Are twin TB's possible?

[Ali]

Was just speaking to a mate who is planning to swap the throttle body on his rover 25 1.8. On the 1.4 it makes something like 15-20bhp difference by swapping it for a larger one but he's struggling to find one but can find loads of the smaller ones. At this point as a silly idea I suggested running two of the smaller ones instead, which then lead to me thinking about my own car!

Not sure how it would work because i'm guessing there would be a lot of complications with the stupid le-jetronic! Would be cheap to get two spare inlet manifolds and throttle bodies though and then start playing. Perhaps a similar setup to how Foggy's twin carbs are with two pipes going into each TB but i'm not sure how the throttle position sensors would work. I guess the pipework leading up to the TB's from the air filter would have to be a single pipe due to the MAF sensor and then just split into two for the TB's?

Really not sure how any of it works but hoping someone with more knowledge might be able to help as it'd be a cheap upgrade and would work well with megasquirt i'd pressume.

[SteveP]

Was just speaking to a mate who is planning to swap the throttle body on his rover 25 1.8.

Good on him, gotta make the most out of it before it breaks. But yeah, my mate upgraded his throttle body on the 1.4 K series and got a pretty noticable increase!

[340cbr]

The best way is... ITB's!

[classicswede]

I think if I remember correcty the 2.3 GLT machanical injection 240's tb is a couple of mm bigger. It would be possible to swap the spindles over and use them. Any fancy checking the size of a 360 one?

[foggyjames]

360 one is the same as all those which use that manifold, including the 2.3 turbos..if someone wants to look it up on Tbricks.

Loads of cars (including many older Volvos) run twin sidedraft constant depression carbs (SUs, etc), and it is indeed a great idea. Two stock 360 injection TBs on a modified 360 (B200K) carb manifold (twin Y) would haul ass. I even have a spare one of those manifolds...can't think why...

You would need MS, no question, as LE-Jet wouldn't begin to cope.

cheers

James

[classicswede]

The way I would do it is use a twin choke carb manifold as it is made up of 2 Y peices. You could cut the rest off and weld on a pair of flanges to take 360 tbs or similar.

[pettaw]

Isn't the throttle body for a 360 oversized anyway? IIRC the same size plate is used on the B230s as well.

Anyway, I've found with MS the throttle is fairly tickly anyway so it doesn't require much opening to cruise so if you were to fit twin TBs I would see if you can do some sort of staggered opening so you don't get driveability problems when not using a lead right foot

[jtbo]

Isn't the throttle body for a 360 oversized anyway? IIRC the same size plate is used on the B230s as well.

Anyway, I've found with MS the throttle is fairly tickly anyway so it doesn't require much opening to cruise so if you were to fit twin TBs I would see if you can do some sort of staggered opening so you don't get driveability problems when not using a lead right foot

Indeed, I have had trouble to adjust idle enough low at warm and enough high when cold because even small opening is giving lot of air.

With naturally aspired engine 360 throttle body is enough to deliver air for over 150hp easily, some site says that turbo does not even need as big throttle body as naturally aspired engine, but don't know about that as some ppl seem to disagree.

Staged throttle plate opening is not too hard to build, but I think manifold is much harder, all that welding involved and how to make it connect tight to head, need quite precise manufacturing, machines I have none of those

Some are using twin barrel carbs as throttle body, don't know how well that works and also that building is problem.

K-Jetronic has bit bigger throttle plate, but there is some resistance in air metering part so I guess it is made bigger for that reason.

Also I think we have little problem with megasquirt to react fast to low throttle area is because originally there is air meter thing to restrict and throttle body is made bit bigger for that reason.

I have even CAIRAM or what the ricerthing was again called, tube to fog lamp hole that makes air being pushed to airfilter box at velocity of car is going so that makes low throttle even more sensitive when cruising 80kph I think that I never use more than 1/3rd of throttle when cruising, goes too fast otherwise and beatufil policewomen gives ticket, lol.

[Chris_C]

I have even CAIRAM or what the ricerthing was again called, tube to fog lamp hole that makes air being pushed to airfilter box at velocity of car is going so that makes low throttle even more sensitive

Just don't go through any deep puddles then Jani

Actually, I'm trying to work out whether a ram air filter thingy would do me any good, but I'm trying to work out where to mount it so I can still go through the odd ford, any ideas?

[jtbo]

I have even CAIRAM or what the ricerthing was again called, tube to fog lamp hole that makes air being pushed to airfilter box at velocity of car is going so that makes low throttle even more sensitive

Just don't go through any deep puddles then Jani

Actually, I'm trying to work out whether a ram air filter thingy would do me any good, but I'm trying to work out where to mount it so I can still go through the odd ford, any ideas?

Problem is that there is no space, front of radiator would be ok place, behind grille, but there is no way to get decent diameter duct there. Ok, you could put it under radiator then back to up, but distance is then so great that I doubt that there is any improvement then.

[foggyjames]

I'd run it through one of the two intake holes either side of the radiator, having enlarged it first. Thats what Husky did to run his intercooler pipes.

It'll be interesting to do a power pull once you get that K cam in Andy...do a direct comparison (albeit ignoring compression ratio).

cheers

James

[classicswede]

Isn't the throttle body for a 360 oversized anyway? IIRC the same size plate is used on the B230s as well.

Anyway, I've found with MS the throttle is fairly tickly anyway so it doesn't require much opening to cruise so if you were to fit twin TBs I would see if you can do some sort of staggered opening so you don't get driveability problems when not using a lead right foot

Spot on the TB is pleanty big enough. What you have to remember is only one cylinder at a time is drawing air through the TB. The reason for putting a twin Tb (or quad in James's case) is to give the air a more direct route with less restriction.
Set up with two TB's on seperate manifolds would need a matched pair opening at the same time.
If you were using a common manifold you could use the same idea as progressive carbs with a small primary butterflly. The other one I have seen done is progresive TB's for each cylinder!! Good low down and very responsive but maybe not the out and out best flowing at the top end.