467-Ratman

Well that was fun and very interesting today at the Dyno. I took the vette to this shop who has a Dynojet chassis dyno. The first pull had 348hp and 380 torque, he said my timming was way off and also the A/F ratio was only about 10.5. Next step was to disconnect the vacuum advance and reset the total timming to 36. That gave another 20 hp and 19torque. He then took the carb apart and leaned out the jets, 73 up front and 75 in back, put in different squirters the end result was 383 hp at 5600 and 423 max torque. For some reason my MSD would not let it reach the rev limiter which is set at 6000? I think I am going to try another pill and see how it pulls. All in all very informative although somewhat dissapointing, it would most likely have made more HP if it could have run higher up to redline. He said figure about a 20 percent driveline loss so the motor is making about 450 - 460 hp, not too bad. I was surpised how rich it was running, the change to smaller jets did the trick, but maybe this cost me some top end HP?

Alwyn678

20% loss with a 4 speed ?????I thought it was only around 15.......Good numbers though :cheers:

Jughead

383 RWHP ain't nothing to sneeze at! :D There's guys here that'd die for those numbers. :thumbs:

Fevre

What did you curves look like? If still climbing at the the 5600 then you might still have some hp to gain. Bet you got a fat torq curve.

bhmyers

congrads, those are good numbers. What is your setup like?

Corey_68

Modern day 6 speeds are about 15% loss, 4speeds, and 700R4's are about 20% and the Th400 are beween 22%-25%! :eek:

400 Turbos are strong trannys, but they soak up some serious power. :(

467-Ratman

Actually it fell off at 5600, I was surprised with my Merlin heads and carb setup. I just figured since they are big on the intake runners, 310cc they would respond well to high rpms? My torque was flat at 2800 all the way to 4400 then it went down. My motor did not like anymore timing then 36 as well, we tried 38-40 and the Hp went down. I wonder if I put the big jets back in if the power would rise. My final set up was 73 jets up front and 75 in back with 5.5 power valves.

zwede

Richer mixture will not make more power. There is an ideal air/fuel ratio that makes the best power. Adding fuel beyond that will make power drop. The ideal mixture is usually 12.5:1 to 13.0:1.

Hopefully you got a printout showing power/torque and AFR?

zwede

BTW, a 20% loss and 383 rwhp means the engine is making close to 480 hp. You take the rwhp/0.80.

467-Ratman

Yes, the graph shows my air fuel ratio after the changes to be 14 at 3000 rpms then stays flat at about 12.5 all the way to 5600. Before he made the changes it was 11 at 3000 then fell to 9.5 and stayed flat untill 5800.

Chuck Harmon

467-Ratman,

Not winding out more sounds like my motor's first dyno run. The throttle bracket slipped and I wasn't getting full throttle. This change alone made 60 horsepower.

Chuck

467-Ratman

Chuck, I will check it out tonight, with all that was going on I did not notice when he put the carb back on!

69 N.O.X. RATT

Ratman: Not too bad. I thought you would be at 400 or a little more. Chuck brought up a good point make sure the carb is opening up all the way, just a little can make a big differance.

The fact the motor will not bump the rev limiter concearns me, something is up there and you need to find out what

Assuming that is the motors potential, and you want more, the first place to look would be a cam change. A bigger solid flat or roller would put you over 400 without making it unstreetable, or you could be happy with a motor that makes way more tourque and 20 rwhp more than a new Z06.

467-Ratman

My mistake on the max rpms for power, I talked to him today and he did a few pulls to 6000 but the power level was flat from 5600 to 6000. He then made the other runs and the final run and stopped at about 5800. Seems funny that my motor would not make more HP from 5600 to 6000?

SmokedTires

:cool: I look forward to going to a dyno again and playing around some :D

zwede

Could the intake be holding you back????

467-Ratman

Good question, its a GM high rise aluminum dual plane style. The motor was originally in a guys high performance boat, so the intake is a marine unit. He also had the big Merlin heads for breathing too. I just figured that because it was in a high perf boat that it should breath very well?

Bob Turner

467-Ratman,

Thanks for sharing your results!! Those number are VERY good. I hope to get at LEAST 350hp at the rear wheels after seeing your numbers. My cam is a little smaller than yours (230/236) and you I am running stock heads that have some porting done to them.

BTW, I ordered a Holley 750.... I think it will better match my setup... I liked the Demon 850 but I think I went too big with it and I think it's for more experienced motorheads...... I will keep you updated once I get it on...

I am going to the dyno once I get the new undercar exhaust in...

Bob :cheers:

GrandSportC3

Well - that's true with late model drivetrains.. Older cars use older not that lightweight technology.. You can expect 20 - 25% drivetrain loss on a C3 with MT and 25 - 35% with AT... (especially the TH400 costs you at least 30%)...
I know several cases that a engine was dynoed for flywheel HP and RWHP.. and there was always at least a 30% difference with a TH400.. I know it from my own experience.. In my '69 I had a 383/429 flywheel - HP engine that only dynoed at just around 300 RWHP wit a TH400...

GrandSportC3

It's not only the tranny that comes into play.. For example - C5's have aluminum driveshaft and half shafts and a better differential.. All those components come into play when dynoing for RWHP...
On C5's 15% for MT and 20% for AT is approx. accurate.. but add another 5 - 15% for older cars...


[Modified by GrandSportC3, 12:21 PM 10/1/2003]