Technical Getting a 2000 RPM Torque Peak

I have a ton of engine building questions for a project that would probably be considered off-topic, but the engine itself will be very HAMB friendly, so hopefully this thread isn't too offensive.

I would like to get into WWI replica aircraft and have been scheming and day dreaming about building an SE5a replica for ages. The big factor that makes aircraft engines different from car engines is that propellers decrease in efficiency as speed increases. This is why RPM (and by extension most horsepower) is basically useless in aircraft. The Se5a was equipped with a lot of slightly different engines, but the most common was the Wolseley Viper. These 102 year old engines made 550 lb/ft of torque at 2000 rpm! The best way to make a replica is to find an original engine, but period engines are suuuuuuper expensive. As you can imagine, this is a really low budget project, so originality is definitely not an option. The second option is sticking in a Lycoming or Continental in it, but I really don’t want to sink $8000.00 into a used engine and I don’t really want an air cooled engine anyway (an SE5a just isn’t without a water cooled V8). What a lot of people do is use a small displacement engine and a reduction drive, but I’ve always loved old engines that lope along at low RPM.

One day it struck me that I could just build the perfect engine! I am a bit partial to the Pontiac V8 and they just so happen to be the perfect weight. The biggest crank I can find is 4.725 ” from Ohio Crankshaft for a 400 block. This gives a displacement of about 518. I could use direct drive and an authentic, loping sound!!

So to sum it all up, I need to get a Pontiac 400 that’s been stroked to 518 to make a torque peak of 550 lb/ft at 2000 RPM (which is 200 HP). I want to make sure I am making educated decisions and eliminate as much guesswork as I can. I really want to avoid killing low end torque with a dumb mistake, so I appreciate the advice!

1. I would really like to use aluminum heads, but the smallest one that I can find has an intake volume of 204cc. I am almost certain that this is too big and I’m worried that it would kill torque and throttle response on an engine that never revs past 2000 RPM. From calculators that I have found online, I think 150cc is much more ideal with this displacement and RPM. I just so happen to have a set of 1955 Pontiac 287 heads that are 150cc. One thing to note is that both the 287 and this theoretical engine are rated at 200 HP. Maybe the ideal intake volume is directly related to horsepower? What do you think I should use? Saving 20 lbs would be nice, but I have enough wiggle room that I can use iron heads if I need to.



2. According to the ideal carburetor formula that is all over the internet I need a 300 CFM carburator. This seems way too small to me. There was an article in Super Chevy that saw significant performance increases with carburetors bigger than this formula predicts. The formula seems to leave a lot of meat on the bone. My gut tells me that 600 CFM is what a 200 HP motor needs. What do you think is right?



3. This engine would require a huge combustion chamber of around 135cc to maintain 9:1 compression if I remember right…..could I use negative piston to deck height to do this?



4. CAM SPECS…….ARGH!!!! This is the aspect of engines that I am least comfortable with by far! I’m sure cam choice will be a huge factor in moving the torque peak where I need it, but I have little experience in this area. I think an ideal cam would have a really tight lobe seperation angle, but a really short duration to reduce overlap. My limited understanding is that low lift increases velocity and is good for my application. Is 5 degrees of cam advance a good idea? Do you have guesses for what the specs on a 2000 RPM cam would look like?



Thanks a million! I really appreciate the advice!



May your horsepower be high and your temperatures be low,

-Falcon H

 

You are going to need custom pistons so why not get them made for the appropriate compression ratio? If you are running on Avgas you can go fairly high. The 300CFM recommendation must reflect the low RPM use. I would go with a stock 2 barrel intake and carb or, why not fuel injection?Small valve heads should also suit this build.

A 518 cu in engine will pump the same amount of air at 2000 RPM as a 260 cu in at 4000. That sounds awful close to a stock 1955 Pontiac. Your 55 Pontiac heads, intake and cam may be just what you need. With straight exhaust pipes of course.

For a cam you might want to talk to a cam grinder and see if they have anything. Your requirements are similar to an industrial engine made to run at a constant RPM and make max power low in the rev range.