So had the car dynoed. 93 with vortech charger. Based on stock HP rating and supercharger was expecting maybe upper 300's at wheels. Only got 319hp but got 501tq. Just doesn't sound right. Anybody ever see such low HP coupled with such high TQ?

 

At what rpms did you get those numbers? That reads as if the dyno operator stopped the run at the torque peak and never got the peak power speed.

 

319hp @3750
501TQ@3180

 

Uhhh, yeah. Your power should peak at roughly 5000-5500rpm, depending on what other mods were done. Just based on that torque figure, you should probably have seen a power figure well into the 400s. Here is just one link to some near-stock dyno charts so you can get an idea.

 

Maybe belt slippage above 3200rpm?

 

You mean the belt for the supercharger? Did the dyno operator run it to higher rpms than 3750rpm? Did he go to redline and the power was just way lower? If so, then perhaps. There are a lot of possibilities. Possibly the spark is failing at higher rpms, if the increased cylinder pressure is making it to hard for the spark to arc to the electrode in each plug (the gaps should be decreased with boost, or maybe the coil is crapping out). Or maybe the ECM picked up a bunch of knock and pulled a ton of timing. Or maybe the fuel pump or injectors are not sized appropriately and can't deliver enough fuel (check fuel pressure and duty cycle for the injectors)? Does the graph show a smooth curve or does it have noise that looks like ignition problems?

One thing is for sure: with 501lf/ft at 3180rpm, you should be making a lot more than 319hp.

 

If Natrlone93 knows how to post the dyno graph, that would help.

With an LTx intake, there's no way peak rpms could be THAT low. Hopefully, you can get power above 3200 rpms worked out because that's some impressive rwtq THAT low.

Maybe it went lean, timing got pulled (big time) and you just didn't have the right mixture above that rpm.

Who tuned the car? Is it tuned? Did you change/pull the cam? Did you alter electronic timing in any way? Did the differential fly out the back? Did you break the rollers on the dyno? LOL

etc.
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Is the car an auto or manual? It sounds like you had a torque converter flash that gave you a higher then expected torque output. It also appears that there was some issue with the low RPM peak engine HP. (Without being there and seeing the graph I cannot really comment on what was the issue)

 

Ok obviously I'm not crazy thinking these numbers are out of line. The dyno guy wasn't a tuner. I'm talking to a boost guy at work this morning and he's suggesting some of the same things you guys are. I'll try to answer some of the questions. First I don't know much about the setup as I bought it recently from a classic car dealer who had 0 info on it. It is a 93 6 speed with a vortech V2, T-Rex fuel system and vortech box with timing retard control with settings of 0-3. Best pull was made set at 1. Doesn't have a boost gauge so don't know boost. Don't know tune. Stock exhaust and from what I can tell stock heads and intake manifold. Doesn't sound like it has a cam by listening to idle but I just don't know anything other than what I can see. As far as the graph I will post a pic later. Torque came on strong really early and was at around 430 @ 2500rpm and peaked at 501 @ 3180 at which time HP was at about 290 and started rising a lot slower peaking at 319@ 3750rpm. He did continue to pull to 4500rpm but HP was falling off. Guy said he would do 4-6 pulls just to see where I'm at on HP for 75 dollars so I did that. Just thought the numbers were out of line and it seems you guys agree so I have some work to do.

 

Graph

 

I wish these graphs were printed in a more normal format. They are hard to read with five pulls layered over one another and in black and white. The graphs in the foreground make it look as if he stopped the pull at ~3700rpm. OTOH, I see a couple pulls in very faint shading where the torque curve extends past 4000rpm and still had over 400lb/ft there. But I can't see the power curves for those pulls, so that's not helpful. As a reference, though, 400lb/ft at 4000rpm should be showing 305hp at that same rpm.

The question right now is whether the dyno results are accurate or not: i.e. do they reflect what the engine is actually doing? With a Vortech, I would not expect the power to build so fast so early, and I definitely would not expect cylinder pressure (torque) to peak so early and drop off 100lb/ft by 4000rpm. Does the car actually feel like that when you drive it? That is, does it actually stop pulling hard before 4000rpm? I wish I still lived in Houston, as I would like to ride in it and use my own butt dyno.

