carb/turbo blowthrough kit fabbing

[240swapped]

hey all. i recently acquired a couple z cars and a host of parts that filled three 10x24 storage units. among the parts are a stroker crank, an f54 block, a BRAND new in the box P90 head, an f54/p90 turbo motor with everything, and a complete L24 (p30/e88) with yet another stroker crank in it and a set of triple mikunis on it with mikuni manifold. feel free to ask any questions as to what else i may have, but nothing is for sale....yet.

 

having been purchased for a price that will remain undisclosed so that no one hates this new member, i'm left with extra cash, and therefore higher ambitions for a buildup. in the black '76 i would like to build and run an l31 with the mikunis and the turbo setup. was wondering if there's anyone who's tried this. surely, being a thirty year old car, i can't be pioneering something like this. i want to run it through a front mount and on through a surge tank which i've all the patience in the world to fab up. is there anything else i'm not thinking of? any roadblock i should forsee?

 

please and thank you for any advice or reference to any previous attempts, accomplished or failed.

 

also an answer to a question that i'm sure will be asked. i'm not going with the entire turbo motor setup because i'm not a big fan of wires. the good body is already converted to and l28(n42/e31) with s.u.'s and all efi stuff has been removed. ok i'm done. now you're free to tell me i'm nuts.

[76s30]

well l31 been done. blow through webersive seen done/run well, mikuni's are easier to tune from what i've noticed so far. but as a general rule blow through sidedrafts just isn't a good idea. further or blow through carbs just kinda lame. i've see draw through work well but boost is limited by lack of intercooling (its impossible, not safely anyway)

if you got the extra cash just do EFI, if your ambious and want to be differnt do mechanical fuel injection.

 

wires can be hidden just look at austin's car, efi stand alone is fairly easy sort of.

you'll curse the day you thought blow through was a good idea.

[Guest TeamNissan]

I would advise just doing efi, blow throughs have proven time and time again to be unpredictable and a pain to tune.

[240swapped]

yeah, did some searching last night and have decided to go N/A stroker high compression in this car and just get another body for the turbo motor. gonna need to sell the rb20 s13 if i wanna do that. decisions decisions.

[Tony D]

i've see draw through work well but boost is limited by lack of intercooling (its impossible, not safely anyway)

 

 

Not that I disagree that a carburetteed turbo is a poor idea, but exactly how can you quantify that statement of "boost is limited"---what constitutes limited? 21 psi? Because I've seen plenty of Holley Drawthrough non-intercooled turbo setups on L-Engines run those kind of numbers (and run loooow 11's in a full bodied S130 in fact...)

 

So saying you are 'limited by lack of intercooling' is probably a bit of internet parrroting than speakingfrom firsthand experience, at least that's my guess.

 

I just want the record straight that at least in my mind, 21+psi of boost is not 'limited' by any stretch of the imagination!

 

EFI, that's the way to go for drivability.

[ww]

EFI is definitely the way to go for modern drivability and reliability.

 

However, running 24/25 psi on a 3.1L triple Mikuni'd blow through T3/T4 hybrid intercooled turbo is no slouch either. Made a 12.4 second 1/4 mi on an open diff and street radials (not R compound). Doesn't seem very lame too me...

 

Car now has a Quaife LSD, 3.545 R&P and Hoosier drag slicks that should put it into the 11's.

 

Don't let anyone tell you you're crazy. If that were a criteria, then 9/10th's of the people on this forum would be certifiable.

[76s30]

Pump gas, and water injection is a form of intercooling.

Just saying theres easier ways of having a more drivable vehicle.

I've never messed with carbs your right on that account but I have plenty of friends that do.

I'm a diesel mechanic by trade so fuel injection is just normal to me (albeit it opperates completely different)

My samurai is mechanicaly fuel injected and superchaged toyota 20r (electronics don't like water)

 

 

Don't ever call me a parrot, since you don't know anything about me.

Thank you

[Tony D]

"I've never messed with carbs your right on that account but I have plenty of friends that do."

 

That was the whole gist of the post. Please don't make such statements and mislead people when it is clear from the statement the access is limited. The 'you don't know me' argument is moot. We are trying to foster an environment of cogent discussion of the topic, and not perpetuate myths.

 

Your post was just a tad on the 'heresay' side of the situation. I.E. not from firsthand experience, nor close firsthand observation. Try to limit that kind of commentary, as it's anecdotal, and not relevant.

 

I'm not moderating you, but if you think this board will let statements of limited technical veracity slide, you've a lot to learn. My statement was simply that I wouldn't consider 21+ psi as 'limited'...

 

If you want to talk about something with water or methanol injection, then the number is QUITE a bit higher.

