Throttle Bodies - why?

[The Black Flash]

900T-R said:

The Black Flash said:

So it still seems to me that they're of most benefit on fairly tuned engines using cams with high overlap, and / or which will run at WOT a lot, and / or which have restrictive inlets to start with, and of much less benefit on a mildly tuned road engine ?

I think that in the latter case, the throttle response advantage still stands.

Oh sure, I guess they'd be of some benefit in most cases. It's just a question of where best to direct limited cash.

Damn that limited cash.

[Snake the Sniper]

With the Alfa V6 upgrading the inlet is worth a good few ponies. A good set of ITBs and megasquirt can be had for about £400. Then you just need to sort 6 manifolds out, although they are basically straight bits of tube with plates on. Unless you want to get fancy and have two crossing sets of 3, or all 6 pointing straight up. Couple that lot with the GTA inlet cams , which can be brought new from Alfa for about £130 each, with re-timed exhaust cams and a decent exhaust and you should see about 230 bhp or so, about 30/40 up on stock.

[900T-R]

The Black Flash said:

Oh sure, I guess they'd be of some benefit in most cases. It's just a question of where best to direct limited cash.

Damn that limited cash.

You've got that right.

[firstmk1]

Q: Throttle Bodies - why?
A: The noise!

[HarryW]

rev-erend said:

Yes - for the SEAC..

No not from John Eales ..

Going with 48mm bodies - hope it will be big enough.

48mm big enough for 400 bhp ?

Jenvey reckon that 48mm TBs are good for 74hp each so 592hp for the V8 is that enough, see here http://www.jenvey.co.uk/Tech_QA.htm

[rev-erend]

That sounds plenty .. was offered upto 55mm.. bit to large for my humble motor

[Mr2Mike]

rev-erend said:

Yes - for the SEAC..

No not from John Eales ..

Going with 48mm bodies - hope it will be big enough.

48mm big enough for 400 bhp ?

I'd say they are too large for 50bhp/cylinder. 45's would more than adequate.

[Snake the Sniper]

40's would be worth a look to. It's better to be slightly under sized than over sized as you get a better throttle response.

[900T-R]

Snake the Sniper said:

40's would be worth a look to. It's better to be slightly under sized than over sized as you get a better throttle response.

OTOH with a plenum each cylinder would see a 65 or 72 mm throttle, so going too small on the TBs could be a restriction even if the total surface area of the eight butterflies combined exceeds that of the single one by far.

[Snake the Sniper]

I suppose it depends what he's looking for from the engine, and whether he's looking at using 8 ITBs or one or two large plenum based ones. I assumed 8 ITBs when saying 40mm.

[Mr2Mike]

Snake the Sniper said:

I suppose it depends what he's looking for from the engine, and whether he's looking at using 8 ITBs or one or two large plenum based ones. I assumed 8 ITBs when saying 40mm.

From Jenveys rough guide 40's would be pretty much at their limit. 48's would flow enough for 50% more power again, which makes me think they are probably too large. A typical 2.0 4 cylinder engine such as the Vauxhall 20XE can produce well in excess of 200bhp on 45mm TB's (with appropriate cams and head mods etc.)