Throttle bodies. DTH vs DCOE style

[Alex Wong1697456877]

I've looked into this a bit but I'm still confused. I remember the CCC article extolling the virtues and extra mid range torque from a DCOE style setup on a caterham manifold (anybody got a copy of this article?) but I've also heard that tapered Direct to Head is the way to go (from FA and SBD - 2 people who I wouldn't have expected to agree on anything!)

 

So what are the views out there?

 

DTH vs manifold

 

Roller vs butterfly

 

tapered vs not tapered

 

Also, what factors determine the ideal bore and length?

 

Alex

[oilyhands]

Alex,

 

I think that the reason the DCOE style bodies worked as well as they did on that particular engine was connected with the bend in the manifold rather than the method of installation, at least that was the conclusion drawn.

 

DCOE style bodies are there as a means to an end, as direct replacements for DCOEs, it is very convenient to be able to re-use the manifolding and componentry carried over from a DCOE installation and you can pretty much guarantee a manifold will be available for any engine.

 

Unfortunately DCOE manifolds are not all wonderful. Since the linkages between the carbs are quite bulky the spacing between the carbs is quite wide and this can cause some misalignment between the barrel and the port, the bodies have fixed spacing between the barrels as in a DCOE which may not match the spacing between the bores of you engine, again causing some misalignment. DCOEs also need to be installed in a near horizontal plane which can cause the manifolds to have a sharp bend (not always good).

 

In most cases a fully tapered, perfectly aligned set of throttle bodies will give the best results and DTH bodies get quite close, especially the single ones where port alignment can be guaranteed. Dual DTH bodies are simply DCOE ones with a manifold flange grafted on rather than a DCOE one, these can be a lot better than the DCOE body/manifold combination WRT to spacing and especially to installed length allowing more flexibility with induction length, they are also less expensive if you dont already have a manifold.

 

Any TB installation will have to reduce in diameter / chan ge shape as it approaches the port entry, the more gently this is done, the less chance there is of the airflow breaking away from the port wall, a fully tapered system does this in a linear manner.

 

Roller barrel bodies should ultimately give more power since on WOT there is less drag thru the body, the body orifice doesn't have to be round either so it can more closely match the port entry shape, on F1 engines these are part of the head and match the port entry exactly. The airflow through them at part throttle has very different characteristics than thru a butterfly equipped body in that the latter has two airstreams at the top and bottom of the butterfly, whereas the roller will have effectively a growing aperture from top to bottom/bottom to top and a large deflection.

 

I have some info somewhere on bore size vs expected BHP and calculation of induction , but cant lay my hands on it right now, induction length would normally be finalised on the dyno.

 

Oily

[EFA]

Hmmm, an outbreak of upgraditus (again) in the Wong camp perhaps. (See once it starts, you can't stop it, says he who knows....)

 

DCOE's on a horizontal manifold (the one with the bend) will reduce top end power. Swindon make a straighter manifold for DCOE style TB's which reduces the effect, but still gives non linear flow across the rpm range which results in flat spots.

 

Taper bodies (whether DTH or 2 piece like the Jenvey SF's I use) speed up the flow at low RPM, giving improved torque, and massiveley improved throttle response if you suddenly open the throttle off cam.

 

Trumpet length - short gives more top end power less torque, long does the reverse.

 

Fat Arn

The NOW PROVEN R500 Eaterid=red>

See the Lotus Seven Club 4 Counties Area Website hereid=green>

 

[I reply to every thread]

At least upgradeitis has now been downgraded to a "class c" offence - in my house at least - but it cost me a ring!

[Blatman]

Congrats.......I think.

Must've been some sparklercool.gif

[I reply to every thread]

Yep - Good old Argos wink.gif

[Simos]

Did you go for the new direct to ring taper fit with rosette cut on the diamond or traditional clasp and octagonal cut ?

[I reply to every thread]

Straight cut, heavy duty with the "Black Pack" and FIA barwink.gif

[I reply to every thread]

In fact I do find it difficult to think of the ring in anything other than upgrade terms - Widetrack + carbon nose + LSD + .....etc etc - Does that make me unsuitable for marriage

 

PS Sorry Alex - bit off track here. I'll let you know if it ever runs again.

[tony pashley]

I've recently seen the website of a company offering a range of engagement and wedding rings machined from a variety of titanium based alloys.

They were a bit limited in their choice of stones though. The 'metalwork' parts were only a few hundred quid top, so would maybe need something special in the way of a stone to let you kid yourself that you've earned a whole lifetime's worth of conscience-free upgrades.

 

[R2D2]

Quote from "The Thoughts of Lazurus Long" out af a book called Time Enough for Love by Robert Heinlein

 

"Why buy expensive jewellery; Flowers work just as well and are much more economical"

 

Worth a try?

[Blatman]

I'm waiting until plastic rings are fashionable....teeth.gif

Oh, and some of that nice Cubic Zirconia please....teeth.gif

 

Edited by - Blatman on 30 Oct 2001 15:55:28