Intake Runner Length and Pullers

[Mopower]

Some of you smarties out there might better explain the effects of more/less intake runner length on a given engine. I am racking my brain trying to apply the principles of physics to this one. I see automotive applications, but still cannot quite see how this affects flow and fuel/air mixture.

 

[mEl]

I am by no means an expert in this area but believe that a tuned system may have advantages at a specific rpm for which the intake and exhaust headers are cut. I believe that the main advantage is the better flow achieved by the smoother radiuses and the flow into the collector on the exhaust side irregardless if its tuned or not. I don't personally believe that "tuning" has any real benefit for a engine used across a broad rpm range such as a pulling engine encounters. I will be interested in others opinions as well, they are every bit as valid as mine. mEl

 

[Anonymous-0]

you simply have to keep the fuel suspended in air. tunning for the best signal does just that.

 

[Mopower]

Propane is easy to keep suspended heh heh heh.

 

[Anonymous-0]

hot propane dont even need much air. hehehe

 

[Full Pull H]

I would have to say it is all about the flow,that is volume and speed. The more and the faster the better to get in the cylinder but I guess cubic inch also has a big factor. Plus if the head and valve train can keep up with the mnaifold and the carb feeding it, everything has to work together to be efficient. Always have said "a big dog has to eat!!"

 

[RandyB(MI)]

mEI , I agree with you to an extent. The problem with the way most tune their engine is they tune for max hp no matter what rpm it takes to get it instead of tuning for the actual rpm range they will encounter most of the time. In other words instead of tuning for max hp they should be tuning for max torque because that is the true measure of the highest volumetric efficiency the engine will achieve and in a pulling tractor this is what you need. And I do believe that the correct length intake runner will compliment that rpm level. That column of intake air will bounce back and forth with the slamming shut and opening of the valves and given the correct length and dia. of runner it will be on the rebound or comming back at the valve right when the valve is opening. I agree this is then rpm dependent to a certain extent but if tuned for torque rpm instead of hp rpm it will help over a larger spread. Then if pullers would use a correctly adjusted governor instead of a direct linked throttle, it would stay in the "tuned" rpm range better than cranking on and off the lever like most "hot dogs" seem to think they have to do. I believe where most pullers go wrong is they read Hot Rod magazines and then try and apply it to their pullers. Drag racing and pulling take two completely different theories for engine building."Screamers" look and sound impressive but a correctly tuned and driven "torquer" will usually take first. Money is still no substitute for brains in some sports. Reminds me of the guy who thinks he gets another 5 hp on his 6:1 comp. 1100 rpm stock JD "A" by adding the infamous "Pertronics" ign. trigger. Why not go all the way with an MSD 7? I'm sure the "7" must mean it will give me 7 hp more!Even got a rev limiter , just what I need!.

 

[Crutch]

Not sure what you see afa the automotive side of things, but I'll try to make this short. If you got this part already, my appologies.

Whent the IV opens a highly energized pulse rushes up the runner. Technical name is finite amplitude wave. When it reches the plenium or carb, a negative reflection is reverted back, which carries particulates with it. It travels at the speed of sound, depending on the temp of the intake charge. If it reaches the IV @ IVC on the 3rd (high rpms) or 4th reflection, more is packed into the cylinder. This is referred to wave tuning. Fitting it under the hood is the problem. @ 2500 rpms, you might need a 36 inch runner for the wave tuning to work out.

The other runner tuning effect is diameter and length. Plenium volume to feed the cylinder and sizing to bring the velocity up to a usable speed.
Oversized ports and valve will make the motor lazy unless you run it up to the rpm point which the port becomes effective. Consider the pressue of air on coming to rest. A 100% conversion of kinetic energy in a 300 fps intake stream into pressure will give you 1.05 atmospheres or 5 percent extra. 650 fps air stream will yeild 1.25 atmospheres or 25% more. This changes volumetric effeciency. So would you rather have 600 cubic inches at 2500 rpms or 600 + (600 X .25)=750 at 2500 rpms. Honestly 125 % VE isn't possible in an ag motor. They probalby only function at 65% VE in stock trim and maybe 80 built with lots of head work. But you get the point. The issue IMO is that piston speed determines effectiveness and at low rpms you can't get the velocity you need, however the gains may be greater since ag motors are such poor breathers to begin with. 12 port head excluded although they are low port heads.

Sorry for the long ramble again and I hope that is what you were looking for.

 

[Anonymous-0]

msd 7 box spark will burn more fuel at proper air flow ratios dont know why you couldnt get more than seven horses out of it. had one on dyno with a 12 volt battery motor was fat took that battery off hooked a 16 volt race battery to the seven box motor showed lean added more fuel made more power.

 

[Anonymous-0]

you simply cannot get a large enough up draft carb to feed 400 plus cubes 80 to 100 percent ve . better to use mm of mercury for updraft sizing. if you could .you could make 2 horses per cfm of cylinder head flow just like the car motors.of coarse theres no telling what rpm that would be at but wheel speed is a friend in pulling and you would definately be able to turnem.

 

[james rumph]

Another good reply, we used the formula about a year ago trying to figure out the proper runner length for my Super M. My freind Mark is a math wiz and knew the formula and how to apply it to figure the signal length.

The only problem was the rules for our antique classes as well as carb location because of the governor. I would like to take the time to make one , it would be strage looking trying to keep all the runners the same and correct length.

We also spent alot of time on the dyno playing with the correct length of tube put behind the carb for the air filter. [ Differnt lengths as well as diameters]

In "our" testing on my set up there was no gain by spacing the air filter back any distance. There isn't enough rpm to increase the intake charge. We got best results with the K&N air filter right on the carb.


Go back to the 60s and the Ram Chargers drag racing team, remember the crazy intakes with 12" runners.

There is also carbs big enough to feed these big motors, there called aircraft carbs but there costly.

 

[Anonymous-0]

according to alan lockheed whos family is lockheed martin there wasnt one capable of 750 cfm at the measure of mercury my aplication was requiring at the time . i will tell you i enjoyed the coversation with him but i struggling to coprehend what he was telling me . aircraft engineers do understand airflow . his program he sells that was set up for indy car engines through audid technologies is amazing also.

 

[Crutch]

Allan's tech note's that came with Engine Expert are most valuable.

Brian Hitt (www.hittmotorsports) might be able to get close on cfm on a S-C carb.

Tuning Intake and Exhaust

 

[Anonymous-0]

yes crutch i new brian was running a resanance tuned intake . i wander what his carb flows? run close to the same cubes four cylinder carb flowed 312 cfms.

 

[Crutch]

I'll ask for the specs. There is another carb that looks like his but is half again bigger but idk what the p/n is. I have access to a Zenith that was supposed to be 430, maybe I can find time too put it on the bench and see if it actually measures that but it would be at 28 inches of W/C. I suppose you could convert to Hg.

 

[Crutch]

Per Brian, the R9 Strombergs will flow around 700.

 

[Anonymous-0]

(quoted from post at 14:53:47 02/01/09) Per Brian, the R9 Strombergs will flow around 700.

Thanks crutch il will see if i can get alan to talk some on that carb. i remember him saying that a holley 750 wouldnt supply the cfm at the inches of mercury . thats been a year maybe two . need refresher coarse any way . by the way either email me or open yours for posting . thanks mitch

 

[Mopower]

I have to agree. It's funny to see some tractors out there. You'd think they were building a 1/4 mile drag tractor with a gazillion RPM.

 

[Crutch]

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