Dual Throttle Bodies vs single plenum Options

[Bleyseng]

What are the benefits or drawbacks to each?

Geoff

[Brad Roberts]

Long runners typically promote torque.

Short runners typically promote RPM/HP.

Think: Pro Stock drag car with tunnel ram and twin 4's on top. High RPM but still needs some torque.

A 2.0 stock engine with dual carbs falls off a little in torque when you ad carbs but gains some on the top end.

This is my experience. Others may very.

Somebody with twin carbs on a stock 2.0 go do a dyno pull. I have the sheets from stock injected cars.


B

[Bleyseng]

That's pretty much what I thought that the plenum would be better for AXing as you are looking for torque not high peaky hp.

I haven't seen a dual carb car at any of the dyno days I have gone to. That would be interesting to see.
Post away carb guys!
Geoff

[JeffBowlsby]

Hey we need a Dyno Day...Hows about somebody organizing one as a future event???

[Bleyseng]

As long as its not a the place where my son's turbo RX7 got ripped off, I'm cool with it.
Geoff

[mightyohm]

Is there any way to retain fuel injection with dual throttle bodies?

Could you go Megasquirt and just put the MAP sensor on one side or is there a reason this won't work?

I have been wondering about that for a while now.

[Bleyseng]

That is what my friend Zach is thinking of trying to do. Use Dual TB, and a wideband O2 sensor, Megasquirt ECU. I guess you would sync the TB's like dual carbs.
Geoff

[Mark Henry]

Brad has it nailed. The dual TB's will give more over all hp especially at WOT but even with the fuel injection you still have the linkage and synchronization issues.

The plenum will have more torque and be better behaved in the daily driver and AX mode.

Once I get my PEFI system up and running I plan to do some experimenting. The one I want to try is a dual TB plenum; I have 2 two-liter TB's that I would like to mount on a plenum.

Now should I try them standing straight up like the stock?
Or a whole new plenum with each TB pointed at a set of runners? Or is this getting back into the old linkage issues?

[Mueller]

Mark...

Fly-by-wire (IMG:style_emoticons/default/smile.gif) no problem with the linkage, the hardest thing to do is to sync them with each other.

I'm pretty sure this is done with the V8 and V12 bimmer's and mercedes

[SPNR]

Well lets see how many replies this will generate. If you are planning to use the dual TB's on a D-jet or L-jet you won't gain much because of the limits on the fuel flow. The injectors can only stay open just so long (read flow so much fuel) no matter how fast you spin the flywheel. On the L-jet system the reduction in manifold pressure will play hell with it becuase it is manifold pressure driven. The best solution is an after market electronic FI that is completely programable or a continuous injection system like on the early seventies 911"s. The system off of a VW rabbit GTI will work well on a 914/4 and can flow enough fuel to support 170 HP (if you could spin it that fast!!). It is fairly easy to convert (I have one on my '76 and it runs very respectable for stock innards). It only has two parts that are electric (small heater for a choke sys and then the pump) so I like the reliability better than the old original FI which for D-jet has something like eleven pieces that are elec.
So di that make it better or does it hurt worse now?? (IMG:style_emoticons/default/blink.gif)

[Bleyseng]

Why is it they say the 2.0l Djet injectors flow enough fuel then for 250hp. I didn't think the injectors or fuel flow was the limiting factor for Djet. You could always install the larger injectors off a 450 MBenz djet set up too that should flow Plenty of fuel for whatever need you might have.
Geoff

[DNHunt]

Geoff;

There is a formula for predicting maximum horsepower of an FI engine.

HP =(#of injectors X desired duty cycle)X Injector size
_____________________________________
Brake Specific Fuel Consumption

Most people choose 85% of the maximum duty cycle(on all the time) as a desired duty cycle.
2.0L injectors will flow 36.8 lb/hr of fuel. That is their size.
The brake specific fuel consumption is how effecient the engine is. NA are usually around .45

HP = (4X.85) X 36.8
___________
.45

HP = 278

Seems like overkill on a 95hp engine.

Dave

[Brad Roberts]

I have to sync the twin triple throat TWM's on the tube car just like a set of carbs... IT sucks. I wish I would have gone with a 3.2 upper intake manifold like my friend Scott Fraiser did.

Stay away from the dual setup. Each of the 4 ports will need to go to a common block that the MAP sensor goes too.. you will also want a common block for a idle air control motor. Its no fun having to warm up a injected car because it cant get more air without you holding the twin throttle bodies open like you would with carbs.

I vote single intake. Even if you have to make one. The twins look cool... but why the hassle ??

B

[SirAndy]

Hey we need a Dyno Day...Hows about somebody organizing one as a future event???

that's a great idea!

now brad has one (actually 2) but if we wait for him to get them running again we might be to old to drive the cars ...

Andy

[Brad Roberts]

We cant get more than 10 cars to show up for breakfast... how many do you think will show up for a dyno day ?? and pay 80$ ??

B

[Tony C]

Something else that no one has mentioned yet is flow restriction. If you look at the top racing engines these days they are either using individual slide valves or a single throtle body. This is because an individual throttle body butterfly set-up actually has more flow restriction than a single throttle body. The individual throttle bodies do provide better throttle response though. So to get the best of both worlds you get a slide valve set up and a VERY light wallet. (IMG:style_emoticons/default/biggrin.gif)

-Tony

[Brad Roberts]

This is true. Something I hadnt put much thought into (until now) each small plate has 2 screws and a shaft impeding flow. A large single one only has 2 screws and one shaft.


B <<< loves the slide valve RSR EVO engines...

[SirAndy]

We cant get more than 10 cars to show up for breakfast... how many do you think will show up for a dyno day ?? and pay 80$ ??

how many do you think we would need to make it worthwhile? (is that a real word?) ...

Andy

[Tony C]

Andy, 10 cars.

-tony

[Bleyseng]

In Seattle when we have a dynodays it cost only $40 because of the group rate. Usually there is about 15-20 cars, mostly 911's or a few 914's like this one. That's one way I have checked to see how my motor mods are really doing. Its great to also see the guys who brag about their 130hp motors put out a lousy 80hp to the rear wheels.
Geoff