The Stovebolt Site Forums The Shop Area The HiPo Shop How strong could one make a GMC 379Ci Big V-6 ?

The shop that rebuilt my 379 V6, that had a magnum conversion.

got an 8.6:1 C/R out of it engine dynoed an impressive 175hp & 388tq.

What if it had a 500cfm 2bbl ? or 10:1 C/R ?

larger camshaft n bigger valves ect . . .

Mike

The big sixes had serious balance issues, so be very careful about hotrodding them. I worked at a machine shop some time ago where we sort of specialized in keeping some older GMC's running for companies that wanted to nurse a few more miles out of these oldtimers. We found that unless some pretty strict weight-matching was done on rotating assemblies, they would break crankshafts and have other catastrophic failures. The higher compression might make a little more torque, but it would demand increased-octane fuel, and lots of it! A carburetor upgrade and/or porting or valve work would allow more RPM, which would result in the engine launching parts in all directions in a hurry. Exceeding the rated RPM on the big six was a death sentence to every one I ever worked with. These things are low-RPM torque monsters with a huge appetite for fuel, and hotrod tricks just don't work on them!
Jerry

Dynoed:
175hp@3,400rpm & 388tq@1,800rpm.

Mods;
7.5:1 C/R bumped up to 8.6:1 C/R.

Mag head & intake.

So it's pretty much set up as strong as it'll safely go ?

Would i gain anything by swapping up to the 500cfm 2bbl ?

or

adding a duel exhaust system ?

Mike

It might pull a little stronger with duals, but I believe you'd have to do some pretty extensive intake and/or port mods to take advantage of the bigger carb. Even then, you'd have to be very careful not to over-rev it with the extra flow capability. I've got a 351 engine in a 1960 GMC American LaFrance fire truck, but it's way down on the project list behind some smaller stovebolts. It runs a really tiny Stromberg 2-barrel, and it seems to be plenty of carburetor for that engine.
Jerry

Is a toro-flow block or crank any better or different than the gas version?
What I'm getting at is can you improve the gas engine (strength) by swapping the gas specific parts over to a diesel block?

Grigg

Same engine, swap the plugs with injectors, swap the dist with an Injector pump. increase the compression from 7.5:1 to 17.5:1 you got a Toro Flow . . .

305-478 V6's 637 V8 could be had either as gas or diesel.

trouble was the torque increased but the horse power went to pot so the Gas version was more sought after . . .

I'm sure even the 702 V-12 could be converted to a diesel if you wanted . . .

Mike

Actually, the GM Training Center engineer I talked with about that conversion told me the only parts that will swap between the Toro-Flow and the gas engine are sheet metal items like the valve covers and the oil pan. None of the major parts are interchangeable, including the block.
Jerry

well anywho, my truck is K3000 and "hotrodding" is none of my concern . . .

i was hopping to replace the SM-420 with an NV4500 i would like it to be able to pull the OD about as strong as it pull's the DD now.

cruising 62.5mph@3,000rpm gets boring, I'd rather be running 65mph@2,500rpm 70mph@2,750rpm 75mph@3,000rpm . . . would be nicer . . .

Mike

Based on those numbers I'd say build your truck around taking advantage of the torque and ignoring the horsepower.

Torque is what moves you.

I do think I'd be a little disappointed by less than 200 horse from a motor that big, but 3,400 is on the slow side for big horsepower numbers and I don't think you want to turn this motor fast enough to change that.

It's not bad for a V-6 gas engine.

My 6.2L V-6 NA Gas engine turns 175hp@3,400rpm & 388tq@1,800rpm.

My 6.5L V-8 turbo diesel only turns 190hp@3,600rpm & 380tq@2,750rpm.

So considering it giving a V-8 turbo diesel that is 33 years newer a run for it's money isn't to bad . . . but when ya figure in the 6.5 being the laughing stock of the turbo diesel world hard telling where this Gasser really rates.

But V-6 gas engine tows 22,000lbs of payload all day long no trouble at all only loses 7mph climbing the steepest of hill's . . .

The V-8 Turbo diesel struggles to tow 4,500lbs . . . 6,000lbs is the absolute max it'll tow and its a real interesting ride . . .

Mike

Ditto on the torque! I believe that 1800 RPM torque peak is just begging for a little taller gear to let the engine grunt a little. Just don't lug it down enough to let it start detonating- - - -that will melt pistons in a hurry. If you can find a medium-sized Brown-Lipe auxiliary transmission and turn that 4-speed into a 12-speed, that would give you all sorts of gear ratio choices. Being able to split every gear up or down, plus a direct-drive choice gives a medium-duty truck all kinds of options for load-pulling and top end speed.
Jerry

1. I have yet to see this engine detonate or rather ping burning 93octane fuel that i run in it.

2. All of that 12 spd slit box bla bla crap sound's really cool, but i'm not interested, if i wanted a million gearing options and 2 stick transmission i'd have a B61T or M123 MACK.

