Technical 38mm TB is too small for my engine

[arc]

If i floor my car, the vacuum gauge reads 0, which is correct. That is, until it reaches around 4000rpm, then it begins reading an ever increasing slight vacuum again.

This says to me that there is a restriction on the inlet. Considering my head has had the valve guides cut back and been ported with the inlet manifold ported to match, it must be the TB.

I could send my spare TB off to tricker and get it taken out to 43mm. BUT, i'm hoping to kill two birds with one stone here. I currently have no idle air control. this is because FIRE units use stepper motors. My ECU cannot control this at the moment (i can modify it to make it work.. but it's a lot of faff), soooo what im looking at doing is making another TB fit. Does anyone have any suggestions of a car with a TB bigger than 38mm, with a normal PWM idle control valve that would be 'easy' to fit onto a P75 manifold?

 

[Brooky]

A bigger bob??

*cough*, all my stuff will be for sale some time in the near future *cough*

 

[arc]

the butterfly is smaller than the bob. it's gotta be the TB

 

[allanhelen]

Brooky might have something here

I remember John going on about bob design a while ago and that the STD 899one was a hinderace to getting enough air into the engine especially at high revs (swirl or something), maybe as yours is a bigger capacity engine you could have reached that limit???? guessing here

 

[arc]

the bob might be a restriction, but i dont think that is causing this. i'll see if i got the k&n kicking about and try that, it'll rule out the bob im pretty sure.

my SPI engine had smaller ports, and used a 40mm TB. The MPI has much bigger ports.. and a smaller TB, silly plan!!

 

[fingers99]

Kripit and Aaron are using K Series TBs (although Aaron recons it's too big). I've TB hunting yet to do..............

 

[h2ypr]

What about a rover TB? The 1.8 vi/gti is a 52mm. So the 1.8 must be 42/44?

Ross

 

[h2ypr]

Kripit and Aaron are using K Series TBs (although Aaron recons it's too big). I've TB hunting yet to do..............

Man thats weird. I just posted that. Didnt know they were running that.

Ross

 

[arc]

i think i'll be spending a while at the scrap yard tomorrow

i'll check out some rover 1.8s

 

[randomizered]

Why not remove the bob and intake, and drop a filter straight on top .... simply for one run down the street at WOT....see what happens

How many bolts hold that down? 2?

For a PWM valve, you still will ahve to have the connection on the intake manifold somewhere after the throttle body

Good luck with your hunting

Krisitan

 

[randomizered]

Man thats weird. I just posted that. Didnt know they were running that.

Ross

Adpating mine to fit is a pain in the arse lol, so its not on yet I woul dalso love to find a simple bolt on, but no luck yet.

 

[J333EVO]

Yeah we run a Rover K series TB on the Sei (which sure Arc knows from speaking to me/looking at car) IIRC its about 45mm, but Chris when he was mapping it thought that it was slightly oversized as engine was making full power before WOT, no gians were made at WOT. Though we will check it out again when we go back hopefully this month with Jamie for some runs as car goes so much better now than it did before.

Aaron.

 

[fingers99]

Yeah we run a Rover K series TB on the Sei (which sure Arc knows from speaking to me/looking at car) IIRC its about 45mm, but Chris when he was mapping it thought that it was slightly oversized as engine was making full power before WOT, no gians were made at WOT. Though we will check it out again when we go back hopefully this month with Jamie for some runs as car goes so much better now than it did before.

It could well be that the engine was simply too tight to give more. Look forward to the results at the dyno!

 

[randomizered]

The rover I have is 48mm, I'll measure later to check. This is a fair bit bigger than the 1.2 16 TB that comes with the 1.2 inlet, but if you compare the butterfly size to the 1.4 manifold and it's TB, its only about 1 or 2 mm larger, so it could also be the 1.2 inlet is too restrictive for the larger throttle body?

Kristian

 

[J333EVO]

The 1.2 inlet is up to the job, the overall area of throttle body is smaller than the combined area of the 4 inlets, so the inlet is not a restriction, although yes I know only one port open at a time, but in thinking that you would need all the inlets to be as big as a throttle body, and then you would think about the fact if it’s too big the air speed will be too low.

As that leads on to the whole thing about volumetric efficiency that dictates that even with lots of flow work mods done a N/A engine is not going to fill the combustion chambers at an engines operational speeds, hence why forced induction as more volumetric efficient.

We have a plastic K-series TB with it's fancy tear drop shaped butterfly that speeds up air flow helping volumetric efficiency, very clever design that was only ruined by overzealous mechanics over tightening the intake pipe and crushing the top of the TB, so they reverted to alloy on later models. The butterfly is a good few MM bigger than the 1.4 one we had, though with the spacer plate it is stepped down to 43mm to match the 1.2 inlet size.

 

[arc]

i thought the Sei TB was 54mm?

Anyhoo, i've just done a test run with the K&N on there instead of the GSR kit and the results are the same, so it's fair to say its not the filter clogged, or bob design causing this one. Once the weather improves i'll mooch on down to the scrap yard and see what i can find

 

[arc]

ok, been doing some more testing.

I opened the idle control valve wide open, this means with the throttle closed the revs are approx 3k. to me, at full throttle now it MUST be getting enough air - granted its not swirling right, but the i should see results on the vacuum gauge. i didn't.

If look on here, next to the very large yellow (!), you can see the MAP value trailing away from the throttle posisiton value as the revs increase.

I've looked at where the take off is for the vacuum gauge and ECU, and i put it here;

Its on the back of the manifold, out of the where i'd expect the air flow to come down. Pete suggested it could just be the placement causing it, which fits. The air is flowing from the TB in the middle of the manifold and then away from the take off toward the inlet ports, i suppose that could cause a vacuum to exist on the vacuum lines.

Might move it, to the other take off and try it again.

 

[arc]

i moved the take off to the back the TB. It still did it, but it also vastly reduced (around 0.3 bar) the minium value that the gauge displayed on overrun. it upset the running of the car too

 

[gazzaman2k]

will not one of these sort it?

 

[arc]

is that a 43mm tricker TB? how much did it cost, and can i borrow it?