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.