WWI Fighter Torque expectations.

[Von Writter]

Hi All;
I have had an engine built for my WWI German Fighter replica and I was wondering if some more knowledgable person than myself can give me a solid idea of how much more power I can expect from the motor (torque is the key here) from the modification I had done. They are as follows;

1 It is a 250cid. with 9.2/1 compression

2 It has a clifford port divider in the heads which have been ported and pollished with the larger SS valves installed.

3 a custom header with only about 4' of 2.5" exhaust pipe and a Dynaflow tube muffler and a CC insert.
Carb is a side draft Zenith carb, about 200cfm, but note this engine will not be reved over 3200 rpm!!! so that should be enough flow for the lower rpm requierments

4 The bottom end has a Comp cams 260H cam .440 lift, 260 deg @ .050 212/212 Lobe spread 110

5- the recipricating parts including the harmonic balancer and billit Aluminum flywheel hve been statically and dynamically (spin) ballanced.

6- All engine components except the castings are new.

Any idea how much more torque (gross) I will be able to realisticaly expect? I'm hoping for 300 at 3100 rpm. Is that to optimistic or pesimistic?
Any help will be very much appreciater.
Thanks;
Troy Wright.

 

[rickwrench]

I think a realistic figure would be in the 260ish range.
You should be able to run fully advanced using 100ll with your c/r.
An option for much more torque (+100ft lbs) would be to use an Eaton M90 from a T-bird supercoupe. With 9.2 compression AND 100ll you shouldn't have to worry about any ping @ 6 lbs of boost. Plus, you wouldn't lose much, in any, power at altitude. Easy intake plumbing too, do a draw through set up and replace the rear rotor bearings with sealed units.
Rick(wrench)

 

[Von Writter]

Hey Rick;
My Performance hand book lists the Gross torque of a 9:1 comp engine at 240 @ 1600rpm. So with all the "Improvements" I've done I'll only pick up about 20 ft lb. Torque?? Man that would be a very expensive 20!
Are you talking Gross or Net torque? I was talking Gross.
Troy.

 

[rickwrench]

The torque peak on the stock engine was at 1600rpm. The torque peak on your engine is probably around 2500?
At 3000 rpm, I'd bet you picked up more than 20-25ft lbs over the stock engine.
How will the engine handle inverted or negative G flight? Are you using an accusump or something similar?
Rick(wrench)

 

[Lazy JW]

At the risk of oversimplifying, torque is proportional to volumetric efficiency. At any given rpm you need to stuff in more air/fuel mixture to get more torque. Increasing compression helps somewhat and timing can be optimized when running avgas but the primary increase in torque has to come from burning more fuel (properly mixed with air, of course).

Volumetric efficiency on these engines runs around 65% in stock form. You will do well to hit 80% with your combination. This would give you about 295 lb/ft. Pretty optimistic, I think.

Joe

 

[Von Writter]

How will the engine handle inverted or negative G flight? Are you using an accusump or something similar?
Rick(wrench)[/quote]


Hey Rick, I won't be doing any negitive G or inverted flight so not a problem there, I'm baffelling the oil sump so I don't starve the engine on momentary -G pushovers.

 

[Von Writter]

Hey Joe, If I can get 265-270 I'll be as happy as a clam in mud! Are the Volumetric efficancys (or I should say "Deficiencys" ) as pronounced at lower (3000ish) RPMs I thought they only became a real problem above 3800-4000 rpm on these engines?
Troy.

At the risk of oversimplifying, torque is proportional to volumetric efficiency. At any given rpm you need to stuff in more air/fuel mixture to get more torque. Increasing compression helps somewhat and timing can be optimized when running avgas but the primary increase in torque has to come from burning more fuel (properly mixed with air, of course).

Volumetric efficiency on these engines runs around 65% in stock form. You will do well to hit 80% with your combination. This would give you about 295 lb/ft. Pretty optimistic, I think.

Joe

 

[Lazy JW]

The flow restrictions on these heads will get worse at higher speeds. That engine should pull like a tractor at the rpm range you will be running. I think you will be happy with it until Mike's aluminum head is available 8) Now THAT would be a sweet application
Joe

 

[Von Writter]

The original Mercedis was basically just that, a BIG tractor motor (900 cid or so) Now once the 250 goes through the PSRU it will be in the neighborhood of 590-640 ft lbs Torque! That should do the trick

The flow restrictions on these heads will get worse at higher speeds. That engine should pull like a tractor at the rpm range you will be running. I think you will be happy with it until Mike's aluminum head is available 8) Now THAT would be a sweet application
Joe

 

[Von Writter]

Is Mikes head almost ready? That would be really increadable!

The flow restrictions on these heads will get worse at higher speeds. That engine should pull like a tractor at the rpm range you will be running. I think you will be happy with it until Mike's aluminum head is available 8) Now THAT would be a sweet application
Joe

 

[Lazy JW]

Not sure how far away the heads are, you could check on his web site. There is a lot of interest here from the small-six folks, I believe he will sell quite a few.
Joe

 

[AzCoupe]

Were getting there. We had to make some changes to the patterns and core boxes after the first proto type was cast and inspected. That's been done and the second proto types are due to be cast and machined in the next week or two. They should be fine this time around, be we want to be sure. Once I have inspected the second one and am satisfied, I'll give the thumbs up on a production run. All the programing is done, so it shouldn't take long once the castings are done.

However, the intakes will lag behind a month or so as we needed to wait for a proto type before finallizing the intake runner designs. We are hoping to start on the pattern work sometime this month, which is the biggest delay. Once the patterns are done, the rest will follow pretty quickly.

I hope to have a fully machined proto type with me when we go to the Falcon Nationals in three weeks.

 

[Von Writter]

Cool, any better idea yet what "End user afordable" will be

Were getting there. We had to make some changes to the patterns and core boxes after the first proto type was cast and inspected. That's been done and the second proto types are due to be cast and machined in the next week or two. They should be fine this time around, be we want to be sure. Once I have inspected the second one and am satisfied, I'll give the thumbs up on a production run. All the programing is done, so it shouldn't take long once the castings are done.

However, the intakes will lag behind a month or so as we needed to wait for a proto type before finallizing the intake runner designs. We are hoping to start on the pattern work sometime this month, which is the biggest delay. Once the patterns are done, the rest will follow pretty quickly.

I hope to have a fully machined proto type with me when we go to the Falcon Nationals in three weeks.