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Dyno Chart Opinions wanted

3K views 31 replies 12 participants last post by  in10ence 
#1 ·
I've been unhappy with my Dyno run done last month and so I've finally decided to post it here and ask for any opinions / suggestions on what could cause this. I believe the readings are low for a Scatpack/Maggie setup with 6 psi and also the chart looks weird in the low rpm.
 

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#2 ·
What was the AFR, Spark and Knock readings?
Why did he dyno in 5th gear on a DynoJet?
 
#6 ·
Great questions that would help us to give you a better answer.

Also, it looks like it was hot out too. If the blower was heat soaked, it would lower the numbers too. Was this the first run or the last run? Was the motor cooled between runs and if so, how long?

My suggestion is that you take your car to the track and check out what it traps. That gives a better reading than a dyno does. I think that Sometimes people forget that a dyno is a tool for tuning and the numbers can be skewed by quite a few variables. Here's a good read form Kenne Bell that could explain it better than I ever could:

http://kennebell.net/KBWebsite/Common/pdfs/DynoTestVariables.pdf
 
#5 ·
Why are you questioning the chart? What specifically is it you are seeking from us? Yes it's a dyno
chart and yes the HP numbers seem about right for 6PSI on a 392. Do you feel there is an issue?
 
#7 ·
If it was hot and humid outside and in the area they dyno'd the car you probably lost some power because of it. One thing I've learned on here and a few other Mopar forums is that pd superchargers get heatsoak really quick and because the manifold sits on top of the engine and they tend to lose a good amount of power on the dyno especially on back to back dyno runs. One known tuner told me at a dyno day last year that pd boosted cars can possibly lose 40 more hp when it's really hot n humid out. If everything is installed correctly and the tune is good I would get it dyno'd again in the fall when its cooler out too see what it makes
 
#8 ·
[disclosure: totally biased as we sell a lot of those superchargers. But I offer facts, too.]

Looks pretty standard to me -- especially with stock CAI and exhaust. The low RPMs on these sheets always look different depending on how the tuner got into the power. Looks like he was at part throttle until about 3500 RPM, then went WOT (or he shifted, is this a M6?). That's not usually the range you are looking at for power readings. Also, as others have said, 5th gear on a hot day is not how you get your highest numbers.

Let me offer some comparisons. Most of mine are at 8 psi boost and are Automatics. So that should be about 35-40 HP higher than your 6 psi setup. Also, the intake and exhaust may be different on these. But none of them suggest that you are way out of range.

This SRT8 has the same 392 (6.4L) engine you have --8 psi supercharged 392

This 392 stroker has 13 psi of boost from a Magnuson and is only 60HP higher than yours on this run -- 392 Stroker with Magnuson -- and also a hot day dyno.

This is a Jeep with a Whipple, but similar engine and similar range -- 8 psi supercharged Jeep

This 8 psi Magnuson supercharged 392 car is similar -- Supercharged Challenger SRT

Sorry I didn't have more 6 psi examples -- I'll try to get some posted.

Browse for more comparisons... ShopHemi.com Arrington customer builds
 
#9 · (Edited)
Thanks to everyone who replied with suggestions/questions. Everyone seems to focus on the HP and I'm not concerned with the HP. It is close enough to others that I've seen to be considered normal. My concern is the torque numbers are over 40 below the HP and not one of Tim's charts shows anything near that. Notice all the HP and torque numbers are fairly equal.
I talked to the guy who ran the dyno and his opinion was that it was a "torque management" issue with the tune.
By the way I took it to the strip last night to see how it feels and I'm an absolute beginner when it comes to racing or launching cars on a drag strip my opinion means nothing but since some asked for it .... My third and best run was 7.69 @ 92mph with a 1.819 60'. I did notice the car was hesitating on launch maybe I was not giving it enough rpm but I never felt any hesitation in any of my runs before the SC was added. My best run stock was last November in 55*F temp and it was 7.701 @90 mph with a 1.750 60' . That was the 1/8 time on a 1/4 mile track when I made my best ET of 11.979 @112mph.
So here is the bottom line. If Tim@Arrington says it's normal I'm not the person to argue with him. I respect his knowledge and honesty completely. I will forever hold my peace. Thanks again to all who wanted to help.:smile:
 
#11 ·
I think running 6lbs of boost you are running very safe for your 6.4 and your numbers looked about spot on on the expected HP/torque gains. Looks to me that you need to get out there and race a bit more to get use to the SC and what it is capable of.

Once you figure your car out your times should start dropping and may start appreciating the SC more.
 
#12 ·
I haven't raced anybody in a long time. Most guys with street cars think I have a Hellcat and avoid even looking in my direction. I still have my Continental 275/40/20 street tires on so launching is not as easy as you might think. It really depends on the track prep.
 
#18 ·
So this is an updated dyno?

Better tq there, but still - and I'm no expert in this area, but isn't +100/100 a little low for a blower at 6psi?
 
#14 ·
You want to run in the gear that gives you 1.00 (trans gear). M6 should be in 4th and A8 should be in 6th gear. Seems Pretty good overall to me. Id look into a different tune as the torque does seem to drop off a bit to soon. Still IMO you gotta run it in the right gear to get a good assessment.
 
