How does my 383 suck so much?
 

Hey guys,
Pretty disappointing torque/hp numbers. This printout was from the tune a couple years ago, since then I've taken it to a dyno once and it managed to do slightly better by about 5-7 hp. Since then I've tried replacing a few minor sensors (iac, coolant temp, etc) as it also has a tendency to stall when idling.
HP- 280
Torque- 317

Holley stealth ram
AFR 195 heads
32# trickflow injectors
Comp 268 XFI cam
700r4/Vigilante 2800 stall converter
Hooker 2055 headers
Magnaflow cat/catback

Re: How does my 383 suck so much?
 

Re: How does my 383 suck so much?
 

Right, I do need to take it down and see what she'll do I suppose.
I figured the 2055's weren't the best, but sub 300 hp? Kinda surprised me.

I've been a little suspicious of the torque converter not locking up, but would that have a substantial impact on the numbers?

Re: How does my 383 suck so much?
 

Re: How does my 383 suck so much?
 

Well, thanks for the insight. I guess I'll wait and see how it does at the track.

Re: How does my 383 suck so much?
 

Re: How does my 383 suck so much?
 

That's more of a cam for a stock 350 than a 383 with AFR heads.

Re: How does my 383 suck so much?
 

Re: How does my 383 suck so much?
 

Your tune sounds way off.

- Rob

Re: How does my 383 suck so much?
 

Re: How does my 383 suck so much?
 

Cam is a bit small for a 383 you have big heads and a stealth ram you need a cam to match. Other than that the stalling and rough running makes me think something is wrong.

Re: How does my 383 suck so much?
 

As a simple point of reference, I have a 383 in my GTA. I estimate it weighs at minimum 3650 with me in it. It has a super tame 383 with 10.5:1 compression, Profiler 180cc heads that I ported, XFI268 cam and a ported Super Ram intake setup. Dyno Don shorties, 3.5" single exhaust, 3.27 gears, T56 trans. It ran 13.7 @ 108mph in Tennessee on a 100 degree day just after a thunderstorm so I'm sure the DA was horrible LOL. At any rate, a 108 trap speed on a 3600lb car should be around 350hp at the wheels. I can't stress how tame this combo is. It runs and drives like stock (with my custom tuning) gets 28mpg on the highway, runs AC like a champ, everything.

So I'd say you've got a problem with your tune if you're only putting 280hp to the wheels. Your combo should breathe way better and make way more power than mine.

Re: How does my 383 suck so much?
 

Hmm.. Thanks for the reference 1Mean.. I knew my set up wasn't super aggressive or anything, but I just couldn't believe it wouldn't even manage 300 hp. I'm gonna get the torque converter checked out next week as I'm almost certain it isn't locking up. And I'll look around for a decent tune shop to get it looked at.

I wanted to go with the 280 xfi cam, but was advised it would be more difficult to get a good tune on it.. I knew i should have gone with the bigger cam!

Re: How does my 383 suck so much?
 

I agree it is a very mild cam for the setup, but you should at least make 350-370. Do you have a wide band for it? How was your timing? I think your tune needs some work, cutting out and dying is a sure sign. The AFR listed on the chart doesn't look bad (a little under 12.4) but who knows how accurate that is.

Re: How does my 383 suck so much?
 

That dyno run on a time based axis isn't the most useful format. Ask them to dig up your old files and send you curves of torque & HP vs. RPM. That's the not answer to your problems but it will help with analysis. Also, I think they aborted the run too early.

Obviously you have a tuneup or hardware problem by the way you describe how the engine runs. Question is whether or not that issue is effecting WOT performance too. Sooner or later you're going to have to look at the tune file and do some data logging if you really want to know what's going on.

Honestly though, a dyno is a tuning tool and a person should be bit careful comparing numbers from one to another. They could have had goofy dyno settings that caused your numbers to read low. That's why Orr89 suggested you put it on the track and see what happens. And if you're any kind of hot rodder then you have already figured out what kind of prey you can eat on the street by comparison.

Re: How does my 383 suck so much?
 

The torque converter isn't supposed to lock up at WOT. I promise. A trick we did back in the day that I got from the GN guys was to jump 2 terminals on the ALDL (cant remember which ones) and the ECM would force lock the converter in every gear but 1st. The converter isn't designed to withstand WOT upshifts while locked, but it was good for a 1/10 in the quarter back then. For your purpose, you could lock it up for a dyno pull and see what happens, but I think you're chasing the wrong issue.

I would NOT change to a different cam until the current combo is performing as it should. You may only be compounding the problem by doing that. If you have an issue with your tune, a larger cam will only compound the complication of getting a good tune I assure you. Get the car ironed out in it's current form, then negotiate from a position of strength with a larger cam in the future if you choose. Your car should be making 330hp at the wheels or more I'd think, and I wouldn't tear the motor apart until you had it running in optimum condition. How are you handling custom tuning? Are you using the stock wiring and ECM?

