14 replies to this topic

[mariner]

Much though I like F1 I also enjoy Top Fuel - 4.5 seconds of pure mechanical violence!

What is amazing about a top fuel run is that the engine does only 700 revolutions in the entire time ( assuming 9,00 rpm and 4.5 seconds) so every cylinder firing has to count. In fact the approx 2,800 firing cycles accelerate 1,000 kg ( 2,200 lb) from zero to nearly 150 metres/second in 4.5 seconds.

This causes me to have a silly idea, as I have neither the engineering know how or money to try it I would like to ask the opinions of the experts here.

Basically as the engines use supercharging and fuel consumption is totally unimportant would it be possible to convert the permitted V-8's to a uniflow two stroke using the crankcase to act as the intake distribution chamber and allowing all the overhead valves to be exhausts?

This may be silly but the superchargers used are based on the GMC 6-71 blower used on an old GM 2 stroke truck engine. Also the engine blocks are CNC machined from solid so arranging entry ports at the lower end of the cylinder liner is feasible from a fabrication viewpoint. As far as I can find out the NHRA does not seem to ban two stokes.

The big problem I see is finding a way to control the air flow into the cylinders. As the blower is on top of the engine valley that should be Ok but such large inlet "valve" timing i.e port area may be needed that the cylinders could not be strong enough for the immense forces involved in a top fuel engine ( about 1,000bhp per cylinder).
Nonetheless twice the firings is twice the power ( and the crank torque is smoother which could help traction at 5G) so a lot of efficiency can be lost and still get another 10% real power.

Question 1 How might it be done?

Quesion 2 Why would it never work?

Any thoughts?

[Todd]

Isn't nitromethane something of a solvent? Small two stroke engines that have it in their fuel mixtures run between 8 and 22% castor oil to compensate. In a top fuel car, the purpose of running 85% nitromethane is to get as much power as possible from that is a relatively rich mixture, as even the supercharger can only do so much of a job of filling an 8 liter engine through one intake valve per cyllinder at 9,000 rpm. How much power would you be sacrificing to keep the engine from siezing on start up?

[Bob Riebe]

When snowmobile racing had mega buck factory sponsors, in the seventies, some of the mod. sleds were running alcohol dope mixes.

Maybe one of those boys could add some info, if any one knows one, or if any read this.

Bob

[Bill Sherwood]

They already have more than enough power to spin the tyres all that way down the 400 metres already, so more power isn't a huge desire.
Traction and clutch control is though.

[mariner]

Whilst it is true that they slip the clutch for the first part of the run they can use more power at the end.

The huge wing gives so much downforce that they can take extra power in the last third of the run. Also from 0 - 100 mph takes 0.9 seconds and the run takes 4.5 seconds for 325 mph so the acceleration drops off significantly once the clutch is fully hooked up. This is partailly due to centrifugal tyre growth raising the gearing in the last one third.

Oil dilution is a good point but that happens away today on the cylinder wall. remember the pistons only run about four runs or 1 mile ( or 3,000 cycles) before they are replaced Crazy engines.

[rhm]

What I love about them is that the tyres act as a kind of continuously variable transmission by growing in diameter during the run.

[Melbourne Park]

Originally posted by Bill Sherwood
They already have more than enough power to spin the tyres all that way down the 400 metres already, so more power isn't a huge desire.
Traction and clutch control is though.

2 strokes are supposed to be lighter though, although using the same engine you wouldn't find any weight saving. But less weight is useful when trying to accelerate.

[Bob Riebe]

A current trend in mod. drag racing engines, which are unlimited in size verses AA/F engines, is to increase bore spacing (there are now versions of the Chebby BB with 5.2 & 5.3 inch bore spacing) so they can still use the the engine size which is closer to nine hundred inches than it is to eight hundred, while still mainting cylinder wall thickness between cylinders to absorb the immense power these cars produce.

SO, I do not think engine weight means too much nowadays, at least not like it once did.

If a two-stroke puts out at least twice as much HP as a four-stroke, how much difference would 16,000 HP make verses the current assumed 8,000 HP?
Bob
PS-- The sound comimg out of AA/F two-stroke engines with megaphone exhausts would probably be wonderful.

[Todd]

Originally posted by Bob Riebe
A current trend in mod. drag racing engines, which are unlimited in size verses AA/F engines, is to increase bore spacing (there are now versions of the Chebby BB with 5.2 & 5.3 inch bore spacing) so they can still use the the engine size which is closer to nine hundred inches than it is to eight hundred, while still mainting cylinder wall thickness between cylinders to absorb the immense power these cars produce.

SO, I do not think engine weight means too much nowadays, at least not like it once did.

If a two-stroke puts out at least twice as much HP as a four-stroke, how much difference would 16,000 HP make verses the current assumed 8,000 HP?
Bob
PS-- The sound comimg out of AA/F two-stroke engines with megaphone exhausts would probably be wonderful.

The topic at hand is top fuel engines, which are limitted to 500 cubic inches. I don't think the large displacement engines you're referring to are anywhere near 8,000 hp.

[Bob Riebe]

Originally posted by Todd


The topic at hand is top fuel engines, which are limitted to 500 cubic inches. I don't think the large displacement engines you're referring to are anywhere near 8,000 hp.

Also as far as that goes, as a two-stroke engine makes double the hp of a four-stroke engine, why use nitro when there are other compounds such as nitro-ethane which can be mixed with gasoline to produce just as much hp but with a less hand grenade type of tuning.

[Bill Sherwood]

How well do two-stroke respond to large amounts of boost?

[Todd]

Also, how do two strokes respond to the extremely rich fuel mixtures needed to produce even 1000 hp/liter?

[alexbiker]

A two stroke would be perfect for a prop-driven dragster, surely?

[Greg Locock]

only if it had a beam axle.

[alexbiker]