low torque and high torque motors

[Kevin M]

Howard,

You make a very good point about the brakes. One of the bonuses you get by going to wider tires is that it forces you to use 17” wheels because you can’t get wide DOT legal rubber for smaller wheels anymore.

The nice byproduct of this is that you have room to run 13” brakes instead of the 11½” brakes that you are stuck with on 15” wheels.

Your mention of bikes is also a very good comparison. As I’m sure you know, the 600cc bikes will lap a racetrack within a second or so of the 1,000cc bikes, and on a tight, technical course will often beat them in spite of a large difference in horsepower. And in the case of the bikes, the weight difference is only 10 to 15 lbs, so it is not because they are a lot lighter. It is strictly because they are more agile from the smaller gyroscopic effect of their cranks.

Kevin

 

[Dave Wharran]

Kevin,
Yes, I'm running Gulf flairs.
245/16 tires on the front. 335/17 on the rears.
I'd have to measure the bars. They are ERA's standard size.
I like the aluminum flywheel. Other than allowing the engine to rev/decel a little faster, you wouldn't know it was aluminum. Very good street manners. The flywheel/clutch/pressure plate are all McLeod. Very smooth engagement although pedal pressure is a bit stiff. You don't seem to notice once underway. /ubbthreads/images/graemlins/grin.gif
Dave

 

[Howard Jones]

Kevin, Most of the time the 125cc machines would be running faster laps at the end of a race than the big bikes. This was because they don't have the power to burn off the rear tire halfway thru a race. Rear tire management is the single most important factor in winning a race on a roadrace bike. The other reason the little guys are so fast is weight. A small bike is, or at least was, about 20-30lbs lighter than a big one. The rider isn't contantly saving it and getting more tired and the power can be applied more at will than on a 100hp bike. The big power requires a sort of roll on and roll off and here again braking is enhanced by the fact that the little guys can go in a lot deeper AND a lot longer. Races are won by the total time it takes to complete a given number of laps, not the fastest lap out of 25 or 50 for that matter.

How does this relate to big power motors, 600HP or more, in a GT40? I am of the opinion that a carefully though out 375hp car with VERY good brakes and wide race rubber along with a good chassis setup would be a lot more fun to drive lap after lap than a tailswapping monster that the driver is constantly worried about breaking the gearbox, clutch, and halfshafts,etc not to mention his neck. Having said that I have never raced anything and NOT wanted more power. Go figure.

 

[Knighton]

In your opinion, what is the best motor/hp/tq combo between the high and low torque (power) options or ranges?

 

[Knighton]

In your opinion, what is the best/ideal streetable motor/hp/tq combo between the high and low torque (power) options or ranges?

A 342/347 stroker with 450hp and 400 lbs-ft with peak torque under 4000 rpm?

 

[Knighton]

In your opinion, what is the best/ideal streetable motor/hp/tq combo between the high and low torque (power) options or ranges?

A 342/347 stroker with 450hp and 400 lbs-ft with peak torque under 4000 rpm running sticky 335/17 rubber?

 

[Kevin M]

My pick would be slightly different. Take the same 3.4” stroke crank that you would use for a 347 and put it in a Dart Aluminum block with the 4.125” Bore.

This will give you a 363 in a 302 size block and 80 lbs less weight. (It will cost you $2,000 to $3,000 more than an iron block).

With AFR 185 heads and the right parts, it will make right about 500hp with a redline of about 6,200 to 6,300 rpm and the rev limiter set at 6,500.

It would use a hydraulic roller cam, be quite reliable, and have plenty of torque for street driving.

This is in fact the motor I am leaning toward building at this point. I will probably use a Pierce manifold and 4 Weber 48 IDAs. (This is very close to the largest motor you could run webers on without starting to loose horsepower).

A lot of people like the MoTeC fuel injection, and it is certainly nice, but it costs about $7,000 and that same money will buy the Webers and the aluminum block, which I think will make a much bigger difference because less weight helps everything the car does and not just the acceleration.

As a side note, I should say that I will use an RBT ZF box and plan to run either 315 or 335 rear tires. I will try Michelin Pilot Sports, but I am prepared to run Kumho V700s on the street if I find it necessary to handle the power output. (I would definitely consider this too much engine with smaller, harder rear tires or an Audi transaxle.)

I should also mention that the car will see both street and track use (Willow Springs, a very fast track). I would consider this too much motor for a pure street car. There I would use a 347 and probably hold it to about 450 hp with torque peaking at somewhat lower RPMs.

I am very interested to hear what other people decided on, how it worked out, and what they would do differently with the advantage of hindsight.

Kevin

 

[Knighton]

Interesting selection Kevin. You are looking at around 425 lbs-ft with those numbers. Any idea where peak torque would be?

I don't recall which motor uses a bit of oil, the 342 or 347?

 

[Kevin M]

In most motors of this type, peak torque will be 1,500 to 1,800 rpm below peak HP. The exact amount depending on if the motor is designed for a broad torque band at the expense of peak power or the opposite. (In the case of the motor I described, probably 4,600 to 4,800 rpm).

The difference between the 342 and 347 is that the 342 is what you get with a new block that doesn’t have to be overbored, and 347 is with a .030” overbore to clean up a used block.

