volumetric efficiency, hp and torque from a dyno test

[Jesse Lackman]

This might be interesting.

Here is a graph that shows horsepower, torque, and volumetric efficiency from an actual dyno test of a 360 IMCA Dodge. Hughs HEV4550, 12.5-1 compression ratio, Holley 700cfm, Edelbrock Victor 340, ported smog heads, and Amoco Ultimate.

(The correction standard used is J1349 add 5% to torque and hp for a J607 comparison)

I wonder if volumetric efficiency is influenced most by intake manifold, header, head flow, and cam tuning. I don't know if the torque CURVE is really tied to volumetric efficiency except in the general way of better volumetric efficiency = better cylinder fill = more torque.

On this engine the static compression (cranking compression test psi) was 160-170 psi even though the compression ratio was 12.5-1. This is because of the cam. Now if I would raise the compression ratio to where the static compression would be 200+psi (and this was the only change), obviously the torque would be up across the entire curve. But would the volumetric efficiency change? If so why?

Just food for thought.

<IMG SRC="http://www.wrtc.com/rvsrchjl/255c.GIF" BORDER=3>

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[340king]

So how are things up nort?

I see you are running the Victor intake and had the Strip Dominator for sale on Ebay. Did the Victor work that much better?

I have a suspicion that the torque and VE curves are one in the same in a lot of respects. I did however see that your VE did not drop off as predicted by my dyno simulation programs in the ranges above 5500 rpm. I assumed that the TQ and VE curves would match closer in that region than the test results show.

VE can be influenced by bore to stroke ratios also. This is evidenced by pro-stock teams using blocks that allow huge bore spacings to get bigger bores with less stroke. This allows a more favorable VE combo within 500 cubes.

I would guess that a 340 with similar components would VE higher than the 360 did. Its bore to stroke ratio is better for VE in my opinion.

If you could magically reach a higher compression in an engine without increasing or changing the timing of cylinder pressure cycles, then yes I believe that you could increase the level of the torque without changing the VE. I don't however think this is really possible given the complexities of the air/pressure cycles in an engine. Trying to isolate the incoming air from any influence the increased cylinder pressure has on it is almost impossible.

I prefer using heads with better low lift flow, to using the 1.6:1 ratio rockers for improving the VE of the 360 engine at low lift. I am currently running 360 high swirl heads that flow over 200 cfm at .300" lift. This is with a 1.94" intake valve and normal seat angles. The engine really runs well, although I have not had it on the dyno for real numbers. I saw the Hughes cam and assumed you had been introduced to their way of thinking. The longer the stroke, the more critical the low lift flow is in an engine when considering VE.

You have a good thought provoking question and I look forward to following this thread.

[sanborn]

The torque curve is greatly influenced by the ability of the cylinder heads to breathe. Our W8 heads carry the torque peak to a much higher rpm. As our torque peak is reached the VE is essentially at peak. As torque declines the VE declines although the slope of the VE is flatter. I think Jesse's curve would reflect the same thing if his heads were really high flow.

Secondly, low lift flow is very critical for long stroke engines especially with limited heads. On short stroke limited head engines, long rods are very helpful(up to 6.7" for a 3.31" stroke). The torque and horsepower improvements are impressive. Long rod, long stroke combinations have a lot of torque and sometimes are hard to hook on an oval track.

[Jesse Lackman]

We found 450 hp hard to hook in IMCA Mod. The driver liked the 400 hp engine much better. This was in a Chrysler tortion bar front, full frame chassis. It had 120" wheelbase and since the engine is placed 79" ahead of the rear end centerline the rear percentage was real good. This car was heavy and for this year a light car (also a homebuilt chassis) is going together and will be powered by a 3.9L V-6 Dodge. We'll see.

Yes the Victor is better. Mainly it is more even on egts. The Holley likes no carb spacers, and short (30") header primary tubes. The Victor likes 2+" carb spacers and 38+" header primary tubes. Weird. The 450 hp engine had the Victor because the 180 degree crossover headers I built for the car were impossible to make shorter than 38".

The flow testing I have done is on the small Superflow that pulls 9". To get the flow at 28" a conversion must be done. I've heard that isn't so accurate. (And that flow numbers done on different benches shouldn't really be compared.) I'm working on the V-6 heads right now. Isn't low lift flow mostly affected by the seat and valves (angles) rather than the ports? If not what is the secret, 340 King? (I told you the Victor is better!!! HA HA) Hughs never told me anything about long stroke and low lift flow. But wouldn't good low lift flow be desireable for any engine? Or is low lift flow less when high lift flow is good? The advantage I see in the Hughs HEV cams is the quick opening of the valve, you are going to get more flow per degree of crank rotation with a quick ramp cam. The V-6 has a roller cam - even better!

Sanborn, what do longer rods do to the torque peak rpm?

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[This message has been edited by Jesse Lackman (edited April 08, 2000).]

[sanborn]

The long rods raised the torque curve but did not extend the peak torque rpm at all. I think the breathing ability of the cylinder heads has the greatest effect on peak torque rpm.

Connecting rod length is just one of those tools that a good engine builder has in their tool bag. Long rods are not always the answer. You only use them if you need the result. For example, our second engine will use short rods to kill some torque for these short, slick, southern dirt tracks in July-
October.

