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Piston Selection

Heywood

Hard-core CEG'er
Joined
Jan 24, 2006
Messages
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Location
Montreal
Wasn't sure whether to post here or 3L section, but anyway here it is...

I am doing a complete rebuild of my engine (Port matched 3L). The top land on one of the pistons let go. Full story and pics here - http://www.contour.org/ceg-vb/showthread.php?76307-Engine-rebuild.

It will be a naturally aspirated track car. I have read a lot of articles saying that forged pistons aren't really necessary without FI. This makes me wonder whether the extra $5-600 for forged pistons is really worth it.

On the other hand, if I get forged pistons, I could up the compression a little, to say 10.5:1, without having to worry about detonation causing another piston failure.

Thoughts? suggestions?
 
If it were me, I would not get custom pistons unless your doing a high compression motor. The cost vs. reward for 0.5 compression is not worth it in my opinion. If you don't have a tune, spend the money on that. You'll gain more hp that way than from a 0.5 compression bump.
 
If it were me, I would not get custom pistons unless your doing a high compression motor. The cost vs. reward for 0.5 compression is not worth it in my opinion. If you don't have a tune, spend the money on that. You'll gain more hp that way than from a 0.5 compression bump.

I do currently have a dyno tune which was done by a shop in Cali (by previous owner), but I plan to get it checked out once I drop the motor back in because I want to make sure its not running too lean. (I have a Wideband AFR gauge that I hadn't got around to installing as well)

What would be the max compression for 91 octane fuel? I said 10.5 because I knew the original motor was 10.25 and required premium. What would you consider high ratio? Also, my reasoning behind forged pistons was more to do with robustness. If I run a somewhat higher ratio and it detonates once in a while, with forged psitons/rods, it shouldn't be a problem but with HE I could be back in the same spot I am today.
 
The top land on one of the pistons let go.

i remember talk of late revision pistons with a larger gap between the crown and top compression ring.

I've seen domed from the early 3.0L and valve relief for the VVT... maybe someone could chip in with a source for the larger land gap pistons for you, if they exist .... G.

edit. I have 04 3.0L pistons with a 4mm top land to crown measurement.
 
How the piston was made and its strength will have no affect on detonation.

If anything, increasing compression will only further necessitate a tune, so if you don't have one already you will definitely need one if you're changing the compression ratio. How high of a ratio can you go? Well it depends...for reference a basic 3L hybrid has 11.25:1 CR. On 91 octane I probably wouldn't push it more than that.
 
Naturally aspirated you should be fine with stock pistons. If you want to bump compression you will need custom pistons anyway so you will be spending the 5-600 bucks. There are other ways to gain horsepower and changing compression ratio from 10:1 to 11:1 typically nets a 4% gain in horse power not quite worth the money. Just use stock pistons keep your A/F rich at WOT and tune timing safely and you'll be just fine
 
So there's a few issues getting mixed up in this discussion.
My initial question was with respect to using Hypereutectic vs forged pistons. HE are $250-300 and forged are $800 or so. HE are effectively stock replacements. They are supposed to be good for NA applications but are no good for FI and can be brittle in lean and or detonation conditions. In my application I see the advantage of forged to be insurance against failure. This is the second motor to be replaced in this car due to piston failiure.

I will check the thickness of the top land on my pistons. If there's a redesign that could be reassuring.
 
How the piston was made and its strength will have no affect on detonation.

If anything, increasing compression will only further necessitate a tune, so if you don't have one already you will definitely need one if you're changing the compression ratio. How high of a ratio can you go? Well it depends...for reference a basic 3L hybrid has 11.25:1 CR. On 91 octane I probably wouldn't push it more than that.

Piston material has no effect on detonation - but detonation effects on piston selection. HE are more prone to failure when detonation occurs.

As stated above, I do already have a custom tune for the 3L and will be taking whatever I build in for a check up and probably a little tweaking.

Naturally aspirated you should be fine with stock pistons. If you want to bump compression you will need custom pistons anyway so you will be spending the 5-600 bucks. There are other ways to gain horsepower and changing compression ratio from 10:1 to 11:1 typically nets a 4% gain in horse power not quite worth the money. Just use stock pistons keep your A/F rich at WOT and tune timing safely and you'll be just fine

Yeah - bumping compression was kind of a "if I'm already going forged I why not" thought. I know that OE all use HE pistons and therefore they should be fine.
The counter points in my head are:
-This will be a track car so constantly beat on
-It relies on the tuner getting the tune right
-Another engine failure will cost a lot more than getting the forged parts now
 
I will check the thickness of the top land on my pistons. If there's a redesign that could be reassuring.

talking to the guy who is doing the machining on my new engine.... I asked him how much my piston ring set would be.... he asked if my pistons had equidistant ring lands. (they are)

It wasn't 'til i was on my way home that i remembered this thread.... i'm guessing/hoping the equal distant ring land spacing is later, (not going back 'til next week).

