New piston options

[Storm728]

planning a rebuild soon. almost certain motor will need new pistons. considering j/e, cp, wiesco, manley, mahle, diamond or those crazy red pistons mmr sells. planning on staying stock compression (for this reason i am also considering stock pistons). car will probably be pullied and boltons after the rebuild so im not looking for anything too insane. looking mainly for a streetable piston a bit better than stock. could anyone chime in on this because i am totally lost when it comes to piston/ring choices. thanks

 

[MalcolmV8]

I would not put stock pistons back in just because the after market forged pistons are so much stronger. They say the pistons are the weak link in these motors... how true I couldn't say for sure. My stock pistons did swell and scratch the cylinder walls but that's from a tight piston to wall clearance more than a failing piston.

I myself went with Diamond although CP and others have fantastic reputations as well. This way if I ever turn up the wick and make some real power the pistons are there.

 

[itSSlow98]

I put Wisecos in mine per the recommendation of the builder who puts them in 1200+rwhp twin turbo c6zs. They are a work of art for sure. I dont think you can go wrong with CP, JE or Wiseco though.

 

[ctgreddy]

any of those mentioned are great. Personally I'd go with diamonds, je, cp, or weisco. However looking at your needs you would have great luck with a sort of "middle" one such as mahle or manley. still great pistons but can be had for a bit less money than the big boys.

 

[KINGCOBRA86]

I would go 9.1.0 -9.5.1 if it was me,any piston is good you listed, areies makes a flat top piston to the compression of your choice

 

[Nolimit]

How safe is it to up the compression when running 91 octane? What about power advantages? I know on race fuel fuel and E85 it is great but what about regular pump gas.

 

[MalcolmV8]

How safe is it to up the compression when running 91 octane? What about power advantages? I know on race fuel fuel and E85 it is great but what about regular pump gas.

It's a balancing act. If you increase compression you'll need to reduce how much boost you're running or possibly just pulling timing would do it. It's more efficient to reduce boost and keep timing in the motor than to run excessive boost with minimal timing.

In theory more compression and less boost will make you more HP since the blower does not need to be spun as hard and you have less parasitic drag turning over that blower.

 

[SlowSVT]

I put Wisecos in mine per the recommendation of the builder who puts them in 1200+rwhp twin turbo c6zs. They are a work of art for sure. I dont think you can go wrong with CP, JE or Wiseco though.

I hope Wiseco builds better 4 stroke pistons then they could building 2 stroke pistons. They failed with "regularity" :nonono:

OP, Manley are good pistons and won't cost as much as Diamond or CP's. Good call on running stock compression. You can pack more boost and charge into the engine and still run pump gas. Stay away from any coatings of any kind. Mod max is a good source for slugs but avoid the mod max pistons they are built like a brick shithouse but weigh a ton (455 grams )

 

[Nolimit]

Since the engine is being opened up and rebuilt with new pistons, is there anything else that should/could be upgrsded/rebuilt to make for a more bullet proof engine?

 

[4601S/C]

• If you have the money you could do some work on the heads (particularly the guides.)
• If you plan do doing a head cooling mod now is the time.
• Timing chain tensioner upgrade
• High flow [billet] oil pump
• J&S Vampire (not internal engine part, but may just save your engine one day)

I have Manley's in my car. I think they weigh 10 grams less than the factory pistons. I also have a melling high flow billet oil pump. I don't beat on my car too much though. It may see 12 1/4mi visits in a year, along with some Auto X, and maybe a track day or two this year.

 

[Posi]

L&M sells some nice pistons as well. Just ask for Michael.

L&M Engines

 

[Nolimit]

• If you have the money you could do some work on the heads (particularly the guides.)
• If you plan do doing a head cooling mod now is the time.
• Timing chain tensioner upgrade
• High flow [billet] oil pump
• J&S Vampire (not internal engine part, but may just save your engine one day)

I have Manley's in my car. I think they weigh 10 grams less than the factory pistons. I also have a melling high flow billet oil pump. I don't beat on my car too much though. It may see 12 1/4mi visits in a year, along with some Auto X, and maybe a track day or two this year.

Bronze guides? Any other work on the heads besides porting?
Never heard of it mining chain tensioner being on the to do list but thanks will look into it!

