Disappointing Day on the Dyno

Originally Posted by 289nate

I can't believe the person doing the tune on the dyno didn't check that! I'd certainly be on the phone wanting to do another session at a big discount.

It was past closing time when I discovered the throttle issue, but I certainly plan on calling them Monday to work something out. In the mean time I'm afraid to get my hopes up too much that this alone will put me over the 400 mark, but an inch of travel could be significant!

An inch is an inch......every little bit helps...
So she says...........

On the bright side thats pretty stout for 3/4 throttle on a chassis dyno!

Originally Posted by allenman85

c) Throttle is not opening 100%???

Originally Posted by 289nate

Good catch on the throttle Mike.

Ummm....I think I got the right answer first.

There are so many things can affect a dyno run, the alitude, figure a 6% loss for every 1000ft. the Baro reading of the day, oil temp can become very critical, always try to do the run at the same oil temp. I use 180 * and a water temp of 160*, . the true test will be in your ET in a 1/4 mile, That alone will show how accurate The dyno figures were. there are several good calulators on the web for converting ET to Horsepower required to get that ET. Dynos measure Torque, no machine in the world measures HorsePower.Yours as a very nice area under the curve. ( the space between the Torque line and the HP line), I can well understand wanting to stay with something that is still tame on the street. the difference in peak may be the stroke of your engine, 4 cycles tend to develop their peak HP at about 4500Ft, per sec of piston speed, peak torque will be about 75% of that. as mentioned earlier losses of power due to waterpump could be as much as 10 HP, and altenator, auto Trans. my main concern would be the very rich mixture washing down the rings. I haven't checked to see want the 825 comes with as std jets.but Grants tend to be rich anyway as delivered , tough to sell a one size fits all Carb. and nobody wants to see a lean engine burned up.but you should be very proud , you have taken this project a long way, and the results are truely professional.

Originally Posted by DynoTomS

the true test will be in your ET in a 1/4 mile, That alone will show how accurate The dyno figures were. there are several good calulators on the web for converting ET to Horsepower required to get that ET. Dynos measure Torque, no machine in the world measures HorsePower.

Bravo!!!!

Originally Posted by allenman85

Ummm....I think I got the right answer first.

Opps!

Originally Posted by DynoTomS

my main concern would be the very rich mixture washing down the rings. I haven't checked to see want the 825 comes with as std jets.but Grants tend to be rich anyway as delivered , tough to sell a one size fits all Carb. and nobody wants to see a lean engine burned up.but you should be very proud , you have taken this project a long way, and the results are truely professional.

Thanks Tom!!! The Mighty Demon 825 came out of the box with 76 primary and 88 secondary jets. We ended up with 80 primary and 92 secondary. I can go back down a size if I need to when we re-dyno it. I'll have to see where we are once we run it on the dyno at full-throttle. When I adjusted the throttle back the rest of the way from where it was stopping, I could hear it squirt another shot of fuel into the carb. Then I drove the car for a while, and regardless of any dyno numbers it is very fast... It just melts both rear tires right into 3rd gear!

Sounds like you are much happier now, Good, Demon's web site list a 76 pri, and a 84 sec. the 8 jet size increase is normal for a blocked power valve , that should put you in about 13.5 AF and a BSFC of about .450 LBS,per hp per hr. make sure there is no etenaol, in the fuel as it specfic gravity is different the pure gasoline. the 12.5 will get you to best power but you couldn't stand to be around it. $ wise or the fumes. Hopefully the dyno guy is a stand up person and will work with you on another pull or two, we never admit it but we like to see the numbers too. i think you will be impressed with how much it comes up, he should have caught the high vac.after the run from before.there is a very good book that has just been released. title "Dynos, Testing and Tuning" . it is written by two very good friends, Harold Bettes, (who was Mr SuperFlow for 35 years)and Bill Hancock of Arrow Racing Engines . SA book # 138 it is a little pricey at $30.00 but well worth it, Barnes and Noble should have it in store . if you wish to learn more about what a dyno can really do.it covers flywheel and chassis both

I'm scheduled to take my car back to the dyno on Friday afternoon, so we'll see what happens at full-throttle!

Tom, I saw your correction factor on the other thread:
"these 80% humidity days are killing us here, correction factor this morning was 1.104"
Is this correction just for the humidity? If I apply it to my dyno run last Thursday on a 80-100% humidity day, it makes my 357 HP into 394!