Is my CO too high?

Avery · 01-31-2005, 06:09 PM

I just completed some load testing on a 2.7 RS MFI motor that I rebuilt. With the new Gunson that I bought, I saw 3.5% CO on my engine dyno at part load. At idle, it read a little higher at 3.8%. This was the first motor that I tested on the stand so I'm not sure if these readings are ok or not. The CMA says 2.5 to 3% CO is spec for this motor but it does say that the dyno test could be about 1% higher as opposed to road testing as I recall.

Should I leave it as is or try to bring the CO down a bit?

Here's a picture of my engine dyno.

911pcars · 01-31-2005, 08:36 PM

I would say 3.8% CO is fine. I settled for 4% with my Weber-inducted 2.7. Once it's installed, you'll know whether your part throttle response is okay with that setting. I'm not an MFI guy, but these engines tend to run on the rich side, so much that oil dilution is something many owners live with.

Interesting setup. Is that a still?

Sherwood
http://members.rennlist.org/911pcars

snowman · 01-31-2005, 09:41 PM

I love it, a home made dyno. Wayne, NEVER underestimate the forum, ref older posts on diy machining. You change your mind on this yet?

Wayne 962 · Wayne 962's Garage

Hmm, that doesn't exactly look home-made...

-Wayne

john walker's workshop · 02-02-2005, 07:10 AM

on the stand, the engine may seem to run fine at that % of CO, but on the street, from my experience, that would still be too lean for a smooth transition on acceleration. it's a good starting point though. more trial and error will be needed once it's in the car i bet.

Avery · 02-02-2005, 05:44 PM

Thanks all: I'm satisfied at this point to plop the engine in the car. Any tuning from here on in can easily be down with the engine in the car. It's really nice to "burn the engine in" on the stand. I can easily fix leaks, and re-torque heads, adjust valves and sync up the TB's with the engine on a stand.

BTW...The stand was made by GO POWER. The oil tank, tranny adapter, water/oil cooler and gas tank were "home made".