Anyone ever tried DIY individual throttle bodies?

[PUSHER]

I wont lie, I frequent honda forums allot and they're latest contibution (beside homedepot garden trim lip) is to use motorcycle itb's on their motors. The really ghetto ones they make, they just cut up their stock intake at the runners and fit on the throttle bodies, weld up some support, and use the stock location injectors. The people with fab equipment buy a flange, have the runners straight and evenly and space out. They then machine the itb's injector location to fit theyre original injectors for better mixture of the fuel and air.

 

After looking at the stock intake manifold on a l28 it doesnt look like the ghetto option will work because the outter runners are to close together for the itbs.(yes you would have to buy 2 sets and cut them up)

So I'm guessing you'd have to cut it after the injector hole and weld on the appropriate sized tubing and weld it on at angles to get the itbs to fit on properly. I dunno, was just tossing around some ideas. Trying to keep efi(megasquirt) with a na motor but know that the stock intake manifold is basically 6 straws connected to a lawmower's throttle body. Looking for a solution that is about 400-600 with somewhat minimum fabrication as ill have to get it welded somewhere else.

 

Here are some examples of diy itbs.

Here you can see the chrome spacers used to evenly space out the throttle bodies.

Here are some on a m20(?) 325i engine

And finally someone that angled the runners instead of spacing out the injectors.

[johnc]

I'm sure it can be done. I'm not sure the effort will be any better then a custom intake manifold with tapered runners, a properly sized plenum, and a single throttle body. Both will probably cost about the same.

[4everDATSUN]

alot of race cars go with individual Throttle plates rather than one, effectively you just end up with one large throttle plate in the end (by adding the areas of each individual). def way better if you can afford it and fabricate what you need. Youd have to make up some sort if air box also.

[johnc]

def way better if you can afford it

 

Careful about broad generalizations like that. My race car did just fine with a tuned plenum and a single 65mm TB. 320hp and at least 200 ft. lbs. of torque from 4,000 to 7,200 rpm (Max of 275 ft. lbs at 5,600). My engine budget was basically unlimited and the engine builder chose a singe TB over individual TBs.

[Guest Mateo]

But isn't it generally accepted that ITB's have better response than one TB?

[fl327]

Ive never seen data that shows that the ITB setup makes any more hp than a big single, but it does look like a fun project. Ive heard that ITB setups are harder to tune, due to engines running leaner in one cyl than the next. I saw the honda thread with gsxr throttle bodies I think it was? Looked awesome and would like to do one just for kicks one of these days.

[4everDATSUN]

the ITBs, in my opinion, are way better than a single TB. ITBs increase Volumetric Efficiency by alot, especially with a ram type air box. they maybe harder to tune, but when tuned right, the throttle response is leagues ahead of a single TB. But the tuning is key, and unless you can do it yourself, its goin to cost big bucks. Buying an after market fuel controller is def recommended.

[PUSHER]

Careful about broad generalizations like that. My race car did just fine with a tuned plenum and a single 65mm TB. 320hp and at least 200 ft. lbs. of torque from 4,000 to 7,200 rpm (Max of 275 ft. lbs at 5,600). My engine budget was basically unlimited and the engine builder chose a singe TB over individual TBs.

 

Where did you get the manifold? Did you make it? if you did would you be able to give the specs? cost?

[Tony D]

A quick trip to E-Bay to pick up a nice used Cannon Triple Manifold by itself should prove cheap enough, and there you have six, nicely spaced and arranged openings for an L-Head, along with a tapered runner and plenty of meat for adapting whatever TB you wish to attach to it via a simple plate adapter.

 

For all the guys making their own runners, it seems to me taking a Cannon Manifold, welding some aluminum trumpets to the face, and then bolting a plenum to it with a single T/B somewhere on it would be a heluva lot faster/cheaper than fabbing the whole thing from scratch.

 

Some MSD Screw-In Injection Bungs, and you're halfway there...

 

Not that I ever gave this any thought, mind you! LOL

 

P.S. I really like the looks of that BMW Manifold...

[katman]

On several L series road race engines I've been responsible for we always achieved better driveability, more consistent power, and a better overall "demeanor" with a big balance tube or bona fida plenum, even with itb's or individual carbs. I don't see how in operation, when you actually have to accelerate a car and not just a freewheeling engine, that a single throttle body like johnc's would have any disadvantage as far as "throttle response" to itb's. They sure look cool though...

[johnc]

Where did you get the manifold? Did you make it? if you did would you be able to give the specs? cost?

 

Sunbelt built it custom. I can make one and I do have the dimensions/specs. Probably be about $1,500 for the manifold itself.

 

Here's a picture of it on the L6:

 

 

FYI... throttle response has more to do with MOI then fuel delivery.

[ZROSSA]

There is probably a good reason why Johns manifold performed better. Have a look at the runners. They are straight. To do I.T.B's on the l6 would need bent runners or 6 individual bodies. Very expensive. I belive the ITB's will make more power on an engine designed to use them. That means that the port spacings would be a equal distance apart. When the world rally car f2 rules changed a few years ago, no longer alowing itb's, the cars lost about 15 h.p if I remember correctly. They were reving these things close to 9000 rpm though and I cant remember if they had to use the standard manifold.

 

Douglas

[Tony D]

TWM has had True ITB's for the nissan L-Series under development similar to what they have available for the Hondas. That setup is not a set of "Weber Clone" Throttle Bodies on their old standard triple manifold, rather individual throttles on staight runners.

