Got some good feedback on a couple of changes to my BB. First, a thanks to Alan33 for setting it up, most Vettes there were C5's. There were only two other C3's. Both were very clean BB Coupes. Enjoyed meeting Pat ('69) and Danny ('70).

Baseline last year: 283 hp @5100 rpm, 333 ftlb @3800 rpm.
This time: 333 hp @5100 rpm, 388 ftlb @ 3900 rpm.

Gained 50 rwhp and 55 rwtq. Switched from Torker II to RPM Air Gap, and replaced factory exhaust pipes and mufflers with H pipe and Super Turbos. No other changes. I will be going back for a true test and tune to sort out the carb. My Silverclaw was very rich-lots of black smoke during the runs. Hope to get another 15-20 hp with proper jetting (current is 78/82).

All tests were done with aircleaner in place and with the hood down. These numbers show how important it is to have a free breathing intake and exhaust system.

Question for you gurus-how does the dyno compensate for a car with tall gears, say 3:08's vs. one with 4:56 gears. It should take less power to spin the wheels and dynamometer drums with shorter gears.

 

Power has a time variable in it, so it should be the same. The torque will increase drastically with 4.56, but the HP will stay the same because the tires are spinning slower, they just got to their speed faster, hense, the same power.

 

Horsepower and torque are tied to each other. If you know the horsepower at a given rpm, you can compute the torque; and. visa versa. One horsepower is moving 550 pounds 1 foot vertically in one minute; or, 1 pound 550 ft in one minute; or, 2 pounds 275 ft in one minute. You get the idea, the amount of work is the same.

If you use a higher numerical gear for more leverage, you are not turning the drum as many times. For example, a car in 1st gear with a 9:1 overall ratio will put twice the force on the drum, but only turn it half as many times compared to being in 4th gear with a 4.5:1 overall gear. The amount of work is the same.

The only advantage to consider is that generally choosing the transmission gear with the direct drive, or 1:1 is the most efficient. Although the difference should be small, there will usually be more drive train power lost using transmission gears other than 1:1.

A chain drive gear like a bicycle is more efficient than a ring and pinion design like a car uses. Shaft drive motorcycles are smoother than chain drive; but, there is a small power price to pay for this smoothness.

Chuck



[Modified by Chuck Harmon, 2:38 PM 3/9/2002]

 

Doug,
Nice improvement! Just outta curiosity, are you running stock exhaust manifolds? Also, what heads/valve size & what cam do you have?

 

Les,

The car has headers (and had them during last year's test). Stock oval port heads with bigger valves. Cam is 224/232 @ .050 and .527/.550 lift with 114 lsa. Fairly mild. 15" vacuum at idle.

The change in the intake really made a difference in driveability. The bottom end is significantly better than when I had the Torker II. Like going from a small block car to a big block car.

Carb definately needs attention, though. Has anyone got experience with using an A/F meter and tuning that way? Might be cheaper and easier on the equipment vs. doing a bunch of dyno pulls.

 

Hey Doug,
I enjoyed meeting you and all of the other guys there.
Let me know when you plan on going back to ACD.
I would be interested in joining you. I would like to try
a different air filter setup and maybe different mufflers.
I would also be interested in seeing what the results would be
with no air filter at all.

 

Doug how many CFM is the carb

 

carb is a 750 cfm with mechanical secondaries.

 

Pat,

Good to meet you as well. The shop charges $125/hr with as many pulls as you can do. They do not know much about my type of carb, though. I need to do a little more research on the difference in tuning this carb vs. a Holley. I will drop you an email. Your car looks and sounds great. I bet your numbers would go up with a little fine tuning.

 

I'm into 750 speed demons. Which should be the same jetting as your Silver Claw. You can't compare Holley double pumper jetting with Demons. Some people claim they flow more CFM than advertised and that's why they make more power than the eq. Holley per CFM rating.

I'm running 76/81 6.5 power valve and drilled the squirters out to .044 or .045 I can't remember which. Also the idle A/F was to rich so I drilled .125 holes in each primary throttle blade to get all four corner idle screws out to about 1 1/2 turns.

Be sure and set it up the idle screws with a with a vacuum gauge and timing right on. I have 13 inches of vac at 950 rpm

To help off idle transistion set the idle RPM with the secondaries slightly more open than the primaries. Any other questions just ask.

:smash:

 

gkull,
I have a rich idle too, but it seems lean at part throttle. I wanted to dial in the main jets before messing too much with the idle and accel. pump. Will an A/F meter help?
I will go back with original settings of 75/81 and try to correct the off idle stumble with cam and shooter adjustment(current shooter is a 37, which helped vs. the stock 31). I have increased the air bleeds .003 per BG. Still too rich. If I go further or drill the throttle plates, my RPM at idle will be too high (primary and secondary plates are about closed at 750 rpm). According to their instructions, next step is to decrease the IFR (idle fuel restrictors). Did you experiment with changes to IFR in metering block?

 

It's hard to answer everything! I was going to buy the a/F meter. They are really a heat sensor. Then they just give you range which doesn't react fast enough to give a true reading. Just like MAf etc. with fuel inj.

When I had a 355 roller motor I spent time on a rear wheel dyno to dial in a 750 edlbrock. Not just at max power curve at WOT. We played with everything with a rear sniffer.

With my new motor. I have not done any of that. I ran out of money when I built it.

I didn't look back up to see what C/R was. If you Stumble to your wide open. You need to understand that a carb has 4 gas cuircuts (sp?) Get on some web page to like Demon.com They will help you.

Just an easy way to tell if your way to fat at idle is pull a small vac line at idle. if your RPM goes up. Your way rich.

I never changed the IFR. Guys with Holley's place a fine diameter wire to restrict the flow. BG & Demons I never did that.

I'm now shifted away from a 750 Speed demon to a 825 cfm race demon.

MY advice is increase your idle to 800-850. Jet it down with everything in the above post and see how it runs. I am a big believer in vacuum advance. So if you have initial at 12 with vac advance you might have 16 or so at idle. Dial 4 corner idle screws for max vac. inches. Then turn down your idle speed to the 8.5 or 900 rpm

You had black smoke so you know your fat!!!!!! Right?


[Modified by gkull, 8:51 AM 3/13/2002]