The V8 Owners Forum -

I have just finished re-building my 3.5 with a new Weber 500, Mallory dizzy, Dual Plane manifold and twin SS block hugger exhausts.
Can anyone recommend a tuner preferably with a rolling road? I live in Milton Keynes (M1 J14)
I contacted a local tuner and was told he did not think my carb/manifold/engine combination was correct!
All I would like is to get the best out of what I have got and a rough idea of the output power.

I have 160 +/- 5 psi on all 8 cylinders. Is this pressure OK for a std SD1 head, 9.75:1 pistons and tin gaskets?

Your help would be appreciated.

Regards

Dave

There's a place over at Blakelands that have a rolling road.
is there anything specific that you need correcting? –
(apart from the default edelbrock pour petrol in until your eyes sting fueling strategy)

Where did u get the carb from? are u sure it's jetted correctly for ur application? PaulB has a good idea of the set up, john

http://www.do-business.net/CompanySelec ... 518cdf6758

It could be worth giving Bob Harman a call, he is a local yank specialist, Watford. and will know who is good on rollers in the area,

these are the ones i'm thinking of:
http://www.racingdevelopments.com/
http://homepage.ntlworld.com/jon.lee53/ ... main-1.htm

and thorney motorsport and i'm sure one other.

Thanks Chaps
I bought my complete system from RPI.
The carb has been set up for a 3.5.
I would like to get a pro's view on the best set up for the carb and dizzy.
Also I would love to know the actual power I have. I expect about 170 at the flywheel but maybe I will be suprised.
Thanks for the help.
Regards
Dave

JSF55 wrote:Where did u get the carb from? are u sure it's jetted correctly for ur application? PaulB has a good idea of the set up, john

John, Dave,
I just popped in here to ask if anybody already had a well set up Weber 500 on a stock motor, and could give me the sizes.

I can't actually remember what sizes I have, but I asked RPI engineering to sell me a set and they sent 2 new primaries jets and 2 metering rods, £18. It definitly sucks less petrol, leaves the plugs a light brown colour, but I'm not sure if it is spot on. There's a slight 'fluff' occasionally off idle.

I also put the old primaries in place of the secondaries, which may be the correct idea, but RPI didn't tell me anything, just sent the stuff.

Dave,
Do you know what size 'bits' you have in it already? I can e mail my wife and gets my details if necessary, as I'm offshore at the monent. I kept them jotted in the Edelbrock book, just in case.

Paul
I am sorry but I do not know what jets etc I have.
RPI sent it set up for my Std unit.
If you want any info I would recommend giving Chris a ring at RPI.
He knows about the kit he sells. He will be able to tell you what size the jets should be and where to put them
I have not run more that 20 miles since my rebuild but when I did the compression tests I found all plugs to have a slight orange tint.
The car has been running pretty well.
I have set up the dizzy and carb as per the FAQ's on the RPI web site and Webber manuals.
I had very bad Pinking when I first built the engine so this was a rebuild. I fould no mechanical problems but quite a few others.
1). HT leads 5&7 were routed together.
2). 1 rocker breathed through the filter, one on the PSV port. I was recommended to put them both to the filter.
3). Timing was jumping and dwell had not been checked. I rewired it all and set the dwell up to the book values.
4). The carb floats were not set correctly.
I hope this is of some help.
Regards
Dave

Tetlow
I'm not far away in Buckingham. Marlin motors in Bletchley are quite good for Dyno testing.
If you have the 1404 Weber/Edelbrock set up the the 3500 you will probably have .086 main jets and 065x52 rods fitted.
These are the stock setup.
I assume you got the manual with the carb ?

You might find the stock setup a little rich for a bog standard engine. I have the tuning kit for the carb if you want to have a tinker before you buy new jets and rods etc. I also have a diy gas tester so you can set up the primaries for emissions etc.
You are more than welcome to pop over and have a fiddle in my garage if you want to.

£18 for two jets and needles?? The whole service kit is only 60 quid with a shed load of jets, needles and piston springs to suit the engines vacuum.

