low percentage nitro/alky mix to be used with a CARB

[alkyal]

I realize this is mostly an FI site, however I need to run 10-15 percent nitro/alky mix to keep up with the Jonses Dont know if the engine will tolerate a higher % mix]. If the carb is jetted correctly for 100% alky, Would you lean/SMALLER main Jet for the 15% mix. I ask this based on your article on low % nitro in a FI system. This is a small engine that uses a float chamber/float bowl below the main jet. The fuel is drawn UP thru the jet via an E-tube that protrudes into the carb Venturi, thus drawing the fuel into the air flow stream. Any suggestions are appreciated. I will run this engine on a Dyno first. I cant measure an air into the engine, but I can Measure EGT and record. On 100% alky, I try to run a Max EGT of 1080-1140 deg. F Thanks Al

[dreracecar]

Nitro carries its own 02 so the everything in the carb has to be bigger,  with FI the "JET" is what gets returned back to the tank and changes fuel pressure to the nozzles, the smaller the jet the less that gets returned and the system becomes richer, likewise the larger the jet, the more that gets returned back to the tank and the system gets leaner.

 One problem I see is that weather the gaskets, o-rings and seals are compatible with nitro

[alkyal]

So far, up to 11% we have had no gasket or O-ring issues. We flush all with a pure gas-lube mix @ the end of the race day. The carbs have been modified to run Methanol. I realize the nitro carries extra 02. And that an addle amount of ignition timing is required. In reading Spuds Nitro notes [unless I am missing the point] He says that low % of nitro [believe up to 30%] dont require any fuel system changes.Additionally it would seem the system will provide a RICH mixture with low % mixes? Thats how I read it. So in my case The carb may be rich enough for our 20% max mix.20% is a self imposed limit due to structual limits of the Basic engine. Have a Forged piston and Alum Rod. Low C/R approx 10:1 currently. Have a good fuel system and only on full open for 4 secs or so on Straight section. Thoughts?  Al

[jeff/21]

Is this for an oval track car? if your EGT is 1140 and you have 100 jets adding nitro will make it leaner so the jets will have to be drilled or removed completely and are the passages in the carb big enough to carry the extra fuel?

[ricardo1967]

I don't have my own experience to share, but the Stromberg 97's on flathead Fords prove that it can be done.

[alkyal]

Its on an oval track Kart,  little less than 1/8 mile.paved. Would LOVE to speak with someone who has/had experience building those Stromberg carbs back in the day. I cant find anyone anymore that can give me direct answers to the carb-nitro questions. Any help is appreciated.These are 25 cu.in. OHV engines that produce approx 30 hp on straight Alky alone with a 10:1 C/R. Only looking to run the low % to get that last 5+ hp without over-stressing the engine.

[ricardo1967]

Its on an oval track Kart,  little less than 1/8 mile.paved. Would LOVE to speak with someone who has/had experience building those Stromberg carbs back in the day. I cant find anyone anymore that can give me direct answers to the carb-nitro questions. Any help is appreciated.These are 25 cu.in. OHV engines that produce approx 30 hp on straight Alky alone with a 10:1 C/R. Only looking to run the low % to get that last 5+ hp without over-stressing the engine.

Here are a few web links:

EVER WONDER HOW IT ALL STARTED? (By Don Prieto): http://wediditforlove.com/how-it-started.html

Nitro for Stromberg 97's: http://www.jalopyjournal.com/forum/threads/nitro-for-stromberg-97s.576730/

Stromberg 97 Carburetor - Mix Master: http://www.hotrod.com/how-to/engine/0804sr-stromberg-97-carburetor/

Converting Stromberg Carburetors for Methanol: http://www.reds-vintage-parts.com/technical-help/50-converting-stromberg-carburetors-for-methanol

[dreracecar]

Posting that it was a kart in the first place would have been nice addition

[hemidakota]

I have some friends that did it with a kart. Don't know a lot about it except they burned up a lot of engines before getting it right. They were 2 stroke engines and the one thing I do remember is they had to adapt a large float bowl to the bottom of the carb before it started working. They started running a higher percentage once they sorted it out. It was all about keeping enough fuel in the float bowl. They did win a lot for quite a few years doing it. They also added something to the fuel to keep the smell down, blendzall comes to mind. I can also tell you their kid really enjoyed beating everyone to death by out running everyone.

