Blown Nitro: boost, compression, and percentage for small engines

[Anvil*]

Still chasing potential engines on paper but I find myself with a very large gap in my education and experience. I have no clue on running a small blown-fuel engine for five miles each way.  Five hundred cubic inches at 6.5:1 compression, 40 pounds boost, and 90% fuel, has a life measured in seconds. Not useful but an upper limit.

So for those with any experience with fuel and boost on engines under 1200cc, what mix of compression, boost, and percent fuel have made it both ways?

I am trying to get a feel for the workable region for a 750cc engine and may build a small twin to blow up test design concepts on next fall.

[willieworld]

anvil   im just up the road from you  if you build it i will run it in sheris or my bike sheris bike is a 500 cc buell blast mine is a 1000cc buell xb9  the 500 , 650,750 or 1000cc class would be fine ---sheri and i both hold the fuel records at el mirage and bonneville in our class  i also have extra motors for both bikes             willie buchta


the motors are 3.5 bore x 3.125 stroke  hers a single mine a twin   

and on the short course you only have to run 2 miles to get timed

[Anvil*]

I think the test engine is likely to be a bit small to push a Buel. The idea is to keep everthing as small as possible until a few ideas are proved out then build the 750. The gas version has a 2.32:1 bore:stroke ratio, 4 valve DOHC, gas springs, and designing for a 270 ft/sec intake port velocity. Running fuel is much closer to running a diesel. Lots of heat and pressure in more of a torque monster. At least for short durations the air seem more to cushion things during compression so the fuel doesn't hydraulic the heads off (IMO).
If I can't find more information I can start with a tiny slightly over-square single (or twin) and start at 15psi and 60%, add instrumentation, and see where it leads. I'm hoping for enough data points by asking to get a general feel for things first rather than taking such a long way around. There is a lot of experience running on the salt not found among books, SAE papers, or in any class of racing I've ever been around.

[Calkins]

I'm not sure if the Top Fuel Harleys and such are blown, but drag bikes might give you a baseline tune up.

[Anvil*]

> Top Fuel Harleys...

Only source I can think of in that direction is Duncan Keller over at Yankee Engineuity. It's worth the asking...

Now I wondering if Russ Collins is still involved with Sifton... (from early 70s) The story with that, I was building a 4-stroke short-track bike at the time. I think he would still talk to strangers if he's around still.

[Anvil*]

As an update it seems most of Sifton Cams (but not the name) is with Black Widow Cams and Russ Collins has RC Engineering still and is marketing electric fuel injectors. Seems Sifton was auctioned off March 21, 2001. Guess the two cams I still have are now rare memorabilia (I think Sifton only ground five track cams total for the CB350).

[Anvil*]

Still researching the topic but the weak area for what I'm designing seems to be pistons and rings. More heat over a longer percentage of the stroke, much more pressure, and washing the cylinder walls (lower lubrication and heat transfer). The two-minute piston is going to be different solution than the 8-second piston.

Also that running Nitro rich moves the design away from the big piston/ultrashort stroke gas setup (2nd motor design required).


Some reading to share found while searching:

Spud's Nitro Notes:  http://www.onehotchilipepper.com/nitro/
 

[wolcottjl]

Here is a little tidbit i have had saved for a while.  SAE paper - not fuel but a little more knowledge.  Motor was fairly reliable.

[Speed Limit 1000]

We ran NITRO in a 750 Honda interceptor motor. Carbs and NITRO not a good combo. Injection is almost a must. Base line 2 times the fuel, gas to alcohol, and I think 1% more for each % of NITRO.   Look for a oil that will stand up to all the blow by. It is really hard on parts.

[Seldom Seen Slim]

Joel:

That snowmobile study -- was done by the students at Michigan Tech, my alma mater.  I expect I could help you find out more if you'd like to dig further.  I know it was and SAE paper -- but the Toots (Tech slang fofr students there) have been taking part in that project for years.  I expect you could start researching at www.mtu.edu if you'd like to do so.

[Freud]

Les Ranger and Ted Gansberger ran blown nitro Honda engines. Ted ran a 750 and Les was 1000cc. Ganberger was just above 200 and Les was 208.
They are in the bay area and they ran in 1985  and 1988. Their records still stand.

FREUD

[wolcottjl]

I have the paper.  I sent a note to the professor listed.  See what I get back from him.  Just a search for knowledge. Might ask for help if I don't get a response.

[jl222]

 
 Anvil how much hp you want to make these guys are making awesome power on gas- turbos and intercoolers without the destruction of nitro and learning fuel curves.

  And as much power as their making the formula I tubo era guys were making over 1350 hp out of 1500ccs

    JL222

[Anvil*]

It's a see what she'll do exercise. With decent horsepower numbers I'll build a streamliner for it and come out to play. I did notice a real problem with the fuel and blown fuel records for the small engine classes, they are almost always slower. The first test bed will be just a single cylinder on the bench but the intent now is to use a CB350 case and transmission and make the crank, cylinders, and head for the 175cc twin. That I can toss in a frame and take to a cycle dyno. So yes I could just buy a bigger motor and racing bits and make horsepower to get to the salt sooner, but I won't learn as much along the way. Well and there is the challenge of designing pistons and rings that hold up.

Now as for how much horsepower... I can calculate the upper limits for each class but reality has a way keeping that a dashed line above where an engine will operate for the required duration. Normally-aspirated gas I'm used to. Fuel looks like will be more error and trial, but I'll read lots and meet people along the way. 

[Anvil*]

Wolcottjl / Seldom Seen Slim
I'll add that SAE paper to my list, but is was running octane and not nitro. Still, it looks a good read. Been ordering papers from SAE in batches about twice a month for some reason. 

Speed Limit 1000
Nitro with carbs is old school. It is a very dense fuel and balancing the jetting with the engine, air, and fuel temperatures, air density and moisture, and the vacuum draw of a carb is an art all its own. I imagine the artists working this craft are mostly over with the various flathead roadsters. Injection provides a very positive metering of the amount of bang in each ignition. Due to the small size pulsed-electronic injection looks like the easiest route for now. It's just too small for the usual pump and pills.

JL222
The small engines running boost have been hampered by how to adapt oversized hardware and then get the mismatched bits to run properly. You'll notice from the records the small boosted-engines have more trouble getting speed than their normally aspirated cousins. To run a turbocharger the impeller and turbine will have to be cut down and both the hot and cold housings redesigned. My engine models are not that far along yet, but yes a small turbo-gas engine is in the mix. The small blown-fuel motor is another problem in proper hardware.
Scaling your numbers would have just over 150Hp for the turbo-gas from 175cc. My numbers run about 40 Hp on gas, 100Hp for turbo-gas, possibly 75Hp on fuel, and the piston limits blown-fuel but 150Hp looks like the upper limit with a working piston design. I don't believe numbers like that have ever seen the salt in such a small engine. So until I build, dyno something and then actually run a vehicle for time, its still funny numbers of what should be possible.