467-Ratman

I am confused about the performance of my motor, last week I had time to spend at the chassis dyno and we tuned the car to have an A/F ratio of about 13 at WOT, it was about 9 before. My question is why does it not seem to be as wild and fast? The motor was really running rich, but it seemed to really kick but, now it just does not seem to have the same rush. I went from jets at 78 and 84 to 74 and 75 in my 850. I know the dyno says my air to fuel ratio is perfect, and its making more hp, but my seat of pants tells me other.

redvetracr

Thats kinda funny!! I spent a whole day on the engine dyno and to be perfectly honest I changed EVERYTHING (and i mean EVERYTHING) the dyno guy did (to make more HP) back to the way it was before I pissed away $550. I must of done something right I finished third at the biggest vintage race in the country (the BRIC at Road America) and I sat on the pole (ouch!!) and won last month (also at R/A) and to top it off my car NEVER went as fast as it did in the heat of July at R/A. ...redvetracr

467-Ratman

Seems to me with the cam and heads that my motor could use the extra fuel and air to make big HP, but seeing the results on the dyno after making changes was very interesting. Good to hear that it is possible without a fancy dyno to make "real" hp!

Langadorf

#1 - You can't FEEL horsepower - you feel torque. Horsepower is what wins races.

#2 - You might try upping your jets just a tad. Running 12.5:1 AFR is better in some engine combinations.

467-Ratman

I know you can't feel HP, and torque is what really makes it move. The results of the day at the dyno were: 40 more hp and 39 more torque. I think that this weekend we will try slightly larger jets, if it runs rich I guess its no big deal?

LAvetteman

I guess thats why alot of old timers say "Don't bother with a A/F meter"

Langadorf

Run too rich and you'll lose power and have carbon buildup on your plugs, heads, pistons, etc. Over time, this will increase your compression ratio possibly causing your engine to experience detonation.


[Modified by Langadorf, 10:37 PM 10/9/2003]

Matt Gruber

a larger primary jet often pleases the SOTP

467-Ratman

Matt, Dumb question, what is SOTP? Thanks!

Fevre

Seat Of The Pants

Chuck Harmon

467-Ratman,

A possibility why SOTP may have felt wilder is that the engine responded better to the over rich condition higher up the rpm curve than it did down low and you could really feel the power coming on. With a flatter (even though it it is higher) torque curve the sensation is more uneventful.

Older Ferrari's had a dual personality. Down low they would trundle around, but at higher revs they would turn ferocious. If you floored it at 2000 rpm you could real feel the personality change once the cam started to come on after about 4500rpm. The newer cars with fuel injection and cam changes that made the car run stronger down low, in part for emission reasons, lost this Dr. Jeckyl/Mr. Hyde personality change. Some of the press reviews were a little critical of this. If I remember correctly, Phil Hill was one.

Chuck

467-Ratman

Thanks! My SOTP factor is having fun today, took the vette to work, the only problem is I want to take the day off now! Its about 75 here in Michigan, lots of sun, a perfect day for a cruise......... :steering:

Fevre

Picking mine up at lunch! Tomorrow is also supposed to be great. :thumbs:

467-Ratman

Great news! On my way back to work I filled up the car and guess what? Since we changed to the smaller jets in my 850DP I got 7mpg, thats up from 6mpg last week.......I guess my car will never be shy of the gas station. :lolg:

Corey_68

Interesting you say that. All the old school racers (my dad included) have always said "HP is for braging rights, Torque is what wins races." Others put it "HP is for bragging, Torque is for dragging."

Both are equally important in my opinion. :cheers:

Matt Gruber

diesels rule! ;)

Brettmc

Yup!! My old 83 K10 6.2 diesel daily driver with 216k miles snags around 18-19 in city driving.

Brett :thumbs:

Langadorf

Which do you think would be faster, assuming proper gearing - a car w/ 5 HP and 1000 FT-LBS of TQ or a car with 1000 HP and 5 FT-LBS of TQ? The car with more horsepower would win every time. Torque is just a measure of force applied. Horsepower is a measure of this force over time.

Corey_68

I have always been told to build motors to have the largest amout of torque over the flatest and broadest rpm range possible. If you do this HP will take care over itself.

HP is NOT a force, it's only a measurement we obtain by plugging in the formula (HP = (RPM X TQ) divided by 5252). It's not cut and dry to say one is particularly better than the other, both are important. A car will accelerate hardest at its torque peak in any given gear, and will not accelerate as hard below that peak, or above it.

427Hotrod

I think you just said the same thing......

"TQxRPM" kind of sounds real close to " TQ(Force) x RPM (time). He said it was a simply a derivative of the TQ measurement over time. :)

I always get a kick out of thse discussions. If you make 500 ft lbs at 4000 rpm you have 380.8 hp. If you can still make 500 ft lbs at 6000 rpm you'll have 571.2 hp. It's great to have a bunch of low end TQ, but it's even better to still have it as the RPM's climb. My recent re-do of my 540 lost about 10 ft lbs or so around 5000 rpm....but the increased breathing allowed it to hang on a LOT longer and it is still making over 600 ft lbs at 7000 rpm as opposed to 444 ft lbs at 7000 with the old combo. It just ran out of air early. At the peaks it is up over 234 hp which I think is a great trade off! Like having a nitrous bottle that never runs dry!

There's a couple of neat sayings that fit in here.

"A TQ motor is just another way of saying the breathing sucks!" I.E. an excuse for it nosing over on the upper end.

And when a head porter wants to talk about a set of heads that are way too big for the combination, he'll say " They will make excellent HP per cubic inch". Translation? They are way too big and he would prefer you to put them on a really little motor and turn it 9000 rpm so it will finally have enough velocity to make some power.

And Warren Johnson's expression is "Whoever makes the "most explosions" (RPM) on the way to the finish line will win!"

I'm definitely not saying that "bigger is better". As Corey did say, you want to make as much as you can over the broadest usable range you need to work in. Often smaller ports and cams will do that best. It's all in the combination. In my case I was able to make a lot more HP without giving up much midrange. That is always a good thing.

JIM