[denverflatheader]

Al – not sure I can help you with your kart carb, maybe though.  I ran a Ford V8 flathead 15 years ago with four “Stromberg 48s” modified to run methanol and had four more “Stromberg 48” bodies modified to run 100% nitro.  The Stromberg carb function similarly to your kart carb via two emulsion tubes with changeable jets in the float bowl.  The Stromberg 48 also has a mechanical power valve that operates in conjunction with depressing the accelerator pump to help tune as well.  Stromberg power valves were available in #50 largest, and #73 smallest.

Carb versus mechanical fuel injection tuning is not similar.  For your kart carb to run methanol and nitro, at a minimum, you’ll need to increase the jet and emulsion tube diameter, and also tune by changing the power valve.  I’m not sure how your kart carb’s power valve works, but that could present you tuning problems if it’s unchangeable.  You should also modify your fuel feed line by increasing the inside diameter and improve the fuel inlet needle and seat to increase flow to your float bowl.  Possibly locate a larger needle and seat to replace your stock one.  Raising your fuel level slightly in your float bowl may help, but may not be possible with the design. If you have opportunity to upgrade to a larger cfm kart carb to modify for nitro, you may consider that move first before you modify your present smaller one. 

Again, this information may or may not help you, but my Stromberg 48 jet area was increased 2.13 over stock to change from gas to methanol fuel, and 6.25 times larger area for 100 percent nitro.  In other words, stock .048 jets for gas, .070 jets for methanol, and .120 jets for 100% nitro.  At a minimum, you have to increase the emulsion tubes inside diameter percentage to match, and keep increasing or decreasing until you find your best setup.  My setup used four carbs in a row, the engine was modified 286ci versus the stock one carb 221ci.  From my perspective, your idea is excellent for learning, actuality for 15% nitro with your kart carb might be marginal.  Alan

[hotrod316]

we have been 20% in a mine sprint with carbs and 1000 cc bike with carbs, boy it does smell good and tec  had a field day we us!  both motors did run little hotter that normal. just having
 fun !!
steve m

[Curly1]

My experience with it at 20% and less (Alcohol injection) is you do not need to add any more fuel or timing and if you do it slows it down. Now at some point over that you will have to add more of both but I have not gone there.  Carb should be the same motor does not know or care if it is carb or injection.

[johnta1]

I would wonder about the 'suction' of the carb being able to move the higher specific gravity of Nitro?

Like sucking on a straw in a milkshake compared to a straw in a Coke?

With injection the pump is pushing the fuel through the lines/jets while the atmosphere is trying to raise the fuel mixture through the orifices, etc.

[denverflatheader]

John – Myself I “wonder” quite a bit too : )   Maybe part of the key with a carb sucking nitro is the needed atmosphere is reduced, a small amount of 100% nitro goes a long way compared to gas.  Alan  p.s.  Like using your online calculators.

From Spud’s Nitro Notes in the FIE website:  Nitro is heavy stuff.  While the specific gravity of water is 1.000, pure methanol is .792 @ 68°F (lighter than water) and pure nitro is 1.139 (heavier than water).

Can you eventually be consistent running nitromethane?  YES!  Yes, in fact, you have a big advantage running nitro because the amount of atmosphere it needs to run is hugely reduced.

In a gas motor, typical air/fuel ratios of 12-14:1 are common.  That’s a lot of air to very little fuel.  As the ambient atmospheric changes throughout the day at the track, the air/fuel mixture is effected and the car’s performance changes drastically as a result.

An alcohol motor typically likes about 5:1. It is much less affected by the weather because so much LESS air is being utilized by the motor.  The fuel brings it’s own oxygen to the party.

A nitro motor running 100% likes a theoretical ratio of about 1.2:1 while a motor on 50% enjoys about 2.6:1.  As you can see, the weather has to change an enormous amount throughout the day for the nitro motor to suffer any effects at all.  The tune-up you choose in the morning will likely last all day.


With Spud’s information using a carb modified and tuned for running 100% nitro, next compare the carb’s jet and emulsion tube to John’s straw example.  The jet and emulsion tube tuned for 100% nitro will allow more gas (Coke) to flow than nitro (milkshake) due in part to weight; what John stated in his question.  The carb modified and tuned for 100% nitro should flow the ideal air/fuel mixture, while this same carb will be overly rich running gas.  In John’s straw example, you would use smaller amount of 100% nitro compared to gas to make maximum power. 

The correction would take a much smaller diameter straw for gas, and modifying the straw’s diameter larger or smaller throughout the day based on atmospheric changes.  The nitro straw would require less upkeep based on the atmosphere.