Throttlebody Design

[Batfink 201]

I have been offered the throttlebodies from a 93 mi16 supertouring car.

Now looking at the pictures they basically look like jenveys but the noticeable difference is the extremely short inlet manifold compared to the generic Longmans design most people have.

 

Now would running the throttlebodies so close to the head give a difference to overall power?

My thinking it would give a very instant throttle response and maybe everything at the top end? If the inlet manifold length is very important then how does the trumpet length affect things? Im confused to what each do now lol

[brianthemagical 1]

the tract length is from valve to trumpet end. longer, generally, lower down power, shorter, more powere high up and narrower power band. more than likely the mi16's reved a lot to get more power, hence the short length or they were made short to allow lots of ajustment in the trumpets.

[Batfink 201]

true. I've just been reading up on the Jenvey site and they stated that for high revving engines then roughly the optimum distance from valve to butterfly is 200mm

Now the touring car inlet manifold is only about an inch in length so i thought this would be a compromised system, but then I forgot that the valves are low down in the head so they may work really well.

 

So are most people then running too long an inlet manifold which is why we are often disappointed with the rr results. Certainly with using the jenvey/longmans setup on a standard mi16 I have seen virtually every car pop out between 170-176bhp at the fly (around 143bhp at the wheels), when many think you should be getting near 200bhp

[kyepan 291]

the pulsar ones, are much closer to the head too, maybe 40-50mm.Jthe pulsar ones, are much closer to the head too, maybe 40-50mm.J

[Sandy 191]

The only way to establish the ideal tract length for a given engine spec is to experiment. The are too many variables to provide a realistic mathematical model or to generalise too insistently.

 

My money though is on most people not running enough length. On engines peaking at less than 8500rpm, it's highly usual to get the best spread of power with less than 330mm from valve to mouth.

 

Here's a recent example I had of the effect of changing the length:

http://forum.205gtidrivers.com/index.php?s...c=80567&hl=

[James_R 3]

Did the 93 engine's still keep the 30deg tilt or were they dry sumped and running vertically upright then?

[Batfink 201]

early ones kept the engine tilted, only the later iron block ones ran with the engine position modified. Good as it means the early gearboxes fit straight on

Edited November 20, 2007 by Batfink

[James_R 3]

Be nice if they could be got hold of one though I've only seen a couple for sale ever

[Batfink 201]

i've only seen two for sale and I bought them! Dont know whether it was a good idea or not but I thought that it was a risk worth taking due to the rarity. Best place to look is on the continent as the 405 was far more successful and popular than its BTCC campaign here.

 

I think it will be interesting to see what the performance difference will be having the throttlebodies closer to the head, especially if I can get long enough trumpets to extend the whole tract enough, so similar method to what Sean did might be necessary.

I'm not expecting it to be better on a standard engine so it may need to rev higher for the advantage to show, which means cams for definite.

Edited November 28, 2007 by Batfink

[Miles 331 1 Cars]

Are you sure the Iron block engine was used, All the one's I;ve seen inc a couple of the phase 2's had the alloy block fitted.

[Batfink 201]

not sure to be honest - I thought the phase two ones were iron block (i'm sure someone told me that - so it may be i was misinformed)

Maybe phase two was just the redeveloped engine position then....

Apparently on the continent they had about 5 evolutions of the engine so that would be more fitting to develop the engine over a longer period rather than move to a different block

[Miles 331 1 Cars]

I know that Europe had at least 10 times the budget we had and they had a reliable engine with good power thanks to Sodemo, Shame we had nothing as both the 405 and 406 could have done well

[pdd144c 0]

They were alloy blocks Kev, the early ones were fitted with engine tilted and used the boxes you now have, the later engines were upright and used a different box. Did you get them from Marcus?

 

Both the 405 and 406 were poor in BTCC, infact no Peugeot backed car has ever won or come close to doing so!

[Batfink 201]

Marcus managed to put me in touch with someone who had a set