Carbs changed for throttle bodies

[richard bradbury]

I have been running my 1992 Vx HPC for 11 years and mileage is now 30k. It is still on the original carbs but with QED 42H cams, DTA ignition and a throttle pot. Big-end bolts are upgraded. I have carried out some SBD mods to help prevent oil surge and loss of oil out of the cam cover breather. I have an Exhaust by Design 4 -2-1 exhaust feeding into a Raceco silencer. Power on Southern Carbs rolling road was 192bhp, but I am now considering going to throttle bodies via SBD, who are not very far from me. I don't want to go to the expense of an injection fuel tank, but understand an alternative is to have a collection tank in the engine bay, and high pressure pump to the throttle bodies.

I am hoping for improved driveability, and a bit more power and torque. I dont want an engine where all the power is at the top end so will be retaining the existing cams. I appreciate that any power gains are not likely to justify the cost involved, but I am expecting to up the power to about 200-210bhp. I understand the Caterham inlet manifold is a restriction to gain more power, but a direct throttle body to head system would seem to overcome this problem.

Has anybody gone down a similar route and what sort of result did you get?

 

bradders

[Gambo]

I got more from going to throttle bodies from Q42h's than going from standard to q42H's , IYSWIM. I converted my carb tank, which worked fine. Now has a problem( but KNow what it is and why) My fault. 😳 Throtle bodies give you much better driveability, BUT, if you do track days, you will find them a lot noisier than carbs with k&n's.

Blat mail me your number and I'll give you a ring , or call me on 01446 773502 if you want to chat about it.

RED 2.0 HPC 230BHP here

 

Edited by - Gambo on 19 Jul 2007 18:54:20

[stevefoster]

I went to TB's with only a little difference in top power I only have standard cams so that may be irrelevant - better driveability definitely.

I got a power jump when I fitted a through the bonnet race exhaust with a 2.5" dia collector.

I did change the tank. Seemed easiest / lightest solution.

You could use a fuel swirl pot with built in injection pump. VW golf one suits. Need to find somewhere suitable to site it.

 

Hants (north) / Berkshire club here

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My Racing here

 

 

Edited by - stevefoster on 20 Jul 2007 12:16:41

[Paul Deslandes]

Hi Richard

 

there was an article in CCC some years ago by Dave Walker showing that whilst you can optimise Webers at any particular revs by changing the jet and choke sizes, its nigh on impossible for them to be correct across the range. Injection/throttle bodies overcome this problem but all types require an ecu and some form of high pressure fuel feed/return.

 

There are three ways to do injection (not including the original Vauxhall Astra approach):

 

1. Jenvey 45 or 48mm Parallel throttle bodies using the Caterham inlet manifold. This minimises any hacking of the bonnet to accommodate the air filter. The main problem from my experience, and not necessarily shared by others, is that the Caterham inlet manifold is very restrictive of airflow. Mine was flowed at the same time as the head and the difference was enormous.

 

2. Direct-to-head type from QED (also Jenvey(?) but I believe proprietary to QED). This overcomes the manifold issue but the air filter will almost certainly need the hole in the bonnet to be enlarged/moved.

 

3. Tapered bodies, also Jenvey and available from SBD, which have a separate manifold section per inlet and the same manifold advantage and bonnet issue as the direct to head.

 

With parallel bodies and the flowed inlet manifold and ported head, my engine torque and power exceeded the expectations of the cams fitted so I see no particular disadvantage in using them over direct to head or tapers.

 

You may get a small increase in peak power from injection over carbs but the biggest improvement will be in all-over driveability because the fuelling and ignition advance will be correct at all engine speeds and throttle openings so the economy improves as well. Given a decent exhaust, which you have, the biggest potential power improvement would be to get your cylinder head gas flowed and ported. You can then tune your engine for road, track, race or what-have-you by cam selection. The inlet trumpet pipes are available in different lengths and can have quite an influence of torque against revs. Generally longer means more torque lower down with a slight loss at the top end. I went from 45 to 90mm which helped a bit. This was also evident from the CCC article which I can email to you if your interested.

 

My car has the standard carb fuel tank with an extra return pipe welded in plus a swirl pot mounted in the boot. Fuel is fed from the tank by the low pressure pump into the swirl pot and then by a high pressure pump to the fuel rail via a couple of filters. The plumbing for this was a pain and since then I've done three cars with CC injection tanks with submerged h/p pump which is a heck of a lot easier. The swirl pot and extra fittings probably come out more expensive than the injection tank so I should do the sums first before rejecting the injection tank which you might be able to get second hand on BC. You have to have an h/p pump either way and the swirl pot hassle shouldn't be underestimated!

 

If you want to come over and look at mine or have a chat give me a call.

 

Paul

 

 

 

Edited by - Paul Deslandes on 20 Jul 2007 15:02:16

[Paul Deslandes]

...oh, and of course there are roller throttle bodies 😳

 

 

[ECR]

I have the parallel Jenvey bodies as I wanted minimal bonnet cutting. They work fine. However I have suffered 5/6 cracked inlet manifolds (one of which was Swindon the rest Caterham) due, I am fairly sure,to harmonic vibration, and can only cure this by running Misab washers instead of the Jenvey O ring seals.

I know of four 16V Vauxhalls that have had this problem but it is by no means universal (only on engines revving above 8K ?). If I was starting again I would go for the Jenvey taper bodies and accept the bonet mods.

[captain chaos]

ECR,

Do you know of anyone who has gone from using the caterham manifold over to DTH set up and if there was any power gains due to the improved airflow?

Also, any ideas how much it would cost us (ex bonnet mods) to make the swap?

 

Gary

[ECR]

Jenvey recommend that I stay with my current set up as the butterflies tend to be a little close to the head/valves on the other variants. This can be overcome with spacers apparently..

I don't know anyone who has made the swap and I haven't costed it out yet.

[richard bradbury]

Thanks for all the info chaps, especially Paul Deslandes who has been a great help already. There is obviously a lot more to consider than I originally thought, and costing it all out might be a bit problematic.

By the way Paul, since we did the work on my engine it seems fine and I had no probs at Prescott, but I still get some funny oil pressure readings, mainly when the engine starts from cold. When warm and pulling it gives normall readings and also at idle, so I don't think there is anything fundemental wrong.

Anyway, food for thought and I think the next move is to have a word with SBD and discuss costs.

 

bradders