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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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. |
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.. |
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 |
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 |
in my opinion 277 and 285 @ .050 camshaft will need some compression. |
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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 |
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 Zip. |
Supergass,...........
I also have just built a 505 (4.310 bore and 4.250 stroke) 505ci= 4.350 bore & 4.250 stroke :roll: :roll: |
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