Vauxhall Inlet Manifold / K&Ns / Bonnet Alignment

[Catgraham]

Hi,

I am in the process of putting a Vauxhall 16V race car back on the road and would like to fit the original K&N air filters, but I'm struggling to get the filters to exit the slot in the bonnet. It's running Weber 48s on an SBD manifold, which leaves the carbs sloping down towards the front (as per the engine) and the front carb barely clearing the bottom of the bonnet slot. I have another unbranded manifold, but it's pretty much identical to the SBD one.

I had intended to lift the front of the engine about 20mm, as there's no belt guard fitted, but it turns out the limit is the exhaust hitting the engine bay side diagonal tube, which will only allow the engine to be lifted a couple of mm. (It has the Caterham race headers fitted).

The build manual states that filter alignment can be achieved by spacing the engine mounts a maximum of +/- 1/8", but also stresses the importance of using the Caterham inlet manifold. Am I correct therefore in assuming that the Caterham manifold has a steeper rake than the SBD one and is "twisted" to lift the front of the carbs back to horizontal with the engine in its usual nose-down attitude?

Many thanks,

Graham.

[Paul Deslandes]

Hi Graham,

It's so long since I ditched the Webers and went Jenvey TBs with a sausage filter that I can't remember whether the original K&N front and rear filters were different but I don't think they were.  The Caterham manifold is offset/cranked upwards equally on all four ports leaving the head face and carb face parallel, so no difference front to rear.  When I fitted the Jenveys and sausage filter I did have to offset the holes along the filter plate so that the edge of the filter was parallel with the chassis rail as the engine slopes down at the front.

You could try raising just the induction side of the engine with a spacer/washers between the engine bracket and the mount.  I doubt it would put appreciable strain on the gearbox box mount.

Paul

 

 

[Wrightpayne]

You could always get the bonnet cut to your set up. 

[Catgraham]

Hi, thanks for your responses...

Paul, sounds like you've answered my question re the Caterham manifold - so the puzzle still remains! Are your Jenveys on the original Caterham manifold or a different one, or direct to head? If they're on a manifold then the set-up should be the same, as they are the same size as 45s carbs, I think. I have a set of direct to head TBs and the port face is square to the TBs, so they take up the angle of the port face on the head - i.e. they slope up at about 30 degrees, requiring a cut-out much higher in the bonnet.

I had thought of re-cutting the filter backplates to offset them, but there is not much room inside to clear the ram  pipes.

Leaning the engine over might help to raise the front, whilst keeping the exhaust clear of the chassis, but doesn't seem very elegant somehow!

Re-cutting the hole in the bonnet unfortunately doesn't work, as the filters are too low - below the chassis rail at the front!

I will try to attach some pics....

The front ram pipe needs to lift about 25mm and the rear about 12mm to centralise the filters in the slot...

Thanks again,

Graham.

[Paul Deslandes]

Hi Graham

mine is the original Caterham manifold that had Weber 45s on until I swapped them for Jenvey 48 TBs.

You can see how the forward hole at left is a bit lower than the rear hole, making the filter parallel to the chassis rail.

The manifold is swept upwards to horizontal to allow the inlet chokes to sit above the chassis rail/bonnet edge, albeit at a slope.

View from the front.

I cut away the bonnet almost down to the bottom edge, plus a lot more to accept the sausage filter.

Incidentally, the Caterham manifold had very poor gas flow characteristics in original form and when I had my cylinder head gas flowed they flowed the manifold at the same time.  They said that the manifold was the limiting factor and, by doing both head and manifold, including bigger valves, raised the flow rate from 108 to 138 cu.ft/min, allowing the engine to develop 245bhp in present form (torque = 194lb.ft)  Awesome to drive!.

I hope this is of some help.

Paul

 

 

 

 

 

 

[Catgraham]

Hi Paul,

Thanks for posting the photos. One of the options I am considering is modifying the filter backplate, as you have done, to get some alignment. Probably not practical with the K&Ns, but Ramair do a foam filter which fits the hole in the bonnet (the only ones who do, I think) and they can be had with a blank backplate. I'm trying to avoid cutting the hole in the bonnet, if I can.

It may just be the photos, but your Caterham manifold seems to be steeper raked than mine?

I also had a closer look at the other manifold I have and it appears that the carb flanges have been machined back at an angle, to point the carbs up a bit, so that might help.

