BBC pump gas motors

Old 03-14-2009, 09:38 PM
  #1  
supergass
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Default BBC pump gas motors

Hey, I am getting a little discusted that I cant seem to make a BBC run the way I want without alot of Compression. I build SBCs and they are just screamers(406 etc.) but I am having trouble building more than 185lbs of cyl pressure with 11:1 BBCs. I always run square port heads and roller cams, just cant get them to 60ft with big stall converters 5000 and up. Is there some camshaft secret? Does it take a 3speed trans to keep the revs up? I can get the dominators to run and rev real responsive but right now I am having a hard time getting a friends 505 with Dart heads and a roller to run better than a 6:70 in a 3400lbs car. It has a dominator and a roller cam. I even went down to a 108 lobe seperation from 110 to see if that would help. The other figures are 708 708 and .277 and 285 at .050 duration. The heads are 320cc. Powerglide and 5200 stall Coan converter. My SBCs are running as good as my 505 I built for the same guy? Maybe the duration on the cam is a little big?
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Old 03-14-2009, 10:02 PM
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ashbros
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Rough calculations indicate your engine is making 680 horse power. Its does not take rocket science to make that kind of power with a big inch BBC. Thats only 1.35 hp per cubic inch.

Are you sure you don't have some type of A/F problem when you are putting the engine on a load.

And yes you are correct, it is pretty easy to build a small block that makes 680 hp. Seems to me that you should be making 750 to 800 HP. Have you pulled a plug after a run to inspect its condition? Is it running really rich?

Its gonna take 800 horse to break into the nines in the quarter mile, but you'll still be running about 6:30 to 6:50's in the eight.

If you can't drop any weight it will take a 1000 HP to put you in the high 5:90's with a 3400 lb car

Throw a 100 or 150 shot to it and see what happends. Maybe your fuel just isn't atomizing correctly.
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Old 03-14-2009, 10:51 PM
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Tod74
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in my opinion 277 and 285 @ .050 camshaft will need some compression.

You bleed off your cylinder preasure.If you want it to have higher cylinder preasure without adding compresion shorten up the camshaft duration. More lift without adding duration will give you more torque I think....but I'm no engine builder, I just bolt my junk together out of a JEGS catalog..
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Old 03-14-2009, 11:34 PM
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zipper06
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Recent engine I built 468" in a 66, Biscyne 3700lb.

Stock 804 rods and Steel crank
Probe forged pistons
10.2 compression
BB2 plus brodix's fully ported
Solid roller XR292 cam .666 int .660 exh 110 lobe sep installed @ 108
1050 dom
454R int with 1" spacer
turbo 400 with brake
5500 stall converter, leaving on 3800 chip
shifting at 6400
4.30 gear
30.5 Hoosers D.O.T. street slicks
2" headers X 3 1/2 collector
Shell 93 octane, no addatives

This is what it ran at Baton Rouge Super Chevy a few weeks ago.
1.39 60'
6.56 1/8
10.59 @ 127 mph qtr.

So your cam could be a little tall and long on the duration as others has stated.
It worked for me

Here's a vid of the car from late last yr.

Zip.

http://video.google.com/videoplay?do...33704889072434
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Old 03-15-2009, 06:20 PM
  #5  
ashbros
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Hey zipper
pretty cool car you have there
The numbers you are posting put you around 780 to 800 hp.
Damb good 1/8 mile number and MPH
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Old 03-15-2009, 06:28 PM
  #6  
thedude
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in my opinion 277 and 285 @ .050 camshaft will need some compression.
Yep Todd74 hit the nail on the head. If this is a lower static compression engine that cam profile that you listed, in my opinion is too big. I realize that the cubic inch is there but for the 320 head and lower C.R. somewhere around a [email protected]" duration would probably be ideal. Too much bump and not enough squeeze.
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Old 03-15-2009, 06:52 PM
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ashbros
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QUOTE OF THE WEEK

"Too much bump and not enough squeeze"

Thats a classic.
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Old 03-15-2009, 08:12 PM
  #8  
supergass
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That is pretty much where I have landed is that the duration is just to much but I didnt want to just shoot from the hip this time. I had a 509 (4.500 bore and 4.00 stroke before in my personal car with pump gas and a powerglide and 4:10 gears but a smaller roller, comp cams 714 714 and 260 and 270 at 050, it was a awesome motor! I think the 3 speed trans really helps to get the 60fts back in check too if you can control the torque. I do appreciate the info, it does help alot. I also have just built a 505 (4.310 bore and 4.250 stroke) with GM 990 rectangle heads and on pump gas with a smaller solid lifter cam of 620 620 and 256 and 262 at 050 and it has a 110 lobe sep. It has converter 4600 stall and 4:56 gears and a 32inch tall tire and it has run a 6:93 so far. It doesnt have a dominator, it has a 950cfm. Just having bad luck lately and I am not happy with the results. These two 505s are in two different cars and I have checked all the obvious with timing, throttle adjustment, fuel flow and pressure, jetting. The engines are running clean and good......just not real hard. I appreciate your time in response!!

CC
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Old 03-16-2009, 12:23 AM
  #9  
zipper06
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Originally Posted by ashbros
Hey zipper
pretty cool car you have there
The numbers you are posting put you around 780 to 800 hp.
Damb good 1/8 mile number and MPH
The car belongs to my friend i just built the motor for him and tuned it. We run 38 degrees timing and just this week we put a 150 plate shot of nitrous on it probably go next sun to test and tune hoping to get close to the bottom 6's and low 10's with it, if we don't get rained out we've had 5 strait days rain, i'll make a vid if we go and post it with time tickets. Then bolt on the exhaust and drive to Sonic and fill up on burgers, it's got a 10 gal fuel cell, and Sonic is only 10 min. away, it's got lights, alternator, 2 seats and all acesseries except wind shield wipers.

Zip.
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Old 03-16-2009, 02:35 PM
  #10  
slickfuel
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Supergass,...........

I also have just built a 505 (4.310 bore and 4.250 stroke)
That is actually a 496 ci,....not 505ci

505ci= 4.350 bore & 4.250 stroke

:roll: :roll:
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