I’ve been working on getting the ITB->intake manifold->spacer->cylinder head doweled to keep everything lined up and port matched to get the best flow possible. It has been a little bit of a hassle, but I will spare you the details and jump straight to the good stuff: a mockup of everything together!
I’ve done some calculations for intake runners, looking at what my current setup is optimized for (at least in theory) and how changing the diameter and length of the runners and trumpets changes things (once again in theory.) No surprise, I have come to the conclusion that my ported bigport is too big for ideal velocity and that the best torque will be produced at high rpms as a result. Lengthening the runners the extra half inch helps optimize the intake side of things for a slightly lower engine speed and should gain a bit below the torque peak at the expense of above the torque peak, and I think that all things considered, it will be beneficial. Doing some research into the theory of the intake side of things and some calculations has also strengthened my resolve to build an airbox for the ITBs, allowing me to duct cold air into them, to more accurately measure the intake air temperature (versus just dangling the sensor in the vicinity of the trumpets) and also hopefully will allow me to take advantage of a bit of pulse tuning to further optimize the powerband…if I can figure out the math and then translate it to an actual part. I also want to get a few different sets of intake trumpets so I can compare on the dyno and see what slightly longer trumpets might do.
I have thought about trying to modify the stock silvertop 20V airbox (I have one) but it is obviously pointed the wrong way and the 2-part asymmetric design made of thin stamped steel sheet is less than ideal for cutting and reconfiguring to reverse into a mirror image.
The difficulty with fabricating one is making sure that it isn’t going to be a mismatch for the rest of the tuning I have done. Figuring out the volume of the airbox and the size of the opening to ensure good flow (and make sure that it can refill fast enough) isn’t too difficult. The tricky part is design a specific shape and dimensions for maximizing both pulse tuning and flow. I guess that big car manufacturers spend tons of time, effort, and money to not only make the airbox a Helmholtz resonator, but also to make the inertial flow optimized for a rev range which corresponds to a particular pulse interference to help offest potential losses. I can understand some of the basic concepts and can dig back into some of my physics textbooks for some basic calculations, but a full understanding and complex modeling is almost certainly beyond me, so I need to figure out how much I am going to worry about chasing some ideal and at what point I just throw something together.
I put the rough spacer in place and had to use some extra washers on the stud, I think the studs are still a bit long and will probably change them for shorter ones. I also still need to do a bit of clearance work for the injectors.
On the backside of the head I am trying to finalize the funky modified AW11 coolant block. There was a steel pipe thread->hose fitting on it, but it also had a tee (probably originally for warm coolant to the throttle body or something) which had been poorly blocked off by the previous owner. I am of two minds about this fitting. Brass is soft enough I don’t have to worry about the imperfect threads in the cast coolant block and I have less chance of cracking the cast aluminum when tightening the tapered pipe threads, but it may have an increased risk of cracking. I may still try to find a steel fitting which wouldn’t be as likely to crack after years of vibration, but might crack the aluminum if overtightened. Steel is also a lot harder to find. Any thoughts or suggestions?
I also plugged a vacuum port the previous owner drilled out on the manifold. I want to run the brake booster off more than one cylinder to reduce the chances of leaning out number four.
One final question for the peanut gallery: what should I use to seal the wood spacer and protect it from getting wet?
