I have been running an OS 12CVR (3 port) in an Associated Gas Truck on the dirt oval for about a year. It was real simple to tune and seemed to have good power any time I pulled the trigger. Now I am running a Custom Works GSX sprint car on the dirt oval but using an OS 12TZ (5 port). The symptom I'm having is: especially when I've been pacing for about 2 laps at 1/4 throttle and I suddenly pull the throttle back fairly quick, the engine will emit quite a bit of smoke and then flame out. I am running the gear ratio other people are running with my type of car, but I'm wondering if the engine might be lugging when I get on it and thus flaming out. To get up to speed, I have take a straightaway or so to get on up to speed. It is better at getting up to speed after running about 2 or 3 laps at racing speed. Is this an indication of needing a little more gear or do I just need to change my way of building up speed after pacing? Once the car is running up to speed it seems to perform just fine. After about 5 minutes of running it comes off the track around 225 - 230 degrees. I've done the pinch test at idle and after about 2 seconds the rpm's start to increase. Oh, I'm using a P6 plug. Also, the 12TZ comes with 2 air inlets (5mm? and 6mm?). Is there a general rule of thumb as to which inlet to use? Right now I'm using the smaller of the two.

It's too rich on the bottom end. Lean the bottom out, since you're basically on the high end needle for oval anyways.

A few of us in NY are running D.O Late Model cars- 4WD. They scream! We are barely letting off the gas to enter the turn then right back on it.

Ok!! Thanks, I'll give it a try. We're running foam tires on dirt, and the most we let off is 1/2 throttle in the corners. Sometimes WOT through the corner if you can hit the groove just right.

Really there is no need to get a five port motor anymore because most 3 ports are if not faster than they are almost fast as five ports now.

After reading these threads I'm realizing that now. Thanks for the info.

What about the different sized inlet ports? (sorry I don't know the correct terminology) On the 12TZ, it has 2 interchangeable inlets. One is larger than the other. What are the advantages/disadvantages? I presume by changing the diameter of the air intake you must be changing the characteristics of something.

Hmmm. No replies. Ok, how bout this. What I'm referring to is the interchangable air inlet on the OS12TZ.

The smaller one will have a wider power band... easier to tune too.