MG Sports Cars

Hello,
I wonder who is the expert on fuel economy with Edelbrock performer (weber 500) 4bbl's on the rover v8's, anyone?

I am getting approx 15 - 18 mpg at the moment, i have just changed the jets since this figure, but will need to advance timing to compensate for uneven cruise.

Can anyone let me know what kid of economy you are getting with a similar setup (if any)

Current setup:
edelbrock 1404 - 500cfm
Primary jet 0.083"
Primary rod 0.067" x 0.055"
Step up spring Orange (5" Hg)
Ignition system Distributorless with Megajolt lite Jnr ignition ECU with Ford EDIS8

Advance curve: (Without vacuum) -

Degrees @rpm
22@600
28@700
28@900
21@1500
25@2000
28@2600
34@3000
34@4200
34@6200
0@6500


i'm still trying o work out the best vacuum MAP advance on this one.
The fuel economy is still the same as when i was using a rover distributor, so i'm thinking i have something wrong on the carb.


many thanks

martin



Edited 4 time(s). Last edit at 05/25/2008 04:52AM by gt6-v8.

Martin,

With the cost of fuel, never mind the green issues we have to be right to be concerned with consumption figres.

Firstly you don't say what mods have been done to the engine, heads, cam? which obviously can effect MPG.

Interesting to see you have megajolt as that is where I'm heading for my new 4.35 Rover engine.

What surprises me is the advance curve 34degrees at 3500 all in is correct for a 3.5 but 22 at 600 seems very excessive the recommended figure is 10degrees at 1000RPM progressing to the max figure of 34 obviously with megajolt you can adjust the curve to give optimum results.

Consumption wise on a relatively standard engine I would have thought 18-20 around town and high 20's in cruise mode should be possible with a relatively light car depending on your final drive ratio and the weight of your right foot!

I think your jetting is too rich, in my 3.5 I run 1441 Rods and 1421 Jets on the primaries which is the accepted correct set up for a mild 3.5 and in an MGB produces the above MPG. the 1421 jet is not on the reference chart but is available from RPI.

Your might also be interested in the [www.v8forum.co.uk] site which is great for all sorts of tech info for the Rover V8.

Kevin.

I take it your ignition curve is at 100kPa? Even at WOT it is a strange curve. Like Kevin said it should be around 10 at 1000rpm as long as you aren't counting any vacuum input.

My guess is your ignition curve it too retarded. I assume you have checked that what the computer shows as 22 degrees at idle agrees with a timing light?

This is just the advice i was looking for.
The engine is completely standard apart from thi ignition and carb.

I sort of assumed (wrongly it seems) that less vacuum means you can advance the timing more (like when decellerating) so i did the same for idle (max vac) even without any vacuum connected,
My 600 and 700 rpm adv was the same to compensate for any fluctuations in idle (which i do annoyingly have, (probably PCV issues)

So without the vac connected should i be looking more like this setup?
Degrees @rpm
10@700
14@900
16@1000
18@1500
25@2000
28@2600
34@3000
34@4200
34@6200
0@6500

then do i add 15degrees max vac as per a distributor or give it extra to just pinking and back off?
I thought the real advantage of mappable was that you could advance more where needed rather than the whole curve as per a dizzy?

problem is im trying to work out the vac mapping, how many degrees can a push it when throttle closed and high trevs decellerating? People mention 51 degrees on ford Pinto engines as you are not accellerating..

confusious he say...



Edited 1 time(s). Last edit at 06/04/2008 05:57PM by gt6-v8.

That looks good for a wide open throttle curve, meaning no vacuum. Then you start adding advance with vacuum for a total of 15 degrees at about 20kPa. My total advance is 60 degrees at 3200 rpm. 10 static, 34 centrifugal, and 16 vacuum. Of course that 60 degrees is almost never actually hit. I would have to be driving with the revs way up the suddenly taking my foot off the accelerator for max vacuum to be pulled.

Does that make sense?

I assume you are talking imperial gallons. One of the biggest factors is gearing. Although my MGB has a Ford 5 liter engine, and a Holley 670 cfm carburetor (vacuum secondaries), I get about 20 mpg (US gallons) in local driving and 25 to 26 in highway driving. Gearing is such that the engine is only turning 2000 rpm at 70 mph. Also, my engine can run as low as about 1,000 rpm in 5th gear with no problem, which is why my local driving economy is not so bad. Another important factor is that I run a vacuum advance on the distributor.

I suspect that you could get close to 30 miles/imperial gallon with the proper set up in highway driving.

Many thanks gentlemen,
I have been away, but now i'll be taking your replies on board and adjusting.
I do need to re-jet so RPI will get a look in.
Yes, IMP gallons, and i can drop in 5th at about 1200 rpm, 70 is about 2500 rpm (if i remember correctly)
im running a 0.75 5th gear with a 3.62 diff

Martin