8.1 Roller rockers & Shorty headers

Cliff1943 · August 30, 2003

Has anyone tried shorty headers and roller rockers on their 8.1. Here's what I know about the rockers.

1. Stock 8.1 rockers are not a roller rocker and they are not adjustable.

2. Crane cams makes a replacement stud that allows you to put roller rockers in this engine. They make the rockers in 1.7 and 1.8 ratio.

3. Comp Cams makes a 1.7 rocker, and 1.8 if you buy the stainless steel rockers.

I want to try the 1.8 rockers and the headers to see if they will wake up the 8.1 like the HT 383 chevy crate engine in Hot Rod and Chevy High Performance magazines.

With these two options the HT 383 went from 325 HP to 355 HP and 415 pound feet of torque to 452 pound feet of torque.

This is so close to the 8.1 (340 HP & 455 lbs. ft. of torque) that it makes me wonder if I can pick up similar power with these changes.

Thanks for the help

02 2500avalanche · September 12, 2003

Cliff, where did you see these rockers and are they specifically for the 8.1? Because the new generation big blocks have a lot more things that are different than the older ones.

Alex

Cliff1943 · September 16, 2003

Alex,

I called Crane Cams about the roller rockers after I read an article about the non adjustable rockers on the 8.1. The 7.4 HO crate engine also has the non adjustable rockers.

I am told by the cam boys that any big block rockers will work if the studs are changed. The new big blocks have a bolt that goes in the head. No adjustment to it.

By the way, I am NOT happy with my 8.1. I don't know if it is jut my engine or this is the way they are. It seems to take an awful lot of throttle to get this thing going. Thenif you back off it doesn't want to roll for squat.

Have you noticed that the 8.1 engine is rated at 330 HP instead of 340 for 2004. If my 2003 8.1 makes 340 (bare engine on a dyno) I would be shocked. I think GM has lied to their customers about this engine. I would never, never buy another one! If I could get rid of this truck without loosing my tail I would in a heart beat.

Cliff

CMNTMXR81 · September 16, 2003

Mine pulls like a freight train, roasts the tires readily and has no problem moving it's near 7,000lbs of mass. Enough to manage a 15.84 @ 86.54mph at that weight and with 60psi in the BFG A/T's.

So it's your engine, not the 8100 in general.

As to the ratings change I have a feeling this is GM manipulating the data for C.A.F.E. requirements more than anything and there ISN'T a power drop for '04.

Cliff1943 · September 17, 2003

To the guy with the great running 8.1.

Do you have headers? I keep looking for someone that has a set of headers and has tried roler rockers.

I still say the 8.1 is under powered for the size. Even if the engine makes 340 HP (I don't believe that for a nano second), that is only .685 HP per CI. In this day that is poor! Torque isn't any better when you figure it out.

Reducing the HP for the CAFE requirement isn't the reason. I worked for GM for 37 years. HP has nothing to do with CAFE. Lowering the HP is admitting the engine is underpowered.

I get so ticked when I get into my 2003 8.1 hunk of junk I just can't believe Chevrolet built this thing.

I also think the Allison sucks also. Mine down shifts when I am going down the freeway and have to tap the brakes. The Allison web site says this is the way it should work. What were the engineers smoking the day they decided to make the transmission do this in normal mode.

Glad you are happy with your truck. As you can tell I am not!

02 2500avalanche · September 17, 2003

Im sorry your not happy with your 8.1, but Im with CM, my 8.1 scares little kids and stikes fear in the dodge and ford boys. I just recieved my TOG headers today and will report at the end of the weekend as to how they perform. Cliff, do you have a specific part number for those studs? I would love to throw a set of comp cams pro magnum rockers, they are very nice as I have a set on my stroked 454.

Alex

tmf6902 · September 17, 2003

maybe it's a 2003 8.1 thing?????

Cliff1943 · September 18, 2003

Alex

I have the part number somewhere. If I can't find it tomorrow I will call Crane and get it again. The stud has a 10mm set of threads on the end that goes into the head. The other end has 7/16 threads just like the 454 studs. That is why any big block rocker can be used.

Are your headers long tube or shorties? I want torque out of my engine for pulling a 5th wheel.

On your 454. are the Comp Pro Magnum 1.7 or 1.8?

Thanks for the help.

Cliff

Cliff1943 · September 18, 2003

Alex,

Part number is 99155-16.

Go to http://www.off-road.com/chevy/reviews/cranecams_studs/

Hope this helps.

