I recently got my car dyno tuned, with the mods in the sig. After many hours of hard work and sweat, frankly I am disappointed. I will try to post up the dyno graphs when I get home. She only dynoed 389rwhp (forgot the torque). I know that my high flow cats robbing me of some power, but probably 2-3 rwhp at the most. I know that my 12 bolt takes some power away, but I am still pretty disappointed. At first I was running a AC Delco FR3LS plug, and we gave the car some more timing 3 degrees more(36total) and made about 3 horsepower more. I then swapped the plug out and put in an NGK FR4,(slightly hotter) and pulled the 3 degrees of timing out, and made the same power that the 3 degrees made. I now have a Bosch platinum plus 4. Some people are saying perhaps, the intake manifold is robbing me of power? (Although I dont believe so) Others are saying perhaps my 52mm tb is too small..Anyway, I am going to get it back to a different dyno, and measure the vacuum at WOT, and see if I need a bigger TB or not. Does anyone have any suggestions? Thanks guys.. (BTW, the AF was at about 12.8-13.0 all the way through..) But we only took her up to about 5900rpm..I think it needs to go higher..It kept making power too..

Also, would anyone know how to tell if the rockers are too tight? I know there not loose, because I have no noise. Thanks for all your help guys..

 

To begin with: I'm certainly not the one to answer your question, but I will say this about that. On the surface it would seem that you should be making a bit more power and since you only took it to 5900 maybe the power was yet to come.

On the other hand, putting large headers on with large cams and big flowing heads, doesn't necessarily equate with getting maximum power across the board. If that were the case, everyone would just go bigger on everthing.

The advantage of dyno tuning would be to try different combinations and see which produces the best results. Sans that approach, I guess the best way would be to see what others have experienced and what engineers would calculate based on different formulas.

I would ask you what you based your combination on and what results you had expected.

 

how are the numbers from other cars on the dyno? i know the dyno i go to, my car only dynoed 275 before the tune with full bolt ons, and i thought it was low but they said it tends to dyno a 10 or so less then others in the area

 

well, I purchased this motor from a friend of mine, that at the time had a lt4 hotcam, and slp midlength headers on it. I put it in my car, and thought I would change the cam, being that the hotcam was kinda small for a stroker. TPiS had done the heads, as they are their own heads. (AFR castings, there port work) Who else would know these heads better than themselves, so I called TPiS and asked for a cam suggestion. They reccomended me their ZZX cam, 240 240 .595/ .595 112. I also put in a set of 1 3/4 stepped to 1 7/8 long tubes. They told me they do this setup all the time, and that they predict it would make about 515 fwhp, which at a 15% drivetrain loss, would put me at about 440rwhp. I still thought this was a bit high, and realistically thought, the car would put out about 420rwhp, unfortunately this was not the case. Are you aiming at possibly the header being to big?

the dyno was a dyno dynamics. I had got dynoed there before, with the hotcam. i did notice that the previous (conversion multiplier) on the dyno was 1.160, and now it is at 1.150. Although its is not much of a change, it would of only brought me up to 392rwhp..Im still down big time..

 

I'd be willing to bet you have some vacuum at wot, which could either be a restriction from the 52mm TB or the exhaust side choked down a little bit. I agree, the cats are not holding you back 30-40 rwhp, but more like 5-7. If the heads are efficient, the 52mm will be a bottleneck with all other things working properly.

More importantly, what's the car run like? Dyno's are not raced, and every one of them different. Your car is strong, but I don't think you're ever going to see 440rwhp with cats, through a 12-bolt and that cam. Any particular reason you didn't spin the car to ~6500 rpm?

 

Injectors?

 

Tell me you're not tuning this thing on stock injectors.

 

I'd probably ditch the single pattern cam...

 

No, the car does not have stock injectors, its got SVO 30's...The car seems to run really good, awesome power. The day the car got tuned, we were really getting a lot of things done at once, and unfortunately, I had to drive about 2 hours home, and it was already about 12 a.m, so we kinda rushed the tune. Plus he said that we had done major changes and to take it like that and see how it was, and bring it back for a final tune. Another thing I was told is that, being that its in a 383, it brings the power level down a bit in the rpm range. So normally in a 350, we would rev it to 6500, now that its in a 383, it would peak at about 6000rpm. yea, i figured it would make probably about 420 through a 12bolt, and cats, at least break the 400 mark! But this was not the case. I need to measure the wot vacuum. Is there anyway to do this through a scan tool, and looking at the MAP? What should the values be? Thanks...

 

Spin it until it stops making power or you get scared!

If your motor is built right, you won't have any problems spinning to 7,000. Big cams like spinning high. I've also never seen someone hit 400rwhp at less than 6k rpm. Look at other dyno graphs, many people don't make that power until 6300 to 6500. I'm not saying that's what the problem is, but start there. A bigger TB might be in order too.

What is your duty cycle on the injectors? 30's get pretty close to maxed out at 400rwhp. If they are maxed or close to it that might tell you if you are making the power. You can make the 30s work if you bump up the fuel pressure.

Just some ideas.

 

very good point...I guess I should take it up higher, and see what happens...I dont know what the duty cycle is on the injectors, how can I calculate that? Currently my fuel pressure is at 43psi..Does that sound ok?

 

43.5 is stock...so thats fine. Most scaning programs list the duty cycle. When you have it tuned or if you have a scanning program check what you are getting at 5500+ RPM. 80% duty cycle is said to be good, but you should be fine at high 80s as long it is only for a short time period. If your injectors can't handle it and are at a high duty cycle, it might be time to upgrade or raise the pressure. (Do a search on that as there are different ideas about adjustable fuel pressure regulators).

What are you doing for a fuel pump? You weren't lean according to your post, but high RPMs can cause it if your pump isn't up to par. Just curious.

 

Do you have a pic of the graph? Had the power leveled off or started to dive? THAT should be the indicator of how high to take it.

30's are only good for 400? That sounds low, though it definitely could be the case. My stockers are at 99 - 100% with 360 rwhp. I'd figure with the larger displacement and better head flow, the BSFC would be a little better and allow about 420 - 430 on 30lbers.

Also, I know I sound like a broken record, but what is the vaccum at idle? Did you degree the cam when you installed it? You are down about 50+ RWHP, which could definitely be the cam off a tooth. A 240 cam should be mild with a 383, and you might not even know the cam is off because the car does have 390 hp. If you didn't degree it, that's where I'd start. Its usually the easy stuff thats missed.

 

The RPM limit is due to both minimum CSA and ci. It's pretty easy to calculate peak hp rpm if you have the port dimensions, search advanced tech, as Bret posted something about that awhile back. It was within 25rpm on my motor, which is amazing if you ask me. There is a guy in my local club who has the ZZ-X cam in his 383ci third gen, and it peaks somewhere between 6500-7000. He is running cnc'd Brodix Track 1's though, and those are a sweet head for that motor, that combo really works well together.

 

I am using Freescan, and i dont believe that shows injecter duty cycle. I am using a stock fuel pump, but its fine, because the car is not leaning out.

As for degreeing the cam, I was not told to do so, they said the degreeing is already in the cam's construction. Last time I checked I was getting about 11" of vacuum at idle. I really dont know what to look for anymore, im out of thoughts, beside th TB, and the power lost from the cats and rearend. I appreciate all the helpful info. Keep it coming..