Techie question
Discussion
Time Machine said:
Furyous said:
Do engine builders really go to the lengths of different rod lengths ?
Yep. A modern fuel motor may have its roots in 1950's pushrod OHV technology but there are some clever tricka applied to it to squeeze the power out.
Setback blowers on TF cars eliminate different rod sizes from front to back as it evens itself out.
Furyous said:
Why in particular no 7 cylinder ?
Generally it's thought to be the design of the head, with a hemi head the journey into the cylinder for fuel and air is a uniform, evenly contoured path. With a Chevy head the flow of fuel and air has a very much more interupted route into the cylinder. As far as I know, this wont necessarily slow down the mixture feed, but the heat present can affect the fuel entering the chamber.
It's common to have hat nozzles all the same size, and port nozzles adjusted to suit weak cylinders, but mainly due to flow of fuel under load and acceleration. The fuel, although directed into the port, will have a tendancy to travel towards the back edge of manifold opening. Using larger jets can counter this.
Time Machine said:
What do you have in the way of returns?
Idle check valve, hi speed, any others?
As we are running normally aspirated we can tune each cylinder completely individually but at the minute all ports are equal as we have no reason to do otherwise.
Idle check valve, hi speed, any others?
As we are running normally aspirated we can tune each cylinder completely individually but at the minute all ports are equal as we have no reason to do otherwise.
The current barrel valve has an idle check valve and a pump relief valve, but no hi-speed relief. It's a one inlet and three out, i.e. one inlet from the pump, which goes to an outlet for the hat, and one for the port nozzles - the other outlets being the forementioned idle check valve and pump relief valve.
Within the barrel valve itself is an anti-spike, I'm not sure if that's still reserved for just nitro BV's though.
I don't have many pics of the ideal side of the BV to explain it, but here's one that shows the simplicity of the setup.
Essentially all the pipes go into one hub, and out in various directions. When the port nozzles are fitted, another distrubution block will be installed. It's all bog standard equipment though.
Edited by Nitro-besty on Thursday 5th April 12:42
Nitro-Besty said:
It highlights the big differences between modern and nostalgia nitro racing. Back in the good ol' days, a fuel system was straightforward, albeit you were tuning by sight, sound, smell and the number of torched pistons you created as a by-product.
Modern fuel systems are so complex now that there's no such thing as a self sufficient part. By that I mean the settings for one aspect of the engine can now, not remain un-changed i.e. any increase in fuel pressure, percentage, jet size has to be countered with clutch and ignition settings. Then there's things like varying rod lengths to alter individual cylinder compression etc.
In terms of my own car, the fuel system is as simple as it gets when it comes to blown nitro. Single pump, single mag, smallish blower and 16 fuel lines into the motor. #7 cylinder on a BBC can run quite lean under load hence some jetting changes have been implemented to resolve this, but on the whole, the tune-up is just a 95% cackle, lots of ignition and lots of clutch setup.
The truth is, no tune-up will run identically in any 2 cars, so a lot of it's down to what happens the 1st time the motor's fired, and the 1st 46.233 foot squirt down the track...
Modern fuel systems are so complex now that there's no such thing as a self sufficient part. By that I mean the settings for one aspect of the engine can now, not remain un-changed i.e. any increase in fuel pressure, percentage, jet size has to be countered with clutch and ignition settings. Then there's things like varying rod lengths to alter individual cylinder compression etc.
In terms of my own car, the fuel system is as simple as it gets when it comes to blown nitro. Single pump, single mag, smallish blower and 16 fuel lines into the motor. #7 cylinder on a BBC can run quite lean under load hence some jetting changes have been implemented to resolve this, but on the whole, the tune-up is just a 95% cackle, lots of ignition and lots of clutch setup.
The truth is, no tune-up will run identically in any 2 cars, so a lot of it's down to what happens the 1st time the motor's fired, and the 1st 46.233 foot squirt down the track...
That's our deal. I stopped being a mechanic years ago when it started looking like a snake pit when you raised the hood. I'm not going to say big show cars weren't supposed to evolve into what they have, but I don't want to get any closer to it than when I spend $50-60 for my spectator ticket once a year. I appreciate their end result as much as anyone. Like I've said over and over, I don't get into the fan thing for any one driver. It's all about the cars for me and the drivers are just the ones holding the steering wheels.
Your engine sounds very similar to what's going together in my nostalgia funny. Rodeck with 6-71, iron heads, birdcatcher, 16 nozzles, etc. My intake (used, like everything else in my engine except crank, rods, and pistons) was opened up for a bigger blower, so I have to use a spacer plate, anyways. Because of this, I have to opportunity put the entry hole anywhere I want (naturally in the center to combat the rotors pushing everything forward), hoping it will help with the distribution problems commonly encountered.
Virgil Hartman explained it well in the nitro tuneups thread (cuz some of us NEED layman terms! LOL) that he started. Once we know the total nozzle area that our engine wants, it doesn't matter how we split it up. The more we put in through the ports, the better we can control idle. The more we put in through the hat, the better it seals the blower and the more power we'll make.
No data recorder. The most I have is headers that just happened to come with bungs in them and an EGT monitor that I can borrow from my bracket dragster (checking one cylinder per run, LOL). The rest will be plugs, bearings, and watching for cracks, LOL.
