The Stovebolt Site Forums The Shop Area Engine Shop straight 6

yeah i was wondering, what is the strongest straight six engine around? and which is the strogest i can put(easily)in my ad truck? i have a 250 in it right now. yeah pain in the arse to put in. real messy. is it all that much stronger than a 235? thanx murdoc

I'm pretty sure that most of the Jimmy guys will quickly tell you that a 302 GMC inline six would be the way to go. I can't remember if we've got anything here in tech tips, but you might want to take a peek in the technical section at chevytrucks.org. I know they have some reading on the GMC-into-Chevy swap there. Hope this helps.

Regards,
Wannabe

A 292 would be your best bet, in my opinion. Sure a 302 would probably produce slightly more hp and torque (I've never seen the stock specs for the 302 so I wouldn't know). But the 292 is much more plentiful than the 302, and probably has equal, if not greater, high end output potential. And the 292 has a more rugged bottom end (7 main bearings vs. 4 for the 302). Plus you have a near endless number of transmission combinations you can run behind the 292 (TH350, TH400, 700R4, M21, T5, T10, Saginaw, etc., etc.) without modifications.

Here are some more factors to consider:

The newest 302s are older than the oldest 292s. 292s ran from '63 to '90 so the latter 292s are just over a decade old. The 292s can also be bought as a new longblock from GM, and many of your auto supply stores (Advance Auto, NAPA, CarQuest) can still get 292 longblocks and shortblocks easily.

No knocks against the 302. I hear it's a great, very strong engine. But the 292 is simply more plentiful, much lighter in weight, has a modern oiling system and 7 main bearings. And hop up components are easier to find.

-ftyler

Cummins Diesel I6 would be pretty strong........ but ease of installation may be another thing.

I have heard of a guy in southern Alberta who put a Cummins Diesel in a Chev pickup. The best of both worlds.

Hey guys, if this dude already has a 250 in it, wouldn't a 292 drop right in for that?

No, the 292 has staggered motor mounts. Not quite a drop-in, but probably a lot less work than converting back to the front/rear motor mounts of the earlier I6 engines.

I saw a Cummins in a 1-ton AD at a show last summer. Didn't get a photo. I'll get one if he returns this summer.

I saw a cummins in a GMC 1-1/2 ton that had been converted to a motor home. I even have pictures! In fact the guy came to the local heritage fair two years in a row and my wife claims I took the same shots two years in a row :rolleyes:

There is a 4bt (3.9L) used in bread trucks which would be much easier to install (the 6b is 1k lbs). Apparently it also has a chevy bellhousing bolt pattern giving more tranny choices. If you can't find 302s, you aren't looking in the right spots. Contact me if you need help. As far as the 292 being stronger JUST because it has 7 main bearings, try to keep things in perspective: the BB cheby only has 5 main bearings and is utilized to get much more HP. Has lower end strength ever really been a factor in the GMCs? Especially in the range most of you guys are going to run it?

Comparing the number of main bearings between an I6 and a V8 doesn't work - the I6's crank is much longer, and therefore needs more support. However, it is a decent point of comparison between two I6 engines, and there is a reason that when the L22 was designed in the early 60s, it had a much larger number of main bearings than the two engine designes that came before (Chevy 216/235/etc. and GMC 228/248/etc.).

Murdoc,

Here's a high tech contender (if ya' believe the marketing guys!)

Chevy 4200 Vortec

[img]http://www.oldgmctrucks.com/photos/gmcsmilie.gif[/img] 302

Well I'm partial to the 302 but there's really no fair comparison to the newer motors...Yes it has only 4 mains, but the motors survive in 7-second drag cars and 250 MPH lakes racers with a big nitro load. It's a heavy, strong engine and though it won't make the top end power and RPM of a well-built 292 (not to mention the F**D 300 L6) it will hold it's own if not exceed the torque of any similar size engine, 6 cyl or otherwise. It's a vintage motor, no question, and that's part of the appeal for many of us. I personally think the 230 and 250 are some of the smoothest and sweetest domestic inlines made, but the new 4.2 L6 Vortec is one sweet motor - as it should be with DOHC and variable cam timing. I still dig the old school bus GMCs though.

Sixpack,

Well remembered the 300 F--D, did not want to break into this because could sound like an offense.

Jason,

This B 3.9L engine is being used a lot here in light trucks, quite reliable, but has that always present harshness and vibration particular to the bigger L4 diesel engines. The B5.9L L6 is by far and large a better option, although a little bigger and harder to install. But the huge amount of torque and the smoothness of the 6 is hard to ignore. Another very good option but I guess not available there would be the Mercedes 366, a turbo diesel L6 engine around the same size, weight and power of the 5.9B, only much cheaper to buy and maintain.

OlBlue,

Did You already see any Hot Rod with the 4200 Vortec? I'm curious about it!

I wish I saved the link, but not over 2-3 weeks ago there was a 40s Brockway tandem highway tractor with a Diamond Reo 450 ohv inline SIX on ebay. 450 cubic inches, can you imagine. Of course, I guess parts are unheard of. I think all the big truck makers had big gas 6-cylinders back then...Mack, Reo, IH, GMC.... :p Probably the 292 or 302 are the only realistic choices for a big gas six in your AD pickup. Good luck!

How about a nice BMW M3 engine? 333HP normally aspirated from a 7 main bearing small straight six. Drop in! Use the tranny and electronics too and all you need to make are mounts and a driveshaft.

Alexandre,

June 2000 HRM has a full tech analysis of the Vortec L6. We have reprint permission for the Inliners magazine, but it's 6 pages long and we haven't found the room yet.

On a tour of the Flint engine plant where these engines are made, I was told that 270 HP is a very mild state of tune for this engine. A version with variable intake cam timing is ready for production, should the market require it. Over 300 HP and 300 ft/lb normally aspirated. a 5-cylinder twin turbo version makes over 700 HP! But due to the tall height of the Vortec design, it will probably never be seen in a GM passenger car - it's for the truck platform only.

Hall Scott made 6 cylinder engines up to 1100 cubic inches,Continental made a 802 cube 6, these engines were generally used for pumps or generators. Mack offered a 707 cube gas inline six, I bet the engine weighs over 1200 lbs.
Yeah a BMW 6 is real nice,probably 5 grand used with the electronics? I once saw a hot rod using the old Jaguar DOHC inline 6,about 260 HP stock, nice vintage looking engine.Or a Toyota Supra had or has a real fine inline, again nasty expensive I bet.Mopar slant sludgers and AMC 6's can make good power.We have a 96 Cherokee, the 4.0 liter(old AMC design reworked by Mopar) inline makes 190 HP, I think you can get the engine ,5 speed and all the electronic stuff for around 2 grand from a recycler or adapt the injection to a GM inline?

Sixpack,

I haven't seen the HRM report, I read some time ago an analissy on PHR, sounded quite good, but would like to know some details like rod/stroke ratio, crank pins specs, rod specs, c-to-c, bearing width, etc... the whole engine looks quiote good and interesting.
I have a tendency to prefer the L6 over the V6 basically for a dinamic point of view, the L6 design is normally ballanced, no umbalances, no shakedowns or whatsoever to disturb them. The V6 is not this simple. And nowadays all big carmakers have changed from the in-line to the V desing. The big exception to this common place is BMW. And this new Vortec stovebolt is a good sight.