Boost and air temp?

Last weekend was the last race of the year for my first blower motor.

In the summer months when it was warm I would average between 14-16 psi boost.

This last race was pretty cold at 50-55 degrees, I went from a .092 pill to a .084 and the plugs looked the same, and it ran very hard!!

My boost went up to 20-21 psi, just seemed like a big jump, I knew it would make a differance I just didnt think it would be that much. I did take out the error from the gauge too, since its sealed its zero changes with atmospheric pressure changes.

Is that all from air density or are there other factors at play here??

 

Air density. Thick air is cool!
buy more pullies, and you can tune to keep the air at the intake valve the same all year

 

A boost jump from 15 psi to 20 because of Density Altitude...
Not on my stuff, not even close to making it jump that much.
Check for valvetrain issues or Did the motor spin faster? I've also had it when I would get a little "bang" under the blower and see higher than normal psi readings, but that is usually higher than a 33% increase


Check for valvetrain issues or Did the motor spin faster?

 

Mike,

I dont have EGT probes, or a data recorder, plug readings only.

I had the tune rich for normal weather made a (attempt) at a pass, got out of it early. I looked at the plugs and they were a little lean for my taste so I added fuel, oh and I forgot to say earlier I did raise the pressure of my high speed 15 psi or so along with my main change.

Next run out I ran my best pass ever, at a 7.99 @ 170, my average through the summer was 8.3s @ 168. I looked at the plugs again and they looked good to me, a little rich and safe.


Sodak, I just took the rockers off yesterday and everything looked good, I havn't checked the spring pressure yet but i didnt see anything wrong and the lash was still good. Rpm's were the same as they were before, I have had the intake poof wild boost readings before, usually starting the thing, but I think it would be strange for it to go up only 5 psi, and it repeated 3 passes.


I only got to make one balls out pass, I run in a 8.5 index so i was pettling alot on race day. And with the rain we got there was only two qualifying passes.

 

I found my stuff has a little different deal.

It's a glide with a converter that stalls @ 6000 with about 11-12lbs. I normally leave @ 3900 and it goes 1.03 60' and 6.8x. This means the car goes .7 ramping RPM & boost till it hits 6000 and the 11 lbs. This .7 zone seems to be effected by big DA changes.

 

Hi, Moparious Maximus,
Have you been able to follow some temperature variation of your intake charge in relation with thoses sudden "boost" changes ?
And, any idea where thoses "boost" changes happened during the run ?
Just curious...
Thanks,
Charles Stewart

 

Charles,

My boost gauge only records peak boost, so I have no idea where the change happened, I think it was through the whole RPM curve. My normal stall speed is 5200 RPM, well that weekend in the good air my stall speed went to 6000 RPM, so it helped out my bottom end too.

And no, I dont have any way of recording intake temps, they had to be cooler, going from 80* air to 50* air has to change intake temps.

Maybe the cold air made my blower seal up better too, I dont know.