Vx - Weber 48 Vs 45 vs Throttle Bodies

[keybaud]

My car is an ex-Vauxhall Challenge car with Weber 48s. which are famous for being lumpy at 3k to 4k RPM, as well as not being vaguely economical. I want to get better economy on the road, without losing the brutal acceleration the 48s have (when they get past their stuttering fit). Has anyone else gone from 48s to 45s or throttle bodies and, if you have, how much was it and was it worth it?

 

The engine was measured at 230 BHP on hydraulic cams, which is their limit, so I may need to change these as well. Again, facts and opinions welcome.

[andy_h]

I too have an ex VX challenge car but I'm not sure I can help too much, however I'll try.

 

When I rescued my 7 from its first owner it already had 45's fitted and 48's in a box, so I never knew what it was like to drive with the 48's fitted. However, the performance was suburb and a rolling road gave 210 but he advised the top end needed a rebuild as the springs were going soft. I didn't (have the funds) and I'm happy missing a few horses. Shortly sold the 48's but every now and again I wished I hadn't. Running the 45's I don't get any stutter as long as they're kept in tune.

 

Ian R on here also has an ex VX challenge and has converted his to throttlebodies and has about 210 from from memory.

 

Summary, try the 45's and if you don't like them swap back. If you want a bit more power I think bodies will give it. It you lose our 'old school' song 😬

 

Cheers,

Andy

 

 

[oilyhands]

I went from 48 DCO/SPs to Jenvey 45s on an natasp YB cosworth with similar output, a single brain cell decision. The 45s should give more power as the efrective venturi area is larger (most 48s have 42 or 44mm chokes) and there is less clutter in the way of the air stream. you dont lose the carburettor 'bark' either. Since the engine will be injected it will suffer less with reversion and 'dirty' mixture due to standoff. There was a marked improvement in output, tractability and economy and still a glorious soundtrack.

 

45mm Jenveys are good for 280BHP at least.

 

Oily

[Paul Deslandes]

I have 48mm Jenvey throttle bodies on my Vx using the original CC Weber inlet manifold and it is very docile and drivable, all down to expert mapping by Steve Greenald at Track n' Road. Unless you go for some form of direct-to-head TB you'll need to retain the inlet manifold which is notoriously poor but can be redeemed by careful gas flowing and matching to the head. This has the advantage of needing only very minor mods to the inlet hole in the bonnet, if at all.

If you're truly getting 230bhp from your engine, your manifold and head must almost certainly have been gas flowed already so you're well on your way and, unless you want even more power, I'd stay with your cams and enjoy the huge improvement in driveability that the TBs will bring.

[keybaud]

OK, I'm going to go for throttle bodies, but I have 2 more questions for the C20XE gurus:

 

1. Is there a noticeable difference between Direct To Head throttle bodies and those running on the Weber manifold?

 

2. As the engine was previously mapped at 230 bhp by Troy, should I be putting 45mm or 48mm throttle bodies?

 

I'm erring on the 48mm on the existing manifold, as I don't want to get a new bonnet and have it resprayed; however, if it's reasonably simple to just expand the existing hole to accomodate DTH, then maybe I ought to do that.

 

Hmm, do they sell decision on ebay?

 

Opinions, facts, red herrings and deviations welcome...

 

Edited by - keybaud on 24 Apr 2012 22:32:58

[Tyrone]

Yeah, but will it help with star cracking in the gel coat?

 

Wish I could help Si, but I can't

[Paul Deslandes]

I stick by my earlier comments re the DCOE manifold, plus:

 

1. probably not if the manifold has been gas flowed. Otherwise definitely

2. 45mm will be good for 230bhp and will improve drivability at small throttle openings over 48s. Although I have to say that my 48s work very well at the bottom end.

3. If the manifold is matched to 48s, fitting 45s may result in a step at the TB/manifold interface which will not improve gas flow. So if you're staying with the DCOE manifold you might be better going for the better matched 48s. As I say, mine drives beautifully with that combination.

[zetec]

Get someone like northampton motorsport to tune carbs & they wont splutter at any revs then you wont need to spend huge money to go throttle bodies & spend it on fuel instead!!

[EFA]

What you need are tapered throtle bodies like Jenvey SFs.

 

They do various sizes - if you are truly getting 230bhp you will be OK to go to 51mm versions (the taper design means they provide far better gas flow than others in the market. For the additional cost over the cheaper DTH versions they are well worth it.

