Custom ITBs

[Sykohtic]

So I've read most of Bulletride's thread on DIY ITBs and talked to him about it a bit. With the budget I have for my build, the RHD ITB kit seems just a touch out of reach, so instead I'm thinking custom stuff.

I aim to build a 3.0L high compression stroker M20, running MS, ported head, and a 290 degree Dblias cam (yes I will be shipping that from overseas if I stay committed to using that cam).

After reading some of the information on the RHD site regarding throttle size selection, I'm not sure the 44mm ID of the Triumph bodies that Bulletride used are my preferred option. I have been doing some research into the GSXR 1000 throttle bodies used often by the Toyota guys on their 4 cylinders. The early (01-02) throttles are separable (the 03-04 are as well, but the come apart in pairs rather than individuals. They do tend to be more expensive than the Triumph throttles, have injector slots id have to plug, and I would have to buy two sets which would leave me with two spare throttles. However, the dimensions peaked my interest.

The throttles I'm interested in have a 50mm inlet. Yes, much bigger than the 44mm I'm already worried are too big. HOWEVER, the outlet is 42mm, which is a pretty serious velocity stack, and matches what RHD recommends for strokers on their site.

So my question is will that internal velocity stack win back the intake velocity I would lose otherwise? Manifold-wise, the ID of the stock intake runners I'd have the new runners welded to may be less than 42mm, but that gives me another opening for another velocity stack or smooth taper.

What do you guys think?

[Sykohtic]

Additionally, I just had an epiphany that RHD now offers their intake manifold with a 42mm inlet. So all I would have to do would be be to fab an adaptor between the outlet of the throttles and the inlet of the manifold, sync them on the new spacing, seal it, figure out the linkage, and presto. Potentially saving me money over even the basic RHD 6cyl kit if I can get the throttles for the right price, albeit I'm sure I'd sacrifice some performance compared to their kit.

[peterman]

Inlet and tb diameters differences will definetly make the engine perform differently. However, I would imagine that the GSXR has shorter runners and longer stacks than its triumph counterpart. Which is why they can get away with a 50mm inlet. The entire geometry matters, not just the diameters. Shorter intake will increase top end torque, longer will give you better low end torque. IF THEY ARE THE CORRECT LENGTH. An arbatrary lenght will not give optimum performance, obviously.
In short, just asking about diameters will not get you very far. What are the lengths of the runners after the tb? Length of the stacks before the tb? The GSXR tbs are for a liter bike with a very short stroke most likely, whats the displacement and stroke of the triumph?

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[Sykohtic]

Inlet and tb diameters differences will definetly make the engine perform differently. However, I would imagine that the GSXR has shorter runners and longer stacks than its triumph counterpart. Which is why they can get away with a 50mm inlet. The entire geometry matters, not just the diameters. Shorter intake will increase top end torque, longer will give you better low end torque. IF THEY ARE THE CORRECT LENGTH. An arbatrary lenght will not give optimum performance, obviously.
In short, just asking about diameters will not get you very far. What are the lengths of the runners after the tb? Length of the stacks before the tb? The GSXR tbs are for a liter bike with a very short stroke most likely, whats the displacement and stroke of the triumph?

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I'm waiting for an email back from RHD regarding their intake. It is no longer listed as a separate entity from the M20 kit, so I asked if it is still available to be purchased separately. Once I know that, I can probably roughly figure out the dimensions, as I fathom there would have to be an adaptor between the GSXR throttles and the RHD manifold, I highly doubt they'll just bolt up.

The GSXR doesn't appear to have much in the way of a velocity stack in stock form. Maybe I'm looking at the wrong photos, but there appears to be very little if any stack there, albeit it looks as if the post-throttle runners don't appear to be very long either. I watched a video where someone INSTALLED velocity stacks or maybe upgraded stacks on their GSXR, which suggests they maybe either don't have them or don't have big ones.

EDIT: Also note that RHD uses what looks to be their 85mm trumpet extender and a 76mm trumpet on the M20 kit. How this length translates in relation to width, I'm not yet sure.

[digger]

It matters how far from the head the throttles are, so 50mm might not be too big of diameter depending how far from the head the 50mm portion is.

To some extent the length can make up for slightly too big of a diameter as it seems to be more critical than diameter, if whatever custom set you implement can’t get at least 11” of runner from the head then It will lack midrange torque.

[Sykohtic]

It matters how far from the head the throttles are, so 50mm might not be too big of diameter depending how far from the head the 50mm portion is.

To some extent the length can make up for slightly too big of a diameter as it seems to be more critical than diameter, if whatever custom set you implement can’t get at least 11” of runner from the head then It will lack midrange torque.

Is that 11" calculated/estimated with the internal taper of the throttle body from 50mm to 42mm in mind? Or does that taper not make a difference? I'll be honest, the math there escapes me.

I did hear back from Rama at RHD Engineering yesterday, and he said that he could sell me any individual part they produce, they just stopped advertising said individual parts on the site. He also informed me that soon they would be offering a horizontal manifold along side their normal curved one. I'm quite pleased with the response time, I wasn't expecting an email back for at least a day or so, so it was a pleasant surprise.

Also, there are extended trumpets made for the GSXR. In theory, I could (and should) add them. Picking up length pre-throttle is influential too, correct? Maybe not as important as the post-throttle runner length, but I know it makes a difference to intake velocity.