I agree with you, however AFR is only half the story. No idea what ignition timing is doing, is there any knock retard going on etc.

Re: How does my 383 suck so much?
 

Exactly. The problem investigation really hasn't even begun until the tune is examined.

Re: How does my 383 suck so much?
 

Re: How does my 383 suck so much?
 

Most factory TPI tunes I have looked at have TCC unlock prevent set around 65-75 mph. GM locked the 4L60E trucks around 75 mph as well. The factory converter can take more abuse than most give it credit for since the rpm delta between locked and unlocked is not very high on the OEM converter.

Re: How does my 383 suck so much?
 

However that being said I believe the tune is off or their is a mechanical issue somewhere.

I recently put a 1987 Firebird on the dyno that has a 10:1 355 with Dart iron eagle 180cc heads, GM LT4 Hotcam, 1.6:1 rockers, LTR TPI with a ported base, stock runners, ported plenum and shorty headers into a dual 2.5" exhaust backed to a TH400 with a 2,800 stall. The car made 280 RWHP and 340 RWTQ on a safe, conservatively rich, street tune that had never seen a wideband prior to the dyno, air/fuel ratio was 12:1 across the board with 30* of total timing.. The car went 8.20s @ 85 mph in the 1/8th in 2800 DA at somewhere around 3,500 lbs despite street tires and a 2.73 rear gear.

Re: How does my 383 suck so much?
 

Well, I checked my TPS in regard to the engines poor idling and noticed it set well below .45 vdc, basically reading 0. So I bumped it up, but then the engine idled terribly. Seems like it only wants to idle well more around .3 which of course triggers an error code for low TPS voltage. I can't seem to really get it dialed in perfectly by just touching the TPS around and checking the idle. Would this be further indication of needing a good tune?

By the way, I appreciate all the help/insight so far.

Re: How does my 383 suck so much?
 

TPS idle voltage won't cause a runs-like-crap problem. Idle-like-crap, YES; down on WOT power, NO.

Not saying "it's right"; not saying "don't fix it"; not saying ANY of that. Only, it isn't the problem of the symptom you complain of.

Typical most common thing that results in that is, slipped inertia ring on the balancer, making you set the timing religiously and rigorously to whatever you and your tuner agreed to; but in fact, it's like 30° retarded or something, because the spooge blob that loosely associates the mark with the motor, isn't associating quite so nearly almost somewhat occasionally closely anymore.

Seriously.

Just try advancing the timing. Not saying, your tuner is wrong, or the designed-in curve is wrong, or your engine is different from all the other hundreds of millions of SBCs out there and needs something so radically different that it's crippled; only, that if you "think" your timing is [whatever], but it's REALLY [whatever else] instead, you're NEVER EVER EVER gonna get it to run right. The engine couldn't give 2 s***s for what YOU THINK; all it cares about is, WHAT IS. If what "you think" isn't "what is", the engine won't agree with you, no matter what.

Try advancing it. See what happens. Put it back if you don't like it. BUTT: if it runs better, advance it some more. If it KEEPS running better, KEEP advancing it, until it stops running better.

Remember:

In words from one of the Greatest Of All Time, in a whole other unrelated field,

"If it RUNS good, it IS good."

Don't outsmart yourself over some "number" and "mark" and all that crap. If it RUNS good, it IS good. Likewise, if it RUNS like crap, it IS crap. And I'm not seeing crap in your parts list, although there's plenty of opportunity for that in machine work and the rest; but the very first thing I'd zero in on, is the tune. And again, not the the tune is "wrong"; rather, that there's something (blob of spooge) preventing you from installing it right.

Re: How does my 383 suck so much?
 

So, I got it idling better by running back through the whole IAC and TPS setup procedures. It's at least not dying and real surgey idling in gear. Had it idling pretty well around 700-800 rpm for about 10 minutes before I called it good. Need to go drive it around a little and see how she gallops.

Re: How does my 383 suck so much?
 

It should get up and go pretty good. Even as mild as your build is you are still close to 1 HP/CID at the crank and doing it with a mild cam that should have a great torque curve in that 383. I looked at your dyno graph and if the dyno wideband is accurate the tune could stand to be leaner, especially at high rpm. If you put your car on any Dynojet it will read about 10% higher than it did on a correctly calibrated Mustang Dyno. Something to think about in my experience 296 RWHP on a Mustang dyno pushed my 5,300 lbs Nissan Titan crew cab to a 13.9x @ 99 mph in the 1/4. I kept beating a truck at the track that had been on a dyno and kept bragging about having 360 RWHP on a different dyno, different day, etc. Take it down the track and see how it traps.