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School me in the ways of intaking fuel and air...

Posted by Mad Matt F 
Mad Matt F
Matt Follett
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School me in the ways of intaking fuel and air...
June 26, 2011 01:43PM
Okay,

So work on Justy continues... slowly.

I now have a rented garage locally where once it's a roller, I'll bring little Justy back to and get to work fast! (Whew Hoo!) (apres July 1st)

In the mean time, I have a few little bits I'm sorting out on the kitchen table.

In stock form the 1st Gen 1.2L 3cyl machine breaths through an anemic Hitachi carb... The 2nd Gen has fuel injection (did you know that the Justy was the last carb'd production car sold in North America?!) Both suck...

So we're hoping to switch to a triple carb set-up since the carbs are sourced for free... we don't have to worry about stand alone, and well, having grown up with bikes, carbs are cool...

Currently in my possession I have a set of beautiful Mikuni 33mm flat slides. I won't say what they are from (in part because I'm not sure of the "model", and in part because most of you would laugh when I said the machine ran on snow (oops let that slip))

The ID on the carbs is pretty close to the cross sectional area of the intake (within the mm) so I think they are a good fit... Yes, No?

Problem being they are set up on 12 cm centers, the intake is 8.5cm centers.

First, I'm trying to sort out is having slightly different intake runner lengths will be an issue? Angling the intake runners out to the 12 cm centers... We're talking less the a cm diff. (12cm vs 12.5cm or so)

Second, what is a decent runner length to make good torxs, and decent throttle response.

The intraweeb is full of opinions on intake runner length, and my limited wave physics mind is having a hard time making sense of the gobbly goop BS spouted.

How much does cam specs play into this?

Here's the pretty pics.

As for the beer, more Quebec micros... mmm mmm good.
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Mad Matt F
Matt Follett
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Re: School me in the ways of intaking fuel and air...
June 26, 2011 01:44PM
Intake and carbs
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Mad Matt F
Matt Follett
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Re: School me in the ways of intaking fuel and air...
June 26, 2011 01:48PM
Plan is to cut off FI intake runners, (from 2nd gen head) and weld up straight aluminum tubing to meet the carbs at 12 cm spacing. Rubber couplers between intake and carbs (ala bike style)

Yes, head needs work... also looking for thoughts on cam specs for a 3 valve/cylinder motor...

Matt
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Mad Matt F
Matt Follett
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Re: School me in the ways of intaking fuel and air...
June 26, 2011 01:52PM
Oh and John...

Wees needds to talk 'boot boingers 'gain...
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starion887
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Re: School me in the ways of intaking fuel and air...
June 26, 2011 02:27PM
Some opinions, but I heve never worked on this engine so this is very generic input:

The existing runners look like they are set to a length to make torque at a certain RPM band. I am making a SWAG at 3-4k rpm. Do you know if the stock engine has a best torque RPM range?

Yes, the cams have a TON to do with it, usually the most by far, but so does the exhaust runner length. Are you planning to do a header? If so, I would think along the following lines:
-Work on the intakes so that they are decently large with as little restriction as you can. Then, the valves and cam will limit the top end.
-Don't worry about the variation in runner length. Tuned intake runners tend make torque 'peaky'; great for maximum peak HP, but not so good for a wide torque band for a N/A engine for rally.
- Tune an exhaust header for the lower end of the desired RPM range and let that peak influence the peak torque.
- Looking at the stock intake runners, do they have coolant flowing into them? If so, that is likely there to help heat the instake fuel-air misture and help make the fuel ;ess likely to condense out and pool in the low spots in the runners. That is good for cold performance and emissions, but heating the intake charge can reduce the flow a bit. So I would think a direct as possible runner with no low spots would be better.
-Large runners on the intake ususally helps top end at the expense of bottom end torque. This can be modifed greatly with cams however. Most 'good' N/A rally cams (that I have worked with at least) that emphsize a good wide band of RPM's and decent low end torque, seem to do Ok with large intakes and medium sized valves and long, medium sized exhaust tubes in the header. The larger intakes seem to help top end (at lest not restrict it), while the cam and exhaust keeps the low end good.
- Any step in size form carb to intake runner should be sligthly larger on the runner side than ther carb side. That applies all the way to the valve.
- And just for reference, a 1.6L Mitsu Colt engine liked 40 mm Weber DCOE's. So 33 mm are smaller than that on a per-cylinder displacement basis. So I would not think these are 'large' carbs from that view for 400 cc per cylinder. But a 33mm downdraft may be different than a 33 mm sidedraft in terms of flow.

I have no clue if carbs for use on snow machinces would be right for cars. Things like floats and such are sometimes special to an application. Hopefully someone knows these carbs well.

But again, this is just general N/A info from my past experience and general reading of what others have done. It may not work with this engine. Is there a site for these things?

Regards,
Mark B.



Edited 1 time(s). Last edit at 06/26/2011 02:28PM by starion887.
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JohnLane
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Re: School me in the ways of intaking fuel and air...
June 27, 2011 09:11AM
OP your slidevalve carbs will be intended for a thing that makes some real power; prolly a two stroke!

The Justy engine.... Yes it is the anemic turd we all know it to be. That said..... More intake flow... Sure won't hurt. It should as mentioned above be matched with better exhaust.... I also suggest looking long and hard at static compression ratio. That smogged Justy sure won't have a compression ratio in two figures as we wish for in a 'fun' engine.

