Topic: Dynatech LT Stainless Headers & Intermediate Tubes w/Cats.

[Fowlhunter]

I really want to add a set of headers and I've been doing some research.  I looked at the stainless JBA shorties which are nice and so is the price but would I really be gaining that much with the shorties?  I've been thinking long tubes, replacing the intermediate tubes and cats.  Most of you (maybe just a few) know what I'm looking for here when it comes to performance for my AV but honestly the LS based engines (LM7 for me) like mid to upper RPMs so the long tubes would be more like it.  I seem to do pretty well from a dead stop right now (without the A/C on) so if I can gain more in the mid to upper range that would probably be better.  Highway driving now is kid of sluggish from let say 50-70 without really kicking the Ole girl in the  .  I know this is a bunch of money but it may be a better route to go instead of the shorties?  Take a look at the links and give me your thoughts.  Also, would there be anything I need to do if these are installed, tune wise?  If so, could I tune it with my Predator?

Thanks!
http://www.afabcorp.com/AFCO_Dynatech_USbrake/merchant.mvc?Screen=PROD&Store_Code=Dynatech&Product_Code=115-841300A&Category_Code=gm-53-truck


http://www.afabcorp.com/AFCO_Dynatech_USbrake/merchant.mvc?Screen=PROD&Store_Code=Dynatech&Product_Code=115-841300B&Category_Code=gm-53-truck

[Main One]

I've got the JBA shorties so I'm probably a little bit biased, but here's my thoughts.

You mention 50-70 being a little sluggish.  (Sounds like Ski Edition!)  These will probably help you around 60-80, (top number depending upon where you shift into 3rd WOT) but probably hurt you around 45-60.

For $1500, I don't think I'd want to be giving anything up.  If you are happy with the top end, but wanting more in the mid-range, why do you want to spend money that isn't addressing what you want to address?

I noticed on a different page on Dynatech's web site a claim of increased HP.  Not seeing a claim of increased torque is very telling.  From what I know, which isn't as much as I'd like, I think you'll see less power from around 4000 rpm down.

For the money, if I were doing it all over again, I'd do shorties again.

[oHIobellboy]

...

You mention 50-70 being a little sluggish.  (Sounds like Ski Edition!) These will probably help you around 60-80, (top number depending upon where you shift into 3rd WOT) but probably hurt you around 45-60.
....

Nothing a little heavier foot wouldn't help 

[Fowlhunter]

I've got the JBA shorties so I'm probably a little bit biased, but here's my thoughts.

You mention 50-70 being a little sluggish.  (Sounds like Ski Edition!)  These will probably help you around 60-80, (top number depending upon where you shift into 3rd WOT) but probably hurt you around 45-60.

For $1500, I don't think I'd want to be giving anything up.  If you are happy with the top end, but wanting more in the mid-range, why do you want to spend money that isn't addressing what you want to address?

I noticed on a different page on Dynatech's web site a claim of increased HP.  Not seeing a claim of increased torque is very telling.  From what I know, which isn't as much as I'd like, I think you'll see less power from around 4000 rpm down.

For the money, if I were doing it all over again, I'd do shorties again.

Mine really seems to drop off once I hit overdrive, if I want more get up and go I really need to put my foot in it, seems like the tranny will drop into third gear without much difference then I really stomp on her and she drops to second.  I like the JBA headers!!  Would I benefit much by changing the cats?

[Main One]

Mine really seems to drop off once I hit overdrive, if I want more get up and go I really need to put my foot in it, seems like the tranny will drop into third gear without much difference then I really stomp on her and she drops to second.  I like the JBA headers!!  Would I benefit much by changing the cats?

Ah the joys of a wide-ratio transmission....

The stock cats supposedly flow pretty well.  I saw a comparison as well on the dynatech web site where they compared theirs to a single cat system.  We've got dual cats stock - I don't believe there is much to gain by going to "high-flow" cats.  Depending upon your state and your commitment to the environment, you may or may not want to gut them and then either ignore or via tuning mask the resulting fault code tripping the SES light.