#15 ·
I don't see it dropping off too soon, I see it too low at the start where I would launch the car. My torque at 3100 rpm is about 350 but the chart above your post is almost 500. MY HP is also low at 3100 but since HP is calculated from torque it's normal. You think that doesn't affect launch? Actually I launch my car at a much lower rpm but...
Yes doing a dyno run in 5th instead of 6th will add a little extra loss but that's not what's causing the torque to be so low at 3100 rpm.
 
#16 ·
The problem without there being video or us knowing what the dyno guy did is all we can do is guess. It could be a simple mistake, like he didn't go WOT until 3500rpm because he was rolling into. This would mean you car wasn't using TQ down low and he was just trying to get you a top end HP dyno run.

How's the car feel on the street? Is it a complete monster at low RPMs and you blow the tires off with ease or does it feel stock until higher RPMs? Who did the tuning for you? Did you ask for a more streetable car (less TQ at lower RPMs) because that would result in what you're seeing on the dyno as well.
 
#17 ·
The car feels tame but I made no special request for that. It will still spin the tires on the street and even at a poorly prepped track. Last nite the track was well prepped and it "hesitated" off the line on all 3 runs even when I raised the rpm to almost 3K ( I usually launch at around 2k). I've not experienced this before even when it was stock. I'd just as soon let this thread die because I can't give enough info for anyone to come up with a possible cause. Some suggest it's the heat and it will come alive in the cooler weather. I doubt it but I plan to wait for cooler weather before testing further.
 
#19 ·
No that chart belongs to Supercharged Scat copied from Tuning/data section post #450. I wish mine was like that. I would be happy. Notice at 3100 rpm he gets about 150 ft/lbs trq more than mine. His peak trq is about 54 ft/lbs more than mine. His HP is 531@5900 rpm and mine is about 515 HP. That's not enough for me to complain about but still it's low.
I also agree with you it's less than expected but I would rather have his than mine.
 
#21 ·
No need to let the thread die, we are here to help. Who did the tuning and could you email them to ask how they did the tune? I know there are some issues going around with tq management kicking in and killing tq but the good tuners found away around it.

Maybe you can send a copy of you tune to a different tuner and they can help you sort it out?
 
#23 ·
Ok Arrington did the tune. It's the second try because the first one had a "flutter" at partial throttle. This second tune smothed out the flutter but in my opinion it killed the low end torque. I'm not a auto mechanic so my opinion carries very little weight but I feel the "lag" at launch that bone stock it never had. I'm not sure if the 1st tune had any lag at launch but I did take it to the strip just before I received the 2nd tune and don't remember having any lag although my times were not great because the wheels were spinning on my best run. I'm considering installing the first tune back in to see what it feels like at launch. Problem is it was most noticeable at the track when it was hooking good. (can't just go to the track any time I want to check it out)
As you can tell Luke at Steve White and Tim@Arrington think I have no problem because it was 97 degrees when I ran the Dyno. The Dyno sheet was compensated 1.05 to account for the heat. Don't know if that was enough. I'm also considering doing another run at a different Dyno to see if it was a problem with the guy who did the Dyno run.
I know nothing about cars (retired Electronics Tech) but I see the chart with very low torque numbers at 3K-3.5K and I feel the hesitation on launch I never had before and I'm not happy.
So I'm at the point of waiting for cooler weather to see if I'm wrong. But even if it perks up in cooler weather I will never be happy every summer when it runs like it does now.
 
#24 ·
Where do you live? I would try to take it to one of the few tried and true modern Hemi specialists and get it dynoed properly and then re-tuned if needed. You want to make sure it's right as for one our cars with the stock pistons leave no room for error in the tune, and two I still think you should be making more than 525 rwhp as that's only 100 over stock. As you noted the dyno operator spotted you 5% due to the atmospheric conditions, and if you are close to sea level you don't lose that much hp just due to it being hot.
 
#25 ·
You also need to bear in mind that what you might think is "lag" is you just making stock HP because
the boost hasn't come on yet. These superchargers are running internal bypass systems and they are
not making boost at low to moderate RPM. With the stock restrictor pill in the Maggie it's not going
to make boost till well into the 3K+ RPM range.

It just seems to me like you are expecting full boost all the time. Of course if you put the pedal to the
floor from a dead stop it should make full boost relatively quickly but it's not 100% instant, at least not
with the stock restrictor pill in the bypass valve.
 
#29 ·
I'm not an expert by any means, so take it with a grain of salt. But it sounds like they pulled TQ down low with the second tune to make it more street friendly and get rid of the fluttering issue. Do you know if there are any dyno tuners in your area that have experience with boosted Hemi's? The $200 or so would be more than worth it for a custom tune. Can/email tunes only get you so far and leave a lot of power on the table because the tuners have to play it very safe, where as a good dyno tune can dial your car in just the way you want it.
 
#31 ·
I live near Pensacola, Fl. There are some Dynos in the area but no Hemi tuners. I'm thinking of taking it to another Dyno just to get a second opinion with charts. I data logged a few runs today 0-60 mph just to see what the chart looks like. Of course I'm not a tuner so I really can't make any judgements. I will say there is absolutely zero short/long knk retard.
I'm really trying to let this thread die. I'm interested in anyone trying to help but prefer a PM so this will go away.
 
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