These manifolds have no provision for exhaust crossover.About a year ago,I plugged the exhaust crossover on my Performer RPM & the thing ran like crap,even after rejetting,re-timing,adjusting,etc.
I called my friend who used to work at Edelbrock & he says,"you should know better than to block the exhaust crossover on a street driven car!".
What gives here?
I always thought a cold charge of air-fuel is more dense resulting in more power("cool-cans",intercooers etc)
How can an Air Gap be benificial on the street with no exhaust crossover? graemlins/clonk.gif

BTW,,my combo is a 1700 lb StreetRoadster,355-350,268 Comp,headers,650 Edelbrock carb,MSD/HEI,3:56 gear.
Thanks & sorry to hear about Lingenfelter.

You just have to take your time and let your motor warm up before you romp on it b/c that's what the heat riser does but quicker...

pdq67

Are you using headers? If not the heat riser valve needs to be locked open when the riser passage is blocked.

I *did* let the motor warm up,,a bunch.
It started off running fat,which I expected & then stayed that way.I tried a bunch of different stuff & it just wasn't right,so i unblocked it.This engine thumped pretty good before I blocked the passage,,i was just trying to get a little more out of it.Anyway,thanks for the suggestions.Its all apart right now,waiting to finish my CHERRY 291 castings. Forever Red (http://img7.photobucket.com/albums/v18/TroyCagle1/Troys_T_Engine.JPG)