 

I was talking about cars set up with a Holley Draw-Through, bolted to a turbo, blowing into the intake of the head. No water injection nor methanol injection supplementing it.

 

Hell, my 73 was running 17psi daily in SoCal for years without supplemental anti-detonant (which as you stated can be considered a poor-man's form of intercooling)....but then again so can excess gasoline. In which case ALL forms of draw-through are inherently intercooled...

 

And the statement would be then more true that blow-throughs are limited in boost unless they are intercooled.

[Kimi]

I have zero experience about turbo-engines so I to have ask this newbie-question

I've been reading most of the carbed turbo -topics here, but I would still like to ask what the biggest issues are about dailydriving a L-engine with triple carbs (e.g. Webers) and blowthrough turbo + intercooler?

I've always liked the looks and the sound on these old-school setups, so I would really like to have one some day. Just a bit scared about all the warnings how difficult they are to keep in good condition. Are they really difficult to work with and is there any particular books or websites that should be read before starting such a project?

Sorry if I've have asked questions that have already been answered here before

[SHO-Z]

I guess I am just a hard headed old man. Everyone says don’t do it but got the carbs for $100 and the supercharger for $60 so why not.

 

I am still working on my blow through SK racing carb, weber clones, set up. I am using a supercharger in lieu of a turbo and plan on around 10 psi of boost. My motivation level is not very high on getting the project done; we are looking at relocating to some other state in the next months.

 

In the last couple of years I have only seen one person at hybridz who is still running blow trough triples and he is thinking of going FI the last I saw. I have collected several pictures of blow through setups, but who knows how may are still running. There is not a lot of information on the internet on blow-through Webers.

[Tony D]

SHO-Z, for your application, I would recommend drawing through the supercharger simply for the fact that the fuel will give the 'inherent intercooling' advantage, and though packaging will be a nightmare, the need for a blowoff valve and supplemental air cleaner would be eliminated.

 

For only 10psi on a blower, given it's characteristics, drawing through it is very easy compared to blowing through and having to blowoff pressure, and setting up a proper compressor bypass valve (that can fail and dump boost while accelerating).

 

Frank 280ZX is working on a blowthrough compound-charged engine (turbo blowing into a supercharger) similar to the old Stratos Rally Cars... But he's EFI, using BMW ITB's... Maybe he can reveal some of his super-secret plumbing ideas to you!

 

The SK is a good Blow-Through Carb, they were really popular in the late 80's in Japan for that application. I have seen engines with 2Bar+ Blowthrough pressure on them, and over 450HP at the rear wheels using a turbo setup and blowthrough SK's.

 

The issues of daily drivability on a PROPERLY SETUP BLOWTHROUGH are not that bad, but most are cobbledtogether Cartech Log-Plenum setups that don't run for sh*t in comparison to an HKS or SK Plenum.

 

Now, speaking of SK BLowthroghs, 'can I interest you in an OEM SK Blowthrough Plenum Box perhaps'? I think I have a spare.... Interested? PM me if you are, I can send photos as long as I don't get sent to BFE again for a month...

[ww]

Hey Tony! I'd like to see some of those pics! Since it's a carb blow through, it's certainly on topic!

 

Here are some pics of one of the CarTech blow through plenums:

 

 

Out of curiosity Tony, what is the design problem with the CarTech blow through that isn't a problem with the SK or HKS blow through setups?

 

I do agree the fuel mileage is abysmal, but I'm now wondering if it isn't an issue with the tune and not the result of 'inherent' issues with a blow through carb setup.

 

Cheers,

WW

[Tony D]

Oh GAWD! I SHUDDER to see those photos.

 

I originally knocked off the HKS Type 1 Plenum on my 73, and it worked great save for me being an idiot and not tapering the front of the thing to clear my hood. At idle: knock knock knock knock..... Till my hood 'autoclearanced'---then the knock was intermittent.

 

So to get something that 'looked better' I figured to make a simple box like the Cartech Plenum, and like everybody else was running here in the USA.

 

WHAT AN ABYSMAL MISTAKE!

 

First, my mileage with 44 Mikuinis and the HKS Type 1 Knockoff was averaging 17mpg in daily commuting to and from Corona and Brea through Carbon Canyon.

 

Put the Plain Box on, and my car started lean surging at light cruise. Had to up the jet sizes. Mileage went...er...down. Still had an annoying pop at light cruise that would NOT go away.

 

Boost response was MUCH quicker and harder with the smaller volume plenum of the 2X4 Box, but going to 3psi on every light throttle application is not the best for mileage either.

 

In short, the SK and the HKS both incorporate different methods of "Modulator Rings" which are present in the Maserati BiTurbo, a car that was OEM with a blowthrough turbo and Dual Dellorto DHLAs (think Mikuini or Weber).

