M20 ITB's

[bradnic]

Here are some more pics I've found

[digger]

Anyone want to comment on the ITBs used on the Hartge H27SP? I found this over on e30zone. note runner length, plenum. Seems like it would perform better than dbilas. Hartge claimed 220HP with 2.7L and 10.2:1 CR.

the runners look pretty fat still, where does the linkage go?

[bradnic]

Anyone want to comment on the ITBs used on the Hartge H27SP? I found this over on e30zone. note runner length, plenum. Seems like it would perform better than dbilas. Hartge claimed 220HP with 2.7L and 10.2:1 CR.

[bradnic]

this thread is friggin awesome. sub'd hoping for future posts

[F34R]

That makes 2 of us then, I suspect there are many others that feel the same way. Comparing an S54 to an M20 is not really what the point of this thread is.

I went the built m20/boost route instead of buying a S52. So that is another loony person on the list.

S54 is amazing, but it is not built as well as a m20. The cost of the piston rings alone are stupid expensive.

I think the work involved in a cam'd, built out the ass m20 with boost it much more amazing than a swap.

[digger]

When you get a chance I would be very curious to see how 38mm throttles ~1-2" from the head would work on a 3.1L stroker, compared to 40mm or 42mm. Hopefully I didn't "choke" it down to much.

a 210hp M20 only needs 32mm diameter at port entry so the fact that the stock 885 is about 38-39mm at the port means it is too big already.

38mm would work fine and can support 300bhp which needs a head that flows ~200CFM @ 0.450-500"

[mr ilia]

I'm using the same tbs on my m42 itb setup and s14 intake plenum. hopefully will done by spring. Everything is custom in my build and not all tools are readily available. It takes time to work out little things.

New setup in progess: 38mm BMW 1200RS Throttle Bodies






This is still a work in progress but I know another person on here has a completed setup using the same bits, and it's running well. 38mm should be able to outflow even a well worked intake port easily while still maintaining proper port velocity. Another plus is it allows the throttles to be placed very close to the head, taking up less space and allowing for a proper plenum.

[e30leigh]

man wish i had itb's. these setups look awesome!

[tinkwithanr]

When you get a chance I would be very curious to see how 38mm throttles ~1-2" from the head would work on a 3.1L stroker, compared to 40mm or 42mm. Hopefully I didn't "choke" it down to much.

[digger]

the reason for not using 45mm is not so much the transient response, it is velocity at WOT, though there would be better throttle 'resolution' with smaller throttles i.e. with big throttle the engine might be at effective full WOT at 75% TPS which might limit the extent of the ECU map usable and driveability would not be ideal

The velocity which needs to be a certain speed to work best without being too fast nor too slow which is determined by the diameter of the runner. I use pipemax which tells the diameter at the head and also the plenum and from that you can work out how big the throttles should be depending on how far along the runner you are.

when i have access i'll run a standard engine and mild stroker, from memory 36mm at the head is a decent starting point so 38mm throttles a bit further upstream is close to hitting the mark or 40mm for a bigger stroker

[SlamedIAm]

Any info on what is required for those 1200rs throttle bodies? I'm curious to see the results.

[fporro]

Maybe is not the size but the motion.

Everyone more or less agrees that 45's bog down and 38's react faster to throttle changes through mid to upper rpm range, yes?

I think butterflyes are the couse of that assertion, why?, well... their airflow increase does not match the headflow volume increase, realistically the slider type itb's would work better as inlet size volume has a more gradual curve while the buttreflyes go from semi open no load to this upper and lower planes in no time, resulting on bog-down feel., they give more flow than actual intake valve can ingest at given rpm, a more gradual increase would be the trick.
A runner inler profile matched to a head rpm flow requirement would be the ...
visualise it, the inlet port and slider can have any proflile design to match any given cam.


It is posted somewhere, but what's the real max flow rate of any given cylinder allowed per inlet valve/whole head?, say like on a 3.1 stroker, and, what itb diameter will acommodate it ? we're talking n/a now. That should clearify what itb diameter is best.

I've always like the idea of spring loaded exhaust pressure regulators, they are this metal flaps that you make, insert given disired pressure springs and install in pipes., they collaps as pressure decreases hence keeping velocity up.

It works same on inlet side, place it in runner and is collapses as map decreases, hence increasing or as I would like to think, manteining velocity in runners.

Sorry for rant.

[tinkwithanr]

New setup in progess: 38mm BMW 1200RS Throttle Bodies






This is still a work in progress but I know another person on here has a completed setup using the same bits, and it's running well. 38mm should be able to outflow even a well worked intake port easily while still maintaining proper port velocity. Another plus is it allows the throttles to be placed very close to the head, taking up less space and allowing for a proper plenum.

[digger]

it's still subjective and typically optimistic. There are so many more things at play that affect drivetrain loss.

also, what it makes at the crank is much less relevant than what it really makes at the wheels.

not really you want the crank hp to know what changes to an engine actually do. you could make a positive change that results in more crank hp that shows up as a lower wheel hp because of something that has increased the drive losses inadvertantly or by error/oversight in the measurements process. Chassis dynos are not accurate or consistent enough to measure some changes especially if not done immediately back to back.

[digger]

i assume it uses coastdown, some only use a fixed percentage. They are approximations and there is nothing majorly wrong using one of these methods as long as the correction used is also shown.

One of the reasons that coastdown is not correct and never will be is that some proportion of the real losses is a proportional to the torque input so when coastingdown as the engine is not loaded in the same manner it can never be perfectly correct