 

What is critical to good low speed running and low down pickup is injector positioning. The SF setup allows the injector to sit closer to the port. You will get away with a 390cc/min injector at 3 bar fuel pressure and get smooth running.

 

They will work with most programable ECU's but MBE is preferred.

 

What you will notice compared to carbs is an astonishing increase in low and midrange and the taper bodies prevent the charge stalling and are not induction dependent for fueling.

 

And there is no change in the noise, other than it is smoother. You still get the bark if it is set up properly and you can program the fuel overrun to give backfires and spit flames from the exhaust as required.

[Paul Deslandes]

I sill have a set of pico 'yellow' injectors available for sale here if you're interested. Offers considered.

[Paul Deslandes]

Incidentally, if you have any doubts about switching from Webers to injection, read this article from CCC some years ago where Dave Walker compared available injection kit against optimised Webers, including the tapers that Arnie referred to. Apart from the comparisons, one of the most interesting outcomes was the differences in performance with varying the trumpet lengths which, whilst not surprising, it was interesting to see them quantified - see also, recent discussions on this site re mixed lengths.

 

I had an interesting conversation with one of the Jenvey engineering guys at Autosport a couple of years ago regarding the pros and cons of tapers versus standard 'parallel' TBs and his view was that it wouldn't be worth changing to tapers from parallel.

 

As always, it ends up by being a budget consideration. If you've got a gas flowed manifold and you'd rather keep and use it with parallel TBs, you can save some money by not going to tapers. However, if you can spend the money, you might see a slight benefit by doing so although I doubt you'd notice it on the road. And you avoid having to restyle your bonnet.

 

Paul

 

Edited by - Paul Deslandes on 25 Apr 2012 13:46:15

[keybaud]

Quoting zetec: 

Get someone like northampton motorsport to tune carbs & they wont splutter at any revs then you wont need to spend huge money to go throttle bodies & spend it on fuel instead!!

 

The car was tuned by Troy, but he couldn't get them to be smooth at low revs and high revs, so the previous owner had it tuned for high revs. The internet seems to concur that Weber 48 can stutter below 4k, but I guess it may depend on how the engine is setup, etc...

[kenny.]

Which hydraulic cams can achieve 230 on a VX, and what other mods are needed to go with it?

[Neil66]

Quoting Paul Deslandes: 

Incidentally, if you have any doubts about switching from Webers to injection, read this article from CCC some years ago where Dave Walker compared available injection kit against optimised Webers, including the tapers that Arnie referred to. Apart from the comparisons, one of the most interesting outcomes was the differences in performance with varying the trumpet lengths which, whilst not surprising, it was interesting to see them quantified - see also, recent discussions on this site re mixed lengths.

 

I had an interesting conversation with one of the Jenvey engineering guys at Autosport a couple of years ago regarding the pros and cons of tapers versus standard 'parallel' TBs and his view was that it wouldn't be worth changing to tapers from parallel.

 

As always, it ends up by being a budget consideration. If you've got a gas flowed manifold and you'd rather keep and use it with parallel TBs, you can save some money by not going to tapers. However, if you can spend the money, you might see a slight benefit by doing so although I doubt you'd notice it on the road. And you avoid having to restyle your bonnet.

 

Paul

 

Edited by - Paul Deslandes on 25 Apr 2012 13:46:15

 

I miss triple C....

[keybaud]

Quoting kenny.: 

Which hydraulic cams can achieve 230 on a VX, and what other mods are needed to go with it?

 

I don't know the exact details, but the relevant bits from the previous owners website (http://www.reeve.ws/Caterham.htm) are listed below:

 

It is fitted with Piper Cams of a development profile, which unusually for an engine of this rating, use hydraulic tappets

 

The cams operate on valve gear using uprated duplex springs, uprated steel spring seats, and uprated titanium retainers, all for reliability at higher operating speeds. The cams are timed using a set of Piper vernier type cam pulley's.

 

Edited by - keybaud on 25 Apr 2012 22:23:28

[EFA]

Oh, I built that engine! - the one with the Bugatti blue block right?

 

 

Edited to say "The car parked behind it is a bit of a give away!"

 

Edited by - EFA on 26 Apr 2012 22:53:42

[Johnty Lyons]

I miss triple C...

He still writes excellent stuff in Track Driver

[kenny.]

