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Old 05-18-2013, 04:47 PM   #1
 
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Default Lost tq with cam and ported heads?

So I finally had my car dyno'd at the dyno day and I'm sort of at a loss/ confused. When i first got the car I had it dyno tuned after basic bolt ons
Slp intake headers catback etc. dyno jet

Made 343hp 363tq.
Now after a custom cam and ported 241s the car put down 389hp 346tq.
Is it normal to lose tq? This was 3 identical back to back pulls on a dyno jet as well.
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Old 05-18-2013, 05:01 PM   #2
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Different dynos put out different numbers? And I'm thinking depending on what kinda cam and heads you got they may lean more towards the HP not the TQ but not positive. Some are setup for more TQy things like tractor pulls or whatever and then some more for HP like certain racing?
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Old 05-18-2013, 05:19 PM   #3
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Quote:
Originally Posted by Shibby50 View Post
So I finally had my car dyno'd at the dyno day and I'm sort of at a loss/ confused. When i first got the car I had it dyno tuned after basic bolt ons
Slp intake headers catback etc. dyno jet

Made 343hp 363tq.
Now after a custom cam and ported 241s the car put down 389hp 346tq.
Is it normal to lose tq? This was 3 identical back to back pulls on a dyno jet as well.

Post up both sheets so that was can see what dyno, what correction factor, smoothing, torque curves look like, etc. There are a multitude of variables that could be at work in skewing the numbers to "appear" lower than what you hoped for. Did the heads change compression; if so then did it drop? How aggressive was the ECM tune before and after the hardware mods, etc?
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Old 05-18-2013, 05:31 PM   #4
 
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Heads weren't milled at all just springs changed and ports done. Ill try a d find the old dyno sheet and scan my new one tonight. Afr was only different by a bit if Iirc.
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Old 05-18-2013, 07:16 PM   #5
 
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Looked like han's was hanging out STD numbers. Were the earlier runs made with SAE or STD numbers?

And yes, when you increase the cross section of the port you can lose torque. Especially if the cam moves the power band higher. MANY thing factor into it as you can imagine. Was it re tuned after the install? Many times revised timing tables can gain some of what was lost.
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Old 05-18-2013, 09:57 PM   #6
 
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Dyno with bolt on's


Dyno after ported heads/cam


The car was tuned, by 2 different shops. Not sure on the timing, but both seem to be right at 13.0 AFR. The power band did move higher with the cam, and this isn't a bashing thread or anything. I was just unsure as to whether or not this is a normal thing or not.
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Old 05-18-2013, 10:33 PM   #7
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Look at the area under the curve. Your new combo has you never less than 325lbft between 5250 and 6K rpm. Not true of your original setup. Torque curve is flatter. Also need to look at how heads and cam really matchup.
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Old 05-19-2013, 12:53 AM   #8
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i had a similar issues when i did the heads cam intake on my supercoupe i lost 35 peak ft lbs but gained 40 average across the board and added nearly 60 hp up top
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Old 05-19-2013, 04:20 AM   #9
 
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Originally Posted by Xfirez51 View Post
Look at the area under the curve. Your new combo has you never less than 325lbft between 5250 and 6K rpm. Not true of your original setup. Torque curve is flatter. Also need to look at how heads and cam really matchup.
I see what you're saying. Makes sense.
And the heads were flowed then the cam was ground to match.
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Old 05-19-2013, 06:20 AM   #10
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Well, I've been preaching since 2008 that HP is much more important than torque. I wouldn't worry about it, your car is much faster under this setup. Peak torque doesn't matter at all really, if you're going to look at torque, look at area under the curve as someone already mentioned. Look how much harder the motor pulls at high rpms which is all that matters cause that's where you are when you race!
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Old 05-19-2013, 07:08 AM   #11
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my buddy had a 00 SS cam/headers/ stall and made more than when he installed an LS6 intake and had it retuned.

is your car an auto ? could it be with / without the TC locked?
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Old 05-19-2013, 08:03 AM   #12
 
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my buddy had a 00 SS cam/headers/ stall and made more than when he installed an LS6 intake and had it retuned.

is your car an auto ? could it be with / without the TC locked?
Didn't think about that. I don't think the converter was locked yesterday when it was done. The first time it was dyno'd it had a stock converter in it so it was most likely locked
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Old 05-19-2013, 09:30 AM   #13
 
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Just for your info, your first dyno is posted in SAE numbers. The second is in STD numbers. There is a 2.6% difference there. Your new peak numbers converted to SAE are more like 378 / 338.

Does it feel lazy down low compared to before? See how it runs at the track. If the ET drops and the MPH comes up that is all that really matters.
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Old 05-19-2013, 10:18 AM   #14
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Quote:
Originally Posted by Shibby50 View Post
Didn't think about that. I don't think the converter was locked yesterday when it was done. The first time it was dyno'd it had a stock converter in it so it was most likely locked
If you look at the 2 graphs you can tell on your second one that the converter was unlocked. Thats your problem right there.
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Old 05-19-2013, 11:41 AM   #15
 
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Car went a whole .3 sec and 2mph faster in the 1/4 lol. Car feels really good. Was just expecting more at the track after it all I guess and when I saw the dyno numbers I was kinda shocked lol
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Old 05-19-2013, 11:52 AM   #16
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Track can vary so much based on weather etc. I remember on my SS I gained 20rwhp and ran 4 tenths SLOWER because of the weather.
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Old 05-19-2013, 12:05 PM   #17
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Quote:
Originally Posted by Shibby50 View Post
Didn't think about that. I don't think the converter was locked yesterday when it was done. The first time it was dyno'd it had a stock converter in it so it was most likely locked

If the TC is locked then it will show higher average hp but lower average torque because it is not torque multiplying but is also not slipping as much (if at all) in the upper RPMs. But, if the TC is unlocked then it will show lower average hp because it is not 1:1 during any portion of the dyno run but higher average tq will result because it is still able to torque multiply; mainly in the lower rev range.
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Old 05-19-2013, 12:16 PM   #18
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Quote:
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Track can vary so much based on weather etc. I remember on my SS I gained 20rwhp and ran 4 tenths SLOWER because of the weather.
Yeah, DA, traction/launch, and the amount of burst knock retard set up in the tune can have huge effects on your ET. Sure DA calculations will add some of that lost ET back in, but there are other losses such as with knock retard and track conditions that a DA calculator cannot add back in. So, like Turk implied, it's all relative to the conditions at hand.
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Old 05-31-2013, 11:49 PM   #19
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how much did your MPH change? That's probably more relevant than your ET. Do you have a WB in the car? Also, how much did you change overlap? You may need to evaluate timing again if you're bleeding off cylinder pressure at low RPMs.
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