Compression #s for a 3.4

syncroid · 05-11-2006, 04:29 PM

What kind of compression #s should one see with a 3.4 liter motor? Pistons are Mahle Sport 98mm. Deck height is .045". Cylinder heads are stock with the exception of the bevel cut for the 98mm pistons.

Jeff Alton · 05-11-2006, 05:21 PM

depends on your cam profile and static compression ratio to some degree....

Cheers

syncroid · 05-11-2006, 06:53 PM

Jeff, What are your #s? Are you running the Mahles or JEs? I just want a base line is all. My cams are stock 3.2. Cam timing (if it matters) 1.22 L and 1.24 R

Jeff Alton · 05-11-2006, 06:57 PM

Mine is not together yet. I have measured the domes, checked the deck height and I am cc-ing my heads tonight, hoping for 10.5 or so. I may have mis understood your question. DId you mead #'s from a compression test or did you mean static compression?

My motor has JE pistons.

Cheers

syncroid · 05-11-2006, 08:51 PM

Quote:

Originally Posted by Jeff

DId you mead #'s from a compression test or did you mean static compression?

My motor has JE pistons.

From an actual compression test. (after the motor has been run...say 1000 miles)

rdane · rdane's Garage

Mahle sports should come out almost exactly as stated. 9.8:1 or 10.5:1 epending on the Mahle 98 you used, RS or Max Moritz.

Jeff Alton · 05-11-2006, 09:22 PM

Hmmm, not sure but I would think you should see 180+ on that motor.

Cheers

Jeff Alton · 05-11-2006, 09:23 PM

Mahle has a bit of a rep for overstating compression ratios..... I know Ralph had a heck of a time getting any thing even remotely close to the stated CR on his set of p/c
Cheers

rdane · rdane's Garage

Check with EBS and the they will tell you the Mahle's do come as stated. My 3.4's did once the early heads were sorted out. I staretd with a 10.8 instead of the 9.8 because of the smaller heads used from a 3L.

Jeff Alton · 05-12-2006, 10:49 AM

We must be talking about different styles of pistons. The Mahle RSR style high domed ones are way overstated..... As are most factory mahle pistons.... At least that is what people have been saying here that have measured them. Ralph and Chris come to mind. That said, I have only measured the JE's and they were bang on 10.5

Cheers

JeremyD · JeremyD's Garage

3.5's are known for being overstated = the 3.4's are typically pretty on. My 3.4 with JE's came in at 9.78 to one - my Mahle Sports came right at 9.74 when some relief was cut for the exhaust valves.