Piston recomendation?

[RipperXX]

Ok I have picked out the rods I want, but now I don't know which pistons to go with.

I am not sure what I need, or if I need anything better than just Topline 8:1 pistons, or maybe something that is forged and 8.5:1. I have DSMLink so editing the timing maps is not an issue. But since I have an Evo 3 turbo and plan on attempting to extreact 380whp from the thing, a slightly larger area for tuning error and added boost might be nice. On the other hand having higher compression would help the low end, but I am not sure if it would even be noticeable.

Also there is the price to consider, I am only planning on spending about 2k on the engine rebuild. maybe a hair more. I have more but want to save it.

 

[NickatBuschurs]

Ok I have picked out the rods I want, but now I don't know which pistons to go with.

I am not sure what I need, or if I need anything better than just Topline 8:1 pistons, or maybe something that is forged and 8.5:1. I have DSMLink so editing the timing maps is not an issue. But since I have an Evo 3 turbo and plan on attempting to extreact 380whp from the thing, a slightly larger area for tuning error and added boost might be nice. On the other hand having higher compression would help the low end, but I am not sure if it would even be noticeable.

Also there is the price to consider, I am only planning on spending about 2k on the engine rebuild. maybe a hair more. I have more but want to save it.

For the hp numbers you will be looking to achieve I would suggest looking into a set of Wiseco's. They are affordable and will get the job done. After that my recommendation would be a set of J&E but, there are a little more money usually.

 

[RipperXX]

How much better are the J&E? I see them on extreme for just $50 more than the Wiesco & they weigh 15grams less pr piston. Also can you give me any reasons for your recommendation?




Thanks!

 

[My1GLaser]

I had that decision to make a few months ago and decided to go forged while I was in there. The topline are already $200, so I figured another $200 would give me room to grow when I get greedy for more power. I went with Wiseco 9:1 because I felt that with DSMLink, Wideband & EGT I could keep an eye on things and not blow anything up. Also, they run a tighter P/W clearance and have an offset wrist pin like stock, so they are less prone to piston slap of some forged pistons on the market. I am sure someone will debate that. The 9:1 gives a better burning flame front so you don't need as much timing advance. The burn is already advanced from the increased pressure, so to speak. Just make sure your CC is cleaned up and there are no sharp edges and that the quech area is about .040 (+ or -.005) Quench area is the space b/w that head and the top of the piston at TDC. Alot of people don't know about quench (including me before this rebuild) but engine builders put alot of stock in this measurement. It forces the air/fuel mix to swirl violently when the piston reaches TDC and helps to fight knock by cooling the mixture. Too little space and the piston can hit the head, too much space and there is not enough turbulence to cool the mix enough and you will be more prone to knocking.

There are MANY, MANY varying opinions on the CR to choose and even after much research I still second-guessed my choice as I was putting the motor together. But I worked thru it and am very happy that I chose them. I don't have any actual feedback since I am cranking the car for the first time tomorrow. It will probably be 250 miles before I really start getting aggressive with the tune and know if I made the right choice.

I have $2000 into the motor, and am running an EVO 16g. I want 400hp out of it until I upgrade whenever it doesn't feel fast anymore. So I know exactly where you are at. I am not saying get the 9:1 or the 8.3:1. I might be able to say in a couple of weeks, but I don't know how it works in the real world yet.

All that said, it is a difficult decision to make because it is pretty much permanent. There is much more to consider than just piston CR when you are figuring your static CR. Which HG, has the block/head been decked...how much. I went a little overboard figuring it all out (as I tend to do) but I feel good about my decision. I have a spreadsheet calculator for figuring CR, but I cant seem to upload it. I will email it if you want. I hope that helps and good luck.

 

[RipperXX]

Hmm just checked out MAHLE pistons, are they more of a race only kind of thing or fine for DD too? I did notice there 8.5:1 and weigh less than the Wiseco by 39 grams per......And cost about $23 less . Wiseco and MAHLE are both coated pistons as well. So is there a reason NOT to go with them?

 

[turboglenn]

My1glaser has some very good points concerning the "quench band" or "area". As much as the proper quench area helps combustion, too small an area with too sharp of edges on the surfaces will cause hot spots and detonation. That's one reason i chose 8:1 on my build, but i think the next set will be 8.5 or 8.8:1. the other is because of some advice i got on the phone.

I had talked to sean glazer and he was saying that they weren't seeing enough benefit out of the 9:1 slugs to offset the limitation of boost and the tighter quench band that is formed when using a piston of that CR when it came to performing under higher boost levels. I believe he said his race car ran 7:1's or some where in there last season so they could push well past 30 PSI ( and he is WELL past 30PSI...i've heard in the 45psi or so range, but he would not confirm that )

As for sharp edges and detonation because of too tight of a quench band, this can be solved by having your machinist modify it slightly. My pistons were modified to have all teh sharp or remotely sharp angles and edges (on the face only) removed to help avoid pre-ignition.

 

[RipperXX]

See that is why I was considering trying to find a piston that was still 7.8:1 or 8:1 but it looks like I would have to get some custom made or use the Topline cast pistons. As I tihnk it will take around 27psi of boost to get close to my power goal. But getting a little more responce and saving some of the low end I will sacrofice with larger cams would be nice.

