Straight 6 vs. V 8

[Grey Wolf]

It has been said numerous times in this thread, it's because of the bigger lever arm

 

[DieselLady]

HBarlow, please don't be embarassed. I was the one who started this thread and everyone is putting out some great ideas. Yours are very thought provoking and make me think more about the whole concept. As far as the 90 degree positioning I think it makes for good thinking too. It's easy to envision the crank and connecting rods on an I6 and the angle that they push at. But with the V config it is harder to picture that because you have the pistons out at 90* and the conecting rods changing angles as the crank turns. This is tougher for me to envision. I am still suspicious that that could be part of the reason for the reduced torque but just speculation.

 

[DieselLady]

It has been said numerous times in this thread, it's because of the bigger lever arm

Hey Ken, So if it's just because of leverage why can't they put longer connecting rods on the V8 and make more torque?

 

[Grey Wolf]

I believe it (TQ) also has to due with the rotational mass and the size of the crank which gives it the leverage along with the longer rods. Unfortunately for me I was never much of a math person so I can't really explain the Physics of this question, however the principal I see in my head

 

[TTfordcummins]

They could put a longer stroke on a v8 and get more torque. But then you'r piston would be to small. So you would have to put bigger pistons in and up goes you'r C. I. D.

and down goes you'r milage. but other than econamy I think it could be done

 

[Vaughn MacKenzie]

So does this mean that and I6 and a V6 of the same displacement and stroke will produce the same amount of torque at the same RPM? I was always under the assumtion that the I6 would do better.

DieselLady I6 engines almost always have a longer stroke because V engines need a short stroke to keep them from being too wide to fit easily in the engine bay.



On 8-cylinder engines it makes no difference if it's a V8 or straight 8 like in my '40 Buick. The firing pulses are every 90 degrees regardless. Just like a V6 and I6 firing pulses are every 120 degrees crank rotation. Unless you're talking about an oddfire V6 but we won't go there :-laf



More cylinders mean a smoother engine, however an inline 6 is inherently more balanced than a V8 because everything moves along the same plane.



The amount of torque is more dependent on bore and stroke than number of cylinders. More stroke gives you more torque, more bores gives you more horses.



Vaughn

 

[cojhl2]

Plug for the I6,, almost all OTR trucks are straight 6's.

 

[Vaughn MacKenzie]

All right since I brought up the oddfire V6 I had to check into it. This goofy engine with 90* cylinder banks and 60* throw crankshaft results in pulses at 108 & 132 degrees crank rotation. So a cylinder fires, crank goes 108 deg, cylinder fires, crank goes 132 deg, fires, goes 108 deg . . . you get it, every other one. So it's



fire1 - 108* - fire2 - 132* - fire 3 - 108* - fire4 - 132* - fire5 -108* fire6 - 132*

 

[Joe G.]

One thing to consider is the RPM you are running the engine at. We run our Cummins at the maximum torque and HP range. Most of the time with a V8 you are running them way below the max points. Another thing is the HP is a derived number using torque and RPM as factors in the equation. Torque is where the power is. HP is some math applied to torque.

 

[PSchwering]

All right since I brought up the oddfire V6 I had to check into it. This goofy engine with 90* cylinder banks and 60* throw crankshaft results in pulses at 108 & 132 degrees crank rotation. So a cylinder fires, crank goes 108 deg, cylinder fires, crank goes 132 deg, fires, goes 108 deg . . . you get it, every other one. So it's



fire1 - 108* - fire2 - 132* - fire 3 - 108* - fire4 - 132* - fire5 -108* fire6 - 132*

Wouldn't this be applicable to any V-engine, where the crankshaft has 1 throw for two cylinders? I alway thought that this was a serious limitation to V-block design - with a 90 degree V, TDC for the front two cylinders will be 90 degrees apart. Obviously, if you made a crankshaft with a seperate throw for each cylinder, this would not apply, but most V engine cranks I have seen have 1 throw for two rods. I am going to have to study this... . P

 

[JUeckert]

HA! yeah I know this with the 6. 0's!!! I had a a little race car, like a mini F1 car in a medium size trailer (20 feet?). . new truck work at the time had 3000 miles on it. No more then 4000 pounds with tools and trailer and car I'm sure.