 

These modulator rings in the Maserati, and the two-plenum or internal baffled design of the SK and HKS boxes allow for a slight pressure differential between what is pushing down on the float bowl, and what is actually present in the main venturi of the carb. This raises the fuel level, richening the mixture ON BOOST ONLY while keeping the SAME smaller N/A size jetting. At higher flows, the pressure differential is more acute, and the richening is greater.

 

The HKS and SK boxes take two different methods for approaching the pressure differential that is better than the Maserati approach of the modulator rings. HKS uses a two-plenum approach whereby the boost enters the top of the plenum box first, pressurizing the floatbowls slightly before the lower plenum is pressurized for the main bores---there are two cast in holes in the dividing wall between upper and lower plenum to regulate the differenital at higher flows. Some racers really hogged out those holes on high-horsepower setups. SK used a baffle to direct the air to the float bowl vent holes in a dynamic way, and then divert it to the main bores past a static diffuser that let the air enter at lower velocity and lower pressure. Maserati used smaller than open bore rings in front of each main throttle bore. You can screw with the rings for a while to line it all out. Generally the modulator rings are of the same diameter as the main venturi/choke, on a Mikuini 44 say somwhere between 34-36mm for a choke size of 34mm. They don't cause a flow impediment at lower airflows, but under boost they start righening the mix.

 

That, from what I have discerned is the MAJOR difference that made the car run SO MUCH BETTER on HKS-Style boxes, than on the simple Cartech Style Box... I NEVER DID get the thing to stop lean popping after the switchover. If it wasn't for that damnable Cartech-Style box, I'd still be driving my blowthrough HKS Knockoff now! I really didn't have many drivability issues with that setup---and I'm thinking since Cartech was the predominant setup here in the USA I can understand why some have such a distaste for them. The drivability and fuel mileage on the HKS was worlds better than the other plenum.

 

Though I could get as low as 5mpg when driving spunkily...LOL

 

Heat soak during stop and go driving on a non-intercooled setup was another issue but it was probably equal in both setups HKS and Cartech. I was running 17psi+ without an intercooler (there were anti-detonant measures) but no matter what, when I was running long and hard at 10psi (before the coolant would kick in) those carb bodies would heatsoak like a big dawg...

 

And THAT is where EFI comes in! LOL

[Dane]

I find this interesting so thought I'd ask a quick question (that I think is relevant)...

 

When you refer to "inherent intercooling", is this just the latent heat of vaporization of the gasoline (energy absorbed by gasoline to convert it from liquid to vapor)? I have heard this effect is greater with carbs than EFI since with EFI the fuel is already highly atomized when it leaves the injector.

 

I remember seeing some pics of one of those Holley draw-through carb set-ups. Seems like it wouldn't be too difficult to tune for driveability and power since you could independently tune the primaries and secondaries on the carb...

[ww]

And THAT is where EFI comes in! LOL

 

That's why I've got TWM on my speed dial!

 

Thanks for the extensive and articulate response.

 

Cheers,

WW

[Kimi]

Great information Tony D, thanks

[Tony D]

When you refer to "inherent intercooling", is this just the latent heat of vaporization of the gasoline.

 

Yerpo!

 

Quite a great effect actually. In this regard, it should actually be said the Blowthrough is the one that is limited, to about 10psi in regards to boost without intercooling.

 

A bolt-on Drawthrough can easily manage 17psi simply due to the fact that the carburettors fuel is impinging on the turbine blades and flashing to vapor during the compression process.

 

The latest trend in smaller Oil Free Industrial Compressors is to use "isothermal compression" using a water-injected screw element. The temperature of the compressed air leaving the element is nearly identical to the temperature of the air ENTERING the element. Revolutionary process in smal packages. Instead of air entering at 85 F and Exiting the typical Oil-Flooded Screw Compressor at 165-175 F, it exits more closer to 90 F, and the water is recovered and separated using conventional means. Imagine that compressor on the front-end of your Z: 125Psi Manifold Pressure at 100% R/H!

 

Turbine Discharge Pressure and Temperature is quite different between the draw-through and blow-through. At say 150Kpa, or 6.5 Psi thereabouts the stock 280ZXT has a discharge temperature of around 60C given a 28C ambient. On the same application in drawthrough, your discharge temperature would be hard pressed to break 40C.

 

Quite a difference! Of course as you up the pressure, so do you up the temperature produced. The manifold temperature will remain constant as more and more of the gasoline is vaporized (at 6psi there are still liquid fuel droplets to puddle in your manifold....muhahahaha!) to the point where you start to see a rise in manifold temperature.