Cliff

montecarlo31 · September 18, 2003

Cliff,

Just wondering have you tried talking to your dealer about the problem? Have you checked to make sure it is all working right? Did you buy new or used? How many miles do you have? Also, the Allision is supposed to work that way, it saves brake wear and help reduce stopping power and distance when loaded. You should also note that this is a TRUCK transmission it is not built for speed and towing. I have drive more than 15 different 8.1s in anything from a suburban to a truck. I think you have something wrong or are expecting your truck to run 15's in the 1/4 mile from the factory while being able to tow 15K lbs. Not to be mean but just don't get on here and post I hate it I hate it and don't explain anything to anyone. If you give people some info here they could probably help you figure your problem out.

Cliff1943 · September 19, 2003

montecarlo

I understand that with the Allison in tow haul mode downshifting would be a good thing. I see no reason for it to down shift during normal driving. Tonight coming home it down shifted twice going down the same hill. Once when I lifted and tapped the brake, it then slowed down enough for me to hit the accelerator, then again when I lifted and tapped the brake the second time. This transmission will down shift if I am driving down the freeway, lift and tap the brake. I have been around cars all my life. I would rather put on new pads than have to have a transmission worked on. Besides, that wastes fuel.

I bought this truck new. It has 2,000 miles on it. My dealer is a little country dealer that hasn't had much to do with the 8.1 and the allison. Most of their truck sales are to farmers and they are 4X4's. If they don't buy a diesel they get the regular 6.0 engine. They didn't know much about the grade brake. The owners manual doesn't say a word about the grade brake. I complained that this truck acted like the brakes were on. It never occured to me that the transmission was downshifting until I saw a mention of grade logic on a travel trailer web site. Thats when I went to the Allison site and found out the darn thing can't be turned off.

Yes monte, I hate this truck. I wish I had never purchased it. I think the stylist/engineers are screwed up when they put a feature into a vehicle that caused useless shifting. They also put in a HVY RPO on a two wheel drive truck. I am 6-2. (My dealer had not sold a 2 wheel drive 2500 HD and had no idea it was this tall. They traded for this truck. I felt obligated to take it after they swapped for it.) This truck is a pain in the behind to get into. Now I have to get some type of running boards so my wife can get into it. I would have rather spent that money on a new handgun. Missouri finally passed a concealed carry law.

Are you a GM engineer?

02 2500avalanche · September 19, 2003

Thanks Cliff, My roller rockers have a 1.7 ratio and my headers are mid-lengths, no one makes true long tube headers for the 8.1 as far as I know.

Alex

Cliff1943 · September 20, 2003

Alex,

TOG headers? I haven't heard of these. Are they "The Other Guys" headers? If so where did you purchase them? They are pretty pricey. Good luck installing them. Please let me know how the installation went.

I really do want to like my truck. I have owned close to 40 GM cars & trucks. Almost all purchased new. I just think it should run better than it does with a advertised 340 HP & 455 lf ft of torque. I am going to take this thing to a dealer and get it checked out. Do you know how to disconnect the grade brake down shift when the transmission is in the normal mode. I can see absolutely no reason for it to work all the time. These are the things that really tick me off about a product. A switch wouldn't have cost very much to install. Then I could turn the downshift off when I don't have a load on the truck (about 90% of the time).

Cliff

miket · September 22, 2003

Hello new to the board:

I was under the impression hydraulic valve trains were non adjustable...

You can pickup some HP/Torque with the addition of a roller rocker...

I am interested to hear from anyone who may have played with this motor in the area of supercharging and /or reprogramming and cam upgardes.

I have had my 2500 'Burb for a few years now and haven't seen/felt a decrease in performance.

You do have to remember though that torque is what you really feel and the 8.1 has a good torque rating....there aren't alot of production motors out there developing that kind of torque...

Gilbert · October 28, 2003

Cliff, your not alone on your feelings about your 2003 8.1 GM. I too am pissed at GM for this thing. Sometimes I feel like I got a lemon. As a work horse, I can't complain. The truck pulls all day long. However, as a performace nut and engine tweaker, I find the 8.1 motor severely under power for an engine of this displacement. I would'nt mind the crappy gas mileage if I could get some serious horses. I don't think 450 to 500 normally aspirated Horse Power is asking to much of this motor.

After installing a pair of TOG headers, I found the 8.1 engine to be in need of some serious heads. I've installed a few other mods, but nothing worth writting home about.

I my search for some aftermarket heads I've checked every major manufacturer I know and no one has yet to produce some after market heads. From what I've heard/read Mercury's Marine division is the only big league player investigating this area. But all their development in this area is kept private. Forum member Americanmuscelman works for them, but can't say anything about Mercury's development. You gotta respect the dude, but d**n, feed me a cooky or something.......are you listening Americanmuscelman........