9 replies to this topic

[Top Fuel F1]

Several years ago I started a Thread about TF and FC Nitro cars mechanically using different compression ratios in different cylinders within the same engine. Since then, in a discussion with one team owner, I found out that typically the Roots blower would provide more pressure in the front cylinders with it decreasing as you went to the rear. As a result they had the choice of different size pistons or rods to compensate for this. What started later last season, and now has proliferated into most of the major cars, was that they have gone to what is referred to as a SET-BACK BLOWER. This is an effort to more evenly distribute the blower's pressure. The results must be effective in that last years TF champion's car was holding out on this; but has now gone to it. This is easy to spot with the long drive shaft and the rotor body only starting about one third the way back over the block.

[Bluehair]

That makes since... for past several years, the rear cylinders were always the first to go when the car began "dropping" cylinders. You can also see the raw fuel come out of the rear headers when they do a burnout. I was under the impression that NHRA did not allow "high helix" superchargers (not to be confused with screw-type), but I believe there is still a small amount of twist in the rotors on the standard roots-type that is currently considered legal. Is that what causes the extra pressure in the front?

[Engineguy]

Ahh, those wacky fuelers. Years (decades) of band-aids on top of band-aids. I don't claim to know the intricacies of current design of the maniflods, injector locations, etc. but if their is any common plenum space that is "wet" or the blower itself is wet, there are probably serious fuel mass inertia problems to contend with under extreme acceleration. I can see huge fuel mixture variations front to rear... not as easy to visualize a pressure differential. But in the TF world, where gushing torrents of fuel replace the vaporizing droplets typical of normal engines' flow, further complicated by the fuel containing more damn oxygen than the accompanying air, it all gets rather baffling.

The way to go (assuming still a roots blower, still mounted up top), I'd think, would be to divide the blower internally into four chambers (picture a typical dry-sump pump) front to rear, sized so that they are spaced the same as the engine's cylinder bore spacing. From a fuel/air standpoint, four V-2 engines, each with its own blower, and NO common plenum between the four before or after the blower... the benefit: same tune-up on all four "engines". The downside: the history of TF/FC seems to be that anyone that strays from the herd with a new idea goes bankrupt before they get the idea developed or find the right combination... or they do get it right and the rulebook is changed to outlaw their innovation.

[McGuire]

Originally posted by Engineguy
The way to go (assuming still a roots blower, still mounted up top), I'd think, would be to divide the blower internally into four chambers (picture a typical dry-sump pump) front to rear, sized so that they are spaced the same as the engine's cylinder bore spacing. From a fuel/air standpoint, four V-2 engines, each with its own blower, and NO common plenum between the four before or after the blower... the benefit: same tune-up on all four "engines". The downside: the history of TF/FC seems to be that anyone that strays from the herd with a new idea goes bankrupt before they get the idea developed or find the right combination... or they do get it right and the rulebook is changed to outlaw their innovation.

You nailed it. The segmented blower you describe would not be legal in the NHRA fuel categories. Ahem: " Restricted to one Roots-type supercharger, rotor helix angle not to exceed that of standard 71-series GM-type rotor. Maximum size: 14-71, 19" rotor case length, 11.25" case width; maximum rotor case cavity diameter 5.840"..."

As you say, while in the fuel categories we have the image of wild, unlimited cars, in fact their rules are extremely tight and formulaic. Here is my favorite regulation: "Maximum 500 CID, minimum 490 CID..." What the...?

[Top Fuel F1]

Originally posted by McGuire


You nailed it. The segmented blower you describe would not be legal in the NHRA fuel categories. Ahem: " Restricted to one Roots-type supercharger, rotor helix angle not to exceed that of standard 71-series GM-type rotor. Maximum size: 14-71, 19" rotor case length, 11.25" case width; maximum rotor case cavity diameter 5.840"..."

Yes that's it, and generally it's a SSI 14-71. SSI is in that category of manufacturers specilizing in Supercharger products used by the Pro class of Fuel and possibly Alcohol cars. Therefore you can find their street address and phone number; but nothing on the Net. After all, all their customers are dealing with them in a closed shop culture. Not surprising, in that there isn't a large market for these unique purpose built machines. This is similar to AFT ( the clutch supplier ). I talked to the owner of AFT years ago about any kind of information. There generally isn't any. The teams simply send their clutch people to AFT for a period of time needed to find out everything they need to know to work with the product. Chrisman rear ends also seems to be like this.

[McGuire]

Originally posted by Top Fuel F1


Yes that's it, and generally it's a SSI 14-71. SSI is in that category of manufacturers specilizing in Supercharger products used by the Pro class of Fuel and possibly Alcohol cars. Therefore you can find their street address and phone number; but nothing on the Net. After all, all their customers are dealing with them in a closed shop culture. Not surprising, in that there isn't a large market for these unique purpose built machines. This is similar to AFT ( the clutch supplier ). I talked to the owner of AFT years ago about any kind of information. There generally isn't any. The teams simply send their clutch people to AFT for a period of time needed to find out everything they need to know to work with the product. Chrisman rear ends also seems to be like this.

