JimK, some more air horn questions

[johnhup]

Jim,

I saw you responded to my post a few pages back but I decided to post again here so you would see it. Anywho, I have seen photos of your setup before and it looks like you have a good clearance but I dont see any air horns. Are they behind your filters? How is your low-end? Thats what I am worried about most (I do have some big hills here in SF).

[jimk]

No, I don't have air horns, just the stubby TWM adapter tubes to fit the air filter back plate. I did machine a bevel on the ID of the tubes to do away with the square entrance corner (the tubes were just straight tubes with squared off ends) to match the somewahat larger hole in the filter backplate. This machining is not a perfect inlet horn bell mouth configuration but cuts the loss compared to a square edge entrance by about half.

You shouldn't worry about hills and low end with EFI. The low end torque is much better than you can achieve with a carburetor. This is not to say that if you were wanting the ultimate performance, the longer intake tube (runner) would give more torque, but only at WOT because at part throttle, the throttle plate effectively limits the effective tube length to that between the throttle plate and the intake valve. The Tii arrangement is much better in this regard.

We have hills here in Denver too. A big change to get used to will be to just let out the clutch and not having to touch the throttle if you don't want to, and it'll just walk away with out a stumble (tuned computer of course).

[johnhup]

Beautiful. Thanks for the help.

One more thing. Do you have a very hot cam? I am running a 278 regrind with no overlap. I am hoping that I can get a good MAP reading around 2k (or less would be great). I know some people have to run Alpha-N but I think its because of extreme overlap.

[jimk]

I'm running a Webcam #169 for the BMW. More lift, some more duration than stock, but not a lot.

Map will work for you if you don't change elevation a lot. Problem is getting MAP readings that represent what the cylinders are seeing because the air from one runer on ITBs shuffles from runner to another and the Map reads high unless at near WOT.

[jimk]

Here are my stubs beveled.

[johnhup]

Hmm. I never thought about that. How do you compensate your AFR/VE tables due to your/our setup? I would imagine that when I begin to tune I will naturally see these trends occur and tuning the ITBs shouldnt be too complex. If you have tables or msq files to share I would love to see them.

BTW.. all my progress being blogged on my wiki (the link is in my sig)