Twin carbs or weber?
Discussion
I'm rebuilding a fast road engine into a hillclimber and changed from a 286 to a 296 cam, along with a sccr box etc etc. I have a pair of HS4s but have been adivsed to go for a weber 45. Problem is the expense and aggro of fitting a weber. The twin su manifold aperture is only 1.25" while the ports are 1.5", has any one tried the Maniflow tubular manifold with any great sucess, is the cost justified? Has any one had sucess with twin HS4s and a 296 or is the weber really the best option?
I've experience with both twin SU's and 40DCOE and 45DCOE Webers. There are advantages and disadvantages with both.
With the SU's, the standard BMC inlet manifold is dreadful and really let's down the potential of the set-up. If you can get an alternative, such as the old 'Torquemaster' alloy unit which looks like the original, that's great. Alternatively a tubular steel one with just a small balance bar is fine. If you are stuck with the original, as I am with my Historic Rally 'S' you just have to make the best of a bad job and polish it out, removing all the sharp edges with as generous a redius as possible. You may find that with your spec twin 1.75" SU's would be good - HS6's. I used them on a rally car a few years ago and it was very good at the top end. Remember, however, the cross sectional area of the inlet tract in the head is the limiting factor with a 5 port head - the 8-port is a different matter.
Webers are a great option and once you get them set up they really don't need much tuning. They give better throttle response, particularly under competition conditions as the accelerator pumps work instantly in feeding in the extra fuel.
You can mod SU's up to work almost as well as the Webers, but you need the little book called 'Power Tuning the SU Carb'. It terms of power, I have an SU powered 'S' at 1293cc and my big buddy Geoff Loos has a rally 1330 cc Clubman GT. We both have 286 cams, but he has 1.5 roller rockers, which I'm not allowed in the Historic class. On the rolling road the power on the cars is almost identical at 110 bhp at 6200 and when you drive them they feel similar, except that the GT is slightly lower geared at 4.1 compared to my 'S' at 3.9.
I reckon that the Weber car is harsher to drive, but slightly more responsive. I feel his throttle springs are too strong, but that's a personal thing I guess.
You pay your money and take your choice, but for a hill-climber or sprint competition car I'd probably go for the Weber. For a rally car I'd choose the SU's.
With the SU's, the standard BMC inlet manifold is dreadful and really let's down the potential of the set-up. If you can get an alternative, such as the old 'Torquemaster' alloy unit which looks like the original, that's great. Alternatively a tubular steel one with just a small balance bar is fine. If you are stuck with the original, as I am with my Historic Rally 'S' you just have to make the best of a bad job and polish it out, removing all the sharp edges with as generous a redius as possible. You may find that with your spec twin 1.75" SU's would be good - HS6's. I used them on a rally car a few years ago and it was very good at the top end. Remember, however, the cross sectional area of the inlet tract in the head is the limiting factor with a 5 port head - the 8-port is a different matter.
Webers are a great option and once you get them set up they really don't need much tuning. They give better throttle response, particularly under competition conditions as the accelerator pumps work instantly in feeding in the extra fuel.
You can mod SU's up to work almost as well as the Webers, but you need the little book called 'Power Tuning the SU Carb'. It terms of power, I have an SU powered 'S' at 1293cc and my big buddy Geoff Loos has a rally 1330 cc Clubman GT. We both have 286 cams, but he has 1.5 roller rockers, which I'm not allowed in the Historic class. On the rolling road the power on the cars is almost identical at 110 bhp at 6200 and when you drive them they feel similar, except that the GT is slightly lower geared at 4.1 compared to my 'S' at 3.9.
I reckon that the Weber car is harsher to drive, but slightly more responsive. I feel his throttle springs are too strong, but that's a personal thing I guess.
You pay your money and take your choice, but for a hill-climber or sprint competition car I'd probably go for the Weber. For a rally car I'd choose the SU's.
Excellent, so many replies so quickly, thanks for all the advice. My inclination is to stick with the twin HS4s for now, particularly as i'm not after winning championships, just improving on my own times. The manifold is from avonbar which they claim has good flow, its just that the manifold port size is that much smaller than the head. I'm inclined to go fo the fabricated manifold, although if it isn't going to offer significant benefits i might as well put the £100 towards a weber in the future.
miniman said:
Hi Haynes. How did you get into hillclimbing? This is something I'd like to try one day, but I've done some research on the web and I'm still a bit baffled. Any advice appreciated!
A good place to start is to choose a championship in your area, get hold of their calendar and technical regs and see what class you'd be in and what regulations your car would need to comply with. For instance if you're in the Midlands you might have a look at the Midlands Speed Championship, www.hinotori.freeserve.co.uk/ms.html . You can also find a massive amount of information online at www.ukmotorsport.com .
