I know its been discussed and i have spent a few hours searching, but i still have some questions. most threads are a few years old and they are so spread out and finding all the answers is taking a long time. so im looking for some updated info. motor will be 454ci ls3 sleeved with a ~240ish/250ish cam.

what are the advantages of a speartech harness over the gmpp harness besides the tech? i called john a few weeks back and he really didnt "sell" it. he told me the e38 is easier to tune and that the harness and ecm have all the unneeded extras removed (vats etc). problem is that ive read the gmpp e67 harness has all of the same done. so whats the difference?

i was also told by a local tuner that the gmpp doesnt have some of the tables available (ve?). he said that they werent turned off, but that they didnt exist. any truth to this? he said that i would never know the difference in the tune, but that he wouldnt be able to get it perfect. he also said that if i ran a big cam and big ci motor that the maf may get messed up with intake pulses and that he could do a SD tune instead of the maf tune. he wasnt sure if he could do that with the gmpp harness although a stock e67 and e38 would work.

with the gmpp harness;

can the fan control still be changed? can i control two fans seperate? one on at "x" temp and the other on at "y"?

can the ac be controlled to have the fans turn on when the ac is on? turn the compressor off at say 4k+ rpm?

full access to tune with hptuners like the factory harness?

can the gmpp harness be flashed and another os be put in to act like a factory ecm?

would it be worth spending 150 bucks for a factory e67 to run with the gmpp kit? its still cheaper to pay the $900 for the gmpp harness since it comes with all the extras. the speartech is closer to 1650 complete.

anything im missing?

thanks, tim

 

While there are going to be differences in some of the physical aspects of harnesses from different manufactures (GMPP kit does not lay the harness out very nice in my opinion and the fuse box is rather large), the question of which setup to buy may come down to customer service. While Speartech and others on this board are competitors with PSI's products, in the end quality and customer service/tech support are paramount to many people. If you have an issue/question with the GMPP kit who are you going to contact? Just another question you may want to ask regardless of whose kit you purchase.

Jon
PSI

 

thanks for the reply.

could you be more specific about the layout? what about it dont you like? ive never run either harness so i have no idea what the issues are. i am going to remote mount the coils, but i figured it wouldnt be too hard to open the harness and move only those wires.

anybody know of any tuning issues?

 

I was planning on using Speartech but so far I've called 3 times and 2 emails and no response! Guess keep trying

 

I got a Speartech harness (LY6 w/VVT) as John has a stellar rep & noone else did them at that time. If I ever do another engine, I'll use PSI. Jon has a great rep here too. Plus, I think PSI has more reasonable prices. I never heard anything bad about EITHER vendor.

BWIROLLA64,
John Spears is one busy dude. He might be on vacation. If you are set on Speartech..... keep trying. His work is top notch.

 

i dont see a "kit" price on psi. maybe they can quote us here with the harness, new ecu, pedal, maf, o2 sensors etc.

i got ahold of him after a few tries thoughout the day. nice guy, but i just dont see any difference in the kit for an extra 800 bucks.

the differences along with the tuning info for the gmpp is what im still after.

 

Thanks JIMBO I have also looked at PSI I've just heard good things about Speartech and know someone who has a harness. I'll see what PSI can do.

 

This thread woud be better if someone posted pics of both harnesses even better all three vendors.

 

The difference between a GMPP harness and a custom aftermarket item, for example from Speartech, PSI, EFI Connection, Lsxworks, Current, is that the custom items are generally high quality hand made items made in house by that business and are laid out to look as good as possible and not be bulky. They can also be made with variations to suit engine bay layout.

The GMPP harness is made quickly to a price in Mexico and the design isone size fits all and is very bulky, quality is definately not OEM, the fuse and relay box is really large as already mentioned.

The GMPP setup will also not support an automatic in its basic form, other than buying the GMPP A4 controller which is almost as much $ again.

If you want to run a manual setup and dont care what it looks like and dont put much weight on quality and after sales support then the GMPP setup is great value.

The factory tune in the GMPP controller is a stripped out version of a regular E67 factory tune. It is just as tunable in most cases as an E38 or other E67 V8tune.

 

There have been issues wit the GMPP harnesses as well as the base programs in the ECM's. Nothing major, but just a pain in the butt. I have used quite a few different serums and now use and recommend Speartech all the time. The main reason is that every harness is built on an actual engine/trans assembly and then each harness is run on that engine to test that it is working properly.
John has about a dozen engine/trans combos at his shop ready to run from a 5.3 and 4L60E to an LS9 and 6L80E and everything in between.
He can literally have all 12 engines running at the same time. What does this mean for the customer? You are pretty much guaranteed to have a good harness and ECM. As far as I know no one else has this capability to verify their work as well as test other competitors products.
This is not to say other folks do not build a good product, just that for me after a couple bad experiences with other harnesses it was is now Speartech all the way. It can be more money to start, but save in the long run diagnosing an issue.
Hope this helps.