Do beware that when you manage to get more out of the engine you will immediately find the limits of the stock drivetrain that was all built to go with the standard engine!
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aj_johnson
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Re: School me in the ways of intaking fuel and air...
June 27, 2011 09:37AM
I have some 38mm mikuni's sitting around doing nothing, complete with K&N adjustable needles and as many jets as your heart desires. Came from a Suzuki can-o-tuna.
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fiasco
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Re: School me in the ways of intaking fuel and air...
June 27, 2011 09:39AM
Put a Saab 2-stroke in the Justy...Saab 92x makes it legal for all sanctioning bodies!!!

smiling smiley
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Pete
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Re: School me in the ways of intaking fuel and air...
June 27, 2011 01:04PM
Quote
fiasco
Put a Saab 2-stroke in the Justy...Saab 92x makes it legal for all sanctioning bodies!!!

smiling smiley

Aw come on, they never put SAAB engines in the Justy. As cool as that would be.

I wonder how cheap you could find one of the three-barrel IDAs that Porsches used. There's gotta be a single carb missing its mate out there, for cheap. I think those were 40 or 46mm.

I also wonder if a single flat-six head would fit on there. SVX would be nice, but it'd probably be XT6. The Justy heads are probably an upgrade for ther XT6 and not the other way around. At least the Justy has three exhaust ports!



Edited 1 time(s). Last edit at 06/27/2011 01:05PM by Pete.
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fliz
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Re: School me in the ways of intaking fuel and air...
June 27, 2011 03:21PM
How much is required to change the spacing?

I don't have any experience myself, but in the VW world, a common ITB solution is GSXR 750/1300 throttle bodies, and then to pull them apart and use different spacers to get them on the right centers.
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dirty_d
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Re: School me in the ways of intaking fuel and air...
June 27, 2011 03:51PM
Didja steal em off a zamboni?

Your bike carb tuning experience will come in handy. Do the carbs have chokes in them or are they full bore @ 33? - they might be a teensy bit on the small side, but free is free!
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john vanlandingham
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Re: School me in the ways of intaking fuel and air...
June 27, 2011 06:04PM
Quote
dirty_d
Didja steal em off a zamboni?

Your bike carb tuning experience will come in handy. Do the carbs have chokes in them or are they full bore @ 33? - they might be a teensy bit on the small side, but free is free!

In bike talk the size is the size.
Those 40 DCOEs may very well have a 32mm venturi and THAT is the real limit.

Some of the nastiest motors in Swedish GpH, the crazy ass 265 bhp Volvos w the "Two Valve Evo" heads use bike carbs.

Matt needs some compression somewhere, and some sort of cams that were never intended to be emission cams or he'll never have any "night emissions", and probably on top of that, some kind of valve springs---Or at a miniumum an idea of what his ARE @ What installed hgt.

A little motor is effectively ALWAYS be run at FULL THROTTLE, and near max revs---Matts limitations are 2: Pump gas and the gaps in the box

What final drive you have Matt?
Ratios in the BOX.
let's look at that info before building the motor...

after all, we drive the whole car, not just the motor.



John Vanlandingham
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Doivi Clarkinen
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Re: School me in the ways of intaking fuel and air...
June 27, 2011 06:21PM
The Justy engines are a completely unique cast iron block thing that has no relation to the opposed engines. An SVX head would not come anywhere close to fitting.
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Mad Matt F
Matt Follett
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Re: School me in the ways of intaking fuel and air...
June 27, 2011 08:25PM
Hey Folks,

All good thoughts! thanks!

Okay, so no, not stolen off a zamboni! That's a federal offense up here! The carbs are from some sort of race sled, I have no idea what displacement, likely sub 1000 cc but more then 800... yes two stoking fun for sure.

I had some Klein CVK's but they were close to 40mm and I think that's just too big.

Dirty d, yes no choke, smooth bore.

Yes, the Justy is not a "sub-a-rat-tat-tat" opposed motor, transverse inline 3 cylinder for the win!

The old Justy motor we ran was head decked, I have no idea what static compressions was (stock was 9:1), I think we took decent skim off though. I can't use that head though, as yes the carb'd Justys had the water jacket run through the intake, and it would be very complicated to make a custom intake and not have coolant all over the place. In the pics, you notice that the coolant port in the FI intake (what is shown) is pretty separate and so I think I can easily cut around it.

So if a half cm or so isn't going to be a deal (I didn't think it would be) it will be easy to do nice straight, slightly sloping down 30 odd mm intake runners, spread out to meet the carb rack. I could re-arrange the carbs, but that would take some mill work and a few new seals to get the throttle linkage right. Easier to spread the intake.


John, here's the big gap gear ratios.

I've done a lot of searching to come up with something bolt in to change this... I think we're stuck. (BTW this is the "better" gearbox from the first Gen, the second gen is taller for better fuel sipping...)

1st 3.071
2nd 1.695
3rd 1.137
4th .771
5th .631
Rev 3.461

Final 5.200, Differential 3.700

As for the robust-ness of the driveline, I think it will be good up to the 100 hp mark or so. I know there were a few trick rally Justys running in the 90's that were in that range, and there's a few running turbos (Chris may not own up to the fact he once ran a turbo Justy as a toy...) with no problems. I've been able to swap the front drive axles over from the 2nd gen too, the 2nd gen is about 300 pounds heavier, and so bit bigger brakes and axles.

As for the SAAB engine... I always thought a 900 turbo would fit real nice in the back seat... Damn that would be stoopid funny.

Oh looking forward to getting back on stage...

Matt



Edited 1 time(s). Last edit at 06/27/2011 08:36PM by Mad Matt F.
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john vanlandingham
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Re: School me in the ways of intaking fuel and air...
June 27, 2011 09:30PM
Please clarify "Final 5.2" and "differential 3.7"



John Vanlandingham
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CALL +1 206 431-9696
Remember! Pacific Standard Time
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