follow up- 2.7 stroker: 2.5 & 2.7 piston/rod combo w/ pics

[rvaughnp]

2.7 crank/ 2.7 rod/ 2.7 piston 206.2 even - Using 206.2 crank to deck height.



2.7 crank/ 2.5 rod/ 2.7 piston 211.2 5 out - Using 206.2 crank to deck height.



2.7 crank/ 2.7 rod/ 2.5 piston 204.7 1.5 in - Using 206.2 crank to deck height.



2.7 crank/ 2.5 rod/ 2.5 piston 209.7 3.5 out - Using 206.2 crank to deck height.


2.5 crank/ 2.5 rod/ 2.5 piston 206.7 .5 out - Using 206.2 crank to deck height.


I said i would do this when i got my 2.7 block. Now we have pics with all the "he saids".

It should be stated that the above measurements aren't mic'd. I used a mm tape (similar to a carb float tape).

Well, that’s it. Piston to go off to see about shaving, I'll post back when I hear from them on whether or not they are willing to shave.
Robert P.

[riverdale21]

I've been in the research process of doing this type of motor. Like you I've read a lot of 2.7i stroker threads in the past. What kind of CR would you expect if one were to use the 2.5 piston with 2.7 crank and rods?

Edit: Found some useful information: http://www.r3vlimited.com/board/showthread.php?t=100939

[e30rapidic]

thanks for taking the time to do that!

[rvaughnp]

What kind of CR would you expect if one were to use the 2.5 piston with 2.7 crank and rods?

Assuming you are referring to the 2.5 rod with this combo... you will have potentially one of two ways... 1) custom pistons, in which you can specify at build what CR you want. 2) <Potentially> Shaved pistons are the unknown. Everything being what it is... The CR should not have much bearing on the piston cut. I will be shooting for 9.4CR. I would imagine the higher the CR the less meat to cut.

I have read that thread you related to... it really is more towards the "e" conversion to the "i" on the stroker side of it. But yes some good info here and there. I have actually found the best info through goggling "stroker", "2.7", etc. Don't discount the turbo threads. A lot of guys do head work and cam stuff and alike for turbo, that NA guys don't; but it might work well with a NA motor. Just for the record... you will get more info searching than going here or there asking a question or two. Through searching you will find the "do's and don'ts" more than hearing that question answered through one voice in one thread. You will find it a benefit to "Google” the main topic of your question. When you get to a point that you need a definitive knowing most of what you need to know come back to r3v and ask in a thread. This is by far the best Forum for this type of build. I asked 3 separate questions on 5 separate forums and r3v was the only one that the guys showed any interest in helping. Will you find the impatience ones... yep, no different than going to the grocery store. Just turn your head and continue with what you were doing. But most are really helpful.

good luck with your search.

thanks for taking the time to do that!

Don't mention it. I am a visual guy. I am in estimating and virtually everything i do has a picture. Pictures just explain better than type.

rvaughnp

[qbuilt]

So your showing above that a stock 2.5 actually has the piston above the deck approx 1mm?

[rvaughnp]

Yup. i don't have micrometer of any sort to get the exact, but it is around there. Not to mention you can plainly see it "out" of the cylinder.
Which would make since if the 2.7 stroke pic is 4mm out, then being the 2.5 has a 6mm less stroke, half of that would be a 3mm difference. 4-3=1.

[eta]

If the 2.5 crank, 2.5 rods and 2.5 pistons pushed the piston out of the bores then the eta block is shorter than the the i block, which goes against recieved wisdom which says they are the same.

[rvaughnp]

_______Stroke______Rod_______Piston (KH off of Mahle specs)
2.5 __75 (37.5)______135________34___ = 206.5

2.7 __81(40.5) ______130________35___ = 205.5

I have heard mulitple numbers on the actual centerline to top of block measurement. If the above measurements are true, that would explain the 1mm difference.

I will try to look around and find a cheap micrometer. It will be a while until i go further with the motor and it would be interesting to find out the true centerline from crank to top of block.

[whodwho]

I believe the blocks are going to be the same and it is just the stack height of the components that are different.

[nando]

If the 2.5 crank, 2.5 rods and 2.5 pistons pushed the piston out of the bores then the eta block is shorter than the the i block, which goes against recieved wisdom which says they are the same.

actually I think the pistons are supposed to come up above the deck. it's part of the design of the hemispherical combustion chamber.

[rvaughnp]

I believe the blocks are going to be the same and it is just the stack height of the components that are different.

the blocks are the same height. I measured with a steel inches ruler. I don't remember the actual measurement just that they where the same height. it is stack height that is different.

Aptyp offered that the actual measurement is 206.1 for the m20. I ran the stack height numbers on paper and as long as the mahle KH measurement (it shows the top of the piston mark to be slightly lower than the actual edge of the piston) then that 206.1 could be right.

I will go ahead and put the deck height and stack heights to each of the crank/rod/piston pics above measuements on the assuntion of 206.1 to be the actual height underlined for the above mentioned pics.

Cheers,

[kennedy]

i need updates please as i am building the same motor

[rvaughnp]

Updates to what, my friend? If you want updates from me, you are going to have to be patient. As i have stated this is a budget build and I have no schedule. As the money comes in, I spend it.
Did someone pray for patience?
I am willing to help as much as possible but i am new to the M20 thing and my knowledge is gained daily. To that extent... if your where to search all my posts... about 7 threads started... you would see my lack of knowledge on this subject. Just learning as i go.

[rvaughnp]

Major setback...
BCRPerformance states they can't shave the pistons due to incompatible machinery.:hitler: na, na, na.

Anyone have any leads on a shop that can?

[kennedy]

have you called Ireland engineering yet i think they actually have a piston for this combo. i need to do some research aswell. lol i am doing the same thing your doing and cheap alternatives are nice