 

[Senkak]

Bronze guides? Any other work on the heads besides porting?
Never heard of it mining chain tensioner being on the to do list but thanks will look into it!

Cobra Engineering secondary timing tensioner fix

 

[Swervedriver]

I recently looked at some specs on the manley pistons for an acquaintance and did not like the thin crown, large pin bore, and raised tip ring groove (which I suspect has to be raised due to the mongo pin bore).

There's only 1 way to make a piston lighter than the already light Mahle. Sacrifice material.

Light pistons work great in high revving engine with no boost, but IMO any of the top 5 off the shelf pistons would be a better choice.

ROSS, JE, CP, Weisco, Diamond.

These all claim to be 2618, similar crown thickness, stock Pin bore, offset pins, and top ring groove location (.275"). However, the diamonds are lighter which I suspect means they have thinner skirts. Most of these details are pretty difficult to find and require spending some time on the phone.

Next thing I want to warn about is the standard pins that come with off the shelf pistons. They are a waste of space. Take them and throw them in the trash! They are usually a lightweight polished alloy steel pin with a .150" wall thickness. The stock Cobra pin is stronger and has a .180" wall.

So like I say, throw those pins away and replace them with some tool steel pins from Trend. Sometimes you can customize your order to replace the crap pins with tool steel pins but it's not really any cheaper.

Next up is rings. Moly coated rings seat super easy and work in a smooth honed cylinder bore. But they don't hold up well to heat or detonation. Stainless or AP steel rings are difficult to seat (don't run synth oil for a few thousand miles, and get max boost on them before switching to synth), difficult to file to target gap, but are simply the strongest and play well with cylinder bores. Ductile or hellfire rings are a strong middle ground that seat easier than AP steel but will wear the bore. IMO Stay far away from any sort of gapless ring. Too many people have had issues getting them seated, and there is no proven benefit over a conventional file fit ring.

For a basic build that can handle 750rwhp for a good long time pick any of the 5 pistons I listed above, a .150" tool steel trend pin, AP steel or hellfire rings, and get up with a good machine shop that uses torque plates. Be sure to stud the block before you drop it off with them or they'll have to use stock bolts which can really mess up the threads in the block. Iron can be cleaned up but Aluminum blocks can end up pulling the threads right out and that'll make everybody involved unhappy.

If you want 800+rwhp I'd say consider custom pistons, .200" wall tool steel pins, AP steel rings, ARP 2k headstuds and rod bolts. ARP main studs...

 

[Nolimit]

I recently looked at some specs on the manley pistons for an acquaintance and did not like the thin crown, large pin bore, and raised tip ring groove (which I suspect has to be raised due to the mongo pin bore).

There's only 1 way to make a piston lighter than the already light Mahle. Sacrifice material.

Light pistons work great in high revving engine with no boost, but IMO any of the top 5 off the shelf pistons would be a better choice.

ROSS, JE, CP, Weisco, Diamond.

These all claim to be 2618, similar crown thickness, stock Pin bore, offset pins, and top ring groove location (.275"). However, the diamonds are lighter which I suspect means they have thinner skirts. Most of these details are pretty difficult to find and require spending some time on the phone.

Next thing I want to warn about is the standard pins that come with off the shelf pistons. They are a waste of space. Take them and throw them in the trash! They are usually a lightweight polished alloy steel pin with a .150" wall thickness. The stock Cobra pin is stronger and has a .180" wall.

So like I say, throw those pins away and replace them with some tool steel pins from Trend. Sometimes you can customize your order to replace the crap pins with tool steel pins but it's not really any cheaper.

Next up is rings. Moly coated rings seat super easy and work in a smooth honed cylinder bore. But they don't hold up well to heat or detonation. Stainless or AP steel rings are difficult to seat (don't run synth oil for a few thousand miles, and get max boost on them before switching to synth), difficult to file to target gap, but are simply the strongest and play well with cylinder bores. Ductile or hellfire rings are a strong middle ground that seat easier than AP steel but will wear the bore. IMO Stay far away from any sort of gapless ring. Too many people have had issues getting them seated, and there is no proven benefit over a conventional file fit ring.