 

They look sweet, and I bet the price is going to be easily twice++ what John will charge to replicate his manifold.... Last I checked a full setup of TWM Manifold and triple throttle bodies and fuel rail was around $3400, $4000....

 

So you really have to see if you "need" the complexity.

 

Look on Indy Cars, and you will see no throttle shafts in there. They use barrel throttle setups to keep the flow disruption in the port nonexistent. This IS an advantage of a Plenum with a single T/B...

 

You simply size your T/B for the ultimate flow, and play with linkage for tip in that you want, and make some nice trumpets on straight runners that run to a properly sized plenum...

 

Makes for a nice Turbo setup...muahahaha!

[cheftrd]

A large single with big plenum combo that's large enough to be no restriction to the intake runners will make the most power. Throttle blades in the intake runners create a restriction and turbulance.

 

johnc mentioned MOI or "moment of inertia". When you snap open a big throttle/big plenum combo, ambient air accelerates from a dead stop and has to fill the entire plenum and move all the way down the runners, which was a huge vacuum a second ago, before the engine "sees" any of this air. ITB's, on the other hand, have ambient air part way down the runners. When the throttles are snapped open, the air only has to accelerate and move a very short distance before entering the engine. Better throttle responce.

 

It's a give and take depending on what type of racing you do. Most manufacturers don't use the ITB because of cost and drivability. Six very small (40-45mm) throttles makes for a huge throttle area. Six 40mm throttles is worth 75 cm2 where a 70mm single is only worth 38 cm2. The single makes for a much smoother transient throttle response, where the ITB's make for a kind of on/off switch. You and I don't mind driving a car with snappy throttle, but most normal people don't.

[johnc]

When you snap open a big throttle/big plenum combo, ambient air accelerates from a dead stop and has to fill the entire plenum and move all the way down the runners, which was a huge vacuum a second ago, before the engine "sees" any of this air.

 

And that's a common misconception. The air in the plenum and in the ITBs is never at a dead stop, there's always velocity in any intake. Proper runner design can keep the velocity up even at part throttle.

 

Again, its MOI, not the fuel or intake system that mostly determines throttle response. The limiting factor on throttle response when the throttle is snapped open is not accelerating the air mass in the intake (and the exhaust, don't forget that part). The limiting factor is accelerating the valvetrain, pistons, rods, crank, flywheel, pressure plate, clutch, transmission, driveshaft, differential, halfshafts, stub axles, wheels, tires, sprung, and unsprung weight.

 

As Keith said above, a race track is very different from blipping the throttle in neutral.

[Guest vvillium3]

As long as we are one the plenum and design. Has anyone ever thought of feeding the air from the center of the intake to better equally destribute the air with shorter runners and a larger chamber???? Also what do you guys think would be the right sized chamber, runner length, runner draft, and radius on the horn??? I have been contemplating making one and I want your guys input...

[1 fast z]

Here is a low res pic of my ITB setup that I made about 3 months ago, pulls to at least 7500, that is when I back off, for the reason of the stock short block.

 

 

 

[datsunlover]

Lots of cool work being shown here, and I agree it would be a cool project.. but I'm willing to bet for half the cost and time, you could just run triple carbs.. Now a turbo engine I can see going to the trouble of this, but if it's more the 'cool look' thing well.. triples looke even better and get 'that' sound too.. A race car is one thing, cause you want to squeeze all the power you can out.. but on a mainly street driven car, how much power are you going to actually notice above say.. stock EFI or carbs?

[clarkspeed]

I have the TWM ITB's. Cost wasn't too bad. I mounted them on an old Cannon manifold and made my own linkage, fuel rail, and air horns.You can look for my other posts on my ITB comments. Even with my set-up which looks awesome and sounds better than webers, I would say a single large TB with a well ported manifold is a better bang for the buck and will perform just as well or better.

[cheftrd]

And that's a common misconception. The air in the plenum and in the ITBs is never at a dead stop' date=' there's always velocity in any intake. Proper runner design can keep the velocity up even at part throttle.

 

Again, its MOI, not the fuel or intake system that mostly determines throttle response. The limiting factor on throttle response when the throttle is snapped open is not accelerating the air mass in the intake (and the exhaust, don't forget that part). The limiting factor is accelerating the valvetrain, pistons, rods, crank, flywheel, pressure plate, clutch, transmission, driveshaft, differential, halfshafts, stub axles, wheels, tires, sprung, and unsprung weight.

 

As Keith said above, a race track is very different from blipping the throttle in neutral.[/quote']

 

I'm sorry, I should have been more clear...When the throttle is closed and the engine is at idle, the air in front of the throttle blade(s) is at a dead stop except for the tiny amount leaking past to idle the engine. There is a vacuum behind the throttle. With a big single plenum and throttle ambient air has to fill the plenum and the runners before it gets to the engine, where with ITB's ambient air has only to fill the area between the blades and valve before it enters the engine. The bigger the plenum after a single, the longer it takes before the engine starts to accelerate.

 

I had no idea you were talking about MOI of the RA because we were discussing why ITB's have (generally) better throttle response (bliping the engine) than a single throttle/large plenum style intake on a common engine. Not accelerating the valvetrain, pistons, rods, crank, flywheel, pressure plate, clutch, transmission, driveshaft, differential, halfshafts, stub axles, wheels, tires, sprung, and unsprung weight.

 

Where you have two identical engines, it's the fuel and intake system that mostly determines throttle response DIFFERENCE between the two.