A/FD why such short burnouts? And such low RPM? (1 Viewer)

[LoPony]

Alky Dragster is one of the classes that I want to watch. Is the short burnout for the injected nitro cars to keep heat from building up? I thought they needed a certain amount of heat, but maybe not too much?

They hit about 5200 RPM at launch, and go through the traps at 6500 or so vs. 9500 RPM of a blown alky motor. Do injected nitro motors just not make power up high, or is this something to do with optimizing the clutch for the run?

Thanks for the expertise here.

 

[M Jones]

Alky Dragster is one of the classes that I want to watch. Is the short burnout for the injected nitro cars to keep heat from building up? I thought they needed a certain amount of heat, but maybe not too much?

They hit about 5200 RPM at launch, and go through the traps at 6500 or so vs. 9500 RPM of a blown alky motor. Do injected nitro motors just not make power up high, or is this something to do with optimizing the clutch for the run?

Thanks for the expertise here.

I know the rpm difference is less expensive than the blower combo maintenance Wise , they might not twist them past 6500 is maybe they can’t keep cylinder load pressures high enough to keep them lit

 

[LoPony]

I know the rpm difference is less expensive than the blower combo maintenance Wise , they might not twist them past 6500 is maybe they can’t keep cylinder load pressures high enough to keep them lit

Your avatar suggests that you might know a thing or two about this?

 

[LoPony]

Your avatar suggests that you might know a thing or two about this?

I know the rpm difference is less expensive than the blower combo maintenance Wise , they might not twist them past 6500 is maybe they can’t keep cylinder load pressures high enough to keep them lit

I can see what you’re saying, since nitro requires so much timing - 70 deg. of the crank revolution would be taken up, so at high RPM this would be self-defeating. Blower-nitro in T/F would be different, since it evacuates the cylinders much more quickly (at 60 PSI of T/F).

Blown alky is actually easier on parts than Nitro? That’s interesting. Is this just due to RPM? Seems like Alky shouldn’t “Burn” anything, but maybe it can pound bearings pretty good.

 

[mike]

I can see what you’re saying, since nitro requires so much timing - 70 deg. of the crank revolution would be taken up, so at high RPM this would be self-defeating. Blower-nitro in T/F would be different, since it evacuates the cylinders much more quickly (at 60 PSI of T/F).

Blown alky is actually easier on parts than Nitro? That’s interesting. Is this just due to RPM? Seems like Alky shouldn’t “Burn” anything, but maybe it can pound bearings pretty good.

The answer is they don't want to put heat in the clutch-that is why you see teams push cars up and back to he line

 

[M Jones]

Your avatar suggests that you might know a thing or two about this?

My avatar is a wrap I did on Shields’s car right before they were sponsored by peak, my brother worked for him, I learned that tuning A/F motors was a very difficult combo to keep consistent but when you hit it right hang on, been away from racing for quite a while so can’t be much help on what there doing now, do miss it though

 

[LoPony]

My avatar is a wrap I did on Shields’s car right before they were sponsored by peak, my brother worked for him, I learned that tuning A/F motors was a very difficult combo to keep consistent but when you hit it right hang on, been away from racing for quite a while so can’t be much help on what there doing now, do miss it though

Very cool!

 

[M Jones]

Very cool!

Thank you

 

[Ramjet]

Why would you do a high rpm burnout when the car launches at just above idle rpm. The Clutch (and the Motor) doesn't need it. I know for a fact back when the A/F cars were running in the 240's they didn't get over 5900/6000 RPM. Even way back when we were running Jr. Fuel with SBC motors we finally figured out that "Small Bore / Longer Stroke engines at less than 310" with a Tall Gear was a better combination. You HAVE to Lug the Motor. Nitro doesn't like RPM and when you force it you get an unacceptable parts bill like the T/F & F/C's have. As the RPM goes up the timing has to increase to get maximum burn time. Peak power from burn should accrue at a few degrees past TDC.

 

[mike]

Why would you do a high rpm burnout when the car launches at just above idle rpm. The Clutch (and the Motor) doesn't need it. I know for a fact back when the A/F cars were running in the 240's they didn't get over 5900/6000 RPM. Even way back when we were running Jr. Fuel with SBC motors we finally figured out that "Small Bore / Longer Stroke engines at less than 310" with a Tall Gear was a better combination. You HAVE to Lug the Motor. Nitro doesn't like RPM and when you force it you get an unacceptable parts bill like the T/F & F/C's have. As the RPM goes up the timing has to increase to get maximum burn time. Peak power from burn should accrue at a few degrees past TDC.

I guess you don't like what I said?

 

[mike]

I guess you don't like what I said?

this is today not JUNIOR dragster

 

[Ramjet]

this is today not JUNIOR dragster JR. FUEL not Junior Dragster - (98% vs Methanol)

I did Not say anything against what you said (agree) and I am well aware that this is not about JR. FUEL on Nitro comparison. It was about the fact that a smaller bore longer stroke engine on Nitro (all Blown Fuel engines have a 4.187" bore and a long stroke) doesn't like RPM but it does like fuel burn time to be the most effective. Temperature in the clutch is of course part of the whole combination.

