Hot Rod Forum banner

gsx itb sbc intake fab?

32K views 65 replies 10 participants last post by  blight 
#1 ·
Anyone build an intake with gsx itbs? I am thinking about fabing a manifold with itbs for my road race engine seeing everyone and their brother says to go fuel injection. If i am am going to go efi then i am going to do it right. and efi setup with proper velocity stacks and itbs is the way to go in my opinion.

each runner tapers down to the back throttle bodies which are 42mm
 

Attachments

See less See more
5
#2 ·
for the point of each picture run your mouse over each attachment and the name of the file is what each of the picture is.

The throttle shaft also looks like it would be a really nice place to put a dry nitrous spray bar through. They have a bolt at the top and bottom that hold them together. Once removed you end up with two sets of two throttle bodies.
 

Attachments

#5 ·
The gsx tb's are WAY too small. They work well on small displacement 4 bangers but become a choke on anything with more than .5l per cylinder. So what is it worth- a 50hp loss at peak. With correctly sized lengths though they can pick up low end torque.
 
#6 ·
Blight,
I've always loved IR setups. You probably will have to experiment with how you read(average) manifold pressure. I'm developing a 4 barrel throttle body and was very surprised about how little air it takes to idle a motor. Throttle response is going to be lightning quick at the price of tip in being hard to control. If you have a manual you may find yourself riding the clutch a lot trying to keep it from bucking. This looks like a cool project. Keep us posted.

That's a great price on that intake, but there are some things Procomp should leave sacred. Is there nothing they won't make cheap Chinese knockoffs of?

Kevin
 
#7 ·
ap72 said:
The gsx tb's are WAY too small. They work well on small displacement 4 bangers but become a choke on anything with more than .5l per cylinder. So what is it worth- a 50hp loss at peak. With correctly sized lengths though they can pick up low end torque.
Ap72 is right, I looked into this back in the 80's and there is a huge lack of flow capacity with motorcycle setups.

Would look cool though.
 
#10 ·
ap72 said:
The gsx tb's are WAY too small. They work well on small displacement 4 bangers but become a choke on anything with more than .5l per cylinder. So what is it worth- a 50hp loss at peak. With correctly sized lengths though they can pick up low end torque.
not meaning to argue with u but how is that possible, the tpi engines of the 80's used a single tb with twin 50mm blades,and most stock tbs have a single 70-75mm tb.

u would think that eight 42mm blades would flow a helluva lot more, whats the throttle blades on a typical 750 or 850 carb measure???
 
#12 ·
Project89 said:
not meaning to argue with u but how is that possible, the tpi engines of the 80's used a single tb with twin 50mm blades,and most stock tbs have a single 70-75mm tb.

u would think that eight 42mm blades would flow a helluva lot more, whats the throttle blades on a typical 750 or 850 carb measure???
the throttle body has to flow what cfm the head is at,at max lift. i can't remember the exact flow rate of each throttle body size but it also has to do with the shape of them also.
 
#14 ·
blight said:
the throttle body has to flow what cfm the head is at,at max lift. i can't remember the exact flow rate of each throttle body size but it also has to do with the shape of them also.
how about a common plenum per 2 cyls, sinc eno 2 cyls on the same side will be pulling air at the same time if u built a common plenum feeding 2 runners using 2 tbs to feed each plenum, should solve the issue of them being to small.

though this woudlnt be a true itb setup, i would assume it would still act the same as if it were
 
#17 ·
Project89 said:
how about a common plenum per 2 cyls, sinc eno 2 cyls on the same side will be pulling air at the same time if u built a common plenum feeding 2 runners using 2 tbs to feed each plenum, should solve the issue of them being to small.

though this woudlnt be a true itb setup, i would assume it would still act the same as if it were
perhaps the worst intake design ever. I'm not going to get into why but you need to balance the pulses.

As for tip in slide carbs, efi throttle bodies, or carbs wil accelerator pumps will fix that.