[peterman]

The length of the intake (and distance to exhaust x pipe) is calculated based on a pressure wave that is created by snapping vavles closed.
The pressure wave travels at the speed of sound and rebounds back down, or up the intake when it hits a large change in hydraulic diameter. The length of the intake is calculated to ensure the pressure wave hits the intake valve just as the valve as opening thereby having a larger initial velocity of air entering the chamber. This is also calculated for the exhaust side. The effectiveness of this concept has to do with cam duration and is most effective at a specific rpm.

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[Sykohtic]

The length of the intake (and distance to exhaust x pipe) is calculated based on a pressure wave that is created by snapping vavles closed.
The pressure wave travels at the speed of sound and rebounds back down, or up the intake when it hits a large change in hydraulic diameter. The length of the intake is calculated to ensure the pressure wave hits the intake valve just as the valve as opening thereby having a larger initial velocity of air entering the chamber. This is also calculated for the exhaust side. The effectiveness of this concept has to do with cam duration and is most effective at a specific rpm.

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Right, so then why not half the runner length so the pulse still meets the valve at opening with less space consumed? In 11" the pulse travels to the throttle, then bounces back to the valve. In 5.5" the pulse will bounce to the throttle, back to the valve, back to the throttle, and then to the opening valve.

[digger]

Is that 11" calculated/estimated with the internal taper of the throttle body from 50mm to 42mm in mind? Or does that taper not make a difference? I'll be honest, the math there escapes me.

I did hear back from Rama at RHD Engineering yesterday, and he said that he could sell me any individual part they produce, they just stopped advertising said individual parts on the site. He also informed me that soon they would be offering a horizontal manifold along side their normal curved one. I'm quite pleased with the response time, I wasn't expecting an email back for at least a day or so, so it was a pleasant surprise.

Also, there are extended trumpets made for the GSXR. In theory, I could (and should) add them. Picking up length pre-throttle is influential too, correct? Maybe not as important as the post-throttle runner length, but I know it makes a difference to intake velocity.

just a ball park number, with more taper more length might be required idk. the issue always is fitting it under the hood and without hitting the booster

pipemax gives you different harmonic lengths for the intake runner length and different areas (diameters) the numbers seem to work as very good guide

[Sykohtic]

just a ball park number, with more taper more length might be required idk. the issue always is fitting it under the hood and without hitting the booster

pipemax gives you different harmonic lengths for the intake runner length and different areas (diameters) the numbers seem to work as very good guide

Update here: I put a lot of stuff in my other thread on Dblias cams, but I was I formed by Rama that the RHD intake manifold has 90mm runners and all have the same head profile regardless of what bore size is selected for the inlet.

90mm being right around 3.5", I then would need to have fabricated a runner extension of around 7.5" assuming I went with the roughly 11" runner. This leaves me with choices. I can get the RHD manifold with an inlet bore of 42mm and then just match the extension ID to that and let the taper to head ports be all in the manifold, or I could go with the standard 40mm manifold and have the runner include the 2mm taper. I'm leaning towards the former option as I don't think it costs any extra to bore the manifold from RHD but it might cost more to find a pipe that will be of that taper.

The use of the GSXR throttles has given me an idea though, and kits a bit of madness but its a thought... Is it possible in megasquirt to run two banks of injectors? I'm not sure how it would be wired into the loom, but since the throttles have a slot for an injector, I could run fuel on one row and water meth on the other, and while the car won't need meth injection to run, it would lower intake temps and keep the motor internally clean and make it less prone to knock. I figured it'd only be spraying above 4 grand. Thoughts?

[digger]

the early RHD i have is

110mm manifold (centreline length)
24mm throttles
50mm extensions
125mm trumpet
309mm / 12.2" TOTAL

i trimmed a bit off, something like 15mm to give additional hood clearance so the length would actually be 11.6"

i think now they now come with

85mm extensions
75mm trumpets

so much the same

[Sykohtic]

the early RHD i have is

110mm manifold (centreline length)
24mm throttles
50mm extensions
125mm trumpet
309mm / 12.2" TOTAL

i trimmed a bit off, something like 15mm to give additional hood clearance so the length would actually be 11.6"

i think now they now come with

85mm extensions
75mm trumpets

so much the same

As I understand it though, you're suggesting more like 11 inches of runner post-throttle as opposed to your setup which is 11.6 overall? If so I might just have to go shorter, as you said you trimmed yours for extra hood clearance with an original length of 12.2". From looking at pictures, I would estimate the gsxr throttles at about 1.5-2" themselves. It might end up I just have to live without a bit of bottom end to make them work. One estimation was around 9 inches or so, which though you said has no gains or advantage over the 11" setup, might fit better.

A saving grave might be the new RHD manifold they're coming out with soon that has straight runners as opposed to the upturned ones. This might allow for more runner. I can always relocate the booster anyhow.

[digger]

it is overall length from the cylinder head face to the entry of the bellmouth. it tunes in at approx 6000 rpm, 2" shorter tunes in for 7000rpm but you need to make sure the rest of the engine is designed around higher rpm otherwise you may not see much topend gains

the distance between the valve and throttle matters for part throttle and response only, because at WOT its like the throttle isn't there except of course for the shaft offering some restriction

9" overall fits better to the hood no questions, but there is a torque loss

i would design it with adjustability and make it as long as you can

removal of the booster should allow longer overall runners, massive offers a nice kit that gives a ton of room