S/C dynograph...experts tke a look

[SuperchargedSHOguy]

Its all over the place. First run 330 h.p 314 torque. 2nd run 331 h.p. 300 torque. Numbers seem too low for the 15 psi I normally hit. They guy doing the dyno must have only hit 11 psi. My car went from its first dyno when David owned it from a 3.48 pulley to a 3.12 pulley currently. From the last dyno I only have a 9 h.p. increase but a whopping 58 increase of ft/lbs torque after dropping 2 pulley sizes. I believe I know the culprits to the "heartbeat" but I want to see what everyone else thinks

 

[Ishodu]

Wheres the air fuel ratio? Its hard to really tell much with out that.

 

[SuperchargedSHOguy]

Wheres the air fuel ratio? Its hard to really tell much with out that.

No wideband O2...it was at a car show where they were donig as many cars as they could as quick as possible on their mobile dyno

 

[Yamaha V6]

FYI, some of my "15psi" pulls were junk, since the belt slipped at 11psi (coincidentally where you mentioned).

The spikes may be indicative of slip & catch, but I think you have something else going on. Also check to make sure you're not blowing the tubing off / air leak after the blower but before the intake, etc.

Agreed, A/F ratio is imperative with every dyno session you do with a blower car, unless you've got a wideband O2 or some other method of tracking.

Good luck!

 

[DavidT]

Chris, do you think the belt was slipping?
TexanTony and Ransom OVERemphasized with me the importance of OVERTIGHTENING the s/c belt. Tony said he goes through the tensioner hex head bolts like water (from getting the belt as tight as possible).
Always make sure the belt is tight before track or dyno runs.
What else do you think it might be?

 

[LOUDSHO92]

What fuel pump are you running? If you are running over 155 then that may be part of your problems, unless you are running you are running a fuel regulator.

 

[SuperchargedSHOguy]

No I hit 15 on the way home and 11 before the show with K-Dawg riding with me. This was just to get an idea of how much power I was shooting right now. What concerns me is why the torque went up 58 ft/lbs and the h.p. only went up 9. Funny you said the piping blowing off...I just fixed that darn problem 2 months ago...bad BOV.

 

[SHOMurph]

What plugs/wires are you running? I would guess you are having an ignition problem up top.

Yes tighten that belt like crazy.

Your numbers are low for 15lbs. Please also give complete list of engine mods.

Also did you change your programming when you went to the smaller pulley?

 

[1stSHO]

Sounds like the car is just a piece of crap. I tell you what, Ill trade you, but i need cash also. Ill suffer and drive that damn SHO. :corn:

 

[Sho-Driver]

What are you using to tune?

 

[AutoSHO]

The reason the torque went up and not the HP is because you aren't making any top-end torque. Thats where you'll get peak HP numbers from, since horsepower is a function of torque and RPM. The reason the torque increased so drastically is that with the smaller pulley, you're seeing more boost sooner, and sincethe computer cannot pull enough timing out to stop detonation due to Vadim's programming, you see more torque before the belt starts slipping badly. I'm guessing the car was pig rich since the MAF was pegged the entire time and the computer has no way of knowing how much air is really going into the engine.

 

[Mike Kopstain]

The reason the torque went up and not the HP is because you aren't making any top-end torque. Thats where you'll get peak HP numbers from, since horsepower is a function of torque and RPM. The reason the torque increased so drastically is that with the smaller pulley, you're seeing more boost sooner, and sincethe computer cannot pull enough timing out to stop detonation due to Vadim's programming, you see more torque before the belt starts slipping badly. I'm guessing the car was pig rich since the MAF was pegged the entire time and the computer has no way of knowing how much air is really going into the engine.

This sounds like an accurate description. What do you have on that car that allows you to run 15psi? When I saw it last it was pulling 12psi and was in no condition to do that.

 

[K-Dawg]

I'll try to answer some of the questions, but I don't know for sure.

I think the motor in the car is a low compression 3.0. Chris bought the car with a 9lb (?) pulley and Sh!tShop LPM. Then he picked up a 12lb (or 15lb?) pulley and LPM with a SS supposed tune for that pulley. Put the pulley in, then the chip. Ran worse with the new chip, so the old one went back in.