Yep. Of course the reference "14-71" itself reminds me of your earlier observation that these engines represent developments on top of developments over many decades. As far as GMC/Detroit Diesel is concerned there is no such thing as a "14-71" blower -- it's an implied continuation of the 71-series blower line that just sort of evolved. Another interesting development: while they are legal in TAF and TAFC, Lysholm-type twin screw blowers are not permitted in the fuel categories. Why? Precisely because they are more volumetrically and thermodynamically efficient. Everyone already has a sizable investment in lobe-type blowers, and the cars are too fast already.

In recent years fuel car tuning has involved ever less art and trial and considerably more science. But as you say, good hard info is hard to come by. That's not only because the knowledge is so specialized but so valuable. To hold on to their hard-won data, I guess they will keep the whole thing a black art as much as they can.

[Engineguy]

I don't know why Neanderthal Association of Stock Car Auto Racing and Neandrthal Hot Rod Association don't just come right out and say it in their rulebooks:

All engine and drivetrain components must be replicas, in principle, of components available in 1955 General Motors, Ford, or Chrysler passenger cars or trucks.

One has to wonder how much of a role the rules of NHRA and NASCAR, by propping up stagnent technologies and configurations, have in a subtle way contributed to the near downfall of the US auto industry.

The funniest thing I seen lately... in order to run in the NASCAR Craftsman Truck Series this year, as a prelude to running NASCAR Nextel Cup soon, Toyota had to design and develop a brand new clean-sheet-of-paper 1955 ChevroFord pickemuptruck motor replica complete with single cam, two pushrod and rocker arm actuated valves per cylinder, single Holley 4-barrel carburator fed from a 1955 style diaphram fuel pump driven by rocker arm off a cam lobe, single coil spark distributed through a distributor driven by bevel gears. At least with Chevrolet, Ford, and Dodge, they can look you in the eye and claim their NASCAR engine is a development of the engine they built for years (decades)... with Toyota it's just bizzare. If I'm not mistaken though, Toyota also backs a Funny Car in NHRA this year with a 2-valve pushrod "Chrysler" V8 and a "General Motors diesel truck" supercharger.

[McGuire]

Originally posted by Engineguy
The funniest thing I seen lately... in order to run in the NASCAR Craftsman Truck Series this year, as a prelude to running NASCAR Nextel Cup soon, Toyota had to design and develop a brand new clean-sheet-of-paper 1955 ChevroFord pickemuptruck motor replica complete with single cam, two pushrod and rocker arm actuated valves per cylinder, single Holley 4-barrel carburator fed from a 1955 style diaphram fuel pump driven by rocker arm off a cam lobe, single coil spark distributed through a distributor driven by bevel gears. At least with Chevrolet, Ford, and Dodge, they can look you in the eye and claim their NASCAR engine is a development of the engine they built for years (decades)... with Toyota it's just bizzare. If I'm not mistaken though, Toyota also backs a Funny Car in NHRA this year with a 2-valve pushrod "Chrysler" V8 and a "General Motors diesel truck" supercharger.

LOL quite right. I had a fascinating conversation with Lee White of Toyota recently about their NASCAR engine. They had no production baseline engine to present, so they went to NASCAR and said essentially "where can we start as a baseline?" NASCAR said the engine could not be better than any of the existing NASCAR engines in any single aspect or dimension (for example, cam height could not be better than the Dodge, intake port volume could not be better than the Ford, etc and so forth.) So Toyota asked well, what are all those dimensions? NASCAR replied well, we have never really compiled all that data. In efect NASCAR could tell them what was illegal, but not what was legal.

So Toyota went out and bought several examples of each of the competing engines and totally reverse-engineered each one, nailing down from five to twelve THOUSAND dimensional hard points for each engine. The box defined by that data became the design template for their engine. Seems like quite an interesting and challenging project, but a very peculiar one.

I had another fascinating conversation last year with John Fernandez of Dodge along these same lines. Early in the year they realized they had a basic carburetion issue, so he began looking around inside the corporation for a real carburetor expert. Since the company built its last carbureted car sometime around 15 or 20 years ago, there weren't any. A whole generation of engineers is now in place with no direct professional experience with carburetors! John had to bring in some retirees for the project.

[McGuire]

One more tale: reportedly, Toyota had great diffculty finding a foundry anywhere in Japan which still had the capability to cast a V8 block in cast iron. Finally some obscure division or supplier to Yamaha was able to do it, or so I'm told.

[McGuire]

One more thing I forgot LOL: the Toyota NASCAR V8's bellhousing bolt pattern is Chev-ro-lay.