Piston Dilema

[ogdougynutty]

So im in the process of building another motor and i have most of the stuff (new pumps, gaskets, yada yada). Now I'm having a problem with piston choice.

Right now I'm looking at Wiseco pistons, I'm shooting for something between 13:1-14:1 compression (This car is already running E85 and megajolt jr. for ignition control) Im just trying to get options here that i don't know about. I know Carrillo make a 12:1 piston, but i think that is calculated with the correct chamber volumes. Where as the Wisecos are calculated at 11.8:1 with the wrong size (they list 39cc which is way too big), but that helps me anyways for the higher compression.

And before it gets started, yes i have all the supporting modifications for this. Please don't start with bottom end this, top end that, the car is already supporting 11:1 compression with a 83mm bore. But i just don't trust that motor to pound around the track with, hence i making a new motor.

Basically what I'm looking for is this.
13:1-14:1 compression (could make that with some head shaving)
19mm wrist pin, this CANNOT be changed
81.5-82.0 mm size

Ideas?

[yoshimitsuspeed]

So im in the process of building another motor and i have most of the stuff (new pumps, gaskets, yada yada). Now I'm having a problem with piston choice.

Right now I'm looking at Wiseco pistons, I'm shooting for something between 13:1-14:1 compression (This car is already running E85 and megajolt jr. for ignition control) Im just trying to get options here that i don't know about. I know Carrillo make a 12:1 piston, but i think that is calculated with the correct chamber volumes. Where as the Wisecos are calculated at 11.8:1 with the wrong size (they list 39cc which is way too big), but that helps me anyways for the higher compression.

And before it gets started, yes i have all the supporting modifications for this. Please don't start with bottom end this, top end that, the car is already supporting 11:1 compression with a 83mm bore. But i just don't trust that motor to pound around the track with, hence i making a new motor.

Basically what I'm looking for is this.
13:1-14:1 compression (could make that with some head shaving)
19mm wrist pin, this CANNOT be changed
81.5-82.0 mm size

Ideas?

Lol you tell us to trust that the motor is built but you neglect to mention things like cam choice which would be very important in choosing a piston.
For a build like this I would not recommend any shelf piston. Much better to get one designed for your build or plan your build around a piston designed for it.
You will need to be very very careful trying to up the compression by shaving the head. Any piston that is that high could hit the head or valves if you bring it down too much.
The only piston that I know of that comes close to that CR is the one I designed for a customer.
CP told me they didn't think I could get it high enough. Wiseco told me that it was too high for them to be able to calculate whether I would have any interference or not. This is when I learned that even the best piston manufactures use oversimplified calculations for valve to piston clearance and depressingly inaccurate chamber geometry to make their pistons.
To make these I modled a 4AGE motor with special detail on the chamber geometry. Then I cut the geometry of the piston directly offset of the chamber model. I then cut the valve reliefs at the point where the pistons overlapped the valves at the greatest point, then added a safe offset.
This original design was for 14:1 with a stock HG.

I left everything from the skirt down up to CP because they know more about that stuff than I do.

The final design the customer decided to take it down to 13.5:1 with the stock HG and the ability to take it down to about .8 HG.


They were designed to just clear the Tomei 304 procams.

Unfortunately the customers build was in the Philippians and I was unable to test real world clearances. I am still waiting to hear back on that but they should work with anything smaller than those cams.
If you went with a very similar cam these would be a great option. Otherwise I could design you a set of pistons specifically for your build.

[oldeskewltoy]

Valve size... and choosing based on changing the engine from non-interference to interference will go a LONG way.... toward a decent design. Do you yet know if this is a standard valve head, or oversize? Do you know what the cams duration will likely be?


from a basic math POV... some of the variables - stock chambers are 36cc, you mention a bore of 82mm(3.228"), stroke is 77mm(3.031"),

You want a tight squish, so you are likely looking at a piston to head distance, "squish", of .030". The stock head gasket seals better then most, if not all the other head gaskets, its thickness is 1.2mm(.047"). That would mean you likely want to shoot for the pistons to stick above the block by .017". With the above dimensions, you'll need a piston crown volume between 6.1cc(13.to 1) up to 9cc(14 to 1).

[ogdougynutty]

Yoshi- Yes, thank you and sorry about that. I have been a little irritated with people just giving the normal quick response of "can you tune duuuurrrr" lol. But, what i plan on doing is contacting the company (like wiseco or others) and design a custom piston based off there off the shelf one for my specific application.

OST- It will have standard size valves (with normal head work of deshrouded chambers, trd spec valve angles, cleaned intake ports, and ported exhaust ports). Right now it is running Hks 272 intake and exhaust cams. Will be switching to a 288/8.35 intake and 272/8.1 exhaust. So for "safeties" sake i will go for a non-interference engine. It's going to be my track car with minimal driving on the street, and for me, when/if things go bad i dont want it to be too bad.