Mike Norris

 

With the quality of the rest of your build I would defiantly not use the GMPP monstrosity. With the time and money you have spent on all the other aspects a factory style split loom harness and large fuseblock would jump out at me.

a Harness akin to this. Though I am not sure I would use this actual builder but but the harness is decidedly better bundled and able to be hidden or at least not draw attention




and fuse block something like this that is significantly smaller in size but still allows plenty of fuses and relays for engine and other upgrades.


Those harness examples are from Chase Bays and the fuse block is the one I wish I had used from currentperformance.com

 

With some time spent on it you could make your own custom harness that looks as good as the Chase one for significantly less using loom and heat shrink from Del-City.

I am not sure on the best way to get the mil spec set up for a reasonable price though. I have been trying to find that information myself

 

thanks for the help guys.

what makes any other harness less bulky? are they using different wire? grouping the wire different? does anybody else make one with the braid on the chase bays harness?

current performance harness. speartech appears similar on johns site


gmpp harness



thanks mike. i saw a thread of yours on hptuners about a change in the os. what other issues have you encountered? is it something system wide, or just individual harnesses?

with the money being spent on a speartech harness, why not just run the holley hp or the mast harness? i know they both pose their own issues, especially mast with needing all of their stuff to tune it. but, the holley comes with the program and is a self learning ecu for 1500 bucks. any thoughts?

 

The Chase harness is more compact because of the braided non-split loom. A cheaper version of that loom can be purchased through Delcity.net I have it and am pleased with the quality. Hopefully i get time to redo my harness with it this year.

That non-split loom is more difficult to work with since you cannot go back and add wires to it nearly as easily as split loom but for a nice car it is worth the effort. Once you run the wires through the loom you pull it tight and heat shrink the ends and it keeps the wires pulled tightly together instead of just loosely bundled into split loom (think Chinese finger cuffs)

 

Excellent info.

 

As far as custom harnesses most will weigh about the same unless you specify extra length for the ECM harness.

I would be curious to how other harness suppliers handle their quality control in that Speartech builds and runs each harness on an engine. This kind of QC is hard to beat.

For the Holley question, I guess it would all depend on what you have already. If you have the factory ECM and other related parts I would stick with factory. If all you have is an e vine and basic sensors, then the new Holley would be a very good option.

I am on the road in FL tuning through Thursday, but if you want you can email me and I can get a quote together for you. It is thevettedr@aol.com

Hope this helps again.

Mike

 

i found one other site that said they run the harnesses inhouse on their engines. its really sad the gmpp harness isnt of better quality. its a great price.


i dont have anything currently. i was going to run a mast motor and therefore their harness so i hadnt really researched anything else. when i was talking with one builder they were pushing the holley pretty hard. local tuners said driveability and fuel mileage will be better with a maf setup though.

 

Speartech harness pics, anyone?

 

My Speartech harness was great.

 

Here are a few pics of my Speartech harness, I just received it the other day but I have decided to go another route on my 2nd project, this is my first harness from Speartech and now I know why their prices are on the high side you definitely get what you pay for, this is a quality harness with great attention to detail. This harness also has a 60" inch wire trunk as i was going to mount the PCM behind the passenger side headlights where the battery would have been. So this harness is for sale this harness is for a 2006 GTO LS2 & T56 set up it has the cruise control wires & A/C wires ran & ready to be connected, it has the1997-2004 Corvette program and ready to run
"411 PCM" which has been re-programmed by Speartech with all emissions and vats deleted it also has the 1997-2004 Corvette accelerator pedal
part# 12565643 and the 1997-2004 corvette TAC Module part# 12578953 It has the f-body alternator plug on it, this harness ir perfect and has not been installed, I sent my accelerator pedal and TAC to Speartech so that everything could be tested for proper operation and this set up was installed on a in house engine at Speartech to verify everything works as it should before the harness was sent back to me. I also have a PCM tray that is brand new from G.M. the PCM tray is originally for a 2000 S-10 but holds the PCM perfectly for mounting on a flat surface. So this set up is ready to run on a LS2 DBW electronic throttle body. $1500.00 + paypal fees unless money sent as a gift shipped to your door. I also have a extra "411 PCM" that has not been programmed yet and a extra TAC & Accelerator Pedal with the same part numbers as above that I was going to keep for spares but I no longer will keep them since I am selling this harness I will sell these with the original harness as extras for $2000.00 + paypal fees unless money sent as a gift or I will sell the extra parts seperately for $600.00 + paypal fees unless money sent as a gift shipped to your door. P.M. with any questions thanks Bob