[Fowlhunter]

Ah the joys of a wide-ratio transmission....

The stock cats supposedly flow pretty well.  I saw a comparison as well on the dynatech web site where they compared theirs to a single cat system.  We've got dual cats stock - I don't believe there is much to gain by going to "high-flow" cats.  Depending upon your state and your commitment to the environment, you may or may not want to gut them and then either ignore or via tuning mask the resulting fault code tripping the SES light.

OK, for now I guess I'll stay with the stock cats, I really don't want to deal with the SES light.  In your opinion, do you think I will notice that much by getting rid of the manifolds and going with the shorties?

Thanks man!

[MyBigToy]

OK, for now I guess I'll stay with the stock cats, I really don't want to deal with the SES light.  In your opinion, do you think I will notice that much by getting rid of the manifolds and going with the shorties?

Thanks man!

You can turn the code off with the Predator. It's just the rear O2 sensors and they don't really do anything functional other than tell you if the cats get clogged. I've seen the same info regarding the stock cats as M1.

Unfortunately, the main thing hurting your performance is the combination of 3.73 gears and the 285 tires. You wouldn't notice the sluggish acceleration nearly as much if you went back to the stock 265s or changed to 4.10s.

I also agree with M1's sentiments regarding long tubes and your truck.

[Main One]

OK, for now I guess I'll stay with the stock cats, I really don't want to deal with the SES light.  In your opinion, do you think I will notice that much by getting rid of the manifolds and going with the shorties?

Thanks man!

To tell you the truth, I wasn't able to seat of the pants detect any help from making air intake changes, although I may have done it too incrementally to notice.  I felt I could notice however a help from the shorties.  Not like the cam, but I think it is noticeable.

You asked about tune a few posts back.  You won't need to do a tune, but your volumetric efficiency will be affected, and tweaking the volumetric efficiency table will give you a bit more.

[Ski Edition]

I went to Transmission Masters to get the plumbing done on my aux cooler and the owner helped me with my Superchips tuning (he builds trannys and dragsters so I trusted his opinion).  We raised all shift points 500 RPMs and shift pressure 6 lbs. and I have found part of what I have been looking for.  We left it at that and he feels that it is still conservative.  We played trial and error for a couple of hours.  My problem was that she was changing gears at too low of RPM to get her into a higher range to carry momentum into 3 and 4, so she was dragging.  I found out that the ol' girl will take a lot more than us soft-footers think.  I also had my tire size all wrong too.  Nitto says my tire is 33.98 diameter, tire conversion chart show 33.8.  We checked pressure and ensured correct inflation and measured them at 33 even. so we changed that also.  She is running a lot better.  FH, you know I got the Edelbrock shorties and really like them.  Sorry for the semi-thread jack, but think this may help a little. 

[MyBigToy]

I also had my tire size all wrong too.  Nitto says my tire is 33.98 diameter, tire conversion chart show 33.8.  We checked pressure and ensured correct inflation and measured them at 33 even. so we changed that also.

0.2" difference between actual and stated size really doesn't amount to a whole bunch on the speedo (I could do the math and bore you with it but I won't  ). However every little bit helps when you are not satisfied with how it's accelerating (like we said earlier, you need a bigger or heavier foot!  ). I've found the easiest way to get the speedo correct is to use a GPS unit, set the cruise control on the Interstate, and check to see how far off the speedo is. Adjust it from there until you get it dialed in exactly.

To give you an idea on how little the 0.2" tire size practically affects things, the last I knew the Federal Government allows the speedo to be off my as much as 10%. I never figured that one out except that it must be to allow for the different tire sizes that go on the different models; 10% is a huge discrepancy to me. Think about it; 10% is 6 mph at 60 mph. I also believe it's much more critical to today's computer-controlled vehicles to get it right so that timing, fueling, and all other parameters controlled by the computer are correct. If the computer thinks you are going 60 mph when you are actually going 66 mph you're not getting enough fuel for the speed you are going.

OK, I've bored everyone enough and I really should go back to work. 

