I am building up a Y8 ITB motor, and am looking to put in some PM7 pistons. utilizing a .048" headgasket I got a 12.7~ compression ratio.

Because I need to keep this streetable, can this work with 91 octane?

TIA!
Bryson

 

definitely not, imo

 

Wow, that compression seems pretty dang high for pump gas .. i'm curious to see what others say about this.

what is the highest compression you can run on pump gas with good tuning? Sorry if this might be OT

 

Also keep in mind that I'm at 5800ft.

I was just thinking that since you can run a lot of boost on 10:1CR I would think 12.6 n/a would be nothing if I tuned it a lil rich.

 

Oh I guess I should also mention that I am going to be using a Zex 105300 Street/Strip Camshaft, so I'm sure that changes the dynamic compression.

 

It can be done with a good tune.

 

Agreed. I'm running 12.4:1 CR with 91 octane.

Skunk2 Stg 2 cams. B series. At 1600ft altitude.

No detonation.

Make sure you tune with a wide band o2 sensor.

 

Really it depends on the camshaft. If you run a cam with lots of overlap, you can get away with with it. Before I switched to a Twin cam, I had a D16Z6 with 12.0 compression. With the stock cam it detonated everyplace I went. When I installed the JG 85VT80 cam, problem was fixed and picked up a bunch of power.

 

bryson, ive noticed that igntition timing has a bigger role in detonation/ping on n/a build than fuel. if u can slot out your distributor enough to pull out timing u can run any compression you want! im running 13.5 on 93 octane with somewhere like 12 degrees timing. dammit i need to buy a digital timing gun!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by johnzm &raquo;</TD></TR><TR><TD CLASS="quote">bryson, ive noticed that igntition timing has a bigger role in detonation/ping on n/a build than fuel. if u can slot out your distributor enough to pull out timing u can run any compression you want! im running 13.5 on 93 octane with somewhere like 12 degrees timing. dammit i need to buy a digital timing gun!</TD></TR></TABLE>

Yeah thats what I assumed. N/A setups are new to me, but I've been boosting for a long time, and since you just retard the timing with more boost, thats what I would assume you could do for a high CR setup.

I guess I'll give them a try, retard the ignition a few degrees from stock, and tune her to the sweet spot from there...

 

93 octane 12.3 cr. runs fine. 12.7 could be do-able if you run really retarded i suppose.