Rover V8 Boxer carb installation blog

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Riley RMF
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Re: Rover V8 Boxer carb installation blog

Post by Riley RMF » Wed Mar 21, 2018 9:50 pm

Video clip of my engine bay walkaround here:




And the initial start:




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ChrisJC
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Re: Rover V8 Boxer carb installation blog

Post by ChrisJC » Thu Mar 22, 2018 4:32 pm

Nice videos. It will be interesting to see the improvement when it's set up properly.

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Re: Rover V8 Boxer carb installation blog

Post by Riley RMF » Tue Mar 27, 2018 5:41 pm

Next instalment, first pass on getting the timing and carbs setup now available:


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Re: Rover V8 Boxer carb installation blog

Post by Riley RMF » Thu Jul 12, 2018 4:08 pm

Been working on other parts of the car for a time, but an opportunity to play around with the carbs this morning.

Just to recap, my engine is a 3.9 recon unit with TVR internals and so is a 4.3. Standard 3.5 heads, so a bit of a mongrel, but it will do what I want. For the time being at least. HIF44 carbs

I've fitted BBG needles as per the Fast Car article posted previously, and yellow springs - standard on the 3.5.

So here's my logic on the springs. I've got 23%ish more air flowing into the engine, so I'm using more of the needle range than I would have done with a 3.5. It's not going to be ideal, but it should work.

Balanced up all the carbs and the engine is now running really nicely. The car isn't driveable yet, so this is just stationary in my garage, but it seems pretty happy.

It'll probably be 3 months or so before I can actually hit the road so next update when that happens...

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Re: Rover V8 Boxer carb installation blog

Post by Darkspeed » Sat Jul 14, 2018 6:43 pm

You may have more engine capacity but with stock heads you have the same air flow. The increase in capacity will just mean things are all over by 4800RPM rather than 5300RPM - (figures are just arbitrary for example). Calculation for establishing the lower RPM maximum horsepower will occur at for the same head flow figure but larger capacity will be easy enough to find.

Not sure what you mean by using more of the needle range because unless you have the heads opened up to flow more air you will be using exactly the same as the 3.5 as they strangle that capacity. -Heavier spring just makes and SU richer for a given air flow - Lighter spring weaker - Engine capacity actually has little bearing on what goes on - apart from when the carb tops out on ultimate flow potential.

Yellow appears to be quite a strong spring so much richer . What the overall effect is you won't know until doing some WOT under load testing.
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Re: Rover V8 Boxer carb installation blog

Post by Riley RMF » Tue Jul 17, 2018 3:17 pm

Hi Darkspeed - yes, thats what I mean by it's a bit of a mongrel. I bought it as a recon unit from RPi engineering for £2,450 in an ebay auction as a turnkey unit, which I thought a pretty good price. It is what it is. The engine is in a 1953 Riley RMF, I doubt that I'd ever take it past 4,0000 RPM.

I've made a few changes, front timing cover that fits under my bonnet, P5B sump that fits in my chassis crossmembers, and of course the Boxer inlet manifold because I like the look more than anything else. I'm not that bothered about how much HP it's putting out - there will be plenty for what I want.

So. Needle range. Happy to be told I'm wrong, but here's my logic:

1. The ideal setup would be a spring that is compatible with my engine/Boxer setup that will operate the needle over the full aperture of the carb. The red 4.5oz springs would probably do that. Problem is there's not a needle that would be "right" for that configuration. I'd have to make my own. That's phase 2 of the project.

2. As far as I can determine all the SU carb 3.5 engines had 8oz yellow springs, and the needles on the different vehicles to which they were fitted are all pretty similar when you plot them on a graph. In the Fast Car article BBG needles are identified, again very similar, but change substantially towards the tip. I'm not likely to spend a lot of time down there anyway. So, all the carb sees is a pressure drop that causes the piston to rise. If you put a Boxer setup on a 3.5 it's only going to work on the first section of the needle - it's never going to fully open, not steady state anyway. But it will work, the mixture will be right because the needle is matched to the airflow. At least if we ignore effects due to the standard inlet manifold characteristics. Now on my engine I've got an additional 23% volume to fill, so there's more (lets call it) suction, and so more of the needle will be used than on a 3.5.

So I'm currently running on 8oz yellow springs with BBG needles.

Does this make any sense?

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