anyone care to explain why they go to an I6 and why it makes so much more torque.


seems like having such a along block is a packaging issue and having a crank/cam so long causes even more strength issues

 

i asked on a supra board about the advantages of an I6 other than engine bay room..........once i sorted out all the retarded 16 year olds saying "because supras 0wn j00"..........i remember something about I6's having great balance, and something about components being directly driven......and other things i forget

hopefully someone here has some specifics

 

An inline 6 doesn't make more torque than an equivalent bore/stroke/flow V6. The I6 has advantages and disadvantages.
Many of them are cost related:

7 main bearings (I6) 4 main bearings (V6) More support for the crank. This means you should be able to cram lots of boost into it.

Long crank (I6) short, stiff crank (V6), but the 7 mains support the I6 very well.

Inherently balanced (I6), very unbalanced (90 degree V6).

For DOHC: 2 cams (I6) 4 cams (V6): BIG cost savings for I6

1 head (I6) 2 heads (V6)

easy packaging in long hood RWD car/truck (I6)
easy packaging in transverse FWD application(V6)

I6 is easily convertible to I5 or I4 for smaller displacements and common parts. That's tough on V6. (Volkswagen VR5 is about the only one I know of, and VR series isn't a conventional V configuration)

A good example of a modern I6 is the GM Vortec 4200 (256 in^3).
275 hp @ 6000/ 275 lb-ft @3600 with a very flat torque curve (90% of max torque from converter stall to about WOT upshift point).

There is the I5 version 3500 (214 in^3) for the new small pickups, and a 2800 I4 (170 in^3) probably coming. This is a low cost way to build a family of engines for trucks compared to 4 cyl and V6 combinations used by others. At 65+ hp/L and lb-ft per liter, it's better than the standard Vette or Camaro SS, 4.8, 5.3 and 6.0 LS1, and equal to the Northstar Cadillac. Unfortunately, externally it's not a pretty engine, so you don't see many swapped into street rods. Too bad.

A current high-end I6 is the BMW M3. Where the GM 4200 is relatively simple, the M3 a 3.2L (198 in^3) super-techno engine with 333 hp @7900 and 262 lb-ft @ 4900. That's over 104 hp/L and 81 lb-ft /L. At that hp/l level, there would be a 590 hp Corvette LS1! That's hard to do for an OEM engine and keep it below 6500.

This engine is probably one of the most expensive OEM engines today in initial cost, and in warranty costs, but it's a flagship engine. FWIW, it will be interesting to see how the Cadillac CTS-V with the LS6 (400/400) engine runs against the slightly smaller M3.

My $.02

 

would i be correct in saying engine configuration (V vs I vs W) has negligable effects on power/torque production?


If this is true, why do most inlines seem to be so much "better" than V's?

Also are there issues with the crank/cams twisting at high rpms? Althought I have never worked on a traditional SBC, didn't racers have complaints that the cam would twist a few degrees and effect timing by a few degrees?? If so what rpm levels and power levels are we talking aout here?

You would think the I6 would have these issues as well, no?

 

IMHO I think more R&D has gone into the I6s in the past. Just look at what they were put into, the Supra, 3&5 series BMWs and Skylines are all expensive cars. That to me shows the companies have done a lot of R&D. The newer I6s (for the most part) are variations of those older designs.
The way I figure it is that back in the 80s when cars had to be cheap and efficient the majority of car manufacturers figured "a V6 is a V8-2 cyls". Therefore they reused R&D from the V8s.

* I could be wrong but this is my take on things. (logically speaking )

 

SBC drove oilpump and distributor from rear of cam which drives from the front. Really dumb for high output engine, but from a packaging standpoint and economy of manufacture in mid 1950's when it came out it was fine. LS1 finally eliminated those problems.

Generally older Inlines drove distributor from middle of cam or near front. With modern ignitions and oil pumps in the accessory drive, that's not an issue. Sure, longer cams may twist a little more, but that's easily fixed with size/stiffness.

 

The #1 thing i was going to say was the strenght of the bottom end, but someone beat me to it.



The supra shortblock can handle 1,000hp+ stock, but only has 2 bolt mains. Pretty crazy

 

Yep. An individual cylinder doesn't really care where it's neighbor is located; it just wants air and fuel. You can go build a radial if that's what fits.


Who says they're better? Sure, there's lots of strong Supras and Skylines out there, but last time I checked the Buick TR guys weren't whining about the configuration of their 6 cylinders. Cosworth got well over 1000 HP from their 1.5 L V6 F1 engine.

The biggest problem with building a stout V6 is simply finding a stout production motor to use as a starting point. Almost any modern V6 is engineered to the point where they're as light and small as possible, so there's simply not much there to work with.

 

I see this figure thrown around the internet from time to time. Is it true, or is it just an internet myth?

 

its amazingly true.............there are quite a few supras peaking between 700-900 rwhp on the stock bottom end, sometimes never even opening up the engine(with race gas and high boost)..........thats about 1000 at the flywheel/crank

 

Actually I have quite a few friends running supras with ~700rwhp. They all have told me that supras stock long block is good till about 800-850rwhp before you hit a wall and its time to start changing cams and porting the head. But bottom line, yes they are pretty well built motors.

 

On the Supra bottom end.

Yeah they are strong, 700hp on any stock bottom end will break. One thing that you notice with Supra guys is the lack of room to work that thing out. The best comment I ever heard was that "we can't find a dyno around here for that guy to race his Supra on." They are fast and very powerful but you rarely ever see them driven so hard at that high power level. Which leads to my point. A 700hp NA V8 is going to need all the strong parts that it can handle because the power is always there. A 700hp Supra or higher is up there with a good amount of boost and only will see that with race gas in the tank. That's the problem, it never gets the constant loads on it because the guy has to run race fuel in it all the time to see them.

On the other hand if I owned one, it would be beaten daily and probably would break. Some guys are just hard on things just out of habit, some are hard on them out of stupidity. Once you watch circle track guys not shift out of 1st gear untill 8500 on a 7000rpm race motor you start to understand what stupid hard on things is. Beaten daily is a gearhead thing to do.

Marc and Eric Kozeluh (the two twins on Super 2NR TV) have some good knowledge with Supra motors. Even they recomend that a 700-750hp will need a bottom end. Then when you get one that far 1000hp is not out of the question. I'm not saying you can't run insane rwhp on a stock bottom end, but just like guys running stupid power in LT1 blocks it only has so long of a shelf life.

Gotta like Supra's for some reasons. Me I'd rather not have a car that I don't drive to keep miles off of it. I've met a couple Supra guys who keep the cars at home because of that. With the times F-Body guys are getting out of street cars and some of the sick RWHP why would you want a Supra? Hell for that money I'd rather have a C5.

Bret

 

bret.........i agree with you for a lot of what you said.............but down in south florida..........there are quite a few high horsepower supra guys that drive their cars very hard, and go out street racing with race gas and super high boost................no internal engine problems at all

its just a very very very well built engine from the factory

 

No doubt, I know most of the guys up here a felines.

One day they will break, it's a better bottom end than a LT1 based one that's for sure. A LS1 is pretty dam strong too, i've yet to see a stock crank break. They will at one point though.

Bret

 

i havent really heard of any lt1 cranks breaking................what is the weakest link in the lt1 bottom end?.............ive heard its the rods or rod bolts..........then after that the pistons

i guess not to many people bother finding out, since once its all apart, its just so easy to do a stroker with all new internals anyway.