[Main One]

0.2" difference between actual and stated size really doesn't amount to a whole bunch on the speedo (I could do the math and bore you with it but I won't  ). However every little bit helps when you are not satisfied with how it's accelerating (like we said earlier, you need a bigger or heavier foot!  ). I've found the easiest way to get the speedo correct is to use a GPS unit, set the cruise control on the Interstate, and check to see how far off the speedo is. Adjust it from there until you get it dialed in exactly.

To give you an idea on how little the 0.2" tire size practically affects things, the last I knew the Federal Government allows the speedo to be off my as much as 10%. I never figured that one out except that it must be to allow for the different tire sizes that go on the different models; 10% is a huge discrepancy to me. Think about it; 10% is 6 mph at 60 mph. I also believe it's much more critical to today's computer-controlled vehicles to get it right so that timing, fueling, and all other parameters controlled by the computer are correct. If the computer thinks you are going 60 mph when you are actually going 66 mph you're not getting enough fuel for the speed you are going.

OK, I've bored everyone enough and I really should go back to work. 

Joe,

I think you needed at least another cup of coffee before posting the above. 

The tire size error looked to be 0.8 or 0.98 inches, since they corrected it to 33 after doing a measurement.  I'll let you bore yourself with the math.   

The computer doesn't do fueling (other than when you lift your foot off of the gas) based upon speed, it does it based upon airflow based upon MAF, MAP, RPM and air temperature inputs.

The speedometer issue does however affect shift points.  Those are determined by speed and throttle position.  Fixing the tire size issue can either help or hurt - it would appear that in this case it helped.  Since the tire size was actually smaller than the computer thuoght, the computer would think the truck was going faster than it actually was by up to 3% (there I went ahead and did the math for you  ).  For a given (held) throttle position, once you accelerate through the programmed shift speed for that throttle position, you will get the upshift.  Everything else being equal, even without the WOT shift RPM change, he should in general be seeing all shifts ocurring at about 3% higher speed.

[Ski Edition]

I'll let you engineers haggle out the percentages, but driving it last evening, she seems like a much lighter vehicle and actually has some pep to her step!!  Still more tinkering to do!!  Power is really contagious!!!   

[Main One]

Ski - I've never used a superchips programmer, but I suspect that like with the Hypertech that I used to own, the shift points that you can change are only the WOT shift points.  Since you have found the changes that affect your shift points very positive so far, you may be interested in changing more of your less than WOT shift points via a custom tune.

Question: do you use Tow/Haul mode very often, and if so, how do you like the stock-programmed shift point in T/H?  They are quite a bit different than the standard shift points.  For instance, in my 03's stock tune, it would shift into 4th I think possibly as low as the low 20s mph-wise, but in T/H, not until I believe 55.

A custom tune besides adjusting your part-throttle shift points, can also adjust how "willing" the tranny is to downshift as well as unlock the torque converter.  You may find tweaking these to be to your liking as well.

The 500 RPM shift bump is quite healthy - I'm not sure I know where that puts you.  I believe I'm currently programmed at 6100 rpm with an engine cutoff at 6300.  I was running I believe 6200/6300 but in hot weather seeing the electronic thottle close on me 'cause the tranny wasn't shifting fast enough and I was hitting 6300.  I upped the 6300 to 6400, but then got a little lifter tick that I found annoying, so went from the 6200/6400 to 6100/6300.  I believe after the upgraded tranny goes back in that I will try 6200/6300 once again.   

How all of this relates to Dynatech headers is beyond me???   

[MyBigToy]

I also had my tire size all wrong too.  Nitto says my tire is 33.98 diameter, tire conversion chart show 33.8.  We checked pressure and ensured correct inflation and measured them at 33 even. so we changed that also.

33.98"-33.8"=0.18"

That's the error I was identifying.  I won't argue that I needed another cup of coffee but I think that math adds up.    That's why I find it easier to use a GPS unit because you are relying on the actual speed you are going rather than calculated tire sizes.

Aren't stock WOT shift points 5200? If so, he's now shifting at 5700.