I also agree with Chris (AutoSHO). The car does run rich. FWIW, it also idle hunts a little, but now that I think about it, the A/C was on and may have caused the fluctuations.

Chris, we definitely need to get a TwEECer and wideband on that thing. I think between the two of us and our two cars, and the help available on the Internet, we can figure it out. Too bad you live right across the street from the Police station though...

 

[Sho-Driver]

He really should not have to do much tuning for a new pulley if he were tuned to begin with and with all supporting modifications. AutoSHO is probably on the money. If your running a Lincoln MAF, you are running a MAF that is incapable of measuring enough airflow for your application. Combine that with Vadim's (this looks cool, I'll change this) programming, you are not going to run well at all.

 

[K-Dawg]

He has a 90mm Lightning MAF ready to go on, but hasn't been able to have the car tuned for it.

Yay, 1500 posts.

 

[Sho-Driver]

Does he have the proper OBD-II connector to make it work? Also, if he is running an LPM, there will be more things to address.

 

[AutoSHO]

The idle hunting is more likely due to the 255 lph fuel pump/stock FPR combo. Be careful tightening the belt up without resetting the computer - that is an easy way to find out the computer added a bunch of lean fuel trims at the expense of your motor.

 

[Mike Kopstain]

The first thing that should be done, and I realize it's easier for me to say this than it is for some people to just do it, is to ditch the LPM. I've said this for awhile, but anyone that's seen the SS LPM tunes knows that they are the farthest thing from what you would want a supercharged car to be running. SHO Shop might have been the best back in it's time but the "best" still fell quite short of acceptable. Anyone that wants to question this one needs not look any further than the timing advance being commanded on a supercharged LPM burn.

The car needs to be tuned and this is not something you can do with an LPM unless you have the ability to reflash it on the fly. The larger fuel pump will not aid in tuning either as the fuel trims at idle are going to influence the fuel trims at wide open throttle.

The heads on the SHO flow quite well for boost stacking to be an issue. Rather one would suspect that timing is being pulled (as Chris stated) and the car is not making any more power because of this. Torque, since it peaks low, will be impressively higher but horsepower, since it peaks high, will have a nominal increase at best. This is a direct result of the supercharger's volumetric efficiency (increases with rpm) and it's adiabatic efficiciency (Outlet temperatures). Adiabatic efficiency tends to drop off quite radically in the upper rpms which is why you'll see the most knock up in the high rpms. This also explains your radical gain in torque and your nominal gain in horsepower.

More or less, look to knock and fuel for your problems but it would be wise to get the vehicle tuned correctly on a safer pulley before increasing the boost.

 

[AutoSHO]

To add to what Mike said - up to 4800 rpms (where you are well into boost on a supercharged car) Vadim is ADDING timing advance. A general rule of thumb is to pull 1 degree of timing for every 2 psi of boost produced. Vadim is adding up to 6 degrees on his mildest S/C program. What this means, is that the computer ends up running only 2 degrees less than the stock curve, when it should be pulling at least 4-5 degrees or more. The computer can only pull 8 degrees of advance due to knock (programming - a tweecer update may soon change that number) and what you end up with is a car that is making decent power but trying to destroy itself with detonation.

Out of curiousity, have you run a compression test on this "low compression" motor? I'd like to see the results.

 

[SuperchargedSHOguy]

The reason the torque went up and not the HP is because you aren't making any top-end torque. Thats where you'll get peak HP numbers from, since horsepower is a function of torque and RPM. The reason the torque increased so drastically is that with the smaller pulley, you're seeing more boost sooner, and sincethe computer cannot pull enough timing out to stop detonation due to Vadim's programming, you see more torque before the belt starts slipping badly. I'm guessing the car was pig rich since the MAF was pegged the entire time and the computer has no way of knowing how much air is really going into the engine.

Bingo...MAF and LPM...maybe by summer...the car was extremely rich at high rpms and I know the MAF was pegged along time ago. The belt is extremely tight...one of the things I did that morning was make sure.