But for squish, i was planning on running the TRD 82.55/.8 and having the pistons basically flush with the block. But your option will be smarter (surprise lol) seeing as that TRD gasket is discontinued now and i dont want to SOL if i need another one.

[burdickjp]

what i plan on doing is contacting the company (like wiseco or others) and design a custom piston based off there off the shelf one for my specific application.

No one at a piston company knows enough about your application to spec your pistons. Like yoshi was saying, they use very oversimplified calculators. To spec a piston correctly you need the cam lift profile, max piston to valve information, and chamber geometry. The piston and chamber need to be thought of like mating surfaces. You have to focus on both, not just one or the other, or both separately. They mate. Think of it that way, and the ways in which they can compliment each other and it becomes increasingly obvious that they should be handled by the same person. Trusting your piston speccing to one company and your porting to another will limit their potential.

So for "safeties" sake i will go for a non-interference engine.

Non interference is a huge compromise to chamber geometry which has no place in a high performance engine. I'd also wager that you would have a VERY difficult time getting that high of compression out of a non-interference motor.

[yoshimitsuspeed]

I would love the opportunity to help you design your pistons and I think that I will be able to give you a better design than any of the shelf piston manufacturers.
It would of course go to one of them to be made.
I do not think you will be able to go non interference with those cams and I would highly recommend you don't try. I am quite certain you would not come close to the CR ratio you are aiming for if you did.

This is my 11.2:1 piston I designed for the Tomei Poncams. It is non interference with the poncams but just barely.
The valve reliefs are quite deep and therefore a considerable amount of material must stick above deck to keep the volume high enough to hit the 11.2:1.
The valve reliefs would almost work for you and would if you went with a cam that was under 8.15mm lift but to get this piston from 11.2 to 14, I just don't think it would be possible and if it was it would have horrid topography.
This is pushing the limits of what I would consider to be acceptable for a non interference setup.

[ogdougynutty]

Well this is why i asked lol, the non-interference is out and i can live with that for what i want. Really what I'm shooting for is more likely around 13:1-13.5:1 compression. Probably a little bit higher, since i will be removing all the sharp edges of the piston (hence losing some, but minimal cc's).

Yoshi- i would love to work with you (seeing as you know what you are doing), and i know this is going to come at a price and i have know problem with that. But, seeing as you have done this before i would like a general cost. Cheapest wiseco i found were $520 shipped to my door and i know its going to be more than that. Just need a somewhat close price to know when i can move on with the project.

[yoshimitsuspeed]

I can get you a number of shelf pistons in that ballpark including Wiseco, CP and Arias. I wouldn't really suggest any of them though.

A custom piston that will be likely to suit other builds that I can add to my collection of designs that I can offer other customers will be in the realm of $700.
A custom one off piston that will either be very unique to your build or one that you want sole rights to the design and concept the cost will be a bit higher.

I think I could come up with something that landed about halfway inbetween the two pistons I have posted here which would be a perfect next step for me to be able to offer. The biggest thing would be getting a good valve relief depth, then I can always raise and lower the dome height easily to suit other customers CR goals. With stock valves and smaller cams we could bring the dome height down a bit which would be great.

[oldeskewltoy]

i know this is going to come at a price and i have know problem with that.
i would like a general cost.
Cheapest wiseco i found were $520 shipped to my door and i know its going to be more than that. Just need a somewhat close price to know when i can move on with the project.

$700 - $750 is a target

I did some more calculations... with a 35cc chamber, you can run a 6cc dome, and end up @ 13.3 to 1.

And while I was at it, I decided to do a bit of testing... Using OST-028 (stock valve, 35cc de-shrouded chambers) I slipped in an intake valve and set it to 8.15mm lift. Why 8.15, when you said you have 8.35, because 8.35 is cam lift, you need to account for valve clearance. Ok, so we have 8.15mm valve lift on a 22 degree angle, what is it in a vertical... as the piston travels in a different angle. I did some more measuring, and the vertical rise of that valve is closer to 6.20mm So the edge of the intake valve, at full lift(approximately 110 degrees after TDC), sits below the edge of the head by 6.2mm I then measured an OEM high comp piston intake valve relief for its depth, and I got 4.85mm. So ***IF** the belt breaks, you will have contact....

So... although this would now be an interference engine, it is no where near a concern of the valve actually hitting the piston during normal operation. You would need about 6mm of valve lift within 15 degrees of TDC to hit a stock piston with a stock valve

[ogdougynutty]

For a $700-$750 price tag, i would be ready to start this at the end of this month.

[yoshimitsuspeed]

I keep forgetting to respond to this but when you are ready you should shoot me an email.
http://www.matrixgarage.com/content/contact-us
If you go with a custom design it will take me about a week or two to get a design to the manufacturer and in my experience with Wiseco and CP probably about 4 weeks for them to make them.