Is it possible that the heads and stock cam are so restrictive that they won't let it fill the cylinders above 3200rpm? That seems doubtful, as the stock LT1 has a very flat torque curve way past that speed. This is still the stock LT1 intake, right? I mean, nobody did something silly like putting a TPI intake on this engine, did they? Because this curve is more reminiscent of an L98. Maybe someone with experience putting a centrifugal blower on a stock LT1 long block can chime in. Also, assuming this is a chassis dyno, I wonder if there was tire slippage on the rollers?

 

I'm not very trusting of the dyno at this point. Didn't seem to be any tire slippage. The car pulls strong and steady on the road right up to about 5k rpm. And yeah his printout sucks lol.

 

Well, I think that's all you need to know. In any one gear, the "pull" you feel is directly proportional to the torque being output by the engine. If it pulls equally hard to 5k rpm, then you should be seeing a flat torque curve (or nearly flat) up to that rpm. BTW, that's what a bone-stock LT1 would do, too. And I would expect the torque curve to be baised even more toward higher rpm with a centrifugal supercharger, which generally builds increasing boost as its rotational speed rises (unlike a positive-displacement blower, which produces nearly constant boost at all rpms).

 

Pretty much what the guy at work who runs boosted mustang told me about supercharger as well. I guess I'll get a boost gauge put on it and fuel pressure gauge and go from there. Just passed emissions for the last time necessary so long tubes, x-pipe and cat delete is probably what my next mod will be. Thanks for the info.

 

It's probably worth putting it on a dyno and getting real measurements, as well as logging it with a wideband O2 sensor installed to make sure it isn't leaning out too much, not detonating, etc. It kind of sounds like someone did the s/c install right, with upgraded fuel system and (hopefully) injectors and tune, but it would be good to verify that for sure to prevent damage. You probably don't want it running more than 12:1 for the air:fuel at WOT, maybe even a little less if it doesn't have an intercooler.

 

Yeah I just got to go up the road a little to find another dyno. Want to know what my boost and fuel pressure is first and maybe get the long tubes on first so I can get dyno and tune done. This dyno only cost me 75 bucks but the tune is quite a bit more as you know.

 

For your $75, I'd be wanting to know why the operator let off the gas at such a low rpm? As MM pointed out, the curve looks more like an L98....except that an L98 doesn't even drop off THAT fast!!!!

I gotta wonder if someone not normally running the car on the rollers looked over and let off because TQ was dropping off? HP doesn't dive like that (either) unless you let off of it.

I assume you were there. I'd have asked WTH...right after seeing pull #1!!! To be honest, I'd still want them to provide an answer....maybe offer another set of pulls? With someone who knows what they are doing?

If they didn't let off at 4k rpms, you have something major going on. You know...a restriction of air, fuel, or spark. Hard to imagine an intake or exhaust restriction...considering your 500 TQ reading.



Oh yeah...One reason I was looking for your dyno was to see the AFR readings. I guess this place didn't put a sniffer in the exhaust? IDK about LTx cars, but some can plug into a spare 02 bung...which is how my pulls (and AFR) were read back during my tuning. I think most dynos display AFR along the bottom....as a function of rpm.

 

I was watching his computer on the pulls and it looked like he was letting off at 4500rpm each time. His printouts are ****. Hard to see what's going on. Not sure its worth going back as he didn't seem to think there was an issue with the numbers. Believe me I asked questions. He went on about his dyno being accurate because it's set right and others set theirs different to give you better numbers blah blah. He wasn't a tuner either. Rather let a turner look at it. I know the car pulls hard and steady right to 5k on the road without any noticeable drop off.

 

Consider the following BEFORE making another Dyno or street run:

Disconnect the AIR INTAKE from the blower. I don't recall the terminology but you may have an intake problem. If this is indeed the problem, Blower Works can help.

Check the Fuel Pressure. The stock pump wont feed the engine.

If your running stock injectors GO BIGGER!

Been There-Done That.

Give me the courtesy of a return E mail with the results.

RVY

 

I plan to put a boost gauge and fuel pressure gauge on. The fuel system is upgraded. T-Rex pump. Have a set of long tubes with x-pipe on the way to be installed before I do anymore dyno and possibly can install. From what I can tell by looking up the numbers on the injectors they are 24#. Not sure what you mean by unhooking the air intake from the blower? The piping? What am I checking for?