Talkin Torque

[Tuna Van]

Comparing a Chevy 4.3 V6 with a Ford 5.0 V8 circa 1995

Horsepower for both engines is very similar - about 190-205, but I would think the V8 would make a significant more amount of torque down low. When looking at the specs for the automobile versions of these engines the
V6 appears to make around 260@2800 RPM and the V8 around
280@3300 RPM.

I can't find any data on the marine versions which I know would be different, but would that be about right? Does anyone have any dyno curves to compare these two? 20 lb-ft doesn't seem like a big difference, but I would like to see what the two are making at 2K RPM

 

[chiefalen]

Re: Talkin Torque

missing pieces size boat? Weight?

Or take the question literally and you just what the modern versions of BOTH.

OR the same year 85' 4.3 vs the 85 305 ? Both four barrels?

 

[QC]

Re: Talkin Torque

A better question is why do you care? Contrary to popular belief, propeller load curves do not require much torque at low speeds. This is why it is rarely published. The exception is a combination that struggles to plane, that is also propped properly and with the throttle wide open. If that is the concern, then you do indeed need more low end grunt. However, if the boat planes easily, then then only thing that will be important to you is horsepower. A lower weight combo can also shift this discussion. Peak torque (at any RPM) is never in play unless the throttle is wide open

 

[Tuna Van]

Re: Talkin Torque

I just want to compare the torque curves of a V6 and V8 making similar horsepower. I was really interested in 95's or close to that, since that is what I have. I know the more modern carbed 5.0s make about 220 horsepower, so I am not really interested in that info.

 

[Tuna Van]

Re: Talkin Torque

I thirst for knowledge QC. So a V6 and V8 making a similar amount of peak horsepower on the same boat will perform about the same? I am not taking about small differences. I mean SOTP.

 

[QC]

Re: Talkin Torque

Define "perform". At the low end I believe the weight benefit of the V6 may compensate for the slightly lower peak torque available, so again, if planing is not a serious concern, you won't notice. At the high end, IF the math is right (hp) and all other things are equal (they never are) then the V6 should be slightly faster top speed, also due to the lower weight.

I always chime in on these threads as the US auto industry (and some others) have confused the entire world about the relative value of torque. It IS extremely important, but less so with marine than most believe. Despite all of the hype, the truth is you can make anything go with enough horsepower and proper gearing. That is not true about torque, as it is a force, not work.

 

[Tuna Van]

Re: Talkin Torque

QC do you know how accurate the ratings of these engines were back then? I am guessing there was no SAE certification, but did a Chevy V6 back in 1995 really make the rated horsepower?

 

[QC]

Re: Talkin Torque

I believe in 1995 hp was already accurately reported at the propshaft. They also allow a 10% leeway though. I want to qualify one thing before I get the usual confusion regarding my torque blasphemy(s)

If all things are equal: weight, gearing, propeller, etc. etc. then the combo with the highest peak torque value will accelerate faster. This is why I ask what it is you want. If acceleration is important, then that changes the answer. Heck, I might want the V8 simply for the exhaust note . . .

 

[TilliamWe]

Re: Talkin Torque

If it wasn't such a problem to find manifolds and stuff for Ford engines, I'd take a 302 Ford over a 4.3 Chevy any day of the week and twice on Sundays.
Contrary to my friend QC, I'll say that a 302 would outperform the V6 throughout the rpm range. And of course the potential for even more horsepower, via camshaft/intake/exhaust modifications is way higher for a 302 Ford, than a 4.3 Chevy. But alas, the aftermarket performance parts market for those Fords, while plentiful, is higher priced than a Chevy.

 

[QC]

Re: Talkin Torque

I agree ^^^^ but I was thinking stock somewhere in there . . .

 

[chiefalen]

Re: Talkin Torque

Ah a ford man, now i understand 351w was used in boats many, many, moons ago.

But now a new day age age has begun, the beginning of the gm block.

As told down from history, it was known to have the ford motor in boats.

But now we talk in terms of 305, 350, 5.0, and 5.7 . Kapice?

 

[Tuna Van]

Re: Talkin Torque

What kind of gains can you get on a 302 with basic bolt ons? I am looking for more top end.

