Camshaft duration for blown alky with powerglide

If the cam is in at 40ºbtdc and has 294º duration, 294 - (40 and 180) than the intake closes at 74º abdc. 40+180+74=294 294 divided by 2 = 147 - 40º intake opening your intake centerline is 107º. If the cam has a lobe seperation of 114º than it's 7º advance. It shouldn't be a problem, I've run my best times with a blown bbc in a door car at 10º advance.

Marty

 

How much difference would a cam be in a big block chevy verses a late model hemi?

I ask because my fed ran 6.70's with only 274* duration and only 100lb less weight than the funny car.

 

Not much. Somebody on this forum ones said that Brad told them that there is only about 30 horse differance between the best and the worst cam in a blown engine. I ran 7.08 @ 194 on my third pass in my trans am with a 14-71hh on a stock block and aluminum head chevrolet with the non blower roller cam that came with the non blower (na aluminum rods and pistons) 14:1 compression engine. It pulled the head studs out of the block and bent all the wrist pins though.

 

Where I'm not familiar with it, what part does your two step play into this issue Kevin or does it?

When was the last time the Mag was really checked out? Mags can cause a multitude of problems that don't appear too obvious.

Bob

 

think what you can do to strengthen the crankshaft at this spacing

 

I dont get it.

smblkbob has a good point, I have seen brand new mags and/or point boxes cause issues where people chased their tail for a hole season or more thinking it mas the fuel system and everything else because the mag was brand new.


If you dont get my math on the cam degreeing I'll clearify; use half of the duration to find the center of the lobe and than subtract the intake opening btdc to find out how far the centerline is from tdc. You can do the same thing on the exhaust except subtract the exhaust closing atdc to find how far the centerline is from tdc. When you advance the cam the intake centerline gets closer to tdc and the exhaust centerline gets farther away.


Martin Creech

 

Bob,the two step might be an issue too,I have a electric lean out that we will have in place by the next time out.Just need to find the thread on here about what percent of fuel to dump.
On the mag issue,I just went from a 44 promag to a 20 and saw no change between the two so I don't think that is an issue.
thanks Bob.

 

Martin,I know how to degree in a cam,but thanks anyway's

 

fuel cam

Kevin, i'm having the same problem after switching to the Hemi, i spent all summer chasing this thing, i can't believe how much fuel i had to pull out to get it to wake up.if i tried running that amount of fuel in my chevy i'd burn it up

i tried different mags that didn't help i run a standard helix 14-71 spun at 37% over and have 20 lbs boost and the best i can muster is 7.40s the same blower on my 433 BBC will give me 20 lbs at 25% over.

I thought the very same thing get rid of the Nitro cam

 

Scott,I was talking with mickey at the PRI show and he told me you were fighting some of the same issues that I was.
What rpm are you launching at?
What cylinder heads do you have?
What fuel pump
" nozzle sizes
" main jet size

maybe we should have kept our Chevy stuff.....LOL
We will figure it out,I never give up.

 

Fuel cam

Kevin, i sent you a PM

Scott

 

Funny but I've been following a thread on another board and guess what?
Bad Mag and it had been checked out once already.
I had a friend send both his in and both were bad.

I'd send it to Spud if for no other reason than to totally rule it out. Hey it's off season might as well. Probably little $$ just to check it out and if it's bad, you can figure out what it's worth to fix later.
Without a totally professional check, you're only hoping it's 100%
If it's fine, run it straight up with no bells and whistles and see what you get.

This just sounds like a timing/mag issue. Light the fire and you may find you don't have to go any leaner.
As you know, we run blown 90% but the truth is we have to lean it out a bit because the Super Mag we have just won't light it. Stick a 44 on it and we'd run a blank.

I'll agree with someone's statement. On a blown motor, cams just don't seem to make that big a difference. At least the amount you're talking about Kevin.
I've got so many grinds lying around and I can't tell the difference in any of then.
Perhaps a bit more top end revs but that's about it.

Bob

 

sir did you ever determine what this issue was ?Im running BBC with a Lunati grind that is 299/299 in at 38.5 and mine has the same symptoms power is off

 

It's a nine year old thread and most of those names have moved on. Don't see them posting anymore.

 

Ron can you expand on this some?