How long to make my ITB runners?

[safe]

Originally Posted by billjam

One of my next problems is to design the throttle linkages. I was planning to adapt standard Triumph throttle cables or something similar. You also seem to have used cables. Do you have any pictures of how you made the connection to the existing throttle crank on the engine?

Sure, this is how I did it. I made a custom bracket and 2 stop screws. I would have preferred to use only one cable and some kind of mechanical linkage between the banks, but I didn't have time for that.
Use some high quality cables that can turn tight turns without binding. I used cheap bicycle stuff, and it isn't great, will change when I get the time.

[billjam]

Originally Posted by PFM

Billjam,

The numbers below are for a very tuned Cosworth 2LTR 4 valve 4 cylinder. The numbers are TQ on the dyno. The EFI is MoTec agian very tuned. The increase is in the 10% range, nothing to sneeze at. Not my motor just some info from a tuning acquaintance.

rpm low inj high inj
4500 82 108
5000 108 130
5500 145 162
6000 150 165
6500 148 163
7000 148 158
7500 145 155
8000 140 146

PFM

Thanks. That is food for thought. There's quite a difference at the lower end of the rev range - as you said, not to be sneezed at.

I'm not so naive to think I would see 10% difference in my situation, but hey, even 5% is worth chasing, especially at lower revs.
Damn. I'd virtually decided to go with low mounted injectors!
I may just stay with injectors in the TBs for now and I can always drop them down later if low speed running is a problem.

[billjam]

Originally Posted by safe

Sure, this is how I did it. I made a custom bracket and 2 stop screws. I would have preferred to use only one cable and some kind of mechanical linkage between the banks, but I didn't have time for that.
Use some high quality cables that can turn tight turns without binding. I used cheap bicycle stuff, and it isn't great, will change when I get the time.

That arrangement is kinda what I had in mind as well.
I was also going to try and use some type of progressive action so that intial throttle movements weren't too severe.

[safe]

Originally Posted by billjam

I was also going to try and use some type of progressive action so that intial throttle movements weren't too severe.

Yes, that's why I used cables. The pulley on the TBs are eccentric making a progressive movement.

[Flieger]

Engines on the dyno are at wide-open throttle during the pull. So, even though the rpms are low, the throttle plate is still open and the engine is not suffering the inefficiencies of pumping turbulent air.

Because the throttle plates are open, the issues of fuel pooling/condensing on the butterfly are not encountered. If you are running high fuel injectors at low rpm on the street, the throttle will be closed and your throttle response will be poor and lumpy upon initial acceleration.

[safe]

The best thing is to use both low and high injectors. You can use small injectors low that can be controlled very accurate and when you need more fuel you open the high injectors.

[billjam]

F*** this!
I'm gonna just stick them half way up the runners!
Best of both worlds and keep everyone happy.

[billjam]

Originally Posted by safe

The best thing is to use both low and high injectors. You can use small injectors low that can be controlled very accurate and when you need more fuel you open the high injectors.

That would be cool, but it adds a extra degree of complication (and cost).
Actually, the standard Triumph injectors would probably be good for the low position and then fit some bigger bosch units into the TBs.

But then as Fleiger implies, the power numbers from PFM probably can't be applied to a street engine at less than full throttle opening.
So I guess it's back to installing injector ports in the bottom of the runners.

[Mark Henry]

If it's an all out race car install them high, but I'd never do it in a car that sees any street time.
Much like a cam, race or street, there is no magic combo that does it all, only a good compromise.

[PFM]

Billjam,

Just to be clear the motor ran a total of 8 injectors on the 4 cylinder, four low and four high. The EFI handled the staging of the injectors, at low RPM and part throttle applications the low injectors were used, the high injectors were staged on as the RPM and throttle angle increased. I would think you would want the throttles closer to the valves for best throttle response.

If you want the numbers for your motor ran through PipeMax PM me the motor info and cam specs you plan on running.

Regards,

PFM

[911pcars]

"I would think you would want the throttles closer to the valves for best throttle response. "

When using fuel injection, fuel delivery is controlled by a pump (MFI) or an ECU (EFI) and various engine and ambient-condition sensors. Thus, the throttle valves in a fuel injected engine only control air flow. Because of this, the placement of the throttle valves are less of an issue than with carbs.

The only issue with FI throttle valve placement is in maximizing the tuning effects of pressure waves created by the length of the intake piping. In that regard, that's one reason to use slide valve throttle assemblies, to create a smoother air flow than a circular flat plate and pivot rod dangling in the middle of an intake pipe.

OTOH, a carburetor must meter and mix both air and fuel and deliver both through the intake tract, a more challenging task than just controlling air flow.

Sherwood

[billjam]

Originally Posted by PFM

If you want the numbers for your motor ran through PipeMax PM me the motor info and cam specs you plan on running.

Regards,

PFM

Sounds interesting. What "numbers" do you need?

