Engine rpm question

[washeduptoo]

We've got this engine that was freshened, dyno over the winter and it would turn 8100-8300 easily. Lately it only turns about 7800 at same track, same gear, no miss about same track conditions. Changed plugs, check fuel filter, timing, fuel pressure and went through valves. All that is ok, carb bowl level, ok. Do you thing a valve spring has gone bad(new this year) or something else. Its an HEI ignition with a new module. Looking for suggestions, thanks and its on 112 race gas if it makes a difference. Thanks

[Dirt Knife]

cam lobe???

Cam lobe issue????

[perfconn]

Not necessarily anything wrong with engine.If you have changed suspension to get more traction then rpm will be less.Track conditions could also be tackier.The way to find out is to put more gear in the car and see if it turns more rpm.If it doesn't then you may have a problem,such as valve springs.

[DaveBauerSS6]

When a valve spring goes weak, the motor will plateau at a lower rpm that it used to run. If nothing else has changed and a spring is going, the motor will pull normal to that point in the track and stop pulling ( but not slow down). A lot of drivers cant hear the miss. A quick check on the track is to hit the plateau and let off the throttle and back on. You will feel the miss, it feel like a wall.

You didn't mention if the car is placing farther back in the field. 300-500 rpm less will get you lapped quick. Tach maybe bad. I would change out the hei next. I carry a complete spare to the track for that reason.
Good luck.

[powerslide]

We've got this engine that was freshened, dyno over the winter and it would turn 8100-8300 easily. Lately it only turns about 7800 at same track, same gear, no miss about same track conditions. Changed plugs, check fuel filter, timing, fuel pressure and went through valves. All that is ok, carb bowl level, ok. Do you thing a valve spring has gone bad(new this year) or something else. Its an HEI ignition with a new module. Looking for suggestions, thanks and its on 112 race gas if it makes a difference. Thanks

Did you make sure the butterflies are opening all the way? i remember u talking about hiring a driver so you probably adjusted your gas pedal

[washeduptoo]

Thanks for all the replies. It did it the last time normal driver raced it, that is why we went through all the stuff and it did it again last weekend. Haven't checked the butterflies yet, its a dry slick carb and it is in the fast position. Engine builder thinks a spring might be bad. It was sluggish off the corner according to new driver but its a lower torque engine then he is used to. I'm not an engine person, but we'll take a look at it best we can. Might have to take carb to get it looked at. Thanks again.

[washeduptoo]

Just wanted to update incase someone else has this problem. Finally had time to look at engine(haven't run car since our last reply), think we found the problem. The vac line port off carb wasn't pulling any vac. Port was clear, not sure why its not but we moved it to another hole and it seems to be working fine in the shop now. Of course this was after going thru everything again, including testing valve springs, compression test, etc. Everything rained out down here this weekend, will be on track next weeknd hopefully. Something else learned about engines and a dry slick carb. Thanks