Personally I like to see an A-series on SU's, the Webber/Delorto just doesn't look right to me....... I think there is a lot of myth and mystery about what equipment you "need" to be serious or competetive, Coop's (and many others) have shown you don't need a Webber to have a powerful, flexible engine.
Packaging is always a problem with a Webber because to get the best from them you need a long inlet manifold. To fit the long manifold you will have to modify the bulkhead, which is fine if your prepairing the car from scratch but not much fun if you're developing as you go along.
SU's can be modifed if you have the skill and nerve, later HIF's are reputed to flow better than earlier H's and HS's (most Rover V8's had a pair of HIF6's if you're looking for some), and the Maniflow tubular twin inlet manifold is a work of art.
If you're feeling really flush, and the regulations allow, how about "proper" twin-point injection ?? See www.mberaceengines.co.uk/ecu_kits.html
>> Edited by phil hill on Wednesday 25th February 08:49
Packaging is always a problem with a Webber because to get the best from them you need a long inlet manifold. To fit the long manifold you will have to modify the bulkhead, which is fine if your prepairing the car from scratch but not much fun if you're developing as you go along.
SU's can be modifed if you have the skill and nerve, later HIF's are reputed to flow better than earlier H's and HS's (most Rover V8's had a pair of HIF6's if you're looking for some), and the Maniflow tubular twin inlet manifold is a work of art.
If you're feeling really flush, and the regulations allow, how about "proper" twin-point injection ?? See www.mberaceengines.co.uk/ecu_kits.html
>> Edited by phil hill on Wednesday 25th February 08:49
miniman said:
Hi Haynes. How did you get into hillclimbing? This is something I'd like to try one day, but I've done some research on the web and I'm still a bit baffled. Any advice appreciated!
It can be baffling, but it really is so so easy and brilliant fun. I live near Guston Down and they do school days where you take your own car and receive instruction. To compete you just send off £30 for a MSA non race national B licence and you have to join an appropriate club who run the events, in my case the BARC, another £30. You then apply for the individual events at £70 or so. Check out www.gurstondown.org You will also need overalls and a helmet, to the required standards. You can start with a standard road going car and develop it as and when. Find out where the local hillclimbs are and go along to find out more.
haynes said:
It can be baffling, but it really is so so easy and brilliant fun. I live near Guston Down and they do school days where you take your own car and receive instruction. To compete you just send off £30 for a MSA non race national B licence and you have to join an appropriate club who run the events, in my case the BARC, another £30. You then apply for the individual events at £70 or so. Check out www.gurstondown.org You will also need overalls and a helmet, to the required standards. You can start with a standard road going car and develop it as and when. Find out where the local hillclimbs are and go along to find out more.
Thanks for the info. I'll pop along to Gurston at some point and see how it all works!
phil hill said:
Personally I like to see an A-series on SU's, the Webber/Delorto just doesn't look right to me....... I think there is a lot of myth and mystery about what equipment you "need" to be serious or competetive, Coop's (and many others) have shown you don't need a Webber to have a powerful, flexible engine.
Packaging is always a problem with a Webber because to get the best from them you need a long inlet manifold. To fit the long manifold you will have to modify the bulkhead, which is fine if your prepairing the car from scratch but not much fun if you're developing as you go along.
SU's can be modifed if you have the skill and nerve, later HIF's are reputed to flow better than earlier H's and HS's (most Rover V8's had a pair of HIF6's if you're looking for some), and the Maniflow tubular twin inlet manifold is a work of art.
If you're feeling really flush, and the regulations allow, how about "proper" twin-point injection ?? See <a href="http://www.mberaceengines.co.uk/ecu_kits.html">www.mberaceengines.co.uk/ecu_kits.html</a>
>> Edited by phil hill on Wednesday 25th February 08:49
But does the maniflow manifold work, ie what sort of power / flow increase does it offer, and is it worth the £100?
haynes said:
But does the maniflow manifold work, ie what sort of power / flow increase does it offer, and is it worth the £100?
The maniflow manifold is very good at what it does. There have been flow test results published, I think the figures are available from MiniSpares. It's difficult to say if changing the manifold will result in more "power". If your current manifold supplies the volume of air the engine needs at peak flow then there would be little to gain at peak flow. If the flow is more consistant, the manifold is less restrictive, air velocity is good, tract lengths are
optimum for the cam you're using, then you could see gains.
phil hill said:
If you're feeling really flush, and the regulations allow, how about "proper" twin-point injection ?? See <a href="http://www.mberaceengines.co.uk/ecu_kits.html"><a href="http://www.mberaceengines.co.uk/ecu_kits.html">www.mberaceengines.co.uk/ecu_kits.html</a></a>
Bloody hell!
Bonkers 8 port injection set up!
looks rather nice :-) Got to be the best solution for keeping the A series I reckon...
>> Edited by Fatboy on Friday 27th February 00:01
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