Hi all,

I posted this on corvetteforum as well but you guys seem to know more about engine building/problems/specifics etc. I'm curious as to if I'll need to get my car re-tuned or not. I have a 2000 C5 M6 coupe that I had dyno tuned awhile back at 21st Century Muscle Cars in Addison (352rwhp/346rwtq on a dynojet). I was actually somewhat disappointed with the results because I see a lot of bolt on cars making 335-350 rwhp and my car has all the bolt ons (TPiS headers, Granatelli MAF, x-pipe, blackwing, ls6 intake, PP throttle body, Corsa Indy Pace Car exhaust, NGK TR-55's, SPEC stg II clutch) but also has a cam as well (comp cams 54-412-11) which is 212/218 .522/.529 114LSA. Granted... this is a baby cam (I would've went bigger and will be doing so soon, but I bought it this way) BUT I feel like it should still be good for more than only about 10 rwhp over stock.

Well, after the dyno tune I decided to change the spark plugs because I wasn't sure what kind of shape the current ones were in (I put the NGK TR55's on there, it had platinums on it before). While doing the job, I noticed that the air bridge was disconnected from the blackwing filter where the MAF is. I swapped my ls1 intake to a ls6 intake a week or two before the dyno tune and I guess I didn't tighten the rubber couplers from the MAF to the blackwing and MAF to the air bridge well enough. I must have hit a bump or something and caused the blackwing and MAF to disconnect from the air bridge... the blackwing was sitting at maybe a 30 degree angle from horizontal (viewed from the front) which is why I even noticed it, and then as I inspected it further I noticed the gap between the pieces.

This got me thinking and now I have a couple of questions...
What if this had become disconnected before the dyno tune and I had been driving the car with it like this since I did the intake swap? The tuner at the shop said the car was detonating when I brought it in and that it had way too much timing in the current tune. I guess I'm damn lucky I didn't suck up anything into the motor since the air wasn't exactly flowing through the filter while I was driving... If this indeed was the case and the MAF and filter were disconnected (plugged into the computer but uncoupled) during the dyno tune, could this account for my low dyno numbers? And, if so, should I go get the car re-tuned now that I have everything solidly tightened up? Or, if this were the case during the tune is it something that the shop would have been able to see while tuning the car (which would mean it probably wasn't uncoupled at the time of the tune)? The other thing I find odd is that my fuel injectors are running at around 88-90% duty cycle at WOT (they're the stock injectors for 2000's which I think are like 26lb). I would figure that these injectors should be good for up to 380-390 rwhp if the 28lb injectors are good for 400+ rwhp, but maybe I'm wrong... if this is the case though could it be related to the uncoupled MAF/air filter?

Looking for some input from the tech guys or anyone experienced with HP tuners (software that they use at the shop)... maybe I'm just expecting too much but I'd figure that 370-375 rwhp is a reasonable expectation for my setup at this point which is why I'm trying to think of explanations... not to mention the whole MAF/filter issue.

Thanks for the advice guys.

 

Lots of views but no responses. Any opinions?

 

Air was bypassing the MAF so the MAF was reporting low... so if it was tuned like that then your tune is not valid...

the tuner should have done a basic visual inspection before proceeding, are you sure the MAF was uncoupled before the tuning session...?

 

I'd say your ideas could definitely be valid. I guess the best way to know is get it back on the rollers.

Could you get it back on the dyno for a couple pulls or would you have to pay for an entire tune?

 

id get a retune but possibly look for a different shop.

 

I am pretty sure the MAF would have been uncoupled during the tune simply because the only time I messed with it was when I installed the LS6 manifold which was before I had the tune done... I didn't touch it after that until I noticed it was undone just recently. They were super busy that day and so I think they might have overlooked it if it were accidentally disconnected.

Would that show up in any of the tuner's tables and do you think that might be why my injectors are at 88% duty cycle at WOT with only 352 rwhp? Do those numbers seem low to you for a M6 with the mods I have done? It's a small cam but I really would've thought I'd be around 365-370 rwhp.

 

I'm definitely looking for a different shop but a retune there would only run around 50-100 bucks since they did my car originally vs a full $500 somewhere else.

 

Someone on corvetteforum said that because 21st Century's dyno is an above-ground dyno jet it will read lower than an in-ground dyno jet. I don't know why this would be the case but does anyone have any info on this? Sounds like crap to me but maybe there's some truth to it?

 

Stop asking tech questions on corvette forum. That place is good for the classifieds and for say "wow bro you have a corvette? I have one too they're awesome, best sports car EVER, everyone who doesnt agree sucks" etc

to answer you're question though no it wont read different but all dynos do read different anyway but no because one is above and th other is in ground