[jpnovak]

Bill, MS can run dual tables for two independently controlled sets of injectors. Tuning to blend the thresholds and transitions could get interesting. You could run purely based on RPM or load. I would think that a blend of the two would be best.

I am surprised there was that much difference between injector placement. Thank you for the data. It is nice to see numbers.

Also, make sure you match spray pattern of the injectors with the location. You don't want wide angle injectors that will only wet the sidewalls and not atomize into the gas stream.

I did this exercise a while back and concluded that it was a lot of work to size the runners when you are targeting a 3rd or 4th harmonic for the rpm tuning band. The difference at these harmonics is minimal. Size them for easy fabrication, fit under the decklid and air cleaners. As others have said, you will do better to match the diameter and taper than the overall length. To be honest, with just a DC21 cam I don't think you will see any effect with runner length other than changing the pitch of the sound at WOT.

btw, it would be easy to respace your throttle bodies. Just machine a spacer and extend the mounting bolt. Also, weld a tab extension on the butterfly actuator lever. Shouldn't take more than an hour to put them directly on top of the head.

[Henry Schmidt]

Seems like a lot of work. Why not just buy these.



or these

[78SCSLANTNOSE]

What about short runners like these

[78SCSLANTNOSE]

Lets try this againhttp://http://s895.photobucket.com/albums/ac160/apl876/stuff/?action=view&current=HPIM3362.jpg&newest=1

[safe]

Originally Posted by billjam

I would try to space them out and get rid of the bends. You just need to weld on a larger tab on the right tb in the picture.
I would then mount them just high enough over the ports to make a nice transition from tb-size to port-size.

[billjam]

Originally Posted by jpnovak

Size them for easy fabrication, fit under the decklid and air cleaners. As others have said, you will do better to match the diameter and taper than the overall length. To be honest, with just a DC21 cam I don't think you will see any effect with runner length other than changing the pitch of the sound at WOT.

btw, it would be easy to respace your throttle bodies. Just machine a spacer and extend the mounting bolt. Also, weld a tab extension on the butterfly actuator lever. Shouldn't take more than an hour to put them directly on top of the head.

Yeah, I know that. I can do that fabrication no sweat, but I want to use a long oval filter and housing similar that used for Webers.
I know that there will be an adverse effect on flow for the bent runners, but I can live without those one or two HP.

Originally Posted by Henry Schmidt

Seems like a lot of work. Why not just buy these.

Your pockets might be a bit deeper than mine Henry.
If money was no object, there are quite a few bolt-on goodies that I would go for, but that is really no fun at all. Half the fun here is going where no man has gone before! How many Triumph-equipped 911s are you aware of?

Originally Posted by 78SCSLANTNOSE

What about short runners like these

Thanks for trying, but I can't get link to work.

Originally Posted by safe

I would try to space them out and get rid of the bends. You just need to weld on a larger tab on the right tb in the picture.
I would then mount them just high enough over the ports to make a nice transition from tb-size to port-size.

Magnus, as I mentioned above in response to Jamie, I understand the issues, but I am going to stick with bent runners. I will be mounting the injectors as low as possible as I think this injector placement is quite important.

[Henry Schmidt]

Originally Posted by billjam

Your pockets might be a bit deeper than mine Henry.
If money was no object, there are quite a few bolt-on goodies that I would go for, but that is really no fun at all. Half the fun here is going where no man has gone before!

Every project has it's cost.
The cost this project I fear is brain damage.
It's impossible to accurately equate brain cells with a monetary value but take it from someone with very few brains cells left, sometimes spending a little money is therapeutic.

Originally Posted by billjam

How many Triumph-equipped 911s are you aware of?

Triumph parts on a Porsche may be like riding a moped:
Fun for a minute but you really don't want your friends to see it.

[Walt Fricke]

Henry - it is going to be a bit tricky to install a decent air filter over those wonderful tall stacked slide valve intakes, isn't it?

I know real racers don't use no stinking air filters - just impedes air flow. Or, at most, they use a wide mesh screek to keep leaves and other biggish bits out. At least back in the days of real racing they did. You see this on vintage cars in museums, and I've even seen it at Vintage racing events.

But I can't imagine doing that. Too much dust at the track, made either by me or by others over whom I have no control. Even more of an issue on the street.

So I understand Billjam's hesitancy here, as air filtration seems pretty important for practical motors.

When, as, and if I get around to dealing with this on a motor of mine (instead of just purchasing a bent manifold), my first thought is to fabricate a different base for one of the standard filter types, and use the stock top and filter element. I think they will be long enough, even if the two end trumpets will be fairly close to the filter sides.

And I've seen photos (on this very forum, I think) of separate filters for each throat. Don't know the brand, or the specs/efficiency.

So how would you filter air for something for which the standard one filter per side available filters doesn't seem like it will bolt on?

Walt