The issue of oil use is because most people building these motors use a 5.400” rod (because it is easy to get and because everyone else does). Unfortunately, it puts the hole for the wrist pin into the oil ring land leaving part of the ring unsupported. That is what causes the oil control problems.

There are 2 solutions to that. The best one is to get your reciprocating assembly from Coast High Performance. They’ve had special 5.315” rods made that keep the wrist pin out of the oil ring land. The second answer is to use pistons from Ross. They use a special heavy “ring” that goes under the oil ring and acts as a support bridge for it. Both approaches will work, although I like Coast’s solution better myself.

 

[James]

Like this thread!

My angle. I wanted everything flat torque, good power and high reving.

The result?

Ford SVO block
Stroker kit to 331ci
Vctr Jnr Heads
All the lovely expensive internals.
Motec M48/Jenvey Throttle bodies.

The dyno figures:

RPM torque BHP
3400 358 232
4000 377 287
4500 414 355
5000 414 393
5500 404 423
6000 378 432
6600 357 449
6800 324 420

Soft Redline is set at 6700RPM.

With over 400lb's & over 400HP at 5500RPM she should fly.

Car should weigh in at 2200lbs or less.

Interestingly my engine builder has based it on the "magic chevy 328ci". i.e the best compromise with power and torque. Seems to have worked very well.

I might be tempted to put some slightly taller trumpets on the throttle bodies, at present they are very short.

Regards,

J.P

 

[Knighton]

JP,

I like those numbers. Will acceleration fall off at 6000 seeing as torque is falling off at that speed?

Are you running a ZF?

What size rubber out back?

I see you have a Motec. Will you set up traction control and all the sensors to make it work?

I am looking into an MDA. I will send you a pm in the next day or two.

Cheers,

Knighton

 

[Kevin M]

I had a thought (rare occurrence, not to be taken lightly) about this whole issue of motor sizing.

I would like to suggest a somewhat different way of deciding on size.

When we talk size we mean stroke, since everything from a 289 to a 408 has the same bore.

What I was thinking, is to select the maximum RPM you want the motor to turn, and then let that select the stroke for you based on normally accepted strain values for the bottom end.

As an example: Let’s say we want to turn 7,000 rpm. We plan to use all 4340 forged bottom end pieces and either a stud girdle or a 4-bolt block.

With these pieces we can certainly accept average piston speeds of 4,000 FPM as safe. (We could go as high as 4,500 FPM if we want to push things some.)

So we would take the 4,000 FPM piston speed, Multiply by 6 (a Constant), and divide by
7,000 (our max RPMs). This gives us a stroke of 3.43”. The closest crank we have actually available would be 3.4”, so that means that a 347 would be the optimum choice for a 7,000 rpm redline if we want to hold piston speed to 4,000 FPM.

In the above example, anything less than a 3.4” crank would be throwing away essentially free horsepower and torque.

For a 6,500-RPM engine (about as high as you would want to go with a hydraulic roller cam) we come up with a 3.69” stroke. The nearest available crank would be a 3.75” so now we find that a 383 built in a 351 block would be our optimum motor for these RPMs.

What do you think?

I am looking forward to hearing people’s thoughts on this approach and suggestions for other approaches.

Kevin

 

[Steve Toner]

Found this article which gives a little more info on piston speed & RPM limits. For a stock cast crank, use 3500 FPM.

 

[Mark Worthington]

Oh boy, now we need to talk about rod ratio and side loads.

 

[James]

Knighton,

I'm running with a Quaiff modified Renault box and Quaif LSD.

Rubber? I don't wear rubber, I usually like to wear leather. It has a better feel on the skin. /ubbthreads/images/graemlins/blush.gif

Regards,

J.P

P.S 255/50 R16 - Have a look under the recent posts for tyre sizes.

 

[Kevin M]

Mark,

I do hope you mean that in jest. The whole “Long Rod” thing has become something of the current fad and doesn’t make nearly as much difference as some people make it out to.

Although, from the sound of it, JP could probably work the “long rod” part in fairly well with the bit about rubber vs. leather, don’t you think?

Kevin

 

[Ron Earp]

There was a very nice technical article in MM&FF some years ago about rod ratios and long rod motors and torque. I wish I'd saved it. The net result, it doesn't make much difference, if any.

 

[Ian K]

Man, now you guys are going to make me dig out all my stuff
about piston speeds, L/R ratios, valve train wear, etc.

Ron, I think I have the reprints of that article. It was about
building a 351W long rod. If it is, the verdict was it was a
vast improvement. Mostly because the breathing in a 351W is
not that great since the intake manifold is "squashed". Of
course, they did more than fit longer rods, they also offset
the piston slightly. This allowed for more time in full
compression, as well as reducing the moment of inertia during
downstroke. By shaving the heads a little (they used TFS Twisted
Wedge S), they got 11:1 comp, and broke 400HP on 87 octane.

I'll dig it up as well and share all the main points if anyone
cares.

Ian

 

[Kevin M]

11 to 1 compression on 87 octane? That thing either had a very long cam or they did something unusual with it.

 

[Steve Toner]

Maybe it made 400 HP right before it broke because they were using 87 octane? /ubbthreads/images/graemlins/tongue.gif