 

[QC]

Re: Talkin Torque

I'll let the performance guys comment on the bolt on stuff. The fact is that displacement allows for more air, which allows more fuel, which makes more torque, which when combined with RPM begets more horsepower, so if you want to build something to go faster, start with the bigger displacement block and you will be further ahead. Maintaining decent torque at higher RPM will result in the biggest top end gains. This is why the newer 6.2s at 5200 RPM are rated higher than older 454s. Enough displacement to make some torque, spin it faster and make more horsepower. The key is the high end, not 2000 RPM performance.

 

[Zackman]

Re: Talkin Torque

I Love this stuff.​

Let's get to an even more basic level...​

Force = Cylinder Pressure X Piston Surface Area (Bore)
Torque = Force X Stroke
Horsepower = Torque X rpm X constant​

So to increase the torque increase the pressure (e.g. more fuel, blower, turbo, etc), increase the piston area (e.g. bore) or increase the stroke.​

To increase the horespower, keeping the torque constant, just increase the speed.​

Of course they all have to work together.​

 

[Bondo]

Re: Talkin Torque

What kind of gains can you get on a 302 with basic bolt ons? I am looking for more top end.

Ayuh,...

A belt driven Blower otta get you a couple larger prop sizes, at the same WOT....

Forced Induction,.... is Imitation Displacement.....

 

[Silvertip]

Re: Talkin Torque

here is the torque/hp curves for the 4.3 GM V6. Sorry but I can't help you with the Ford but you can check the Chevy 305 in the same link. The 302 Ford and 305 Chevy should show very similar curves but keep in mind the automotive vs marine situation.

I've probably owned more of these GM V6's in trucks than the average guy and they are very stout engines and pull like mules. If you look carefully at the torque curve you will see it is pretty flat and about 90% of maximum at somewhere around 1500 - 1700 RPM and peaking at 268 at 4000 or so. If you want to get HP out of these things check the GM Performance Parts books. The parts are not what you want for a boat unless you want strictly upper end HP.

http://www.gm.com/experience/technology/gmpowertrain/engines/specialized/marine/2010_4300_Marine.pdf

 

[TilliamWe]

Re: Talkin Torque

What kind of gains can you get on a 302 with basic bolt ons? I am looking for more top end.

Well, starting in 1987 Mustang GT's 5.0 HO was rated at 225hp at 4500rpm and 300lb-fy of torque at 3200rpm. That was with the "truck style heads" a roller camshaft, and some very smallish tubular headers. yes a production car with factory tube headers. Later on, for the Cobras (in 1993 I believe) they switched to the GT40 lower intake manifold for some extra HP.
And since a Ford 302 has a 4" bore with a short 3" stroke, it can be made to rev. And it likes it, too. As far as specific cams and such, I don't know. We never modified our 1988 Mustang GT. It was plenty fast, and dangerous, for a 16 year old to be driving!

 

[TilliamWe]

Re: Talkin Torque

Sorry but I can't help you with the Ford but you can check the Chevy 305 in the same link. The 302 Ford and 305 Chevy should show very similar curves...

Other than being 8 cylinders and close in displacement, I highly doubt their torque curves are all that alike. Again due to the 4" bore and 3" stroke of the 302 vs the 3.74" bore and 3.48" stroke of a 305. Compared to a 302 Ford a 305 Chevy ain't crap. Just ask all those IROC Z-28 guys who got mauled by 5.0 Mustangs in the mid 80s!
(oh and by the way a 302 Ford or the 5.0 as they like to call it, is actually 4942cc, which is of course 4.9 liters. But since Ford's 300cid inline 6 truck engine is also 4.9 liters, Ford has always rounded up the 302 to 5.0)

 

[180shabah]

Re: Talkin Torque

Yup - 305's before the vortec heads were complete pigs

 

[Tuna Van]

Re: Talkin Torque

It seems to me that the Chevy 4.3 and Ford 5.0 back then make very similar numbers - maybe 10% more horsepower and torque for the 5.0. Has anyone compared these two on a similar boat and been able to notice a difference in hole shot or top speed?

I know in a car the difference would be apparent but not sure on a boat. I don't have any specific reason to know this, just wondering.