Turbo MB carby options

MightyBoy tech questions and answers.
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Swampy
Posts: 12
Joined: Tue Aug 19, 2014 8:24 pm
Location: Noosa

Hi all I'm fairly new to the MB seen I got a MB with a f8b already which does ok but of course I want more :D so I'm throwing around a few options of upgrades like a f8c transplant out of a matiz then maybe turbo on that also but undecided another option is just straight turbo the f8b already in it Iv seen some using a carb from a charade but unsure off what year n model type and what type of air surge tank (top hat ) the turbo build side of things r not a prob for me but where I get myself into trouble is fuel side and the dizzy n timing :( :( I won't be doing any of the tuning but want to start out on the right foot to save time n money when paying somebody to sort it out thanks any info or ideas much appreciated Joel
BLSTIC
Posts: 51
Joined: Tue Jul 05, 2011 10:04 am

So you've decided you want to turbocharge the F8B and keep it carby.

1: Any *turbo* charade carby will do. Some of them have extra emissions functions incompatible with the 'Boy but they can all be reduced down to the same basic form which is very much usable.

2: The factory top hat from the charade turbo carb is a nice thing to have (even says turbo on it!). But if you can't get one, no big deal, as the float bowl is vented to the main air intakes anyway, so you just have the usual design horrors about ensuring even airflow down the throat of the carby and not worrying about other pressurised things

3: Get a G10 (3 cyl Swift) distributor as it is electronic ignition and a bolt in fit. Then get a Jaycar programmable ignition kit or some other ignition only computer. You *want* a computer on the ignition side as that's responsible for about half the gains of going to full engine management (the other 50% being made of inlet manifold design and the lack of atomisation problems that a carby has).

4: Bonus question you never asked: You'll be wanting a fuel pump upgrade. The mighty boy pump *may* be able to be boost referenced (not sure, some mechanical pumps are, but others vent into the engine and sealing them not really a thing that is done) but if not you'll be wanting an electric pump with a regulator & return system. A surge tank isn't necessary with a carby (carbs can handle momentary fuel supply problems without issue) but you *will* need one to run EFI.
BLSTIC
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Joined: Tue Jul 05, 2011 10:04 am

Ahaha a bot got me with a thread revival. Oh well, it's still good information
Zeeky
Posts: 19
Joined: Sun Mar 20, 2016 1:01 am

Holy crap mate... Thanks for the info, youls see i was also asking on another thread named "some pics"...
Did you do this to an f8b? Could i see some pics?
Does the carby give too much of a disadvantage with a turbo.
I have an ihi rhf4 turbo, im unsure if its too big for my f8b(which is now 820cc.) Do you know if this would be good?

Sorry for all the questions...im goin balls deep over here.
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Brayden
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Zeeky wrote:Does the carby give too much of a disadvantage with a turbo.
Yes, it is a huge pain in the arse to set up and tune a carby turbo. I've done it using the carby from a Charade CB60 turbo and switched to EFI as soon as I could.
F8B EFI turbo - Three pots and a snail.
BLSTIC
Posts: 51
Joined: Tue Jul 05, 2011 10:04 am

What problems were you having brayden?

Biggest problem with mine (on an actual cb60 engine) was finding the right restrictor for the secondary throttle valve opener. Without a restrictor the secondaries would snap open at 1psi and I would get a flat spot climbing onto boost, no exceptions ever. With a restrictor it was all sunshine & lollipops as the secondaries opened slowly enough for venturi magic to react

Brayden do you still have the charade turbo carb?
BLSTIC
Posts: 51
Joined: Tue Jul 05, 2011 10:04 am

The main problem with carby turbo setups comes about because carbs run off the venturi effect. Which basically means that carbies sense airflow by volume, not by mass. (Which is affected by volume *and* boost. For example 1L of air at 15psi actually needs to be mixed with enough fuel to treat 2L of air. To a lesser extent temperature plays a part).

On a n/a car the air pressure & temp at the venturis (*before* the throttle plates) is pretty constant (within 1psi & 15 degrees over most operating conditions in any single climate/location).

On a turbo car conditions at the venturi vary constantly, wildly, and in a manner that makes it impossible to tune for everything.

Most 'boost converted' carbies (including the factory charade one) have a normal primary throat, and a boost actuated secondary throat with a mechanical lockout (very similar to vacuum secondaries). The 'power valve' (low vacuum fuel dump) is converted to trigger at light boost levels instead. The secondary throat is also jetted much richer than usual as it needs to make up for the lean primary throat (which has no boost related fuel mechanisms).

After all that you're left with a fuel system that can't compensate for full throttle boost changes much (if you have it tuned for 15psi but turn it down to 6psi it will run rich until re-tuned) or temperature at all (which can change required fuel delivery by 20%, for example after the fitment of an intercooler on a high boost engine).

It's not that carby turbo is particularly difficult, it's that it's a lot more *specific* and needs to be adjusted after every change.

With EFI you can program it 'close enough' for situations you have no hope of testing and then rely on safety systems & superior sensors when conditions change
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Brayden
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BLSTIC wrote:It's not that carby turbo is particularly difficult, it's that it's a lot more *specific* and needs to be adjusted after every change.
I reckon it's difficult for your average punter, simply because a carby turbo setup gives you no data to tune with, and making adjustments is a complex task involving changing and/or modifying physical components. I spent months just trying to build and graph a distributor that would retard timing on boost properly. You need expertise, patience and time. Because I have limited amounts of all three, my carby setup went in the bin... well, sold to a new home. 
For me, going EFI was the more expensive route, but easily justified by improvements in power, reliability and driveability - and that's with a shitty MicroTech that requires manual tuning. I'm looking forward to upgrading to a Haltech or Adaptronic for the self-learning function.
EFI isn't the right answer for everyone though, and that's fair enough.
F8B EFI turbo - Three pots and a snail.
Zeeky
Posts: 19
Joined: Sun Mar 20, 2016 1:01 am

Hey guys thankyou so much for the info.

I know efi is the way to go, but the parts are so hard to source and expensive once you do. My mighty boy is a ground up restoration on a budget. And i think turboing with the carby should be good enough for me. However i will just be assembling the regular carbied engine for now. I can make the manifold and stuff while i drive it around.
If i were to go efi, what parts do i have to look for to convert my f8b. Cos i see a lot of discussion on what head fits, but not much agreeing.
Additionally, where could i find a charade turbo carby?
Having trouble using the net cos im restricted to my phone for a while.
Also... Is the IHI rhf4 too big? Couldnt find any info for this. Dont wanna throw a rod trying to build boost lol.
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Brayden
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EFI parts are easier to source than a Charade turbo carby in working condition! John Verban sells F6A SOHC manifolds that will bolt directly to your F8B head. Convert the distributor to electronic and you're half way done. I can't argue about the price of doing the whole EFI setup though. Mine was not cheap, and it isn't high performance.
I have no experience with the RH4F, but the specs suggest it is largish for an F8B. RHB32 or GT15 is as big as I'd go on a modest, low boost setup.
F8B EFI turbo - Three pots and a snail.
BLSTIC
Posts: 51
Joined: Tue Jul 05, 2011 10:04 am

There's a new ecu called "Speeduino" that's around $140 US plus postage. Can't recall if it needs assembly or not though.

It's pretty weak by modern standards (as in, in terms of computing power it's in the early 90's) but as long as you aren't trying to run continuously variable valve timing or an electronic throttle it will do well. No one ever complained in the 90's that their current model Haltech's or Motec's weren't good enough...
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