1.8 Piston-- What is the Piston Compression Height?
 

Looking for info on the Piston Compression Height (CH) of the pistons used in the 1.8 engines.
It is measured from the centerline of the pin bore to the top of the piston. Please include the compression ratio .
This is for research into building a stroker motor. Thanks

Damn, Really, I just trashed my pistons a couple weeks ago since I am moving. I am sure your super awesome stroker motor will be sweet.

I will be mad jelly if it works though, since mine is built, and I just have wiring now.

30.5mm for stock-like squish (easily found in any table of aftermarket pistons for BPs). CR is created with dish/dome.
http://www.google.com/search?q=miata...on%20height%22 ...

You going to stroke your own crank? Keep this going if that is your plan.

Yeah, thats the plan. I'm trying to find out more about how far the rod circle can be moved before there are clearance issues.
Meanwhile, if the bore is increased to 85mm then we can look at the pistons from the Mitsubishi 4G63 1G (100mm stroker kit). The compression height is 28.79mm (NB is 30.5). Some other rods I checked into were from BMW (82-99 E30/E36) 5.510" (139.95mm). Honda is 5.394" (137.007mm)

Rod length + compression height (mm) CH Difference(mm)
Stock Miata=163.271
Stock + Evo= 161.594 -1.677
Honda + Evo=165.811 +2.54

It seems we need to find a piston with the shortest compression height possible. Better than 28.79mm.

If you have all of the measurements you can just have customs sizes made. It shouldnt be much more it will just take a while longer, Yeah?

I'll try to call a couple of piston companies this week. I'm also having trouble calculating the rod ratio. If you alter the rod circle to a larger, or slightly smaller one the stroke is different to calculate the correct rod ratio. The 475whp thread doesn't make sense cause you would have to regrind for a smaller rod circle which is less stroke and less engine size. (If I'm understanding correctly whats going on there)

Yeah, I wouldnt look at that thread.
I would measure for yourselve and just go from there. You will need to decide what you want to do. You could probably get to almost a 2.1. It will depend on what you see comfortable for the angle those rods are going to start seeing.
Just have it ground to an easy honda size. That way it will be easier to find rods.

Wiseco comes to mind immediately. They will custom-fab pretty much any piston you can imagine.

You might also call FM and see if they'd be willing to sell you a set of the pistons that they normally use with their Stroker kit. They are also made by Wiseco, but are a super-secret recipe of 11 herbs and spices that Wiseco won't sell you directly.

Talked to the wiseco tech. He said to give him a couple days to get back to him. He was talking about $600 for a custom set. I ask him about oil consumption issues with putting the pin behind the oil ring. He said it wasn't an issue with their design. Will have to continue searching for rods. If you were going to have a crank welded/reground you could go slightly larger in size, and opening the possibilities of other off the shelf rod lengths.

Did you call JE?

I got an email back from the tech at Wiseco. He said the shortest compression height they could make is 1.020". So with the Honda rod (5.394") that makes the overall length 6.414". .014 under stock. Not bad, and the rod ratio increases from 1:56 to 1:61. That's with the stock rod circle. I don't know if it's that big a difference to matter.
More info, I had the opportunity to talk to Jim Stewart at Stewart Racing Engines, super nice guy, took the time to answer all my questions about stroking the 1.8 Miata motor. He felt you could go 85mm bore, but would highly recommend checking the wall thickness first. As far as welding and regrinding the crank, he wasn't too keen on doing it but if that's what you wanted to do that would be about a grand. My final question with him was using his engine building experience, how would he approach the bottom end of this build if we were to break into the 400 hp level. His answer was to use the highest quality pistons and rods available (he likes Carrillo rods and Wiseco pistons),second tier Eagle and Manley. Prefers ACL Race series cearings. On pistons, he suggests a full round piston, meaning there is more shirt area when it rocks against the cyl wall on the power stroke. Gaining a little more on the bore wasn't a big deal, but building a really solid bottom end and spending the money on getting the air to flow through the head would net your best HP gains. He felt with the well built bottom end you could run more boost to compensate for the 200cc less in size.
Now, having said all this, you guys need to call some of the engine builders in your area and see what they say.

400 is no biggy on the bottom end. I do it all day and so do many other others.
I dont know if you need to go to 85. If the walls are fine maybe, but I think 84 will be fine.
He doesnt like the weld/grind crank idea because he doesnt have someone he really trusts?
ACl and ARP are the way to go.
More boost isnt the answer we are looking for here. We are looking to run boost on a bigger engine. On an engine that is troked at a much lower cost than FMs stroker kit.
More boost wont bring in the better power band and ftlbs that a bigger engine will with the same boost, ya know.

He just thought the weld regrind was the wrong way to get the horse power. But if I wanted to go that direction it would be about a grand. I don't know if that's a fair price or not. Talked like he would do it in house.
I agree there's no substitute for cc's, but it seem that our motors have kinda a short deck height. I guess this makes it more of a challenge.
Have you talked to any of your people to put together something?

My people are ready to rock. We just have to see what JE is willing to give us for the project.
PRI was going on so I havent had the chance to contact them.

My goal is a bigger engine and still run alot of boost. I have a somewhat inefficient turbo set up and run 27psi. its not a problem. Iwant the bigger engine.
More boost isnt an issue. Thats easy. Just build a solid bottom end and run 25-30psi.

So it depends on what you want.

That's great. So what exactly did you decide to do? Bore size, piston height, rod length, how much did you shift the rod circle? Inquiring minds want to know.

McCulley put a sleeve in a 1.8 block to get it 'safely' to a larger bore.
http://www.mccullyracingmotors.com/i...s/Page1100.htm

Jason is local and a nice guy. I was seriously interested in purchasing one of their strokers but they stopped replying to my emails. To the best of my knowledge, they only built one or two and none are running because they couldn't find a head gasket. I found a few and that's when they stopped replying. So anyway....perhaps sleeving is cheaper than offset grinding a crank.

My 2.5l 85mm wisecos have a 1.148" (29.16mm) comp. dist. 21mm pin. Gorgeous forging.

So Turns, how did you decide to solve your bigger engine Build??