How many 8.1L/496's out there?

[83GMCK2500]

I dug around a little and I swear I've read most of DirtyLarry's 8.1 posts, have yet to find the answers I am seeking.

My DD, Vortec 7400 powered, love it, am looking into some upgrades for it. I get that heads/intake/block all have different bolt hole locations, bolt patterns, etc, nothing interchangeable there with other engines(excluding classic bellhousing pattern). One of the upgrades I'm researching is coil-over-plug ignition, another is headers...they are slim pickings for GMT-400 7.4 powered trucks.

- Will 8.1 exhaust manifolds/aftermarket headers bolt to a Gen VI? If so, recommended brand/model, or is there a nice high flowing factory manifold?
- Do 8.1 valve covers bolt to Gen VI heads?
- Does the 8.1 timing cover bolt to my Gen VI?

[DirtyLarry]

Originally Posted by 83GMCK2500

I dug around a little and I swear I've read most of DirtyLarry's 8.1 posts, have yet to find the answers I am seeking.

My DD, Vortec 7400 powered, love it, am looking into some upgrades for it. I get that heads/intake/block all have different bolt hole locations, bolt patterns, etc, nothing interchangeable there with other engines(excluding classic bellhousing pattern). One of the upgrades I'm researching is coil-over-plug ignition, another is headers...they are slim pickings for GMT-400 7.4 powered trucks.


Coil on plug did exist on a somewhat rare L21 7.4L used in GM medium duty trucks. I believe this engine was only used from 1998 to 2000. Many people get this engine confused with an 8.1L because the coils are on the valve cover. I’ve personally only seen 1 L21 7.4L in person. L21's are easy to spot once you look for the throttle body on the side of the intake instead of in the front like an 8.1L. The L21 also has a huge cam sensor where the distributor would be and were the ONLY 7.4L to have electronic throttle.





- Will 8.1 exhaust manifolds/aftermarket headers bolt to a Gen VI? If so, recommended brand/model, or is there a nice high flowing factory manifold?
All older BB (396, 366, 402, 454, 502) exhaust manifolds and headers will interchange with the 8.1L. I run a pair of 1980's motorhome 454 exhaust manifolds on my 8.1L, as I am not a believer in headers on a driver. In all reality, there is nothing special about 8.1L exhaust manifolds that would benefit an older BB. Below is a picture of the various BB heads I had laying around a few years ago where you can see the intake port differences and exhaust port similarities. Even though the exhaust port sizes are different the exhaust manifolds are the same size




- Do 8.1 valve covers bolt to Gen VI heads?
Yes and no. Yes, it is the same dimension but the 8.1L valve cover depth is very shallow due to the taller heads. The 8.1L valve covers would bolt on to older BB but there would be no room for valve springs and rocker arms.

- Does the 8.1 timing cover bolt to my Gen VI?

No the timing covers are entirely different

[83GMCK2500]

DirtyLarry, you are the man! Thank you very much for the information. Yes, I first came across the L21s in the GM Electronic Parts Catalog (that is where I started thinking it might be possible for me to get C-O-P on my L29), my research shows them to be C-O-P in 1999 & 2000, carrying the RPOs L21 & LP4. In 1998 the EPC shows, 366 (LS0) & 427 (LR0) V8s with distributors...I would presume them to be the fuelie versions of the classic tall deck BBCs.

From what I can tell I need one of the L21 cam sensors, crank sensor, and reluctor wheel. Don't remember, might need L21 timing cover. I am bundling this with an 0411 PCM swap, btw.

Looks like I'm on the hunt for some 2-year only valve covers, sweet, I love rare parts.

[LEEVON]

I just picked up a 2002 2500HD crew cab with the 8.1L/Allison. So far, I'm very impressed with the combo.

[MalibuSSwagon]

I just bought a 2002 GMC Dually with the 8.1L/Allison. Needs a little work (crank sensor broken off in the block) but I got a screaming deal and it only has 59k miles. I bought it for the engine to put in my C10 but the truck is too good to trash, I'm going to fix it and re-sell it. I have my eye on a Yukon XL with an 8.1 that I may buy for a tow rig.

[jocko]

Now how on earth did I miss THIS thread??
Here's my 2001 2500HD 8.1/Allison. A little over 13k mi. I gotta dump those steps. Wish Kodiak still made there retractable steps. Thinking of the shortened AMP steps that some members have show pictures of, but I'm kinda cheap...

[jgr]

Love my truck 60,000 miles very clean!

[Texasdeere]

Hey Guys,

Just picked up one of these 8.1 Trucks!

I have a question. Does this engine have factory roller lifters?

Thanks