I'd never heard of those piper development cams before. The figures seem to suggest they are a far better bet if retaining the hydraulic lifters.I've used 420H on three occasions now and have also had the the Swindon Hydaulic items.

 

One of the 420 set ups had a ported head, larger valves and ran on Jenveys/DTA and a few other insurance bits.

 

The Swindon set up had a lightly ported head,matched and gas flowed inlet and ran on 45s (carbs).............best I got at WGT (very mean rolling road, no "shoot out" days etc) was 190 @wheels.

 

Do they still make these or are they badged with a number?, as I'd like to give them a go in my VX powered Mini..........which at present also has the QED offerings and runs on 45s.

[keybaud]

Quoting EFA: 

Oh, I built that engine! - the one with the Bugatti blue block right?

 

 

Edited to say "The car parked behind it is a bit of a give away!"

 

Edited by - EFA on 26 Apr 2012 22:53:42

 

Do you have any more information about the engine, over and above what John has written on his website? For example, I think the head and inlet manifold have been worked on, but I don't know what was actually done apart from 'porting'.

[EFA]

Keybaud,

 

It was lightly ported and the manifold was matched. I say "was" as John had to have it rebuilt when it spun a bearing - I'm not sure how much of what you have now is original.

 

It did have steel rods and forged pistons, and lots of other good bits I accumulated over 15 years of messing with XE engines but I can't vouch for what is in it now. There was valve-piston contact I believe.

 

A quick search on my PC revealed this spec document from when John purchased it: here

 

Kenny,

 

"190 at the wheels" is a pretty meaningless figure, as has been discussed on this forum in the past, as you have no idea what the losses are. And the losses vary so much due to tyre width/compound/pressure, tightness of straps, ambient conditions, weight of car/ driver. etc.

 

Said Piper cams are very old and have some odd attributes in terms of lift vs duration. They were my first delve into weird cams used in K2RUM all of which had very long duration and limited lift, hence K2RUM unusually strong tracktability vs power.

 

Edited by - EFA on 28 Apr 2012 08:36:27

[keybaud]

Quoting EFA: 

Keybaud,

 

It was lightly ported and the manifold was matched. I say "was" as John had to have it rebuilt when it spun a bearing - I'm not sure how much of what you have now is original.

 

It did have steel rods and forged pistons, and lots of other good bits I accumulated over 15 years of messing with XE engines but I can't vouch for what is in it now. There was valve-piston contact I believe.

 

A quick search on my PC revealed this spec document from when John purchased it: here

 

That's fantastic, thanks a million. The key bit for me is the information about the head, as I was unsure whether I should swap it for the Coscast. Having read your document, you've put my fears to rest.

 

 

 

Edited by - keybaud on 28 Apr 2012 08:32:42

[EFA]

No all the Coscast stuff is bollox.

 

If they have not gone porous, the GM heads are fine. And they would have gone porous years ago if they were ever going to.

 

If the innards of the engine are of similar spec, the best thing you can do is fit it out with Jenvey SF injection. Won't do much for top end power, but will do huge things in the midrange and bottom end. (not to mention fuel economy)

[keybaud]

Thanks for the information everyone has provided, but I have a few final questions, afterwhich, you can all relax again:

 

Looking at Jenvey's website, is this what I should be looking at: http://www.jenvey.co.uk/home/throttle-body-kits/jenvey-dynamics/opel-vx-2l-xe-sf-taper-throttle-body-kit-ckvx07. I assume that if I want to go for the individual Jenvey SF tapered throttle bodies I'll need the dedicated manifold as the current one with the Webers won't be suitable, or will it?

 

Is there a reason for choosing tapered over parrallel and individual over pairs?

 

If I need an new manifold, is there an angled manifold that would put these throttle bodies at the same angle as the carbs, to avoid cutting a new hole in the bonnet or could I make the cut-out large enough without ruining the bonnet or making the hole look ridiculous?

 

My brain hasn't exploded from all the excellent extra information I've received so far, but I think I may be getting close... :-)

 

Edited by - keybaud on 29 Apr 2012 10:08:51

[Neil66]

Quoting Johnty Lyons: 

I miss triple C...

He still writes excellent stuff in Track Driver

 

Thanks Johnty - good tip just got the iPad app ;-) It's hard to keep up with things when out of the UK scene for so long!

 

Still miss triple c as a whole package not only Dave's articles though great they were (are) ;-)

Looked fwd to it dropping through the letterbox every month...

 

 

[millsn]

he does still write monthly in practical performance car