6 speed transmission, and since like I said before, it's new, at one light the truck wouldn't slip into 1st easly, but would into 2nd, I even gave it a little extra RPM but the motor fell on it's face and stalled after rolling about 1 foot.



This is something I would easly do with the 3500 dodges!!! Even the SO 03 could just MOVE.



Never pulled anything with the duramax, but did cruise around town with one for a weekend before buying a new truck.



I obviously picked the dodge.

jason,you sure you were putting the ford in to 2nd gear as marked on the gear shift?

 

[JasonCzerak]

This is EXACTLY why I do not understand the thinking of Jeep, who is dumping the 4. 0L inline 6 for the 3. 7L v-6 in the '07 Wrangler!! Go smaller AND with less torque? In a vehicle that is designed to USE torque? I do not understand. The only SAVIOR to the Jeep Wrangler will be the diesel WITH A MANUAL TRANSMISSION. They had better offer it or the Wrangler will become just another gutless pavement pounder/grocery getter like the Liberty. whose highlight is the diesel option.

No more XJ, The 06 Grand Cherrokee I think doesn't offer and I6 for the low end motor anymore, The only reason the Wrangler is still around is becuase of the Liberty and Grand Cherrokee sell so much, they compasate for the losses the Wranger has.



So, it makes business sence to drop the I6 all together. Plus smog and other things contribute to that.



The Wranger is just like the Vette, Corvette does not make GM any money, it's just an icon for selling. I think they come close to breaking even. The Wrangler is a historic design and off roader, it will be around as so long as the rest of hte jeep line supports it.

 

[JasonCzerak]

jason,you sure you were putting the ford in to 2nd gear as marked on the gear shift?

NO, second as in the next fowardward gear, the ZF has creaper down from reverse, so as it's marked I stalled the truck in 1st. not "L"



Sorry for the confusion.

 

[DieselLady]

Wouldn't this be applicable to any V-engine, where the crankshaft has 1 throw for two cylinders? I alway thought that this was a serious limitation to V-block design - with a 90 degree V, TDC for the front two cylinders will be 90 degrees apart. Obviously, if you made a crankshaft with a seperate throw for each cylinder, this would not apply, but most V engine cranks I have seen have 1 throw for two rods. I am going to have to study this... . P

Okay heres another dumb question. What do you mean by Throw exactly? Is that where 2 rods share the same arm on the crank???? Can you do that?

Maybe I should clear up the original question too. Lets compare a V6 to a Straight 6 with the same displacement and same RPM and for the sake of comparing apples to apples the same stroke. Will the I6 still produce more torque or not? I am beginning to think that it just boils down to configuration and nothing else.

 

[HRDROKN]

Another thing to consider... . a I6 has less internal friction than a V8

 

[Joe G.]

The original reason for the V configuration was engine length. A V8 will fit in almost the same engine room as a I4.

 

[JasonCzerak]

The original reason for the V configuration was engine length. A V8 will fit in almost the same engine room as a I4.

Yeah, just look at the Auid S4's V8 that's shoehorned in that car.

 

[Joe G.]

I have also read some discussions on engine configurations. According to what I read, Ferdinand Prosche considered the I6 as the 2nd best engine configuration. Naturally smooth with plenty of torque. I read what he said about it, but don't have it now. His best choice was the boxer six like used in his air cooled sports cars.

 

[nps]

Stroke produces torque. Bigger stroke and the I config also produces a heavier, longer crank, which aids in torque. However it is not practical to consider a V and I config with the same stroke. Vaughn said it before - the V config with the I stroke would be too big to fit under the hood. There may also be some physical limits with making a V bottom end capable of handling the I config's stroke.



Theoretically if a V and I config had the same number of pistons, bore and stroke, the I would still put out more torque due to the longer, heavier crank.

 

[Grizzly]

Does the longer crank of the I6 help develop more torque then a V8 shorter crank?

Another question. The Ford gasser V10 seems to be a popular engine on class B motorhomes. The total displacement size is not particularly big, that means that the bore and stroke must be small. What does that do to the torque?