Give Me Head(s)

Gilbert · May 13, 2003

This thread is directed to Gear-Heads like me, who are constantly on the lookout for aftermarket products, and who are constantly trying to find ways to squeeze out those de-tuned Horses from our engines. I'm not here to bash anybody's product(s), but instead inform you of my experience with aftermarket item that I personally have purchased and installed on my vehicle.

About 2 weeks ago I installed a pair of headers for my 2003 GMC 8.1 liter (w/ Allison). I did a fair bit a research on the subject and ended up purchasing "The Other Guys Headers", (www.theotherguysproducts). I first read about them from (www.tbyrnemotorsports.com); Over the years I've installed approx. 7 or 8 headers for different vehicles I've owned; And I must say that these headers have the best finished, by far, that I have ever seen. The inlets are actually die-grinded for smooth exhaust entry. The installation was a snap (about 6 hrs), and the fit is absolutely perfect. Plenty of clearance all the way around.

However, "The Other Guys Products" web site is misleading in their performace description of these headers. There is no claimed-40 HP increase, that claim is pure B.S. Based on my experience, I don't believe there's 30 or even a 20 HP increase. Nothing noticable by the seat of your pants anyway. These headers are not true equal-length headers, if I had to compare them with anything, I'd compare them with shorty's.

Before I purchased the headers I asked Wayne at "The Other Guys Products" to provide me with Dyno-Charts substanciating their performace claims, he did not produce anything. I myself have not dyno'ed my vehicle to provide you with true Before and After results. But, come to think of it, I don't think I've ever been able to obtain dynamometer results from any header manufacturer, including Headman, Hooker. But I've built enough engines, and installed enough aftermarket performace products in my life to know that there is no significant increase in horse power.

HOWEVER, the headers look excellent, and I do beleive that these headers are currently the best available for the 8.1L.

During the installation of these headers I learned that the root of this engines breathing problem is GM's stock heads. The size of the stock exhaust ports on the factory heads are a disgrace; or more appropriately, they are a joke.

If you own an 8.1 L and are looking to increase the horse power, I would highly recommend waiting until someone out there produces a good aftermarket Head. Don't waste your money on headers or anything else claiming to improve the breathing of this engine. I truely do not beleive there is any product out there that can do this engine justice until Better Heads become available. Sure you can dump a few grand on a SuperCharger, or even more on a Turbo, but you'll still have an engine with a beathing disorder.

I just can't beleive that GM's 496 cubic inches (even though it's stock) can only put out 340HP at the crankshaft. That's only 0.68HP per cubic inch. What a joke. What a shame. And to make matters worst, from what I've read, the Allison tranny sucks out approx. 100HP leaving you with only 240 at the rear wheels. The only great thing I've come to learn about my truck's drive train is the gearing.

I have some very good digital photo's of the ehaust manifold (Stock vs Header), and of the exhaust ports on the stock GM heads. If your interested, I'll be happy to email them to you. They will show you what I'm talking about.

ShortCrew · July 14, 2003

Gilbert,

I'd love to get an email of the pictures if you still have them. Also, a cam might be your interim solution until heads come out. I've heard the marine versions of the 8.1L that make big power use the exact same heads, but have bigger cam specs.

Cliff1943 · August 30, 2003

Dear Heads,

I just bought a 2003 2500 HD with the 8.1 and Allison. I think the whole setup sucks. I too figured the engine only puts out 0.685 HP and 0.917 pounds feet of torque per CI. What a joke!

I wish I had gotten a 6.0 and spent the extra money I spent on the darn big block and the Allison to hop up the 6.0.

It really frosts me when I pulled out some old issues of Hot Rod and Chevy High Performance and read where the GM HT 383 crate engine makes 325 HP & 415 lb. ft. of torque stock. With 1.6 roller rockers and headers they were pulling 355 HP and 452 lb. ft. of torque.

I had one dealing with big blocks back in the 70's. I sold that hunk of junk after I spent a lot of money hopping it up and build a 350 with a mild cam that ran better than the big block. I swore I would never have another one. I got this 8.1 to pull a 5th wheel. Now I wish I had bought a used older truck and rebuilt the engine. I would be much happer than this truck that is about as efficient as a snail.

Sorry owner

PSWired · October 28, 2003

Email me those pictures to pshoemak(at)bucknell.edu and I'll host them for you.

Gilbert · October 28, 2003

I'll digg'em up and send your way wired. Sorry for the delayed response, I had not visited this area of the forum in a while. Sit tight, the photo's will come your way.

On another note, in one of the other areas on this forum, Tybrne posted some photo's of them, the difference between mine and his is this...I placed a measuring tape across the exhaust ports on the head to show their rediculously small size. I also placed my stock manifold next to the TOG's I installed to show the differences between the 2.

Anyway, sit tight and I'll email you couple of photo's.

Regards,

Gilbert