I had heard that the Caterham manifold was a bit restrictive, but 245bhp would probably indicate that you have that solved now! Is it a 2 litre?

Cheers,

Graham.

[Paul Deslandes]

You might be right about the manifold rake but it's hard to be sure from the photos.  I originally had 45mm Webers so maybe the 48 manifold is different.

Yes, it is a 2 litre and I did a lot of work on the engine with the help of SBD who supplied the bits and Simon Armstrong who gas flowed the head and manifold and machined the pistons.  Our aim was to get maximum torque at the lower end of the rev range which is ideal for speed events, especially hills as you're more often than not making a series of slow starts rather than going flat out around a circuit.  As well as rally cams we fitted a 4 into 2 into 1 exhaust system which helps bring the torque curve down the rev range, albeit sacrificing top end power which you don't really need.  It was then mapped by the 2 Steves at Track N' Road.

Paul

[Paul Deslandes]

Graham

a few more pictures in an attempt to show the heights of the chokes in relation to the chassis rail and of the tops of the manifold flanges in relation to the bottom edge of the cam cover.

It gave me some practice at uploading pictures anyway!

atb

Paul

 

[Andrew Gilbert]

Hi, where did you find an ex race 16v VX? Great to see one coming back together.

I was told they did re-engineer the manifold to improve flow for the 48's but I'm also told that the 45 and 48 share the same inlet manifold.

Can I ask, are you sure you have the right engine mounts or that the inlet side is correctly fitted?

[Paul Deslandes]

I would guess that as a minimum the manifold for 48s would have had the ports opened up to match.  Ultimate Performance said that the inside of the manifold was very restrictive but fortunately there was enough meat on the casting to open it up and achieve good gas flow.

BTW, if you don't have a copy of the Vx car build manual, the 1995 edition can be found here. It includes details of the Caterham dry sump which presumably your car has.

Paul

[Andrew Gilbert]

Paul, you would have thought so.

Mine is a VX race car that wasn't used in anger but was a Palmer motorsports car, and it has the caterham dry sump (bell housing tank), it did have 48's at one point in its life but they were changed for 45's and in my ownership we've changed those chokes to improve its road manners.

When I'm next with my car I'll grab a photo of mine to see what differences there are.

I'm thinking of going heritage bodies or direct to head TB's so the carbs etc will be redundant which is a shame.

[Catgraham]

Hi Paul, Andrew,

Thanks for your contributions. The trumpets on your car, Paul, do seem to be a bit higher over the chassis than on mine. Maybe because the TBs are sloping up a bit?

I had a closer look at the installation today and it turns out the engine is already leaning over slightly towards the exhaust. The engine mounts appear correct and there are no spacers underneath, so I guess the engine is sitting where it's supposed to be? I'll post some pics below - please let me know if anything looks incorrect. Caterham don't appear to list the RH mount so don't know what this should look like, but the LH one looks correct. When I get a bit more time I will see how much I can get under the mounts before the exhaust hits the chassis side diagonal.

The car is a '96 Vauxhall Challenge car originally supplied with all the usual race bits plus big brakes, full cage and honeycomb floor. It was registered in early '98 but I don't think it's been on the road since '99. Following a shunt it was rebuilt in 2004 into a brand new '94 spec Vauxhall Race CBU and hasn't done much since - in fact not turned a wheel in the last 10 years.

It does have the Caterham dry sump set-up - with an extension on top of the belltank to increase oil capacity, two large oil coolers, two oil filters, two oil temperature gauges and a rear fog lamp on top of the dash as an oil pressure warning light!!

 

 Engine mounts above, looking from the front. Let me know if anything looks wrong....

Thanks again for your interest and info. I would be interested to see what the installation in your car looks like, Andrew, if you get the chance. Can never have too much info..!

Cheers,

Graham.

 

[elie boone]

It's a long time i had a VX2.0 to look at but from memory the engine sits as high as possible so it just doesn't touch the nosecone and if my memory serves me well there could be a support before the engine on the nose cone so it can't drop onto the timing belt. 2 oil filters and 2 oil coolers seems a bit much BTW the big low oil pressure light on the dash is called an idiot light.

[Andrew Gilbert]

hard to show with mine, light was rubbish but you can see the carbs are level, std Caterham manifold.

[Andrew Gilbert]

I'll get whatever photos you need.

Twin this and that, were they building it for an extreme endurance race of sorts?