For a basic build that can handle 750rwhp for a good long time pick any of the 5 pistons I listed above, a .150" tool steel trend pin, AP steel or hellfire rings, and get up with a good machine shop that uses torque plates. Be sure to stud the block before you drop it off with them or they'll have to use stock bolts which can really mess up the threads in the block. Iron can be cleaned up but Aluminum blocks can end up pulling the threads right out and that'll make everybody involved unhappy.

If you want 800+rwhp I'd say consider custom pistons, .200" wall tool steel pins, AP steel rings, ARP 2k headstuds and rod bolts. ARP main studs...

Thank you for the detailed information and break down, why go with 2618 vs 4032 pitons? I also read that pistons with a lower top ring will due better in our boosted application; what pistons have this design already engineered if the top 5 manufactures keep that ring in its stock location? Or is this when we would have to go to a custom piston? Thanks again.

 

[MalcolmV8]

why go with 2618 vs 4032 pitons?

2618 is stronger. Both have pros and cons though. A 2618 piston usually has piston slap noise on a cold motor. They require more piston to wall clearance and the pistons are tapered narrower at the top due to the nature of the compound and the way the piston expands when heated. That causes the noise. Honestly I don't hardly notice it in my Cobra at all. Minimal if any on a cold start and it goes away with in seconds if its there at all. My Cobra has Diamond pistons. Very happy with the setup.

Now my turbo'd honda was a different story. I swapped to some 2618 alloy CP pistons in it before really cranking up the boost and the piston slap noise was horrible on it. Sounds like a diesel motor idling lol and when it's 10F out and the car sat out all day and you fire it up cold you'd swear it has a rod knock it's so loud. I'm not sure if its because those pistons are so tiny vs our Cobra pistons or if it's the tiny aluminum block in there echo'ing out the sound better or what. All I know is if my Cobra did that I'd be pissed and swapping pistons again.

 

[Swervedriver]

Now my turbo'd honda was a different story. I swapped to some 2618 alloy CP pistons in it before really cranking up the boost and the piston slap noise was horrible on it. Sounds like a diesel motor idling lol and when it's 10F out and the car sat out all day and you fire it up cold you'd swear it has a rod knock it's so loud. I'm not sure if its because those pistons are so tiny vs our Cobra pistons or if it's the tiny aluminum block in there echo'ing out the sound better or what. All I know is if my Cobra did that I'd be pissed and swapping pistons again.

I've got flat top diamonds in my motor setup pretty loose at 6.5-7 thousandths and it'll sit there and rattle at idle when cold but once up to temp everything is fine.

I suspect the difference in slap between your cobra and honda has more to do with offset pins vs centered pins than bore size. Just a guess though.

I also read that pistons with a lower top ring will due better in our boosted application; what pistons have this design already engineered if the top 5 manufactures keep that ring in its stock location? Or is this when we would have to go to a custom piston? Thanks again.

None of the off the shelf pistons have greater than .275" down top ring. BIG boost guys prefer .300" down top and they pay for custom pistons to get it but IMO .275" is plenty for up to 1krwhp especially with AP steel or stainless steel top rings.

 

[MalcolmV8]

I've got flat top diamonds in my motor setup pretty loose at 6.5-7 thousandths and it'll sit there and rattle at idle when cold but once up to temp everything is fine.

I suspect the difference in slap between your cobra and honda has more to do with offset pins vs centered pins than bore size. Just a guess though.

I bet you are right. I'll have to look over some of the spare pistons I have laying around.

BTW what did flat top pistons do for your CR? I'm running -19 CC dish which puts me around 8.15:1 CR.

 

[Swervedriver]

I bet you are right. I'll have to look over some of the spare pistons I have laying around.

BTW what did flat top pistons do for your CR? I'm running -19 CC dish which puts me around 8.15:1 CR.

Right about 10.5:1 It's an E85 setup. Pretty snappy on 22psi. :rolling:

 

[MalcolmV8]

Right about 10.5:1 It's an E85 setup. Pretty snappy on 22psi. :rolling:

I bet. I wish I went with flat top or at least smaller dish. The -19cc dish was to much and killed throttle response. It was minimal but immediately noticable. I'm used to it now though.