8.1/ZF6

496Cubes · June 11, 2003

Hi guys, new guy here looking for some advice. I have a 2003 2500 HD Reg Cab with the 8.1/ZF6 combo. I have added new wheels and 285/75 tires. The only other mod I have made is replacing the muffler with two straight pipes. I'm looking to increase the power out of my engine. I was going to add a higher air flow filter, have heard replacing the whole intake wasn't worth the money. Your thoughts? Is a programmer worth the money, if so what do you suggest? Comp cams has 3 different styles of cams available, has anyone tried them? A Whipple Supercharger looks like a good addition, but I don't want to be forced into using 93 octane all the time as it can get expensive. What mods would you guys suggest for me? What's the best bang for my buck. I plan on taking it to some truck pulls this summer, hoping to show those Juiced DMaxes up. Has anybody here pulled that has a few tricks to share? Thanks for the responses.

Gilbert · June 11, 2003

Hey Cubes:

I've got the 8.1L with Allison combo on a 2500HD. Currently the engine has 4300 miles on it. At 3000 mi. I installed a pair of Headers from (The Other Guys Products).

I didn't notice much, if any, increase in performance with the headers, but wasn't surprised. I say I wasn't surprised because in the process of removing the old exhaust manifold, I found that the 8.1L heads are stranggling this motor. It can not breath. I know this motor is built for torque but the size of the exhaust ports are a joke.

After a discussion with a couple of guys that work at the local speed shop, I was told that several customers had complained about the heads. They've nicked name them PEANUT PORT HEADS. If you saw the size of the port you'd understand. Forget about forced induction, you won't get the most out of it with the stock heads.

With respect to programmers though, I've read where several guys on this Forum have said positive things about the Predetor Programmer by Granatelli. They say it's much better than the Hypertech. That's going to be my next and only other mod on this engine until I get some good Aluminum heads. I will be getting the Predator before the end of the month.

Good Luck....

awdvkd · June 11, 2003

Look into the "Westers chip upgrade" a lot of talk around here and most seem really impressed. Just a thought

americanmuscleman · June 11, 2003

Gilbert, in response to your comment about "Peanut Port Heads", I agree. I work for Mercury Marine and see 8.1 heads all the time. (Mercury uses the same 8.1/496 used in GM trucks for marine duty). The exhaust ports do look really small. The "496 HO" we build uses a more aggressive cam with stock heads through water-injected manifolds, and makes on average 440-450hp and about 520tq on the dyno. Thats all produced at or under about 5000rpm.

I think the 8.1/496 heads have some potential stock (though they could definitely use more), they just need a more aggressive cam to get more air in the chambers. Also the factory GM 496 tuning is really conservative.

tbyrne · June 12, 2003

There are quite a few options available for the 8.1. I've gone naturally aspirated with my 8.1 Silverado HD and use the intercooled Whipple on an 8.1 Suburban. Performance mods for the HD are a Volant induction, ported throttlebody, Poweraid throttlebody spacer, The Other Guys mid-length headers, Direct Hits Ignition. mild Comp Cam (206/212 .510/.510 112), Flex-a-lite electric fans and custom programming. The truck has plenty of power for towing and is definately quicker than stock. I'm researching head options now. There isn't to much available for aftermarket heads. I think the reason for this is because there aren't to many 8.1 owners that are interested in opening them up.

As for the Suburban, it's fast for a truck! I can tip into the throttle a little and be doing 90 without even realizing it. Besides the Whipple I've also installed a Volant induction, The Other Guys headers, Direct Hits ignition and had some custom programming done. This 6800lb truck eats up the 1/4 mile in 14.5 seconds which surprizes some cars on the road

The boat 8.1 is nice. I have this in a 23' Chaparral bowrider. GM's programming tends to be pretty conservative for the truck computers. Have you seen much of a benefit in reprogramming any of the boat computers?