 

[glofria]

Could be if their running Hoosier slicks like we do, they don't recommend long burnouts because they grip better when not too hotter than the track temp. Just enough to clean the tires, but we like doing a burnout over the starting line to mark our tracks.

 

[BaldyLochs]

I remember way back in the very early 1990’s - they posted a blurb in National Dragster; asking Mr. Kalitta something like why does he do such short burnouts compared to other drivers…. He replied with something like, “You’re not buying the tires are you…. Well, I am!”. LOL

 

[r2]

Could be if their running Hoosier slicks like we do, they don't recommend long burnouts because they grip better when not too hotter than the track temp. Just enough to clean the tires, but we like doing a burnout over the starting line to mark our tracks.

Every A/Fuel car run GoodYear. Hoosier doesn't even make a fuel tire.

 

[Randy]

I've never really been involved technically so take this for whatever it's worth. Wheel speed AF vs TAD. AF can run as low as a 2.90 rear end gear while most blown alcohol combinations are in the low to mid 4's. Higher geared (lower numeric ration) AF doesn't need high RPM's to get the desired wheel/tire speed out of the water box like the lower geared alcohol fueled.

Nitro burns very slow compared to supercharched alcohol. Running nitro past a certain RPM produces no benefit other than losing power and tearing up stuff. Think of a diesel engine. High torque at low rpm due to slow burn rate through the power stroke. Higher RPM would mean blowing power out the exhaust since combustion wasn't completed.

 

[sammi]

Interesting and informative. (much better thread than worry warts worrying if what's her name gave the bird to the crowd at Indy)

Here is an interesting (to me at least) thought exercise. Let's say Amazon removes their trucks and Fontana comes back from the dead again. The local promoter wants to field a modern Junior Fuel class. Stock block and heads, 310 cid, no tranny, one magneto, Surfers fuel nitro restrictions (none). What would you build to fit this "everyman" class? How fast would it run?

 

[Ramjet]

Interesting and informative. (much better thread than worry warts worrying if what's her name gave the bird to the crowd at Indy)

Here is an interesting (to me at least) thought exercise. Let's say Amazon removes their trucks and Fontana comes back from the dead again. The local promoter wants to field a modern Junior Fuel class. Stock block and heads, 310 cid, no tranny, one magneto, Surfers fuel nitro restrictions (none). What would you build to fit this "everyman" class? How fast would it run?

While this would be something to think about it would not be an "everyman" class with those parameters. First of all the stock block and heads pretty much limit the class to SBC and DeSoto (Dodge**) to be any thing anywhere near competative. Those stock blocks and heads are few and far between now days. The Chevy has a problem because as has been said Nitro is slow burning and the more % you run the longer it takes to burn. To stay under 310" with a "longer" stroke the bore is so small that the valve size is limited. Also: It is almost impossible to get much compression without killing the flame travel with the size of the Chambers in any stock Chevrolet casting. The DeSoto was 271C.I. and could be 310 with a lot of work and expense. The Chrysler/Dodge was 331C.I. and could be sleeved but they are heavy. It is hard to make the fuel burn completely without losing it to the exhaust without adding an exicter. Lower RPM gives longer for the fuel to burn. Nitro increases torque and so does a longer stroke. With the scarcity of these OEM parts as well as the fact that they are reasonable Fragile we can't really "go back" and have an "everyman" class. BUT - to your hypothetical qusetion in todays world I'm not sure if you could go a whole lot Faster (or Quicker) than the old days. Some of those cars weighed 700 lbs with Open Tube rearends (One Brake Caliper) - Single Hoop Small Diameter Thin Wall Short Wheelbase Chassis - Pruned Blocks - Aluminum Clutch cans and Shorty Magnesium Bodies. A whole lot of that can't happen in todays world.

 

[Cliff]

I kinda sorta think the closest thing we have to the old JR/F class is the A/ND alky dragsters in Comp Elim. They do run cast iron blocks and heads too, I think.

 

[Ramjet]

I kinda sorta think the closest thing we have to the old JR/F class is the A/ND alky dragsters in Comp Elim. They do run cast iron blocks and heads too, I think.

Cast Iron And OEM Stock are 2 different things. I have a pair of brand new cast iron 12 degree Chevy Small Block heads but they are from Australia not Chevrolet and they are about $3000. More with Titanium valves - Retainers Good Springs & Girdle. Beside that they don't make them in iron any more. The Heritage series allowes them in JR. Fuel A not B Jr. Fuel class. Scott Parks is pretty much recognised as the Face of the new Jr. Fuel. The class is for Front engine 410 C.I. cars on Methanol with Iron Motors (and they "AIN"T) cheap. They run in the sixes but they have PowerGlide transmissions. Its kind of Apples and Pineapples.
P.S. A/F can run Alloy Heads & Blocks.