Neddy

Hi,

What is the max compression ratio that is easily attainable on a naturally aspirated motor? For use with e85 on a dedicated track car.

By easily attainable I mean off the shelf or custom but existing (& ideally 85.5mm) pistons, and sensible amounts of head/block skimming that don't cause other issues.

Cheers.

Neddy

Anyone? Anyone?...Bueller???

Monk

iTrader: (3)

I'm not sure if I've seen any over 11:1. This guy is running11:1
on corn juice and boost.
https://www.miataturbo.net/build-thr...-thread-80256/

jpreston

iTrader: (4)

According to this guy, you can shave the head roughly .080" with a stock 2001+ bottom end and a BP4W head. Internet wisdom for head shaving says that should be roughly 12:1.

My 172whp N/A Engine. Stock bottom end. No Porting. - MX-5 Miata Forum

I'm about to drop a .060" shaved VVT head in my car with E85, but I won't have any dyno results for a month or two.

Twibs415

iTrader: (8)

As much as you can fit in there. Id probably call up weisco and have them make you some 12:1 slugs and then clay it and see how much you can take off the head with the cams you will use. If i had to put a number on it, you'd probably end up around 13:1. It gets pretty tight in there with high lift cams.

Too much work? Here are easy off the shelf pistons

TMD CCP0001 TMD Racing Forged Aluminum Piston. from the EPMiata.Com Online Store!

joyrider

iTrader: (8)

Get some Supertech piston XX ring combo 11:1 from 949 racing and shave the head to get 12:1 or really aggressive and almost 13:1

Neddy

Thanks for the replies and links.

It would be nice to get to 13:1.

At what point are there issues with timing? Physical clearance will be easy enough to clay and measure before skimming the head.

joyrider

iTrader: (8)

Don't know, but which computer do you plan on running ?

nitrodann

11.2:1

23PSI





Dann

Neddy

MS, but to clarify when I said issues with timing, I was talking about the physical effect on camshaft timing from a big head skim, not ignition timing.

MiataGarage

@Neddy wich Motor do you have ?
Does it make sence to go 13:1 on a 94 1.8 stock Engine Na Miata exept skimming ....I guess no....
Depends on your entire Setup if such cr ratio make sence or not
Sorry my english isn't the best ,so if i understood something wrong please tell me

concealer404

iTrader: (3)

Wossner makes 12:1 pistons.

Neddy

Does it make sense to go for max easily attainable compression on a track only engine build?

Keeping in mind e85 is readily available, to me it makes perfect sense

Neddy

Cheers. Have ordered some 85.5 supertech 11:1.