The folly of individual throttle bodies.

[Speedar]

What a fantastic resource for a EFI bunny like me. This is my first post so please be gentle with me.

Like many I have a fondness for the aethetics of 8 ITBs on a V8. I see that Mike Sinnard has dealt with his similar affliction but I can't post my questions in the "success stories" area.

I like open systems so Megasquirt will be my ECU choice for the project.
Currently I have an AC, a 351C cleveland, 190cfm heads, and about 400hp. I also have acquired some huge Cleveland 65mm hilborne throttle bodies modified to accept EFI injectors. Now my questions...

I doubt I will exceed 500hp so wouldn't 36lb injectors be sufficient?

Will the oversize TBs lean out the motor during hard acceleration/WOT and require larger injectors? I notice Mike S is using much larger injectors with smaller 56mm TBs.

Will 8 x 5mm brakeline to a common plenum provide sufficient vacuum for MAP pickup and maintaining vacuum for the brake booster?

Has anybody tried a progressive cam-type accelerator linkage to make such a setup less throttle sensitive (more streetable) for part throttle cruise and idling about? Presumably the TPS would still need to be proportional?

Finally what are the peculiar VE (or was it VR) requirements of ITBs that Mike S alluded to.

[Brad-Man]

Sorry I can't help with the vacuum situation, although if you were to look at some of the Datsun Z car forums, say Hybrid Z, I daresay that some advice on the size of a "reservoir" for vacuum could be ascertained. A lot of Z car owners like putting on triple dual throat carbs (webers, dellortos, mikunis and solexes) and have run across this issue. I would suspect that with an engine twice the size, a reseroir would only need to be half the size....

As far as the TPS goes, If you made a progressive linkage (I'm assuming that you want more movement at the pedal at the start and getting faster opening at the end), if you have the TPS work off of the actual movement at one of the throttle bodies, you should be fine, as opposed to what the pedal is doing....

[dooveeboy]

Hi Speedar
Brad-man is right ,The nissan gtir 2.0 turbo has
quad throttle bodies and uses a vacuum chamber
To settle the hg and even out the lumps and bumps
I have modded a throttle cable wheel to change the gearing
as my pedal pull is quite small but throttle travel needed
to be gentle.
The nissan 1.8 and 2.0 use a pulley pivot with ball type
rose joints you could set a couple up and make it change the
gearing ratio for you ?
Heres a we pic .
Cheers

[Deaninkc]

I'm working on a Cleveland setup myself. I have not been lucky enough to find the Hilborn ITB so I'm either going with a 351W EFI manifold and adapter or a modified tunnel ram. Since the injectors are going to supply with the correct amount of fuel for the amount of air you are passing you don't have to worry about leaning out but you may get full power on what seems to be like parital throttle which can be a major PITA on the street. I guess you could play with some sort of a restrictor.

[Mike Simard]

I like open systems so Megasquirt will be my ECU choice for the project.
Currently I have an AC, a 351C cleveland, 190cfm heads, and about 400hp. I also have acquired some huge Cleveland 65mm hilborne throttle bodies modified to accept EFI injectors. Now my questions...

65mm? that's big. What's the history of the Hilborns? Are you sure your Cleveland heads only flow 190cc? That sounds low.

I doubt I will exceed 500hp so wouldn't 36lb injectors be sufficient?

36 lb injectors probably would be sufficient for 500 hp. You can get up to 42 lb ones easily and cheaply if you want some wiggle room but 36 would probably work. In my case I have 50 lb injectors and approx 600 hp and have never seen over 80% duty cycle. They also idle well and can even take smaller pulsewidth 4 squirts instead of 2 which seems to make for a nicer idle.

Will the oversize TBs lean out the motor during hard acceleration/WOT and require larger injectors? I notice Mike S is using much larger injectors with smaller 56mm TBs.

They don't lean the motor out, there's a given amount of air going in that takes a corresponding amount of fuel.

Will 8 x 5mm brakeline to a common plenum provide sufficient vacuum for MAP pickup and maintaining vacuum for the brake booster?

I find that .15 ID going to a common plenum works well and even supports a brake booster, at least with an engine that makes about 10 in. of vacuum.

