DOHC EFI modification underway

[Eternal]

nice work that looks fab!

[rapidtornado]

nice work there mate, that's looks like a proper jobbie... good effort!!

[deezee]

Hi Enoch, whats the internal diameter of that hose between the filter and manifold?

[Enoch]

Hi Deezee, don't know is the short answer :-)
The flexible pipe is the one off the Sierra, the rigid pipe is a bit of drain pipe, I think it is 2 1/2 inches diameter, I will measure it when I get back later today. It is larger in diameter than the point at which the throttle body connects to the inlet, I figured if I kept everything bigger than the original Sierra I should not have a problem with it being restrictive. Hope that makes sense??
Enoch

[deezee]

Thats a fair point. I'm trying to get some info together for the diameter of my inlet manifold on my 16v version of the DOHC. In theory it should only need to be around 65mm (2 1/2") but it seems a little small considering each carb has a 38mm choke in it. I suppose only one cylinder is drawing in air at anyone time though.

[Enoch]

Quite. If you look at the cross sectional area of the inlet ports on the head they are actually quite small. The area of the point where the manifold meets the throttle body is a lot less than 2 1/2 diameter. I think I may have made my inlet "box" too big, I think it may have been better with a similar volume to the original but as I am not an engine designer I don't know what effect it will have. I drove the car briefly yesterday, it goes like stink so there can't be too much wrong :-)
Enoch

[rapidtornado]

Been meaning to put this post up for a week or so now but just haven't got round to it. Finally finished the shaping of the riser and then got the primer coat on, unfortunately battery ran out on the camera before I took a shot of it finished in black but I think it came out OK, considering this is my first attempt.

Manifold is now fitted to the car and hopefully I'll get a pic of that tomorrow so you can see it fitted. I plumbed it all back up and connected all the tricity and to my surprise the car fired first time sweet as a nut.

As I removed the power steering system I also had to use a shortened belt and that went on a treat, I think it was an Alfa Romeo belt, I got the PN somewhere if anyone wants it.

Anyway a few pics attached of the before and after primer stage.

Cheers
Matt

[mr henderson]

Inlet manifold sizing is a lot to do with gas speed. If the diameter is too large, what happens is that the gas slows down and doesn't fill the cylinder so well at lower speeds, and can lead to a loss of torque. In a sporty car that may not matter as much as it would in a shopping car.

[davidimurray]

Originally Posted by mr henderson

Inlet manifold sizing is a lot to do with gas speed. If the diameter is too large, what happens is that the gas slows down and doesn't fill the cylinder so well at lower speeds, and can lead to a loss of torque. In a sporty car that may not matter as much as it would in a shopping car.

But looking at the mods that have been made the diameter should be the same, the difference is the shortened runners which will change the resonance of the system.

[mr henderson]

Originally Posted by davidimurray

But looking at the mods that have been made the diameter should be the same, the difference is the shortened runners which will change the resonance of the system.

Don't know very much about this stuff, but I do know that runner length is considered very inportant by manufacturers of production cars, and in general the rule is the longer the better. Having said that, their concern is not only the headline max power, but how well the car pulls in a high gear at 1500 rpm, sas it will often be called on to do in traffic situations, whereas our concerns are different.

Even so, I know Jenvey, the performance throttle body makers, reckon that you should try for runners as long as reasonably possible. Not too sure about the resonance issue because resonance is something that happens at a particular frequency, and may have more to do (in a production car sense) with reducing intake noise than power characterisitics. Note that I said I don't know much about this stuff, though