*sigh* I may just go with the Wiseco since there 8.3:1 but then the question is, is .2 REALLY going to matter, I doubt it... but I know there will be a difference in how easy it will be to tune compairing 7.8:1 to 8.5:1. And I am by no means "good" at tuning , a lot of times my foot out ways my logic.


Also I wonder if I go with the Mahle pistons and Scat rods, since there both lighter than oem parts will I need to have the assembly balanced? I know the pistons alone are like 296grams not sure of the weight of the stock pistons but I am sure it's more than that.

 

[outkastracing]

alirght i know that this is a decision that no one likes to make just like you i had to make mine only i did it Sunday ive done the research everyone said no to toplines i discussed it with people and some have great luck and some made it two blocks before there pistons came apart!!! now i know i didnt want to be that guy! so i started looking now i know wiseco and je are great pistons but i was in the money factor also so i was looking on eBay and found some arias 8.7.1 .020 over and started to research guys with blown v-8s run these and love them making way more power then i ever dream of... so i ordered them 380 dollars shipped to my house thats a good deal if you ask me! look at the arias web site there pistons look impressive ill be receiving them like Wednesday so ill let you know what i think then if you want. good luck also if you choose wiesco or je i dont think you can go wrong

 

[brute]

For what it's worth, I have Topline 8.0:1 on my 6 bolt rebuild with a few thousand miles on it. Absolutely no problems with them; I'm happy overall with them. It all comes down to personal preference and how much money you have.

 

[1992awdlaser]

I know a few people who use the mahle pistons on daily driven cars. I am also going to be using them when I build my bottom end. They are very light. They don't expand as much as other pistons, so the clearance can be tighter. And the coating on the piston tops help to reduce knock.

 

[SBR Joe]

I would suggest Wiseco or Manley. They are less rough on the bank account compared to some of theyre competitors, and they WORK!!



Joe

 

[90laserRSfwd]

I've pretty much made up my mind to just go ahead with the Mahle 8.5:1's. I don't see any reason why they wouldn't do the job. I'm looking to make just a tad bit more power then you (well I'm looking for 500 to 600awhp actually). Let us know what your final decision was and some reasons why, for future researchers....

 

[RipperXX]

I am still researching but I will go ahead and tell you with what I know right now I am leaning strongly towards them. They don't expand as much as some, there plenty strong, more affordable than compairable pistons if you know where to buy them. There coated etc.

Bang for the buck they seem to be pretty darn good, while not cheap there not the most costly piston out there and for what you pay you get a good bit.


I only have two or three more to look at before I make my choice but if I had to go with one right now it would be Mahle

 

[90laserRSfwd]

I saw that you posted in my other thread (mahle vs. wiseco vs ross) and I just wondered if you saw that I just listed a new post. Through some other searching on here some are saying ( or suggesting ) that the skirts are to short on the mahle pistons and could cause piston slap. I spoke another guy on here who's using the mahle's right now and he said he doesn't have any problems with them. I really like them for a couple reasons. Let me know what you decide. I'm thinking I'm going with them too. I know the skirts are coated but are the piston tops coated as well, like with a ceramic coating or something ? I may just call Hung in the morning (extremepsi.com) and see what info he can give me. Keep us updated.

 

[RipperXX]

As far as I know the tops are coated as well, but do not quote me on that.

 

[1992awdlaser]

Yes the tops are coated.

 

[90laserRSfwd]

ok well there you go. I assumed that we coated since even the tops of the top line pistons are coated, just wasn't sure..

 

[me612]

I run a Mahle/Eagle combo on my car. There is piston slap on a cold start-up. It fades away after a minute of idling though. I bought them because they cost less, they are hard anodized, and had a significant weight advantage over the Wiseco's. I have no real issues with them, except that I do not like the piston slap on start-up. Actually if you look at MAP's engine build page, that picture is my motor with the Mahle's in it.

If/When I do my next build, Wiseco will be the pistons I use.

 

[RipperXX]

hmm I think thats twice now someone has mentioned piston slap with those pistons.... Maybe I will go with the tried and true Wiseco then...


Question though, could this be from a shorter skirt? As that would reduce the weight of the piston and I would guess could cause the piston slap problem.

 

[1992awdlaser]

What kind of piston to wall clearance did you set the pistons to?

 

[me612]

I didn't set any clearances. I had the motor built by a shop.

Part of the reason is I believe the Mahle's are made of a different material than the Wiseco and Ross pistons are. If I remember right, those are made with a higher silicon content to stop them from expanding/extracting as much, allowing you to run slightly tighter clearances, and helping to avoid piston slap.

 

[1992awdlaser]

I was asking because of the tight clearances you can run with the mahle's. They shouldn't really have any piston slap.

 

[RipperXX]

Thats what I was thinking. But if I find many more case's of piston slap with these I am going to just go with wiseco.

 

[Irrational]

what about Ross? I'm asking not recommending.

 

[1992awdlaser]

Ross makes good pistons. I will be using Mahle's though. I think the two cases of piston slap I have heard of from them is due to improper clearance being set.