Sound's like Insanity for a glorified dually truck, the thing is no larger then a pickup truck its actually 1.5ft shorter then my standard issue Reg Cab Reg Box K2500, tho center of axle to center of axle its 9" further apart prolly why it out maneuvers my pickup truck in the woods. . .


I would rather swap the SM420 for an NV4500 and call it good enough, i have 5.13 gear's & 19.5's i don't 10 low range gear's just an OD is plenty . . .

Mike

I guess the advantage of this gas powered V-6 is that it performs like a Diesel except for the fuel consumption...

I don't know how your 6.5 is geared, but I wonder if it would perform better if the torque peak were lower in the RPM range.

It's just another failed attempt at GM trying to build a diesel . . .

factory gearing has it cruising 65mph@2,500rpm in OD 4.10 gears & 30" tires.

Truck is real gutless doggy slow sluggish puke, that is also very unreliable only reason the diesel is still around is because i owe money on it other wise that 6.5 would have replaced by now 22 failed parts in 15 break downs over 18 months.

shame too only got 139K miles on it body is in awesome shape too boot . . .

I dug my little 88' Comanche out the weed's after sitting 5 years tossed on the road been a great truck performs flawlessly. . .

GM can build gas engines they can't build diesels period !

I'm a big fan of AMC's & GMC's my first GMC failure was diesel go figure . . .

I'll never ever never OWN a second GM diesel powered truck.

Mike

Friend of mine hauls apples with a Dodge tandem axle and a swapped 378 V6 with a 13 speed Roadranger.
Last season he said mileage was 2-3 MPG average for loaded to the plant and empty to the orchard.
I'll have to ask the weight again, but it was as much or a little more than a tandem axle truck can legally haul, it's got a pretty long flat bed and they stack the bins.

A 378 will haul most anything with the right gears and plenty of fuel....

On one of the Cadillac boards there is a guy who has replaced a couple of those 6.2 and 6.5 Diesels with Cadillac 472 and 500 motors. Better mileage and better performance than the Diesel. He sounds very happy with the swap.

The lowest year for horsepower and torque on those motors is a bit more horsepower and similar torque to the 379 V-6. They can get a lot stronger but are limited by a weak valve train. They don't turn much past 4500 without serious investment.

If I were I Diesel guy I might go with the current GM Diesel. Everyone I know who has a Duramax is pretty happy with it.

I'm not sure,but I think the Duramax is made by Isuzu, I could be wrong.

I know a couple of people with them and they seem to be happy with them. 27Capital has one. Maybe he will chime in.

That is true, somewhat. Isuzu did design it, but GM does tha manufacturing. And since GM owns Isuzu anyway, well, it still works out as a GM design engine.

The duramax still has a few issues here and there but at least it actually makes some diesel power first D-max was 300hp & 520tq . . . topped out at about 365hp & 650tq last i heard . . .

I don't much care that few issue they had where warranty repaired and quickly solved, still not worth it to me . . .

The Duramax & Power Stroke been duking it out for #2 for years, but the Cummins still seems to outperform . . .

Mike

I'll stick to my gasoline powered V-8s!

Good idea by far better then any V-8 Diesel that's for sure . . .

I personally try to avoid Detroit diesel's high reving slightly doggy SOB's known to leak gallons of oil, little did i know i was smacked dab involved with an F'in Detroit puke box diesel again tho this one don't leak but it also don't have any power !

My GMC V-6 out performs my V-8 turbo charged diesel routinely, heck its given my 454's a run for there money in pulling power . . . It certainly out lived them that is for sure

379/6 = 63.167 x 8 = 505.33.

So my 379Ci V-6 is the same as having a 505Ci V-8 !

I'll take my Big Block V-6 over most Small Block V-8's any day . . .

I'll take a Cummins diesel anyday weather its a 3.9L I-4 or 19.0L I-6.

Mike

If it eases your mind any the 6.2 and 6.5 GM diesels are NOT Detroit Diesels.
You can blame GM directly for them and leave Detroit out of it.

I've got a whole bunch of Detroit Diesel literature, manuals, spec sheets, advertisements, data books.. and so on, a few shelves on the book case full. And not once in all of that is a 6.2 or a 6.5 General Motors diesel mentioned.

Grigg

Either way, i have 6.5-T and i'm not impressed with it . . . But its a financed Rig so part of the fleet it shall remain . . .

Anywho, back in track . . .

so the few Mod's that where done to my 379 V6 in the past are about all that can be done to it ?

Its NOT struggling for power by any means its got plenty, but i don't want to swap out my 4sod for a 5spd and find out it won't pull the OD like the DD.

Mike