LOL, whichever of us gets running first, the other can sit back and watch for their guinea pig! We should be a couple months away from testing.
I own a semi-truck. At one time I had three with drivers on them. Since downsizing, one of them went on to buy his own truck and we've used each other for the same thing ever since. Pretty much all the companies we contract to will lie about this or that or hold something back that you don't find out about until you're already in, so for years he's watched me and I've watched him. Sometimes he ends up where I'm at, sometimes I end up where he's at. Right now we're together at a company he was at (and if it weren't for that, I wouldn't even HAVE a funny car right now)
I own a semi-truck. At one time I had three with drivers on them. Since downsizing, one of them went on to buy his own truck and we've used each other for the same thing ever since. Pretty much all the companies we contract to will lie about this or that or hold something back that you don't find out about until you're already in, so for years he's watched me and I've watched him. Sometimes he ends up where I'm at, sometimes I end up where he's at. Right now we're together at a company he was at (and if it weren't for that, I wouldn't even HAVE a funny car right now)
The Funny Car guys are very good in terms of sharing info. At the end of the day, they want to see as many cars out there, running nicely and consistently. Ron, the engine specs are very similar, albeit a bigger blower here, and solid Dart heads. Nitro loads will be similar I guess, albeit I have no rulebook to run to, so can do what I want with it 
.
From memory, the only exotic thing I'm intending on using is some nice rods from Brooks, since it'll have to be revved to make the trap speed respectable. Other than that, everything's a modern repro of 1969...
.but with an ounce more oomph.
Ron, e-mail me when you get a chance, it'd be good to compare nitro notes...
You should have my e-mail addy from back in November last year.
. From memory, the only exotic thing I'm intending on using is some nice rods from Brooks, since it'll have to be revved to make the trap speed respectable. Other than that, everything's a modern repro of 1969...
.but with an ounce more oomph.
Ron, e-mail me when you get a chance, it'd be good to compare nitro notes...
You should have my e-mail addy from back in November last year.
Should still have it. If you want to send me one at nitrohaulic@aol then I'll have it for sure. Yeah, I'm going into this with a VERY open mind. I plan on paying Spud Miller for a tuneup, letting him know what I've got before I even buy a pump and cam, then sending it to him for flowing. Just want to run low 4s in the 1/8. I originally wanted to start with whatever pump that I thought we'd end up with, so we could start with methanol, return more to the tank in the beginning, then grow into it as we went up with percentage and volume. Would also be more forgiving concerning time/heat while I get used to a new configuration of car.
Now a good friend who's been around this for a long time says that's a mistake, that he saw someone trying the same thing. Couldn't get it to run right no matter what he did. The friend says he walked up, looked at it, and told him his (1200) pump was too big. The guy kinda blew him off. Said two or three other people walked up, looked at it, and told him his pump was too big. Says Virgil finally walked up, looked at it, and told him his pump was too big! Now I either have to plan on using a smaller pump for a very short time, or starting right out with some percentage. Apparently using a big pump and returning too much screws the pressure curve up too much. I just don't want to waste a lot of time and motor while I'm trying to learn to keep up with it.
I'm sure shipping overseas might be too expensive, but I did just stumble onto and acquire a birdcatcher that I'm going to be taking the square alcohol valve off of and selling cheap so I can replace it with a K valve. Someone going to a manifold injection setup on a bracket car might be able to use it.
Now a good friend who's been around this for a long time says that's a mistake, that he saw someone trying the same thing. Couldn't get it to run right no matter what he did. The friend says he walked up, looked at it, and told him his (1200) pump was too big. The guy kinda blew him off. Said two or three other people walked up, looked at it, and told him his pump was too big. Says Virgil finally walked up, looked at it, and told him his pump was too big! Now I either have to plan on using a smaller pump for a very short time, or starting right out with some percentage. Apparently using a big pump and returning too much screws the pressure curve up too much. I just don't want to waste a lot of time and motor while I'm trying to learn to keep up with it.
I'm sure shipping overseas might be too expensive, but I did just stumble onto and acquire a birdcatcher that I'm going to be taking the square alcohol valve off of and selling cheap so I can replace it with a K valve. Someone going to a manifold injection setup on a bracket car might be able to use it.
Hi Nitro-sniffers and users !
For the fans of 2-wheeled nitro science,
there is something interesting on harleydrags.com
The page run by piPPi,the sympathic "know-it-all" from sweden,
(and guest commentator for Super Twin Top Fuel @ Pod) is in swedish.
But click on the "nitromethane class 101" button,
there is a thread in english about facts and mysteries of CH3NO2 tuning,
where even the late and great Jim McClure contributed some posts.
Cheers, and "good Race" for everyone who is at the Thunderball,
Benni
For the fans of 2-wheeled nitro science,
there is something interesting on harleydrags.com
The page run by piPPi,the sympathic "know-it-all" from sweden,
(and guest commentator for Super Twin Top Fuel @ Pod) is in swedish.
But click on the "nitromethane class 101" button,
there is a thread in english about facts and mysteries of CH3NO2 tuning,
where even the late and great Jim McClure contributed some posts.
Cheers, and "good Race" for everyone who is at the Thunderball,
Benni
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