SUs Or Holley

oldbloke

Active Member
#1
Simple (?) question, 1970 3500s driver (not for show). On my recent engine rebuild should I have the SUs rebuilt or use a Holley 390 4-barrel?
 
#2
SUs are pretty simple really but not widely understood on your side of the pond. Holley 390 is basic but not a very good carb. Better bet would be the Edelbrock performer manifold and Edelbrock 500cfm carb (sold as a Weber in the UK). Would take a bit of fiddling to swap manifolds and adapt to cable linkage but you can get them with electric choke. People who have the 4 barrels reckon you get better throttle response and driveability. But it's probably cheaper to just rebuild the SUs if that's a concern and you get to keep the hood scoop intake.
 

ghce

Well-Known Member
#3
The Weber 500 is the better carb for the P6, Installation is straight forward with the Edlebrock manifold, some minor details such as the radiator outlet maybe needing changed to the early type. a lot of details on the RPi site and reasons for the Weber rather than the Holley.
As my signature shows I have the 500 in my car, made a huge difference to performance even on my auto, in manual the difference will be even more pronounced over the SU carbs.


Graeme
 

mrtask

Well-Known Member
#5
Hi Oldbloke. A properly set-up Holley 390 on the Edelbrock Performer manifold is a joy, much more responsive throttle than the SUs, but thirstier. The new found ability to take off encouraged me to drive in a more aggressive fashion, which soon empties the petrol tank! The good old 390 gets maligned, but I loved it when I put one on my old automatic '73 3500. I prefer the look of the dull gold colour on the older ones to the shiny new Edelbrock/Weber 500 carbs too. Your kneck of the woods there must surely be a local Holley wizard who can tune it to perfection!? Use the extra power plates (I think they're called?) for extra tuneability.
If you do swap from SUs to a four barrel and you have no use for your old parts, I am looking for a better example of the big rubber gasket that seals the US export air canister to the underside of the bonnet!
 

PeterZRH

Well-Known Member
#6
Another option is EFi. Complete 1990s Discovery or Range Rover systems are very cheap and they are purely fuel delivery systems, they don't affect the ignition setup. That'll give you better performance, throttle response and economy.

A 10.5:1 engine should give you 200bhp with the later better breathing cyclinder heads (which I'd change first anyway - mine were £50) given the Vitesse with a cruder injection system and 9.7:1 ratio gives 190bhp (claimed). That's realistically at least 30% over an SU setup. You'd feel that :) but it'd be missing the point, real world, part throttle driving would be transformed.

But it won't sound as good as a Holley ;-)
 

ghce

Well-Known Member
#7
smokin1942 said:
Graeme

Looking at your Fuelly figs, surely that's a rather thirsty set-up(14+ mpg UK) - or have I missed an earlier trail about it?

John

Yes truly woeful at the moment, I had some fuel line problems and it has affected figures but I have yet to do some other things to get the economy back to normal such as rerouting the crankcase gasses via a PCV back to the carb then get it dyno tuned which should restore the car back to its previous 25 to 27 MPG figures of old.

Though of late I have been thinking Megasquirt and injection setup.


Graeme
 

Quagmire

Active Member
#9
I MS'd my 3500s a few weeks ago now using a GEMS manifold and plenum from a 4.6, but the first EFI pump I fitted died after a few days (I think the feed to it was too restrictive), and it took a while for me to get the system replumbed and replacement fitted.

Just driven it into work (35 miles) for the first time today - we'll see how my economy goes... I am not expecting anything great for the first tank or two, until I have got the fuelling dialled in at least! :shock:
 
#10
Am I missing the point here? you either want performance OR economy you cant have both with a v8
Performance wise get the holley carb as its easier to set up and as it closely copies the rochester that was on the 216 Buick to begin with --Rover wanted supply but had contract problems with SU
Economy--sell it and get a 4 pot
Fuel injection is a happy medium but then again so would a diesel engine if economy is your goal==and dont mention originality-as fuel injection isnt exactly
 

PeterZRH

Well-Known Member
#11
Surely if you break the "originality" seal then it really doesn't matter. You could argue the Rover EFi is closer to "original" than a Holley, like using the LT77 gearbox or later and much better cylinder heads.

I think the economy improvement is likely to be more significant than a couple mpg cruising would suggest. In lambda mode around town when you dip down to single figures the differences are likely far more stark. More accurate fueling in variable throttle situations being the key and that really is performance and economy as a virtuous circle. No carb can come close to this.

It is interesting to note that in Classic Range Rover builds it really very pronounced. I've read economy improvements of 30% or more talked about and that isn't so much about fuel costs as much as restoring a useful range between fuel stops. You see this again with the V12 XJS. The HE model with EFi being hugely more economical than the earlier car (relatively speaking of course :) it isn't a nissan micra)
 
#12
symes said:
Am I missing the point here? you either want performance OR economy you cant have both with a v8
Personally when I talk about economy I mean good economy for the rover v8 and I probably should have qualified it as such. After all both my P6 and one of my two LR's are RV8 powered, so if I was super bothered about crazy economy figures I wouldn't own them :D

As for having power and economy you can have both - you set the car up in the most efficient manner, and only use the power you have available when you need it or want it. Take my car for example, it spends each day trolling up and down the M3 which for a good 15 miles is now average speed set at 50mph. At this point I don't need any power, and the cruise AFR is leaned out accordingly currently to 15.5, although I can probably go leaner at such low loads. However when I do put my foot down the AFR goes to 12.5:1 (or whatever I want it to be)- which is a good way to burn a lot of fuel quickly, but the trade off is that the car literally takes off.

I want my car to be as economical as possible on my boring commute, but as fun as possible at the weekends. EFI should allow me to do both. Personally I like the challenge of trying to improve it. My car was doing 24mpg on carbs previously, and I was pretty happy with that, i'll see what happens over the next few weeks with the injection fitted :D
 

ghce

Well-Known Member
#15
symes said:
Am I missing the point here? you either want performance OR economy you cant have both with a v8
Performance wise get the holley carb as its easier to set up and as it closely copies the rochester that was on the 216 Buick to begin with --Rover wanted supply but had contract problems with SU
Economy--sell it and get a 4 pot
Fuel injection is a happy medium but then again so would a diesel engine if economy is your goal==and dont mention originality-as fuel injection isnt exactly

Not sure I agree with that, you can easily have both, plenty of examples here, take as a for instance Rons' 4.6 extremely good economy and performance even on SU's. Put it on injection and I would guess even better performance and economy.


Graeme
 
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