marlinspike

Haven't you ever wanted to know something for no reason other than that you don't already know it?

marlinspike

Ah. Hmmm, I'll have to get a magnet to be sure, but both pieces feel like aluminum on mine (i've got a spare laying around here).

tucker5129

you couls always run a 'intercooler' type thing pre TB

tucker5129

it might be nonfaris but still harder. a think aliminum plate would be to fragle

Fabrik8

The throttle shaft bushings get moisture in them from condensation at cold temps, and the shaft will freeze to the throttle body. Ice can also build up on the throttle plate and make it stick open like a doorstop. It's affected mostly by air temp and air velocity, so if both of those are within an acceptable range that it won't happen. Venturis are pretty notorious for that too, for the same reason. Carbs for aircraft are really carefully designed for that reason, because if the venturi ices up or the throttle plate cakes with ice then there are obvious problems.

marlinspike

Ah. Interesting. I've never lived anywhere north of the Mason Dixon line, so I've never experienced that. Now you're making me wonder if I shouldn't get this throttle body coated with thermal barrier ceramic.

Oh, btw Fabrik8, we're starting to move on bigger intake stuff. The plan right now is just to bore out everything as much as can be done on both intake and head. then have custom valves made with longer stems (because I want to keep the factory hydraulic lifters) and go for more lift/duration on the cams.

Fabrik8

I wouldn't bother with the throttle body coating unless the entire rest of the intake tract is coated also, and even then I wouldn't worry about it because the temp difference from the outside to the inside is easy to maintain if the throttle body is thick. The plenum box (on your specific engine) has a lot more surface area to conduct heat, so that would be the more important area to coat if you're looking for temp improvements.


So you want to go with longer valves, AND go higher lift/duration on the cams? You better make sure those valves are plenty stiff and durable.

Wait, why do you need longer valves for that? Are you doing something radical enough that a small change in rocker/follower geometry isn't going to cover it...? Are you doing regrinds with a significant change in base circle diameter or something like that? Or do the valves just not have enough usable travel for what you need?


I know I've already said this, but I think a new intake design would help a lot, but I know how attached you are to that mechanical fuel injection setup and the other OEM anachronisms on that engine.

marlinspike

Well, yeah, I'd be coating everything. The throttle body isn't thick to begin with, and we will be shaving another 6mm off it. The air filter housing is covered in Reflect-A-Gold (can't be coated because there are integrated pieces on it that are plastic and won't stand the heat required).

And yes, I'm doing regrinds because there is only one company that will make blanks, it is in England, and it requires 1500 GBP to make one pair of cam blanks. The reason this necessitates longer valves is the regrind cams I have in there already use the largest available shims, and even then they're at the low edge of the acceptable range. When I say more lift/duration, I guess what I really mean is more duration and effectively more lift.

A guy who does regrinds for these (or did in the 80s and is still able to do them) told me that according to his memory boring out the throttle body made a big difference on cars that he had made cams for.

Laserjock

Look up the meaning of the term "law of diminishing returns" The reason I posted that comment is engines operate in a wiiiide temperature range and not in some fixed controlled laboratory environment. If you were to find this magic formula of air temperature, fueling, timing etc. how exactly are you going to apply this to real world scenarios?

Sorry, but I realize I don't have the skills or talent or time. It is great to question, theorize and discuss - but also intelligent to know the boundaries of reality. But then again, you may be the marlinspike of superlow-temp intake charge (nitrous oxide ring a bell?) of relativity engine tuning that the world has not realised, yet.

I wouldn't feel too terrible to be proven wrong if you can come up with the technology to turn my 38mpg 1.6 ltr SOHC into a 400whp, 90mpg daily driver with perfect drive-ability and -25 hydrocarbon, NOX, CO2 emissions that smells like lavender blossoms.