[JoeD]

Why do torque and horsepower curves always cross at 5250? Does it have something to do with the equation used to derive horsepower or just some weird quirk of nature?

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[Jesse Lackman]

hp = torque x rpm / 5252

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[340king]

Jesse, I think that there are no secrets in racing. Rather there are just superior combinations. We use the Ferrea Pro-Flow valves in my engines exclusively. I have found that they make the most consistent flow for the money. The low lift flow is really great with this valve profile. The cost is not IMCA compatible, thankfully I run Wissota.

A friendof mine had his best luck in IMCA trim with lower compression engines. I would like to try a 318 with decent heads. I just wish somebody would make a nice cost effective piston for one. I think they would be an awesome IMCA engine. A buddy of mine ran one in what is now my car down in Oklahoma. It had custom Probe pistons, ported W-2's, Roller cam and a direct drive 904. He said it was too wild. It would bog up to 4,500 rpm and then just fry the tires, hitting 8,000 rpm in the process.

I would not worry about converting flow numbers to 28" either. Most of my heads flow well enough to require measurements at 10" and converting up to 28". I have had the same head flow tested at two different shops, at two different elevations, on two different benches and the numbers nearly matched. I think that you can compare them as long as the testing is done with special care in accounting for all atmospheric conditions during the test. Otherwise, the numbers are worthless.

What type of rear suspension are you planning to use? I have recently been enlightened by an experience at the practice track during a light rain/snow storm. I was practicing in IMCA trim. By the way, when is Ivan going to open the track(s) for practice?

[SB Racer]

Last autumn David Reher said on his National Dragster column that they have found out that Bore to stroke ratios aren't that important at all??? He surely knows his business so at least I was surprised.

TeRo http://www.angelfire.com/mo/racevaliant

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[Jesse Lackman]

340King,
Have you seen the stock valves on the Magnum heads? They are small stem and there is no ski jump at all. I will be using the stock valves on the V-6. It has Magnum style heads.I don't know when Ivan is opening the tracks. Here is a web site for the Bismarck-Mandan tracks; http://www.kbmr.com/BRaceway.htm

I talked to the guy who is building the new IMCA mod this weekend. He and the driver had it on scales and it is light. He is the chassis man, I am the engine man, and someone else is the driver. I will say that with the V-6 at 275 hp the pounds per hp ratio will be better than the old car.

The rear suspension is "rear trailing arms"(from a Packard, I think) with a transverse leaf spring. I hear this trailing arms setup is similar to what the NASCAR cars use.

Do you ever race up here?

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[This message has been edited by Jesse Lackman (edited April 10, 2000).]

[340king]

SB Racer, I cannot speak to the article by the respected engine builder or what he was referencing, but from what little I have seen the bore to stroke ratio is important. It all has to do with friction horsepower and where that friction loss occurs in the rpm band. The 360 engine for instance has a much larger friction HP loss at rpm's over 5500. That is why the power of the listed 360 engine failed to continue to climb while the VE was still over 100%. In a 340, you would have to reach about 6500 rpm to get to the same friction loss. This is due to the differing strokes and the parasitic losses the longer stroke produces.

The best way to think of this is by looking at the angle the rod makes with the cylinder wall. With everything staying the same except stroke, the longer stroke crank swings farther away from the bore center line causing the rod to make a larger angle. Since the rod is a two force member, it has bearings on each end and can transmit forces along its centerline only, the increase in angle causes more force to be exerted on the cylinder wall. This is friction. As the stroke is increased this friction also increases. It goes up with the square of the rpm or some other squared factor rather than being linear. Much over 6500 and the 360 is consuming over 150 hp in friction. I still think the ratio is important, but I am not building Pro-Stock engines either.

Jesse, no I haven't raced up there yet. I would like to sometime this year. The engine in my car used to belong to John Gartner. It was an internally balanced 360 until the rear crank throw split into three pieces. I had to replace the crank and go back to external balance last year.

You may be on to something though. The guy that my friend bought the car from ran a 302 Ford in the car with good success. My friend ran it until the powerglide expired for the second time and went back to Mopar power. He said the 302 was light, low on torque and really fast on dry slick.

[billyclub]

When talking about frictional losses, don't forget the 360 has a larger main journal diameter. more bearing= more friction

[sanborn]

This chat topic is wandering everywhere so let add my $.02 worth. I'm an oval track racer so I tend to look where the Winston Cup engine builders are going. They are going toward the largest bore/shortest stroke possible(within the rules). Bearing sizes for race engines are generally 2.250" mains and 2.000" rods. Qualifying engines use 1.880"(Honda) rods. Don't try this with stock type cranks. Bore/stroke and bearing size must impact horsepower.

[shannon]

Anohter factor that causes a 360 to peak at a lower rpm than a 340 is the rod sweep. The rod in a 360 has to travel farther per rpm than that of a 340. This means that the 360 rod has more inertia than the 340 rod, which does not have to travel far. As the rpm's increase the 360 rods bob weight increases more quickly than the 340 rods bobweight due to the longer stroke. The result is an engine that peaks lower (but has more low end torque due to the long stroke) and has more of a tendency to throw a rod (due the the increased inertia)