Dynoed pulley/intake/catback; Questions...

[kilrb]

I went by to pick my car up last night, and got to watch it get tuned. They dialed in the A/F, and the car hit 425/440, and then they set out to playing with the timing. The tech told me the numbers would go up when they started on the timing. Unfortunately, they didn't. The original baseline was 401/385, with a K&N air filter (not intake), and a Flowmaster catback. I added a JTL intake and 2.8 pulley, and this is what I got for my final numbers... 420/443 (see baseline and modified graphs below). The technician tells me it's my stock H-pipe that's holding it back (I was expecting 450ish). Does this sound about right to you guys? Any advice as to what to expect if I were to add an aftermarket H/X pipe with cats? I absolutely, positively want cats, and I really want to keep the sound at a modest level. Any advice on which system to buy? I have heard that X's tend to rasp out the sound, which doesn't sound all that great to me...

What also confuses me is how stout the baseline was, considering the car didn't have an aftermarket H. Maybe my car was one of those cars that was pretty stout stock, and the K&N and catback beefed it up another 20whp?

Don't get me wrong, I'm not dissapointed at all; the seat of the pants feel of the 57 foot pounds of torque, and the scream of the pullied SC through the JLT is incredible.

Edit: I didn't mention originally that the sniffer in the tailpipe turned out to be bad, and the tech did multiple pull/tweak sessions that weren't resulting in a change in A/F. In fact, the A/F went really bizarre on us, and after several partial pulls, he switched out the sniffer, and it turned out it was bad. I got to thinking, how many pulls does it take to get heat soak that would rob power? He did at least three full pulls, and then at least three half-pulls (he stopped when he saw the screwy A/F at about 4,500rpm). Then, when the sniffer was replaced, there were at least three more full pulls. Would these pulls done over an hour's time be enough to get the SC hot enough to drag my numbers down?

(sorry these aren't on the same graph)
Pullied

Baseline

 

[Wayne64SS]

you're A/F ratio looks ****ed to me... esp right after 5500 looks super rich. who is tuning your car?? I'm unpullied and put down 443/413 with just intake, and full exhaust no cats & a shitty box tune. You should be around 460 IMO, and clearly you're not running out of fuel. Bring it somewhere else.

 

[kilrb]

you're A/F ratio looks ****ed to me... esp right after 5500 looks super rich. who is tuning your car?? I'm unpullied and put down 443/413 with just intake, and full exhaust no cats & a shitty box tune. You should be around 460 IMO, and clearly you're not running out of fuel. Bring it somewhere else.

Are you possibly looking at my baseline, un-tuned dyno pull at the bottom? Yeah, it was super-rich, but the one from last night was right around 11.5 in the upper rpm's. Check out the dyno on top (maybe I should have put the baseline at the top).

 

[Bdubbs]

On may 15th mine will be hitting up a dyno. Mods so far are, JLT RAI, bassani catted x pipe, and bassani catback. The tuners will be adding a 2.8 pulley as well. I will post up my results, they told me I should be in the 450-470rwhp, we will see.

 

[Furinox]

you're A/F ratio looks ****ed to me... esp right after 5500 looks super rich. who is tuning your car?? I'm unpullied and put down 443/413 with just intake, and full exhaust no cats & a shitty box tune. You should be around 460 IMO, and clearly you're not running out of fuel. Bring it somewhere else.

Pay attention dummy. The first graph is after it's tuned and the AF looks perfect.

I could see you gaining almost 20 once you switch to a O/R mid. Catted mid just slightly less. Definitely worth getting.

 

[Furinox]

On may 15th mine will be hitting up a dyno. Mods so far are, JLT RAI, bassani catted x pipe, and bassani catback. The tuners will be adding a 2.8 pulley as well. I will post up my results, they told me I should be in the 450-470rwhp, we will see.

Maybe 450, but not 470 unless you have a ported blower or their dyno reads extremely high.

 

[Wayne64SS]

Pay attention dummy. The first graph is after it's tuned and the AF looks perfect.

I could see you gaining almost 20 once you switch to a O/R mid. Catted mid just slightly less. Definitely worth getting.

ohhhhhhhhhhhhhhh yea that looks alot better... the scrolling on my laptop is kinda ****ed up, so i scrolled past the first a/f chart by mistake. :beer:

 

[96stanggt]

AFR looks good, but without knowing your timing its hard to tell if the low power could be in the tune. Those numbers are low though, especially considering STD correction. Looks like its breaking up in the upper rpms, were you having any belt slip? What plugs are you running and what are they gapped at?

 

[kilrb]

AFR looks good, but without knowing your timing its hard to tell if the low power could be in the tune. Those numbers are low though, especially considering STD correction. Looks like its breaking up in the upper rpms, were you having any belt slip? What plugs are you running and what are they gapped at?

I had the shop put in new plugs, but I don't know what plugs, or what the gap is. I could find out. The shop in question has done tons of Terminators (as well as lots of other cars), so I'm pretty sure they went with the right setup as far as plugs are concerned... How do you confirm whether or not the belt was slipping? On one run, I watched the stock boost gauge, and it went way above 10, and seemed to hold where it was through redline.

 

[96stanggt]

One thing is for sure, you car flat lines on power and breaks up above 5500. That is usually spark blowout or belt slip. Pull a plug and see what it is and what it's gapped at, don't trust them to tell you. What is your pulley combo and belt size?