 

It is at that point, using thermometers and thermocouples that you use your old trusty and reliable Two-Stage Spearco Water Injection system to spray methanol, windshield washer fluid, or water into the manifold to act as a supplemental anti-detonant.

 

With this system operating, your boost then went to 20+ easily, depending on your carburettion. A Single Z SU on a Turbo Corvair would not supply enough fuel through a .125" mainjet to keep from detonating at 17psi, a drawthrough Z SU on a similarly-sized 240Z with the same Corvair Turbo driving the Crown Turbo kit was almost identical in terms of detonation. You had to supply anti-detonant to make 17psi reliably.

 

BUT, put a Holley 650 on either of them, and MAN! 17psi? No problem. Being we are talking stone-age NON-WASTEGATED systems here, once you got to the 17psi you were effectively choked on the Corvair Turbo in either setup. Derestrict the front end some more, and then you saw that old Vair Turbo (or the Rajay Equivalent) would make upwards of 20 psi! And knock knock knock 'Mr Holey Piston' started sniffing aroudn again... So back to Spearco to stop the Knocks, and then you keep your foot into it till about 22-23psi where you surged the damn thing. Boost was totally dependent on your right foot in those old systems.

 

I actually long pondered reinstalling my Crown Kit on the 240 as a period resto, but instead using the stock wastegated turbo and a manual boost control valve. The problem with the early kits was they really relied on inlet and exhaust restrictions to keep the boost under control...gawd help you if your Turbo Vair shook it's muffler off or got a sizeable exhaust leak: you would detonate the thing to DEATH in an overboost condition due to tunaway turbine speed! I was thinking restricting the boost would allow me to conquer the woes of the old SU setup.... Of course I was also thinking of driving the thing with twin 550CC fuel injectors and a Megasquirt so it LOOKED vintage, but DROVE MODERN!

 

Looks are a big thing, and something that looks old, and vintage-period correct is really neat IMO...especially if you can hide the technology and actually enjoy the ride. I know tuning the MS and twin 550's would be FAR easier than what I had to do in 79...... That took literally WEEKS after work with the hood off, watching the station pole in the top of the SU and listening for detonation sitting unbelted BACKWARDS looking out the back window while a friend drove the car...

 

Ugh... you made me remember...YOU BASTARD!

 

LOL

[ww]

Dude, you crack me up! I was thinking about doing a retro looking resto with gutted SU's and a pair of injectors mounted in the SU "dome's" on a stock intake manifold. The injectors would be hidden inside the carburetors which are now simply acting like throttle bodies with MS keeping things running. I'm still working on the fuel rail and hose routing to keep it hidden as much as possible without ruining the SU's. I thought about using a pair of '73/'74 Hitachi flat tops. That would be a fitting end to the spare set in my garage. Oh well, another project on the pile... I now have 4 simultaneous projects in the works... Although, only three are currently active...

 

I'll be putting the CarTech turbo setup back together in the next couple of weeks. That's when I'll find out if I'm going to live with it or go ahead and bite the bullet on a set of TWM/Mikuni ITB's.

 

If I go with the ITB's I'm going to make whatever modifications are necessary to re-use the CarTech surge tank to keep it as retro as possible.

[SHO-Z]

Great Info Tony D.

 

My current design is a Mercedes SLK Super charger, Subaru WRX intercooler, electric fuel pump, Malory pressure sencing fuel regulator and 4" square intake box and the 45mm Sk carbs. Your write up was the first info that I have seen on the need for a higher pressure in the floats. I was planning on adding a blow of valve on the intercooler. It looks like I have 2 options, change the intake box or take a seperate line from the compressor discharge to the float bowls and let the pressure drop through the intercooler take care of the pressure diffence. This would also requied a small bleed hole from the bowls to the box. I would rather go the first route.

 

Could the added pressure in the floats have something to do with the air emusion tubes? I really have not read exactly how they work.

 

One neat thing on this supercharger is the electric clutch. It can be turned on and off with a flick of the switch. In my mad engineer design I was thinking a adding a check valve to another air cleaner on the down steam side of the intercooler to allow running without the supercharger. I know the jetting would be to rich but it would be and option.

 

Now Jetting would be another issue. Did some pressure drop calcs across the venturi to see what the change in density of the air would create. Looks like the jet change would be smaller than one would think. I am planning on adding an Air/Fuel meter to help with the jetting.

[mario_82_ZXT]

I love that supercharger! There's a twin turbo + supercharged WRX running around in Phoenix with it. The supercharger's clutch is controlled by a pressure switch along with a bypass valve. As soon as the turbo's push out a certain amount of boost the s/c is disengaged and bypassed.

 

On a side note, isn't the s/c undersized for the Z?

I really hope to get my MegaSquirted and s/c'd project on the road this summer.

Mario