Tetlow
Mine is a pre SD1 3500, Rhoades lifters, ported heads with standard size valves, Typhoon cam and home brew free flow exhaust with the weber 1404 500 carb. She puts out 187 t the fly, 150 at the wheels without gas if that helps.

Well your 500cfm carb is probably way to big. Its more suited on a 4.6

enginecid x rpm : 3456 = cfm required
215ci x 6000 rpm : 3456 = 373 cfm @ 100%Ve

A proper build naturally aspirated engine will reach about 90% Ve so thats mean a 335 cfm is max what you need. Well the Holley 390cfm is the closest one in that neighboorhood.

Most common jet sizes on a 3.5 engine are 52 primaries and 56 secondairies.
The 390 likes a lighter diagram spring for the secondairies on a 3.5 engine.

Thanks for the offer mgbv8.
I had a Holley 390 before I rebuilt the engine.
I was told that the 1404 / 500 was able to cope with a larger engine than the 3.5, but as I have a dual port manifold it would be more efficient at the bottom end. I would get much better mpg than the 290 and there would be more power and the Weber is much easier to set up.
The only problem I had was initially stopping the carb from flooding. I have since adjusted the floats and fitted a red top fuel pump with a pressure regulator. It seems fine now, but I did boil the carb a few times when I had a air lock in the manifold
Over all I am happy I have changed , but one consideration upon purchase was that I hope to ungrade to a 4.9 or 5.3 and wanted to be able to keep the carb / manifold / dizzy combination.
I know injection is the way to go but I do not want to modify the bonnet and change the look of my MGB so carbs will stay.
Dave

when i ran the weber, i recirculated the fuel back to the tank. I put an old jet in the return line as a restrictor. this along with a carb spacer prevented vaporisation and hot start problems.

Get yourself the needle and jet kit - then you can dial it in yourself. At the time i used a narrow band lambda, but widebands are very affordable now - and it allows you to see exactly whats going on in real time - suddenly the instructions that come with the jet kit for AFR's make sense!

when you get your "fluff" - you will be able to see if its a rich or lean spike. I found that i could get one part nice, but another part would then move in the wrong direction (so the carb sits on the loft now and i use efi)

Bill Shurvinton on this board sells Innovate Widebands.

Ah right ! the holleys and webbers are rated diffrently so 390 holley is actually bigger than a 500 webber, i read it somewhere ! pauls jets were as follows
" RPI jet kit arrived less than 24 hrs after ordering on the phone.
The new metering rods are # 6252, old ones were #6552, new primary jets
are 0.080", old ones were 0.086"

Now i have a jet kit by the side of the PC !! the smallest mine goes to is 0.083" so RPI must be sourcing the smaller ones from else where, but the metering rods are in the kit ............. along with some pretty coloured springs !! i'm sur i'll find out in time ! hope this info helps, john

JSF55 wrote:Ah right ! the holleys and webbers are rated diffrently so 390 holley is actually bigger than a 500 webber, i read it somewhere ! pauls jets were as follows
" RPI jet kit arrived less than 24 hrs after ordering on the phone.
The new metering rods are # 6252, old ones were #6552, new primary jets
are 0.080", old ones were 0.086"

Now i have a jet kit by the side of the PC !! the smallest mine goes to is 0.083" so RPI must be sourcing the smaller ones from else where, but the metering rods are in the kit ............. along with some pretty coloured springs !! i'm sur i'll find out in time ! hope this info helps, john

Hi John, I guess that is the jet info i emailed you a week or so back. I have since put the old primaries into the secondaries place, which brings them from 0.096" down to 0.086"

I need to do more checking on the metering rods, to see what the numbers actually mean.



Apparently the Weber and the Holley air flow is measured at a different air pressure/vacuum, thus the Weber flows less cfm, even though it says more on the tin.

MGBV8,
RPI did indeed charge £18 for the jets and rods, but that included next day arrival costs, packaging, credit card processing and signed for delivery, which costs a few quid on its own. I also stated 'ASAP' when I ordered them. Plus I assume I am paying for some of their expertise, development costs etc, rather than just buying specific parts by number.