Vortec 7.4 or 8.1??

[lurch1980]

Hi Guys,

I'm looking to get a 3/4 ton suburban and I'm trying to decide between a 7.4 and a 8.1. I'm a little ways out from pulling the trigger but I thought I would ask you guys for some gathering info to make my decision.

I started reading through the massive Vortec 454 thread, but there were so many different things going on in that thread and I didn't make it all the way through it, so I apologize if this has already been covered before.

So here's the scoop.. I've about $8K to spend (selling my Jeep GC and some cash). I've seen some suburbans on CL with the 8.1 in my price range but they usually have pretty high miles (usually close to or above 200K). I've also seen a few 7.4 with lower miles (about 120K) for cheaper. The purpose for this is mainly to fit the family and for me to be comfortable while driving (I'm 6'6") so either engine will work for that, but occasionally I'll hook up my 16' flat bed with my lifted jeep (6000lbs+) and go to Moab. That means I'll travel I-70 through the mountains, which explains why I want a 3/4 ton big block and not a 1/2 ton small block.

So the questions..

1) Should I be worried of 120K on a 7.4 or 200K on a 8.1? (I know part of that depends on how well it was maintained)
2) If I have to or decide to overhaul a 7.4 can I match the 8.1 power (or better) and keep it reliable and driveable ?
3) If yes to #2 is it a cam, injectors, and tune, or am I looking at new heads and possibly forged bottom end internals?
4) Should I have any concerns about a 4L80E and towing that much weight?

and oh yeah, I really don't care about the body style, I guess if it came down to that I like the older body style a touch more.

Thanks for the insight in advance!

[Quyonmob]

8.1L is a beast compared to the 7.4L.

But, for what you want to do, the 7.4L will do it all day long.

[someotherguy]

1) Should I be worried of 120K on a 7.4 or 200K on a 8.1? (I know part of that depends on how well it was maintained)
2) If I have to or decide to overhaul a 7.4 can I match the 8.1 power (or better) and keep it reliable and driveable ?
3) If yes to #2 is it a cam, injectors, and tune, or am I looking at new heads and possibly forged bottom end internals?
4) Should I have any concerns about a 4L80E and towing that much weight?
120K isn't much on the 7.4; 200K is getting a little long in the tooth for any engine depending on maintenance/abuse. At least on the 8.1 you don't have to worry about a worn-out distributor. :D You could get a 200K 8.1 that might last another 100K without issue, or it could break tomorrow. One thing to watch out for and this is totally unsubstantiated, just repeating opinions/experiences from one guy that is in love with 8.1's - he says the first few years of them are the ones known for being a little problematic with oil consumption and other issues - http://3500hd.com/index.php?topic=260.msg1336#msg1336 - it's easier to believe this when you consider the guy isn't an 8.1-hater, he likes them, but has identified some apparent "problem years."

I don't think you'll easily build a reliable 7.4 that can truly compare to the 8.1, power-wise, but I could be wrong about that. I haven't personally done any kind of build-up on a Vortec 7.4 but I know several other members here have so hopefully they'll chime in.

The 4L80E should be just fine at that weight; they spec that same trans in the GMT400 3500HD's (15,000 lb GVWR truck) and they do fine. If the Suburbans you're looking at don't already have an auxiliary transmission cooler, you should install one, and any regular towing would benefit from a transmission temperature gauge.


8.1L is a beast compared to the 7.4L.

But, for what you want to do, the 7.4L will do it all day long.
Yes, and yes. :D

RIchard

[lurch1980]

Awesome, Thanks for the quick feedback! I'm still hoping that some guys that have hopped up the Vortec 7.4 will chime in.

Maybe I can't meet the 8.1 level, but I can probably do pretty well.
I guess there's always a HT502 crate motor option :cool:

[Miles B]

Everything I've read says that the 8.1 is another major change in the big block. That means even less old big block parts work. And that would include heads. I personally don't see you having a problem matching the 8.1 if you have some cash left over to work on the 7.4. I'm swapping to the 411 ECU, CNP, distributorless, and adding Brodix aluminum heads and a mercruiser cam. I know a guy with an '02 8.1 ECLB dually so when it's done I'm going to compare my '97 7.4 ECLB dually to his power-wise. I have very little doubt I'll best him.

If you buy the 7.4 truck, you're getting something with less miles on the clock, and enough power stock to do the job easily. With a little dough you can top the 8.1 IMHO too.

Of course if you buy the 8.1 truck, you're getting a truck that looks nicer, has more comfortable seats, and better brakes. All of that CAN be fixed with the dollar difference. I'd argue that a truck with 200k miles, you're looking at a major brake job soon anyway. I've bought '02 spindles, half shafts, calipers, rotors etc to upgrade my 7.4 to later model brakes.

So there are pluses and minuses both sides. I'd buy the truck that was in better shape and that you like better for the money. If you find a nice looking 8.1 with decent miles, go for it. If you find a 7.4 in great shape and you like the GMT400 look, well that's a great deal too.

[1998454]

Pulling 6k lbs is easy for either engine so don't make a decision based on towing. I personally like the old body better. My 4L80 has been used to tow well over 12k without issue. My 454 has headers, underdrive pulleys, cold air intake and a programmer and i would bet money that my truck can run with a stock 8.1. If you plan on mods in the future, i would go 454 just for the aftermarket parts availability.

[lurch1980]

Thanks!! I'm leaning towards the OBS 7.4 after reading these replies and looking some more on CL.

It seems I can get a better base truck for less then have some money left over to play with a few upgrades.

Now off to start looking up 7.4 parts!

[skills4lou]

7.4 is gonna need injectors/FPR if they haven't been done already. 98+ will have what's called the black box PCM, which has better support for tuning. Or as a few guys have done you can easily upgrade to the newer 0411 LS1 PCM.

Injectors can be had for less than $100 sometimes if you use takeouts. I bought new ones for $300. ($300 is the MOST you should spend on injectors).

[N0DIH]

Me, I want to go the other way, 427 Vortec. 454 L29 with a 4" stroke crank in it. More of trying to be different and build for hp and not as much for torque, let it spin some rpms if needed, but shoot for a bit smaller CID and build for high flow in the heads.

Even a 366 would be sorta fun to do too in a small block truck like a 1500 Burb/Tahoe or Silverado/Sierra.

[1998454]

a 427 has a 3.75 doesn't it?

[N0DIH]

Yup, I think you are right, sorry about that!



Mar 4th, 00, 09:02 PM


396 is 4.094 bore 3.76 stroke
400 is 4.125 bore 3.76 stroke.
427 is 4.250 bore 3.76 stroke.
454 is 4.250 bore 4.00 stroke.
495 is 4.440 bore 4.00 stroke.
510 is 4.500 bore 4.00 stroke.


The 366 is a 3.935 x 3.76 stroke.

a 427 has a 3.75 doesn't it?