Rover V8 Boxer carb installation blog

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Riley RMF
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Post by Riley RMF »

Ok - that's not going to happen then. What do people generally use on here?



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Post by DaveEFI »

Riley RMF wrote:Ok - that's not going to happen then. What do people generally use on here?
I'll be interested to know too. I used PB, and they only withdrew the service this week.
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Post by ChrisJC »

I host my own pictures on my own site, and link to them from here.

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stevieturbo
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Post by stevieturbo »

just google image hosting or uploader. There are loads of sites that do it

https://imageupload.co.uk/

http://tinypic.com/

https://imgbb.com/

http://freeimagehosting.net/

etc etc etc
9.85 @ 144.75mph
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http://www.youtube.com/watch?v=XgWRCDtiTQ0

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Post by Riley RMF »

Ok thanks, I'll give imgbb.com a go as it seems to have the biggest allowance at 16Mb. Reckon I'll soon use that up!

Back to the plot...

So here are some Boxer manifolds that have appeared on Ebay. This one looks reasonably complete:

Image Image

And this is what I bought - I kept the pics from the original listing:

Image Image

And here's a pic of the bare manifolds cleaned up and mounted on my engine:

Image

So lets's start with a simple question. Clearly from what's gone before, the vacuum balance is an important issue. In the first pair of pics all four carbs are connected together, in the second they are connected in pairs. Which is most likely to be correct?

Even better, anybody have any direct experience of the balance pipe issue on this manifold?

The first pair of pictures look like a more original system, and the metal pipe connector running along the top looks authentic.

Phill

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Post by ChrisJC »

I would connect all four together, but I can't justify that.

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Post by Riley RMF »

Well it seems to me that with the vacuum balance being "the key", the balance pipes need to connect all four carbs to maintain the suction on the 5-7 carb to minimise the pulsing effect...

... but you guys will know much more about this than I do.

Any other contributions welcome!

Thanks

Phill

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Post by Riley RMF »

Some thoughts on carb needles for the Boxer manifold...

If we take a standard 3.5 RV8 2-carb setup (I don't believe carbs were ever factory fitted as standard to anything above this cc?), it will have been tested comprehensively and be "correct".

So what happens when we we go to a 4-carb setup? Well, as in my particular interest, if we're going from 2 HIF44's to 4 HIF44's it means that the average airflow through the carbs at any given RPM will be halved. Assuming any changes due the different inlet manifold are small.

So to preserve the correct air-fuel mixture the "correct" needle will be the one we started with on the 2-carb setup stretched over the total travel of the 4-carb needle.

So what was, say, point 3 on the 2-carb needle will need to be point 6 on the 4-carb needle. Point 4 will need to be point 8 etc. When we hit full travel of the 4-carb needle it will be at the halfway point on the 2-carb one.

Does this make sense?

If so, that needle doesn't exist - I've been through them all, each and every one.

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Post by ChrisJC »

I think you are wrong.
If I over simplify it for a start, then the 2-carb needles / springs will be fine for the boxer manifold.
The drawback will be that the springs will be too stiff, so the pistons will only move over half the distance because the airflow will be halved. So it perhaps won't be as accurate at low engine speeds.

So you would change the spring to be softer, and the fit a matching needle.

Then the fine tuning is because the engine doesn't run best on the 14.7:1 air/fuel ratio under all conditions, so you are effectively mapping it by changing the needle profile to find the best result (i.e. max power or max economy) for a given engine condition.

Then when you have a boxer manifold, it's all confounded because the SU needs a consistent air-flow through it, which is best achieved from 4 cylinders for each carb drawing at evenly spaced intervals in time (which is what the standard dual-plane manifold does). When you go to the boxer manifold, each carb sees uneven pulses, which makes setting the carb up just an approximation. The 5&7 carb has a really lousy job as the firing order is 18436572 so that gets two overlapping suction pulses then a really long pause!!! It's on that basis that I would have the largest balance pipe I could covering all four carbs to try to even things out.

If you were really wanting to do four carbs, I would have a plenum chamber from a fuel injected engine and attach the four carbs to that. At least they'd all have the same even airflow through each one so they could be set up the same and would work properly.

Chris.
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Post by Riley RMF »

Hi Chris,

Thanks for your thoughts - I would be happy to be wrong because that would involve me in a lot less work and money!

Yes, we've halved the airflow so we need to put in softer springs. I'd figured that out as a piece of logic, but aside from that the SU Spare Parts/Spec catalogue gives standard twin carb Rover V8 springs as 8oz (yellow), and I measure what has come out of my Boxer carbs as 4.5oz (Red) - so at least that makes sense.

So when you say "then fit a matching needle" what do you mean by that? That's where I came in last time!

Cheers

Phill

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Post by ChrisJC »

Riley RMF wrote:
So when you say "then fit a matching needle" what do you mean by that? That's where I came in last time!

Cheers

Phill
That's the magical bit! I suppose you have to put it on a rolling road, and tinker around with needles, power and emissions until you get something that is OK. I would see if these guys:
http://www.wilshers-garage.com/rolling-road
could set it up for you. I used them to set up a pair of 2" SU's on my V8, because Peter Baldwin is an expert on SU's and has a massive stash of needles to play with.

Chris.
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R/R L405 4.4 SDV8

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Post by Riley RMF »

Hi Chris,

Thanks for the link, but I'm in Penzance and they're 300 miles away. Perhaps if I can get it running first - I'll give them a ring.

But what you've got there probably holds the key to the calculations I'm doing...

Any chance you could let me know the following:

1. What engine is it, and are there any other mods from standard?

2. What carbs are you using - HS8?

3. What jet size?

4. What needles did you end up with?

5. Were those needles modified or are they off the shelf standard?

6. And what springs?

Apologies that it's a long list, but you might just be able to help de-mystify the magic.

Thanks

Phill

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Post by ChrisJC »

Ahaaaaa, I can't be specific on most of those as I don't know and the engine doesn't exist any more. But I will say what I do know:
It was a 4.6 with 4.0 pistons (high compression in other words), with ported heads but standard valves. It had a camshaft from RPi which they called the Torquemax (I don't know it's numbers).
Carbs were HS8 from a 6 cylinder Jaguar (not sure which one), and I modified them to suit the Rover inlet manifold.
The needles were standard (i.e. they weren't modified for the vehicle - they came from Pete Baldwins' drawers)
I think the springs were the ones they came with, I don't remember them being changed. Just the needles.
The jet size was what they came with too.
I don't know what needles Pete put in there as he just fiddled with the needles and did lots of runs on the rolling road until he was happy with it.

HTH,

Chris.
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Post by DaveEFI »

I'd heard of some tuners 'sanding down' needles to get the tune spot on.
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Post by Riley RMF »

Ok - thanks Chris

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