Tom

2002 8.1 Silverado HD - Comp Cam, TOGs headers, Volant induction, Direct Hits ignition, 6" lift 18" wheels/tires + more

2002 8.1 Suburban -Intercooled Whipple supercharger, TOGs headers, Volant induction, 22" wheels/tires + more - 14.54 @ 92.43

www.tbyrnemotorsports.com

02 2500avalanche · June 12, 2003

Tom, do you feel that the comp cam you put in your truck was worth it? This particular cam is supposed to pruduce more tq but I don't want to put this cam in my truck if it is not going to have alot more tq. I am very serious when I say im putting a cam in my truck so your opinions are important. Thanks

Alex

496Cubes · June 12, 2003

Thanks for the replies guys.

I think the Westers chip may be my best first upgrade. He replied to a few questions I sent him, currently waiting for him to send me some HP and Torque data. Does anyone already have this info? Only drawback is the $600 price tag.

Westers says, "you can use 87 octane through 93 octane. At each "fillup" the truck runs a self test to determine which octane table will be used. There's a low octane and high octane spark table (both of which are modified)."

Did you guys know our trucks did this? This means I can use any octane gas I want and the premium will improve my performance, which is great.

I think my next upgrade will be either the mild or moderate Comp Cam, offered for the 8.1. Tbyrne, what were your impressions of the cam change? Anyone else have experience with doing that upgrade in an 8.1. Westers has told me to upgrade their programming for the cam change would be free, which is nice to know. The main difference between the 496HO marine engine and the truck engine seems to be a more aggressive cam.

Thanks for the info about the heads, I'll keep that in mind as I start my upgrades.

tbyrne · June 13, 2003

The cam went in with alot of the other mods. I'd say that it does produce more torque than other 8.1s that I've driven with roughly the same mods and the stock cam.

americanmuscleman · June 13, 2003

tbryne, I don't think very many people are reprogramming the PCM 555 computers used to control the marine 496. The programming on it is very close to getting the max power out of it. I don't think I can talk about the programming specifics though, as its Mercury protected information. I know it took a long time for Whipple Industries to come out with their marine 496 Whipplecharger because of the programming issues. I've heard there is a programmer that does modify the 555 controller though for aftermarket modifications.

496cubes, the main difference between the 496 Mag and 496 Mag HO is the camshaft. The HO also used to get a forged crank. It was found though that the forged crank wasn't needed. The GM factory cast crank could handle sitting under full load at 5000rpm all day long with the HO camshaft with no durability issues, so thats why they switched over to the cast crank.

I wish I could talk about more of this stuff in detail, as its really interesting, but most of the information is Mercury Marine protected.

tbyrne · July 10, 2003

Here are some pictures of the stock 8.1 heads -

Tom

www.tbyrnemotorsports.com

bigtruck21 · July 11, 2003

At each "fillup" the truck runs a self test to determine which octane table will be used. There's a low octane and high octane spark table (both of which are modified)."

Did you guys know our trucks did this? This means I can use any octane gas I want and the premium will improve my performance, which is great.

I don't know if my engine is different in any case, but I only tested enough to have 1 pure tank of each grade of gas 93, 91, 89, 87 (that means run out the old stuff almost all the way fill up with the next stuff and do one more fillup and test the 2nd tank) I kept the driving habits the same (same route to work) I also made sure the temps were roughly the same. Basically, I got the worst power and mileage the higher the octaine I used. I assumed since it says run 87 in the book, it is optimally tuned for it.

Gilbert · July 13, 2003

Tybrne, put a measuring tape against those exhaust ports, I'll bet it makes some of the guys on this forum cry. It sure broke my heart.

Gilbert · July 13, 2003

Hi Muscleman, I see your here in the Tulsa area. I live in Broken Arrow.

I was'nt aware that Mercury had a factory here in Greeen Country. You mentioned that you work on the Mercury 496 HO. Where are the engines actually tested. You also mentioned that the 8.1L HO gets 440HP at the crank with just a cam change?? That's a whopping 100HP over my stock engine. And more than guys on this forum are getting with a non-intercooled whipples added to a stock 8.1.

I've read a little on the web about the Mercury, but had no idea it was that close to stock.

The fact that GM produces a factory 496cu in motor that can only spit out a measily 340HP makes me very angry.

How soon till Mercury releases some specifics about the cam profile? Can you divulge any info on some aftermarket heads?