car stops pulling after the shift.

So up at PJ Iowa this weekend my driver said that the car just quit pulling after the shift. The car is 1500# 468 ci 6-71 alky. glide with a 4.10 gear and 33/17/15s. 20# at 45% over. This combo has been 4.60 at 153 same track similar conditions same tune. Only diff. was 24# at 45% over. Any Ideas on why it would do this?

I will throw this in to confuse you even more, the motor is hurt a little with a bad cyl. letting the compression blow by. until this run it has not slowed that much at all(5.009 at 142) normaly around a 4.70 145. MPH seems to be there but et is way off.

Thanks for the help in advance.
Bob

 

I will guess that bad cylinder is showing most at the shift point. You may notice a bigger drop in tire growth at that point as well.

 

If I understand you correctly, you changed nothing and the boost increased from 20 to 24 psi. If this is the case than you have an intake valve that is not opening.

 

yes tire growth is down for the looks of it in videos. The valve train is haveing issues as well we found out to night. Its time for a visit to parts depot with the check book.