[Tazio]

Do you have the two spacers between the RH mount and the block?

[bxhunt]

I had a similar problem when I switched from Weber 45s to Omex injection.  I found that a Pipercross sausage filter and a blank backplate could just be made to fit.  Very tight but just possible.

[Catgraham]

Hi All,

elie - it was my intention to lift the engine as high as possible under the nose. I was going to fabricate a thin stainless guard close to the belt to prevent contact between the belt and the nose. However, I can only lift the engine a few mm before the exhaust contacts the diagonal tube in the side of the chassis (standard Caterham race exhaust). Plenty of room under the top diagonal and the engine is already leaning towards the exhaust.

Andrew - your carbs certainly look higher than mine, as the filters are over the chassis side! I assume the engine's on standard mounts and the filters are not modified? When viewed from the side are the filters parallel to the chassis tube and does the engine have the usual nose-down attitude?

Tazio - no spacers on mine as it has the dry sump pump sandwiched between the RH mount and the block. The spacers take the place of the pump, I believe, when wet sumped. Although the manual does say there should be washers between the pump and the block, which mine has not got, but my pump has steel bushes fitted, which sit proud of the casting, holding the pump slightly away from the bosses on the block. Don't know if this is standard?

Barry - I have been looking at a Ramair filter as an option, as they do a small one specifically to fit the hole in the Vauxhall bonnet, and it's available with a blank backplate. Is your Omex set-up on the original 45s manifold and is it a Caterham one?

Regarding the oil cooling - I believe from various sources that these motors are prone to running their oil hot, and I guess the guy who raced it didn't want to take any chances! There's a cooler and filter on the pump feed into the engine and another of each on the scavenge line back to the tank. As far as I know it only did sprint races, but not sure which series. The engine's a 2.3 and it was running 8" and 9" slicks!

Thanks again for all your input...

Cheers,

Graham.

[elie boone]

Cat graham, a few mm on the exhaust side will may give you a cm on the carb side. Doesn't the diagonal on the exhaust side is removable ? if so you could flatten ( oval) it a bit that it would give just that little bit more clearance.

[bxhunt]

Graham, the answer is yes and yes; original 45s Caterham manifold fitted when built by Caterham as a race car in1994.

[bxhunt]

[Andrew Gilbert]

Hi, yes mine is on standard CC mounts and it does have a nose down type of install, the timing cover just about clears the upper line of the nose cone. Filters are more of less inline with the chassis tube and the filters are std KN items as fitted when new. Hard to see but hopefully this shows their relationship, the rear filter is slightly higher than the front 

[Andrew Gilbert]

I had a ramair filter on my crossflow and I'm pretty sure the bonnet opening is the same on the c20xe cars (happy to be corrected though) but the fit was tight but OK.

[Andrew Gilbert]

odd question, do you know exactly what SBD inlet manifold you have fitted? They do a 7 degree manifold for engines fitted at an angle so if this is one of those and the engine is sat level then you'd have the issue you seem to be experiencing?.

https://www.sbdmotorsport.co.uk/index.php/products/index/2324

 

[Catgraham]

Hi, thanks again all for your posts...

The offending chassis tube that interferes with the exhaust headers is the diagonal in the side of the engine bay. I was thinking that I would have to open up the hole in the body side to allow the exhaust to sit higher, but when I took a closer look I realised that there's a tube right behind the hole anyway. As it sits currently there's 6 or 7mm clearance. It might allow me to get 10mm under the mounts, but haven't tried yet. The diagonal across the top of the engine bay is fixed, but has reasonable clearance.

I am coming to the conclusion that the engine is sitting in more or less the right position and there's not much I can do to improve it, so the "problem" must lie with the inlet manifold arrangement. From Andrew's pictures and information above, it does look like the Caterham manifold lifts the carbs higher and possibly levels them front to back as well.

I don't think it's a 7 degree manifold, although I will now go and check! I did consider these and thought I might be able to raise the carbs using one, but was unsure which way the 7 degrees went! But I think the engine in the Vauxhall leans towards the exhaust, so the 7 degrees would lower the carbs, as you suggest.

I do have another manifold which appears to have had the carb flanges machined back at an angle, to raise the carbs, so I will give that a go. I might also try an ad on here to see if I can find a Caterham one, but I suspect it's a long shot. Other than that I think I will have to ditch the K&Ns and fit a modified Ramair, and hopefully that will get me away...

Graham.