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Disapointing dyno numbers

 
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pro60chevy
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Joined: 01 Jan 2004
Posts: 406

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PostPosted: Sun May 02, 2004 6:26 am    Post subject: Disapointing dyno numbers Reply with quote

I got on the chassis dyno Saturday. I was not impressed with the numbers I ended up with. 449.93 rwhp and 592.83 ftlbs of torque @ 7500 rpm.There is something going on from 5500 to 6200 where it feels like I'm pulling a truck. After it creeps past that point, it runs right up to 7500. We tried pulling some of the timing out, and it did get a little better, but not what I would of expected. I must get rid of that before Wednesday. We did a total of 10 pulls in about 1 1/2 hrs. The guy did a MPH comparison on the good pull, and it toped out at 151 MPH. He seems to think I may not have enough carburetor. I have a Holley 850 on it now, is it possible it's not enough? Here is the clip anyway. Remember to right click and save target as.

http://1960belair.8m.com/Videos/dyno-three.AVI
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jeep_406
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Location: Tewksbury, Mass 01876
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1972 Chevrolet Nova

PostPosted: Sun May 02, 2004 12:22 pm    Post subject: Reply with quote

If it was carburetion wouldn't you think it would get worse instead of turning back on at 6200RPM and then go to 7500 ok?

Is that normally aspirated or are you hitting it with the bottle? If you have a staged set-up could it be a problem there?

I'd almost think the timing is doing something screwy from 55-6200RPM.

I've never seen a chassis dyno in operation. Do they have printouts of timing, air-fuel ratio etc at each RPM point?

Hope you find it before Wednesday and I hope you have good air and traction.
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pro60chevy
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PostPosted: Sun May 02, 2004 2:26 pm    Post subject: Reply with quote

jeep_406 wrote:
If it was carburetion wouldn't you think it would get worse instead of turning back on at 6200RPM and then go to 7500 ok?

Is that normally aspirated or are you hitting it with the bottle? If you have a staged set-up could it be a problem there?

I'd almost think the timing is doing something screwy from 55-6200RPM.

I've never seen a chassis dyno in operation. Do they have printouts of timing, air-fuel ratio etc at each RPM point?

Hope you find it before Wednesday and I hope you have good air and traction.


I totally agree with everything you said. I had two empty bottles so it was all motor. I got an air-fuel reading, but it showed that it was just right all the way thru the run. I don't think there was a timing reading though. I must do some hard thinking on this. Thanks.
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2x4
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PostPosted: Sun May 02, 2004 3:20 pm    Post subject: Reply with quote

Your running a auto trans in that arent you? Could it be converter troubles? Just seems like if your A/F numbers are fine all the way through, it would be hard to be anything in the carburation.
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pro60chevy
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PostPosted: Sun May 02, 2004 3:25 pm    Post subject: Reply with quote

The converter slipping was one of my concerns also, but the torque curve would have showed that, and it didn't. The guy that was running the dyno feels like I could use a bigger carburetor, bit I disagree. I have an 850 on there now.
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jeep_406
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PostPosted: Sun May 02, 2004 10:19 pm    Post subject: Reply with quote

What do you have in it for a converter?
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pro60chevy
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PostPosted: Mon May 03, 2004 5:01 am    Post subject: Reply with quote

jeep_406 wrote:
What do you have in it for a converter?


The converter is 4500 stall made by Converter Design Specialist in N.C.
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jeep_406
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Location: Tewksbury, Mass 01876
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1972 Chevrolet Nova

PostPosted: Mon May 03, 2004 10:19 am    Post subject: Reply with quote

You could call them and tell them what you're experiencing but I'm thinking it's not in the converter.

You might try calling the people that make your ignition system. That's the area I suspect but I've never run into what's happening to you.

Do you think you can make your license runs the way it is without hurting the engine?

Sounds far fetched but could your rev limiter be pulling out a cylinder for some reason. Can you borrow a distributor, box, etc to try.

What have you changed since you last ran it that might have in anyway given you the problem.

Maybe the Tech Inspector, Rich, or regulars at a strip have heard of anyone with this problem. I know you are running out of time, maybe you could PM him.
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pro60chevy
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PostPosted: Mon May 03, 2004 12:00 pm    Post subject: Reply with quote

jeep_406 wrote:
You could call them and tell them what you're experiencing but I'm thinking it's not in the converter.

You might try calling the people that make your ignition system. That's the area I suspect but I've never run into what's happening to you.

Do you think you can make your license runs the way it is without hurting the engine?

Sounds far fetched but could your rev limiter be pulling out a cylinder for some reason. Can you borrow a distributor, box, etc to try.

What have you changed since you last ran it that might have in anyway given you the problem.

Maybe the Tech Inspector, Rich, or regulars at a strip have heard of anyone with this problem. I know you are running out of time, maybe you could PM him.


I agree that it's not in the converter. The torque line on the readout would have shown any slippage, and it was fine. The A/F ratio was 13 straight across the screen. One thing I have to change is the ground for the MSD box. It runs to the firewall right now, and I have to move it to the battery. That may be some of the problem.

I never ran this before, the guy I bought it from had run it in the 1/8th, but I can't get ahold of him. I'll see what happens after I change the ground.
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2x4
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PostPosted: Mon May 03, 2004 1:44 pm    Post subject: Reply with quote

I'll bet a buck that MaxRaceSoftware has something to help you out, maybe he'll pop in here.
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pro60chevy
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PostPosted: Tue May 04, 2004 4:14 pm    Post subject: Reply with quote

Guess what, I may have found the problem. To make a long story short, what it all comes down to is the cam profile, and the design of the heads, AFR227's. The exact spot where the troubles begin, is exactly where the cam and heads are made to flow their best. This is a nitrous motor, and they do not perform very good on a dyno without spraying. Unfortunatley I am out of time as I go tomorrow for the license runs, or I would have been back there for a few more pulls. I now have 4 full bottles of juice, and I'm ready. I'll be sure to post tomorrow's results when I get home.
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SMOKEmUP
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PostPosted: Tue May 04, 2004 4:15 pm    Post subject: Reply with quote

Where did you dyno the car?
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pro60chevy
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PostPosted: Tue May 04, 2004 4:20 pm    Post subject: Reply with quote

There is a dyno about a stones throw from where I work and I never knew it. The place is called Manny's Complete Auto & Dyno Testing in Weymouth. He's not a tuner, and you drive the car. $50.00 per hour.
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Hanz
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2003 Dodge Ram

PostPosted: Tue May 04, 2004 5:01 pm    Post subject: Reply with quote

I think that you may have found your problem- and I also have read this post and it didn't hit me-

I had customer that (accidently) put a nitrous designed cam in a naturally aspirated motor, and it was a freakin dog. The lift and duration were almost identical to a street cam that we used alot, but something else was very different about it, don't remember now it was 14 years ago. Swapped the correct cam in and solved his problem.

Hanz

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HotRodDaddy
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1994 Eagle Talon

PostPosted: Tue May 04, 2004 5:03 pm    Post subject: Reply with quote

lucky dog LOL the closest dyno to me is an hour away (less the way i drive) !!
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