Compared to a tpi unit the total throttle plate area is bigger but each runner doesn't pull from the total area.

A rule of thumb is that the throttle bore should be about the size of an intake valve on a good ir setup (assuming a hot well sorted out engine build). That puts you at no less than a 50mm throttle bore. Depending on the carb design going to a 52 or 54 may be needed.
 
#19 ·
I think i am going to run a carb while i build this setup - this is fairly complicated. I am planning on running efi with itbs not carbing it. a carb setup sounds like a pita to tune and keep running with out adjusting it every time i take it out of the garage.

I was thinking a max of 50 with what I am doing. I am not sure if there is a motorbike with that large of throttle bodies with efi.
 
#20 ·
ap72 said:
perhaps the worst intake design ever. I'm not going to get into why but you need to balance the pulses.
please do im here to learn just like most are.over the years i have designed and built many one off custom inatkes for my own v6 turbo camaro.
some have worked very well with hp gains of almost 40hp over a ported stock intake. and some while making big numbers had lots of issues at cruise.
i did all of these by trial and error along with a few others that i can post actual pics of once i rember my photobucket password lo.

so id love to learn more for future intake builds





another




and one other itb design i never did finish

 
#21 ·
While I'm sure you enjoy making intake manifolds, your approach is all wrong. You need to tune the intake dimensions based off of total runner length, csa, and taper. They also need to transition from the plenum and head in a manner that is as least disruptive as possible. I'm not going to get into it here but Google is your friend. If you spend more time with a calculator and paper before you bust out the welder you'll have MUCH better results. Intake manifold tuning is even more complex than exhaust tuning.
 
#22 ·
ap72 said:
While I'm sure you enjoy making intake manifolds, your approach is all wrong. You need to tune the intake dimensions based off of total runner length, csa, and taper. They also need to transition from the plenum and head in a manner that is as least disruptive as possible. I'm not going to get into it here but Google is your friend. If you spend more time with a calculator and paper before you bust out the welder you'll have MUCH better results. Intake manifold tuning is even more complex than exhaust tuning.
funny you say with a calculator, that is literally how i think. i plan then do. in other words i 100% agree with ap72 here.
 
#23 · (Edited)
ap72 said:
While I'm sure you enjoy making intake manifolds, your approach is all wrong. You need to tune the intake dimensions based off of total runner length, csa, and taper. They also need to transition from the plenum and head in a manner that is as least disruptive as possible. I'm not going to get into it here but Google is your friend. If you spend more time with a calculator and paper before you bust out the welder you'll have MUCH better results. Intake manifold tuning is even more complex than exhaust tuning.

those were rough drawings just to get my ideas into a visual state, the actualy manifolds were all bellmouthed were runners met the plenum, tapered runners etc also not shown is the base, they were all 2 part manilfolds. at the time when i drew those up i didnt know how to draw in bellmouths and how to draw complicated bevels so i did them as simple as possible.

i actually need to remember my photobucket password so i can get picks of some of the finished manifolds i built

the top manifold was also adjustable the plenum and base bolterd together over the runners i had 3 diff lenght runners that could be swaped out

and i also wouldnt call a 40hp gain a wrong aproch
 
#25 ·
Many, many years ago, Ed Iskenderian used to recommend, I think, 1 square inch of venturi for each 40 hp. A venturi diameter of 1.13" will yield a venturi area of 1.002 square inches. I'm thinkin' that 1.125" would work (0.994 square inches) and might be easier to machine to. We're talking venturi size here, not throttle bore size.
 
#26 ·
ITBs would look cool. How about a stand alone EFI "carb style" like the FAST EZ EFI or Powerjection III. You could run a carb now and then upgrade later with out switching manifolds or complicated fuel mapping. Where does the MAF sensor go with the ITB set up you are looking at? Is there one per cylinder or do you need a common plenum feeding the ITBs?


Also you mentioned plumbing in dry nitrous. Just an FYI, you can't get on a road race course with a bottle in the car. Even if it's empty and disconnected.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top