Triple 40mm Dellorto carbs on a 7m

[andrew_mx83]

gday gents,

i am taking my gold mx83 off the road to be used for track only, and the lpg system is coming off to go on the new (white) daily one.

for a fuel system i am planning to run a lovely set of triples off the side i know this is going backwards in technology but the huge increase in throttle area should well and truly make up for it, plus i just love the way carbys drive and sound. we have sucessfully done the conversion on my dads track CRX, with amazing results.

i have already got a pair of carbs and am currently looking for a third.

i have a lot of it worked out already, am going to start making the manifold shortly and then work on throttle linkages etc etc. i already have an aftermarket ignition system to go in, and am running a 5 spd so there is no need for the ecu anymore.

what i do not know is what size fuel pump to use. roughly what litres/hour should i go for? i want the fuel system to be capable of 200rwkw (not that i am expecting this much power but would rather be safe and not lean out).
is there a formula for working out how many litres/hour for how many kw you are going for? of course this will all be low pressure stuff.

i will try and get some pics of the carbs etc tonight and keep this thread upto date as i go.

[Gavatron]

THIS guy did it to a 7M in an MA61. There's a photo gallery in there too. Says he used a "Carter 4070 fuel pump for a steady 4PSI"

[crowncustom]

Any electric fuel pump to suit carbs will suffice.Back in the day when I was building worked Holden Reds and Ford 6's that were running Triple Webers or Dellortos I use to just run a standard off the shelf Repco electric pump rated between 4 and 8psi and an adjustable pressure regulator and alot of these engines were running between 200-300 plus hp depending on what mods the customer wanted done to there perspective engine plus most were running 48mm carbs or if they had the dollars we would try and get 50 or 52mm carbs but unsure if these are still available as we all know now that anything that is carbed is hard to aquire the bits for them.
Cheers Brett.

[ecko]

this sounds cool, but why not keep it injected and use 4age individual throttle bodies?
it has been done on a few 2jzge..
also wouldn't it be excessivly hard to tune the thing running on a efi computer?

[CELICASUPRA7M]

he wont need the computer any more!
good concept cus it eliminates a lot of probs 7m's have with idle control etc, and no inlet restrictions

[RAd28]

I love the idea... We're about to have an abundance of 45DCOE webers here, and i've been looking for an engine to use them on... I got searching and I found this... http://www.youtube.com/watch?v=1wXeuirt6is It's a 7MG running triple webers... quality of the clip is crap, so you really can't tell what it sounds like... but I can only imagine it would sound awesome.

7M is a great choice in my opinion, it's a VERY cheap engine to get a hold of, and it's 3L so that should suit the webers nicely.

Definately gonna be watching this one.

Edit: i just realised the youtube clip belongs to the guy who did the build in the first post's link..

[andrew_mx83]

thanks for the encouragement guys. the youtube video (and 1 more i found) have given me a bit more confidence. pretty sure i read that guys thread a while ago, ill have to have a better look through it again.

good point about the fuel pump, i guess having a float bowl etc means that carbs dont have the huge peak flow demand of a high hp efi system. might just go a holley blue or similar.

not really interested in going itb's & management.....the cost would EASILY blow out over 2 grand plus i am a big fan of how carby engines drive/sound.


started measuring everything up over the weekend in between putting the head back on the new one, have decided to modify the standard bottom manifold and run the carbs a short distance off the head in line with the ports. in order to keep the intake length as long as possible (carbs are very close to the head) i will make up a set of trumpets with a 90deg bend in each, coming upto around bonnet height with all 6 trumpets all facing up. as much as i dont like vents/scoops etc in bonnets i may well cut some holes/slots to get lots of air in. i will now have to sit down and do the numbers to see exactly how long the intake should be and where i want it to make power etc.

[SilverRA23]

Check what a Holley Blue runs at, I think it's pressure is even too strong for Webers and you will need to run a regulator.

They only like about 4psi.

[WDE_BDY]

The setup that was used on my 4V hemi V8 with a 4 barrel was a Holley Red pump and adjustable regulator running from 3 to 5.5psi. Was set at 5.5psi for the Holley and given the engine is a worked over 3.4L a similar pump should be sufficient for your needs.

Callum

[gianttomato]

IMHO, by the time you buy a set of triples, rebuild them, setup a manifold, reverse engineer a 5M dizzy to fit in the 7MGE head, reverse engineer your fuel system and have the fuckers tuned, you could have a set of RB26 throttle plates fabricated to suit the manifold and buy a Microleb/Adaptronic and be about a mile ahead.

[RAd28]

True though that may be, how do you address the "i just love the way carbys drive and sound" bit? In my opinion.. if you want to do something 'cause I want something different, then go for it... I hugely support the idea, and Hope it gets pulled off...

[white_sandshoe]

You know... I will be really keen to see how you go with this, as it's what I would quite like to slap on the side of my 5MGE...

[gianttomato]

True though that may be, how do you address the "i just love the way carbies drive and sound" bit?

ITB EFI and multiple Webers will sound the same. As for drive, EFI will be better unless OP has unlimited funds to splash around.

I notice (as per thread title) you want to use 40mm Dell'Ortos. I'd recommend 45s. GTR throttle plates are 45mm.

That said, I recommend you look into supporting mods otherwise your gains will be limited. Very expensive modification just because you like the sound.

[andrew_mx83]

IMHO, by the time you buy a set of triples, rebuild them, setup a manifold, reverse engineer a 5M dizzy to fit in the 7MGE head, reverse engineer your fuel system and have the fuckers tuned, you could have a set of RB26 throttle plates fabricated to suit the manifold and buy a Microleb/Adaptronic and be about a mile ahead.

2 carbs for free (just gotta buy 1 more)
rebuilding -old man has a lot of parts
manifold -got a spare manifold & tools for chopping it up. will only have to pay to have the new flange aluminium welded onto the runners.
trumpets -will make myself
there is currently no fuel system as it is running straight lpg for road use. so even an efi system means new lines, pump, tank etc etc
dizzy -have already started modifying a 7m jobie to take a hall sensor as it was required for my aftermarket ignition for the lpg anyway (no ecu)
tuning - the old man is a gun with these things, always tuned his lotus running twin 45's by ear. if anything it will only need an hour on the dyno for little tweaks not a full session like a standalone ecu would.


so cost should be fuck all (im hoping for around $500)

and also, no efi system is going to dump in as much fuel when you quickly open the throttle as dellorto's or webers. i love that surge when you put ur foot down accelerator pumps FTW


its not just for the sound, i am expecting a good power increase for fairly little outlay. as i said we have sucessfully done this on a crx and the gains were amazing. the 7m already breathes quite well and even on gas it will munch a stock 5litre. i also have plans for a set of ground cams after the carbs go on to really get some air into the motor.

engine is currently balanced, blueprinted, around 11:1 comp, 40thou oversize pistons, superlight flywheel/clutch, extractors & straight-thru exhaust, screwed with cam and ignition timing and is currently breathing through an impco 425 mixer which is starting to restrict it a bit up top but isnt overfueling it or anything like that.




i will try and get some details on the holley blue/red pumps, id say i will need an adjustable pressure reg no matter what pump i go with.

[RAd28]

ITB EFI and multiple Webers will sound the same.

Lol... Funny you should say that... I spend a good deal of time argueing with another guy because he loves the sound of ITBs and hates webers, and I'm the opposite (though I can appreciate a nice ITB engine too)...