looses power
 

GT/HA '66 Plymouth Belvedere, 426 Street Wedge, 3,675 lbs.
2.77 first gear ratio, 4.89 rear gear, shifting @ 6,500 rpm, 7,500 rpm at the finish line.
1.44 60', 4.35 @ 330, 10.80 @ 122.00 mph.

Problem is it runs out of steam at the top of the first gear.

Running an Edelbrock Super Victor with a Carter AFB 585 cfm, fresh Product Engineering 9500 Fuel Pump and 4 port regulator.

What do you guys think?

Re: looses power
 

Hi Frank, Jim Hale could be very helpful with that combo but my thought is you're turning it too high, I would go with a 4.56 gear and back to a 2.45 first and advance the cam a little.

Re: looses power
 

Try shifting 1-2 at 6000-6200 see if it goes faster.

Re: looses power
 

I was thinking the same thing. I always have to get out of low gear much sooner than second.

Re: looses power
 

Just to be on the safe side, if clearances and other factors allow it, try upping spring pressures a bit. It's better to have a LITTLE more than needed than a little less. Do some research on what your overall engine combo should like in springs.

Being a long stroke big block, it could work better with less rpm, as suggested.

Re: looses power
 

Okay, I'm good with lower rpm, but I'm thinking the intake has too much plenum and runner, agree?

Re: looses power
 

Too much plenum or runner cross section won't cost power at higher RPM. My experience has been the other way around.

Re: looses power
 

426ci + 525 CFM don't = 7500 rpm at the end or 6500 rpm on the shifts..

Just sayin'


PS:
But I could be wrong......................

Re: looses power
 

Please explain your thought.

Re: looses power
 

If I may.....Try breathing through a straw (small carb), then try breathing through the cardboard spool out of a paper towel roll (big carb). You can only take in so much air in so much time through a small hole. The restriction doesn't allow you (or the engine) to breathe enough volume quickly enough to satisfy the needs. (High rpm or you running.)

Re: looses power
 

Thanks Myron,

I agree about lower shifts points, but I still suspect the Super Victor intake manifold is the wrong choice, and going to test a Victor which is designed for lower rpm applications.

Re: looses power
 

Just trying to help with my perspective, and hoping Mr. Mulry doesn't mind me cutting in.

The manifold change appears to be a very good idea also. I've heard of several people disappointed with the small block version of the SV as well, noting the larger plenum volume and recommended rpm range.

Re: looses power
 

Be my guest.....

You broke it down better than I did.........

Take care,
Bob



PS:

But on the other hand, a large plenum and a small runner can fool the engine into thinking that it has a larger carb..

There are a lot of ways to fool an engine..........

Re: looses power
 

Everything seems ok. 1-2 shift sooner.

Don't go to 4.56 and 2.45 low gear. It won't leave starting line at all.

Re: looses power
 

I would agree that a large runner and plenum wouldn't cause a lack of power. Sprint cup restrictor plate motors (similar to the big motor, small carb setup) actually make power using the biggest runner size they can cut into the manifold casting. More likely a fuel delivery issue if it only occurs in low gear as that is when there is the highest 'G' loading on the fuel system.

Re: looses power
 

Frank , has this combo been on an engine dyno? All the guessing and possibilities are answered.

Re: looses power
 

Thanks Glenn,

This is not my car, but a friends who is not a Class Racer member and cannot post here. It was my idea to post because he's is frustrated and I knew you guys could help.

I know the engine has been dyno tested, but not flogged and I'm not familiar with the data.

Because of the small carburetor I think the Super Victor intake is too much, and he's going to try the smaller Victor at the track.

The fuel delivery theory has been adequately addressed, and I agree the 2.77 low gear and 4.89 rear are correct for the combination, also shifting at 6,000 seems to make sense.

Thanks to everyone for the thoughts, but if there are more ideas, I'm all ears.

He's only looking to go 10.40s or 50s.

Re: looses power
 

1320/122=10.819 It sounds like he's right on target with the power he's making.

Re: looses power
 

There's always more!

Re: looses power
 

Yes. But there's not 3 or 4 tenths more with the same hp to run 122mph.

Just curious does anybody have good data on what it takes hp wise to pick up 1 tenth at this level?

Re: looses power
 

You're right. If he's looking for 3 to 4 tenths, he's down on power big time.

Re: looses power
 

This is what I was going off of.

Re: looses power
 

I'm with Paul in post #2. Jim Hale could be a big help on that combination. His '64 Sport Fury can run those times in G/SA at about the same weight. I wouldn't expect him to give away all his secrets but he might point you in the right direction. I don't know how tall of a tire you have on there but that seems like a lot of rpm for 122 mph. Converter slippage?

Re: looses power
 

Approx 15 HP per tenth in this range and weight. Four tenth's quicker with the present gearing would put this car through the traps around 8,000 RPM with a motor that makes peak HP below 7,000, not good for ET or the life of the motor. Without knowing the cam specs, head casting and flow specs it's hard to know what the potential is and that's assuming the short block is up to snuff. The carb should be set up on a flow bench because just a couple of degree's on the secondaries with an AFB can make a huge difference in flow, and when you're running a carb that's the equivalent of a 2BRL carb on a motor this size that is very important.

Re: looses power
 

Based on some MPH, RPM, Gear ratio calculations assuming he's using a 30" tire with very little % slip. He's either running 136MPH, a 5.49 gear or only really turning it about 6,681RPM's. Obviously we know what his real MPH and gear ratio is, so that only leave a couple things. Either its only running about 6700 out the back or the converter is flat gone and slipping over 10%.