agressive tune.

I'll be checking mine before spring too. I'll post my findings here.

I'm going to be incredibly pissed if they need to be replaced already.
 
boost fluid will stop knock.. jk LOL

i have a friend with JEs for over a year with no problems but then again hes tuned around 350 400 so i dont about big numbers
 
I heard the skirts crack on wisecos....I'd prob go with Ross or JE pistons

I heard you should site factual information, and know of sources to prove it if your going to state such things / advice. Because your the first person I know of, to make this claim.

The perfect piston does not exist btw, pick what suits your needs/goals. Personally I like Mahale if your the kind of chap that tunes a little on the safe side, and are not going for 800hp. There the lightest on the market and since they supply many manufactures with forged pistons, they know what there doing, there quality control seems to be very high as well.

If you want a more forgiving piston, something like the HD Wiseco is fine, or JE etc.
 
i've heard alot of piston slap with JE pistons ive been reading that their only good for track cars not for daily drivers but just read not seen
 
RipperXX said:
I heard you should site factual information, and know of sources to prove it if your going to state such things / advice. Because your the first person I know of, to make this claim.

The perfect piston does not exist btw, pick what suits your needs/goals. Personally I like Mahale if your the kind of chap that tunes a little on the safe side, and are not going for 800hp. There the lightest on the market and since they supply many manufactures with forged pistons, they know what there doing, there quality control seems to be very high as well.

If you want a more forgiving piston, something like the HD Wiseco is fine, or JE etc.


Wow get all defensive right away!! Actually there was a thread posted not long ago with pictures and everything about how a guy had the skirts crack on his low mileage wisecos with a few other people agreeing... I didn't say wisecos are junk and it's a proven fact... I said I've seen pictures and heard bad things about them and that's my opinion... Don't take your bad day out on me
 
i make 475 at the wheels on pump with weiscos and have over 13,000mi on my motor. alex of dogbox ran them in his laser and swore by them.
 
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