Maybe this snippet of info. might help you to find out something useful, if you choose to go OEM pistons..... G.
 
I measured the top land on my pistons this morning - seems to be 4 mm.

Also took the block to the engine builder who is going to hone the cylinders yesterday. We chatted for a bit and seems like detonation was the problem. He showed me a brand new LS3 engine that blew during track tuning due to detonation - top land was gone just like mine.

After talking to him he said that stock pistons would be OK and that forged would only last a little longer, but also said he doesn't like HE. Has anyone found cheap forged pistons? I will be ordering 0.020" oversized to allow him to bore the cylinders before honing.

At this point I am leaning towards a custom forged set - will probably go with Ross ($890) but I found Wiseco customs ($900) or the diamond forged from Nautilus ($1000).
I will most likely go for 11:1 compression.

Other work he suggested for a race engine which I will have done:
Hone the crank journals to allow more oil into the main bearings
Deck the block and heads for even compression across the cylinders
Shim the oil pump spring to increase system oil pressure
 
Hone the crank journals to allow more oil into the main bearings
i while chillin in the bath yesterday... i was wondering if extrude honing the oil galleries on the crank would help the oil flow.... any thoughts ??


Shim the oil pump spring to increase system oil pressure
interested in this too .... any pictures/info. ?

as far as detonation goes, ..... would water injection be worth considering ? ..... G.
 
i while chillin in the bath yesterday... i was wondering if extrude honing the oil galleries on the crank would help the oil flow.... any thoughts ??


interested in this too .... any pictures/info. ?

as far as detonation goes, ..... would water injection be worth considering ? ..... G.

Extrude honing would probably improve flow, but is probably unnecessary. My machinist said he ports the exits from the pump to minimise loses leaving the pump. My gauge would show 50psi cruising at 3k rpm, I'm pretty sure the system pressure isn't a huge problem in our cars.

There is a spring in the oil pump - I assume it is a pressure relief system. He said he always opens up the pump for any engine he builds and inserts a shim under the spring which would increase the pressure required to open the relief valve. I don't know 100% that this is how it works but seems logical to me.

As far as the detonation in my car - maybe the timing was advanced too far in my tune? I don't really know why it was happening but it shouldn't have been. Properly tuned it should be fine. I will be tuning the new engine from the get go to make sure everything is good to go.
 
I believe the CSVT#49 was able to determine our oil pump is pretty damn good, would have to go search through his thread to find specifics. The Nobles use the same oil pump after all.
 
Extrude honing would probably improve flow, but is probably unnecessary. My machinist said he ports the exits from the pump to minimise loses leaving the pump. My gauge would show 50psi cruising at 3k rpm, I'm pretty sure the system pressure isn't a huge problem in our cars.

There is a spring in the oil pump - I assume it is a pressure relief system. He said he always opens up the pump for any engine he builds and inserts a shim under the spring which would increase the pressure required to open the relief valve. I don't know 100% that this is how it works but seems logical to me..
thanks for that. I'm rebuilding a 3.0l engine so interested in any small improvements.


As far as the detonation in my car - maybe the timing was advanced too far in my tune? I don't really know why it was happening but it shouldn't have been. Properly tuned it should be fine. I will be tuning the new engine from the get go to make sure everything is good to go.
i'm running an SC, so i'm seriously thinking about squirters to minimize any chance of detonation on stock internals .... G.
 
thanks for that. I'm rebuilding a 3.0l engine so interested in any small improvements.


i'm running an SC, so i'm seriously thinking about squirters to minimize any chance of detonation on stock internals .... G.

Water injection sounds like a pretty good solution if you are going with boost, though I only looked into it superficially.

Full disclosure - this is the first engine I have torn down past the short block. Eveything I put in here is based on reading or expectation, not experience.
 
Have you addressed the detonation problem yet? Higher compression only makes that worse. How much cam are you running, stock cams with higher compression run cylinder pressures up to make detonation, common mistake. Generally higher compression is used with more cam timing. Cooling system performance and spark advance affect detonation..............

Forged pistons always hold ring lands better but enough detonation breaks all of them. Cast pistons are more brittle even sitting on a desk, forged will bend or smear aluminum slightly before they break. Forgings hold up better at high temp, they also can warp slightly out of shape and rebound back when stress stops, cast will simply crack there. We used to consider 6500 rpm the point at which high enough piston speed could break up cast pistons on bigger American V-8 engines. Even so, I strummed some engines over that and no fails, but the 6500 is a good point to go to forgings. If the cast piston is 'autothermic' with steel inserts up inside then they break faster.

Check wall clearances, forgings generally require more piston to wall than cast. Trying to set them close will tear up skirts unless the forgings are SPECIFICALLY molded for tight clearance (a few specialty ones are, most aren't, much has to do with the alloy used).

Have no idea where the forged for FI statement comes from, FI or not has ultimately nothing to do with piston choice.

If machine shop guy is hot he will know proper cylinder wall finish for the rings (ceramic, moly) used. You should discuss it.