Has anybody tried a progressive cam-type accelerator linkage to make such a setup less throttle sensitive (more streetable) for part throttle cruise and idling about? Presumably the TPS would still need to be proportional?

I didn't use a progressive type linkage but I did need to upgrade the shaft mounted to the firewall that carried torsional load because it would twist with the greater spring resistance. The new shaft is a larger, hardened stainless one and doesn't twist, that's all it took to make for a driveable throttle feel.

Finally what are the peculiar VE (or was it VR) requirements of ITBs that Mike S alluded to.

ITB's tend to have a VE table 'curve' that stays somewhat steady from idle vacuum and then goes up greatly near full throttle. A normal intake system might have a VE curve that increases at a steady rate. Mine is around 25 at idle and low rpms and starts going especially higher around 85 pka to a maxumum of 125.

[Speedar]

Thanks for the responses so far.

1. Correction...The heads have 190cc runners and flow 300cfm.

2. Theoretical Hp is heading toward 500 but I like to live in the real world but 450 is quite possible

3. The 65mm TBs were an opportunistic budget buy as there is very little injection stuff for a 351C. They are ex a dirt track production saloon that was probably running alcohol. I would have much preferred 48~56mm but my thinking was hey the motor is just a pump and it will only draw what it needs. I understand that the race car did have throttle feel issues but never explored progressive throttle opening. Will narrower tubes above the throttle plates help?

4. I planned on 36lb injectors purely on the basis of the megasite formulae. Mike, I am interested that you chose bigger. Is that to keep up with the big dump of air under acceleration. I thought it was better to go smaller for idle & economy around town but that's why I am here seeking guidance.

5. A real concern is how to fit the fuel rail(s) in the centre of the valley. Not much room. Mike, How did you manage with a Windsor?

6. Following the suggested threads I am less concerned abount the vacuum lines supporting the brake booster and MAP.

7. Last question Mike how did you change direction with your rod linkage from for and aft to east west?

[Speedar]

Mike, would you be able to email your VE map? speedar@hotmail.com

[Mike Simard]

I understand that the race car did have throttle feel issues but never explored progressive throttle opening. Will narrower tubes above the throttle plates help?

I'm not sure what you mean by narrower tubes but one feature I designed into the throttle bodies was a fairly shallow 7 degree angle that the butterfly rests against the bore. As that angle gets less it makes the off idle transition less sensitive but requires closely machined parts. I put alot of effort into the linkage going to the car and that's paid off in a throttle that has a good feel with good modulation and no awkwardness. I never even think about it until a discussion like this comes up. Even the old carb setup had some issues, because the spring pressure was too light your foot could blip the throttle from bumps in curves and it required concentration to modulate. It's hard to pin down why my current setup is succesful, the throttle pedal travel is about 4" with moderate resistance but no flexing in the linkage, I believe that's important to accurate modulation.

4. I planned on 36lb injectors purely on the basis of the megasite formulae. Mike, I am interested that you chose bigger. Is that to keep up with the big dump of air under acceleration. I thought it was better to go smaller for idle & economy around town but that's why I am here seeking guidance.

A 600 hp engine would require 44 lb injectors according to the chart, I just wanted to have a safety margin because I have had problems with fuel starvation in the past and never want that again. Fortunatly the bigger 50 lb injectors handle the idle pulse so well that I was even able to double the number of squirts which reduces the idle pulsewidth in half, they still handle the idle very well.

5. A real concern is how to fit the fuel rail(s) in the centre of the valley. Not much room. Mike, How did you manage with a Windsor?

A good question. In order to have the injectors point at the intake valve, they must me angled inward significantly. Here's a picture of the CAD model of my engine. The injectors actually cross each other and required a complex machined fuel rail but the injector is pointing right at the center of the valve.

7. Last question Mike how did you change direction with your rod linkage from for and aft to east west?

I just uploaded 2 pictures of the linkage in my success story, my car is a Superformance Cobra which has an arm coming out of the footwell, a rod going back to the firewall. I made a stronger firewall shaft from hardened stainless with a hex machined on each end, it had to be long enough to reach the center of the car and must not have any flex. Attatched to that shaft are machined arms, it took a couple of attempts to get the ratios correct. I also used spherical bearings on all linkages.