 

[kilrb]

One thing is for sure, you car flat lines on power and breaks up above 5500. That is usually spark blowout or belt slip. Pull a plug and see what it is and what it's gapped at, don't trust them to tell you. What is your pulley combo and belt size?

I'll yank a plug and gap it. The pulley is a 2.8", and I'm uncertain as to what belt they put on. I can check with them on that as well. Do you think heat soak could be an issue after three full pulls, followed by four half-pulls, followed by three full pulls, all within an hour or so?

 

[96stanggt]

Do you have an aux idler? The belt should have a part number on it, post it up and we can tell you what size it is. Doubtfull heatsoak was the issue, provided your IC pump works as it should and the shop had a fan blowing.

 

[kilrb]

Do you have an aux idler? The belt should have a part number on it, post it up and we can tell you what size it is. Doubtfull heatsoak was the issue, provided your IC pump works as it should and the shop had a fan blowing.

Ok, so I talked to the sales guy at my tuner this morning, who wasn't there last night. He agrees that the pull seems off, and he's going to get with his people there to discuss. My thinking is, it was very late, and the tuner's wife was calling, and maybe he was trying to get it done, and didn't think of something he could have missed. So my main point of contact confirmed that the pulley is a 2.8, and the belt is a 74 1/2" Gates. They didn't install an idler, as he claims although he'd love to make more money, they don't see any reduction of slip without them. He also said he saw the guy who installed the plugs gapped them at a number he thought was too tight, but he didn't think it would make that much of an impact. He said they were gapped at 38, and that he prefers 40-42. Last, but not least, he thinks maybe the tech didn't do something right with a knock sensor that could be causing a problem. They are going to get back with me this afternoon. I'll post up with their recommendation.

 

[96stanggt]

Ok, so I talked to the "sales" guy at my tuner this morning, who wasn't there last night. He agrees that the pull seems off, and he's going to get with his people there to discuss. My thinking is, it was very late, and the tuner's wife was calling, and maybe he was trying to get it done, and didn't think of something he could have missed. So my main point of contact confirmed that the pulley is a 2.8, and the belt is a 74 1/2" Gates. They didn't install an idler, as he claims although he'd love to make more money, they don't see any reduction of slip without them. He also said he saw the guy who installed the plugs gapped them at a number he thought was too tight, but he didn't think it would make that much of an impact. He said they were gapped at 38, and that he prefers 40-42. Last, but not least, he thinks maybe the tech didn't do something right with a knock sensor that could be causing a problem. They are going to get back with me this afternoon. I'll post up with their recommendation.

Well there's the answers, you have both spark blowout and belt slip. That belt is about 1.5" too long, and your gap is too big. A 74.5" belt is what you would use with the addition of a 100mm aux idler pulley below the blower pulley, and yes they do help with belt slip. If you're not using that additional pulley you'll want to run a 73" belt. Plugs gap recommendation for a pullied car is .035, though most like it a little tighter at around .032 to prevent blowout in the upper rpms. I run mine around .029 because I'm spinning my blower considerably harder and spraying nitrous.

Our cars don't have knock sensors either. Who in the hell is tuning your car and installing these mods? Ask them to email you datalogs from your dyno pulls.

 

[DICobra]

You should be around 440-460ish with your mods.... With almost the same mods except with mine has a Bassani catted xpipe mad 459/469. Check and make sure your IC pump is working, mine died during when had it Dyno tuned. Got a new one installed now.

 

[AmazonTuning]

you should have a 740 belt with a 280 pulley..

plug gap should be at .035

AF should be in the mid 11s

 

[03cobra#694]

Well there's the answers, you have both spark blowout and belt slip. That belt is about 1.5" too long, and your gap is too big. A 74.5" belt is what you would use with the addition of a 100mm aux idler pulley below the blower pulley, and yes they do help with belt slip. If you're not using that additional pulley you'll want to run a 73" belt. Plugs gap recommendation for a pullied car is .035, though most like it a little tighter at around .032 to prevent blowout in the upper rpms. I run mine around .029 because I'm spinning my blower considerably harder and spraying nitrous.

Our cars don't have knock sensors either. Who in the hell is tuning your car and installing these mods? Ask them to email you datalogs from your dyno pulls.

This

 

[kilrb]

So I went and looked under the hood, and looked closely at the belt tensioner. It appears to be almost, but not quite, pegged against the tight end, which to me suggests the belt is indeed too long. Am I correct in this assumption, or does this not really prove anything? Thanks.

 

[96stanggt]

Yep, there is almost zero tension on that belt. Who is this shop?

 

[kilrb]

Yep, there is almost zero tension on that belt. Who is this shop?

And if it's like that six hours after it was last driven, doesn't that mean as it heats up, it'll get even worse? If the belt is indeed slipping, and I throw on a new belt, they'll definitely have to re-tune, right? As far as the shop's name, it's in the dyno sheet... They're looking into it. It could be that the guy pulled a brain-fart, and grabbed the belt size they use for idlered setups, or off another setup... I want to give them the benefit of the doubt here... If they still say it's the right size, then I'll show them the tensioner and talk some more. I know they have done 40+ 03/04 Cobras with pulleys; I'm sure they will figure out what went wrong...