Extrude honing is a joke, forget it. It cannot be tightly controlled no matter what they say. Material comes off where it comes off, you cannot change that. On say intake no two ports will flow or be the same afterwards.

I bump up the oil pressure spring in almost anything I take apart that is going to get hotdogged after going back together. Most classical type pumps maybe 1/8", you must then check that after shimming the bypass piston can still access the port opening that relieves the pressure. If spring were to coil bind then no pressure relief and pump blows up.

While water injection definitely works, I've seen it work too many times when it shouldn't have to tear up motors. The steam eventually pits the cylinder walls and then they start losing pieces. The rings chip out running over the pits too.

Don't make apologies for reading more than doing. I started out that way and while doing the doing I made very few mistakes as versus those starting with a clean slate. When both are put together it's awesome. Push that reading hard, it will further your physical work efforts by a factor of ten. The reading will allow you to weed out 90% of pitfalls that the ones who do not read must fall into to make progress.
 
Have you addressed the detonation problem yet? Higher compression only makes that worse. How much cam are you running, stock cams with higher compression run cylinder pressures up to make detonation, common mistake. Generally higher compression is used with more cam timing. Cooling system performance and spark advance affect detonation..............

Engine is currently sitting in pieces in my shed. I had read about the difference between static compression ratio and dynamic. I donèt have the details of my tune, but this is where I thought there might be a problem - too much spark advance. Current engine 3L short block so should have been only 10:1 CR (static).

Check wall clearances, forgings generally require more piston to wall than cast. Trying to set them close will tear up skirts unless the forgings are SPECIFICALLY molded for tight clearance (a few specialty ones are, most aren't, much has to do with the alloy used).

I am aware of this. most piston makers state clearly to specify the bore and not the desired piston diameter. In any case I will double check when placing the order.
I put this fact as a plus for the HE pistons because its also said that the extra wall clearance makes forged pistons noisier until the engine warms up.
Also my engine builder said that he individually matches each piston to it bore to ensure correct clearance.

Have no idea where the forged for FI statement comes from, FI or not has ultimately nothing to do with piston choice.

If machine shop guy is hot he will know proper cylinder wall finish for the rings (ceramic, moly) used. You should discuss it.
will do!
Extrude honing is a joke, forget it. It cannot be tightly controlled no matter what they say. Material comes off where it comes off, you cannot change that. On say intake no two ports will flow or be the same afterwards.

I bump up the oil pressure spring in almost anything I take apart that is going to get hotdogged after going back together. Most classical type pumps maybe 1/8", you must then check that after shimming the bypass piston can still access the port opening that relieves the pressure. If spring were to coil bind then no pressure relief and pump blows up.
thanks for confirming my understanding.

While water injection definitely works, I've seen it work too many times when it shouldn't have to tear up motors. The steam eventually pits the cylinder walls and then they start losing pieces. The rings chip out running over the pits too.

Not using it for my application. Methanol injection works on the same principle right? Does that avoid those issues?


To finish - I'm pretty well set on forged pistons now. Will probably order them up in the next week or so.
 
As for your piston's the prices your stating seem quite high. Here were my findings...

Pistons
Diamond Pistons - No replies yet, they were closed when I got out of work. NPG sells them in a kit for $899.95
Wiseco - Custom pistons guy is out of the office
Ross Pistons - Custom piston forged and dished will run me $660 for the pistons. Upgrading the wrist pins adds another $150

Another piston manf. that I ended up looking into was Arias Pistons. They come highly recommended from a lot of the Honda/Acura forums. Talking to them on the phone their pistons were in the $650 region as well IIRC. The Wiseco pistons above also ended up coming in at around $700. Diamond Racing pistons are cheaper ordering directly from them. I ended up going with the Diamond Racing pistons purchased through Wagamon Brother's. Total ended up being ~$690, but with the rings it went up to ~$820.
 
As for your piston's the prices your stating seem quite high. Here were my findings...



Another piston manf. that I ended up looking into was Arias Pistons. They come highly recommended from a lot of the Honda/Acura forums. Talking to them on the phone their pistons were in the $650 region as well IIRC. The Wiseco pistons above also ended up coming in at around $700. Diamond Racing pistons are cheaper ordering directly from them. I ended up going with the Diamond Racing pistons purchased through Wagamon Brother's. Total ended up being ~$690, but with the rings it went up to ~$820.


Diamond at NPG are listed at 995 now. Wiseco price was through my machinists contact, but is canadian price - so might be a little higher.
I have heard good things about Arias also but haven't investigated them further.
All prices I listed are with rings, pins and locks. I would love to get them cheaper. I called ross again today and I need to take a moulding of the head if I want them domed for 11:1 CR but still same price.

Don't forget its been a couple of years since you started your build :laugh:
 
ive been dealing with pistons from NPG for over 3 months and its been a cluster eff. we talked to ross and at the time they were on a back log on top of the 3 weeks for production
 
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