Rover 3.5 + SU's - MAP takeoff point?

Quagmire · Post by **Quagmire** » Tue Aug 04, 2009 6:51 am

Guys,

I have ordered my Megajolt (MAP, not TPS) and am eagerly anticipating its arrival. I have everything else ready so am thinking about how i am going to go about installing it all.

The vehicle is a Landrover 90, and it is fitted with a 3.5 rover v8 running SU's. This is to be changed for EFi later, but for now i have the SU's, so have to deal with them...

So my question is this:

What am i best doing in terms of tapping into the inlet manifold for the map reading? Tapping into all 8 branches is going to be a nightmare and look pretty messy, so can i get away with only doing a couple? What would happen if i took the reading from where the brake servo takes its vacuum? I assume that this would mess up the MAP reading when you applied the brakes and vacuum dropped?

Current view of engine bay

Bare-naked manifold

Shot of the manifold plus carbs on installation

My baby (with my Dad hanging off the trailer)

Thanks!

Gilesy998 · Post by **Gilesy998** » Tue Aug 04, 2009 12:36 pm

On the inlet manifold, the "lump" the two carbs bolt to is an ideal place to tap for take-offs. If the carbs feed a separate bank each (I forget how the stock RV8 manifold works), then one union fitted after each carb, to a small reservoir, then off to the ECU would be perfick.
On your second pic, there's a hose fitted just to the front of the carbs, somewhere there is ideal.

chris.rawe · Post by **chris.rawe** » Tue Aug 04, 2009 1:26 pm

this pipe going to your dizzy is the vacuum advance... its just a vacuum pipe from the carbs i would just use this as you won;t need it using megajolt... any area behind the throttle plate will give you the same pressure reading as it the throttle plate that allows air to pass into the manifolt (as you probably know), so you can drill and tap a hole if you want or just use the exsiting vacuum take off from the carbs....hope this helps

Quagmire · Post by **Quagmire** » Tue Aug 04, 2009 2:25 pm

Thanks for the replies guys, i was just asking because i was thinking of using the original vac advance on the SU- but had read that the air was too turbulent in this area to give a good reading? Can anyone confirm?

Midas · Post by **Midas** » Tue Aug 04, 2009 4:19 pm

Quagmire wrote:Thanks for the replies guys, i was just asking because i was thinking of using the original vac advance on the SU- but had read that the air was too turbulent in this area to give a good reading? Can anyone confirm?

I get a stable MAP reading from the stock take-off point on my SU HIF44 carb.

Rich

Quagmire · Post by **Quagmire** » Tue Aug 04, 2009 4:49 pm

Brilliant! Thanks!

Gilesy998 · Post by **Gilesy998** » Tue Aug 04, 2009 9:48 pm

Midas wrote:
Quagmire wrote:Thanks for the replies guys, i was just asking because i was thinking of using the original vac advance on the SU- but had read that the air was too turbulent in this area to give a good reading? Can anyone confirm?
I get a stable MAP reading from the stock take-off point on my SU HIF44 carb.

Rich

I've seen it on other cars, and while it is stable, it's not MAP. Compare them back to back and you'll see what I mean.

TwoSheds · Post by **TwoSheds** » Wed Aug 05, 2009 4:38 am

Lovely work on the engine Quagmire

Is that LPG equipment I see?

Where are you BTW?

Quagmire · Post by **Quagmire** » Wed Aug 05, 2009 6:40 am

Gilesy998 wrote: I've seen it on other cars, and while it is stable, it's not MAP. Compare them back to back and you'll see what I mean.

Gilesy- so is it completely different to MAP, or is it simply a different value that then increases/decreases in line with MAP (sort of like taking a graph of MAP across revs and then simply moving it up or down the y-axis)

So would the servo take off be any better or should i use the vacuum ports that the rocker covers vent into? My only concern with that would be oil contamination of the map sensor over time...

I would tap into the tower where the carbs attach to the manifold, but am worried about hitting the water jacket in that area.

ThreeSheds- Thanks for the kind words, its not that clean anymore!

TwoSheds · Post by **TwoSheds** » Wed Aug 05, 2009 8:14 am

The tower would probably be the best bet - thr problem with the normal carb take-off is that it is too near to the butterfly and gets affected by turbulence and strange and unpredicatable venturi effects as the butterfly opens - apparently (I have not proved this) giving seemingly random fluctuations when compared to the real MAP. It would be a shame to fit a brilliantly controled and predictable ignition setup and then feed it with duff input parameters!
So - Carb take-off no good
Too close to one trumpet/inlet manifold branch no good
If you can find a spot clear of anything that would cause variations stick it there.

The tower would probably be brilliant if you can mange it

NITROPIXIE · Post by **NITROPIXIE** » Wed Aug 05, 2009 9:59 pm

The problem with Hif with a built in vacuum port is that it is located on the atmosphere side of the throttle valve. So when the throttle valve is fully closed there is no vacuum pressure and no MAP (Manifold Absolute Pressure). Once the throttle valve is partly open then an increased vacuum can be seen at the vacuum port, as the vacuum is now created between the carb piston and the engines inlet valve. Once the throttle valve is fully open then you can see the same vacuum pressure as when the throttle was fully closed. What you need is a vacuum port anywhere between the inlet valve and the throttle valve. The brake servo vacuum would be good to use. The crankcase breathers wouldn't as agian these are located on the atmosphere side of the throttle valve.

Hope this helps

Midas · Post by **Midas** » Wed Aug 05, 2009 10:09 pm

NITROPIXIE wrote:The problem with Hif with a built in vacuum port is that it is located on the atmosphere side of the throttle valve. So when the throttle valve is fully closed there is no vacuum pressure and no MAP (Manifold Absolute Pressure). Once the throttle valve is partly open then an increased vacuum can be seen at the vacuum port, as the vacuum is now created between the carb piston and the engines inlet valve. Once the throttle valve is fully open then you can see the same vacuum pressure as when the throttle was fully closed. What you need is a vacuum port anywhere between the inlet valve and the throttle valve. The brake servo vacuum would be good to use. The crankcase breathers wouldn't as agian these are located on the atmosphere side of the throttle valve.

Hope this helps

I checked this, unless I'm looking at completely the wrong port on my HIF44 it's most definitely on the engine side of the butterfly.

Rich

NITROPIXIE · Post by **NITROPIXIE** » Fri Aug 07, 2009 8:34 am

Not sure if yours is the same Midas but hopefully the diagram below shows the type of HIF44 i have and also the orientation of the throttle valve and MAP take-off (circled)

Midas · Post by **Midas** » Fri Aug 07, 2009 10:02 am

I'll pull the carb off the next time I'm under the bonnet, still 95% sure that the takeoff is engine side, but it wouldn't be the first time I've been wrong.....