HKS Plenum

[savageskaterkid]

Tony D, do you have a good baseline setup for an L28 running triples and boost. I need to get some jets, and want to know where to start atleast, then change from there. Seeing as how the turbo not only changes the pressure, but the temperature as well, then wouldn't it not really matter where your located as long as its similar climate conditions? This is all assuming a stock T3

[Tony D]

If you have properly jetted the engine for N/A operation, with an HKS plenum up to around 5-10psi you will be amazed to find no (or very little) jetting is required to be changed. The temperature could come into play with higher boosts un-intercooled, but if you run a cooler, then it's not an issue.

 

That is what I was getting at for the longest time: The pressuirzation of the float bowl, even by a fraction of an inch of water will allow MUCH more fuel in to the circuit under boost situations (same as if you changed the float bowl level the same ammount on an N/A)

 

I'd say run it and go from there, there's no 'baseline' without knowing where the engine was as an N/A. I've pulled my plenum off, pulled the turbo and then reinstalled headers and run the car the next morning as an N/A vehicle! Did it at the last MSA I took my 73 to---Sammy trashed my turbo bearings and the next morning before the car show I pulled out the turbo and drove it into the show 80 miles R/T no problem.

[Tony D]

Fine, the map sensor reading taken WITH a smaller plenum. I think you knew what I meant.

 

Improved throttle response makes it harder to drive conservatively, certainly. But I think that's why most of us went with ITB's in the first place. I think I'll hold off chucking my cartech plenum in the bin.

 

Forrest, I don't know if you are intending to be a smarta-- throwing in little comments like this or not, but I really have no idea what you are talking about!

 

THE MAP SENSOR IS IN THE MANIFOLD BELOW THE THROTTLE PLATES AND WILL NOT BE AFFECTED BY PLENUM SIZE, incipient boost conditions below the throttle will be difficult to judge. If you have ITB's and are sensing MAP in the plenum above the throttles, I don't know how I can help you. Best I can say is that the comments in this thread are SUPPOSED to be directed towards CARBURETTED applications.

 

You seem to have a real problem with my statements. I guess that will have to be your problem from this point. You're muddying the post asking about MAP in a Carburetted Thread. I've tried to expalin exactly what I've been referring to, and you seem to not be getting it---I don't know how to make it clearer. If you live at WOT, then so be it. You are picking flypoop out of pepper with boxing gloves and lumping the 2X4 plenum voulme problems with your personal choice of the Cartech plenum (in a NON-CARBURETTED APPLICATION). Though similar in the sense that it's terrible as a CARBURETTED PLENUM compared to the HKS or SK, it may well have suitable volume as an EFI plenum.

 

You seemed to take offense that I said the Cartech Plenum was trash FOR A CARBURETTED SYSTEM, even though you are using it in an EFI setup and are having some sort of luck doing so. Frankly what you do with your Cartech Plenum is up to you. Keep it, but before you start making smarta-- commentary quoting me about 'chucking it in the bin' try it with carburettors and a turbo that will spool at 3400rpms and see if you like what it does...

 

I don't really know what the problem here is, but partial throttle drivability and tractability while in transit at 60mph IS a concern. A 2X4 Plenum will not have sufficient volume to prevent any sort of...you know what? It's your problem, not mine. Figure it out. I don't know what more I can say other than what has already been said.

[Forrest]

THE MAP SENSOR IS IN THE MANIFOLD BELOW THE THROTTLE PLATES AND WILL NOT BE AFFECTED BY PLENUM SIZE, incipient boost conditions below the throttle will be difficult to judge. If you have ITB's and are sensing MAP in the plenum above the throttles, I don't know how I can help you.

 

I know exactly where the map readings are taken from. I thought my question was pretty clear. I was asking if you were implying, in your statement specifically about EFI with this plenum, where you said gas mileage would "go to hell", that it would go to hell because the map readings were inaccurate and a MAP based system would provide a mixture richer than it was supposed to for a given pressure vs RPM point of the fuel map.

 

You seem to have a real problem with my statements. I guess that will have to be your problem from this point.

 

I only have a problem with the statements that were potentially misleading, because they weren't clear. The reason I hang out here and not Zcar.com is because people discuss these kind of things instead of having misinformation floating around, just because someone might get angry if their word wasn't taken as gospel truth.

 

You're muddying the post asking about MAP in a Carburetted Thread...You seemed to take offense that I said the Cartech Plenum was trash FOR A CARBURETTED SYSTEM, even though you are using it in an EFI setup and are having some sort of luck doing so. Frankly what you do with your Cartech Plenum is up to you. Keep it, but before you start making smarta-- commentary quoting me about 'chucking it in the bin' try it with carburettors and a turbo that will spool at 3400rpms and see if you like what it does...

 

You DID NOT qualify MANY of your statements, especially the initial ones.

 

The original poster has Megasquirt listed in his signature. It seems reasonable to assume he wanted to use the plenum with an EFI setup. He never said anything about carb'd applications, you brought them up. You made many negative statements about the cartech manifold that were unqualified as to which type of fuel delivery application you were referring to.

 

I was certainly not trying to make "smartass" comments. I was actually trying to keep things a little lighthearted by saying I wasn't going to throw my plenum out with the garbage. I was doing so because I got the feeling you were getting defensive - clearly I was right.

 

If you get riled up so easily when someone asks you to clarify sweeping negative statements about aftermarket parts, maybe you shouldn't make them. I can't stop you from taking it personally, but it wasn't meant that way. I just want people reading this site to have the best information possible, and if this is what it takes to save all those cartech manifolds from getting scrapped, so be it.

[RTz]

Keep it civil, guy's.

[Tony D]

Why's that?

 

You go onto boost mapping with the slightest touch of the pedal due to insufficient plenum volume. The Centrifugal compressor will overfeed the reciprocating compressor (engine) really quickly. It's why they put such large receivers on screw and centrifugal compressors (suction bottles is another name for them) when feeding a reciprocating booster compressor.

 

As a result of the instant boosting in the manifold, you end up running in a 12:1 mapping, instead of something more conservative. Your mileage goes to hell... Now, if you put a much larger turbine section on, so it's slightly laggier you may restore the balance of NA cruising, but it kind of defeats the idea of having a turbine optimized for response. With a larger plenum, small throttle excursions will not result in the increased flow causing a bump to say 3psi instead of '0'.... In a megasquirt the difference in sized can be seen as a jump almost instantly from a 54kpa cruise to 108 or 110kpa instead of from 54 to 80kpa with the larger plenum. The only thing changed in the test was the plenum.

Also I note the BOV tuning has to be retweaked due to the plenum change. The blowoff action is much harsher on the smaller plenum from what I can hear.

 

Exasperation is more like it. I don't know how much clearer those statements can be!

 

I'm not asking my words be taken as gospel, but I do ask that those who ask the questions give me the common courtesy to actually read the replies I have given to their previous questions.

 

Your question about the MAP reading being inaccurate is so far afield, I don't know where it's coming from, I can not draw a logical link between the highlighted sections above---which are in direct response to 'why's that'---to me saying the MAP readings are innacurate.

 

The reason the mileage goes to hell is precisely because the MAP is accurate. I thought that was clearly and adequately addressed in the above passages (the first two sentences of each paragraph specifically).

 

I'm not getting defensive, I'm getting exaasperated as I am at a loss to figure out how to convey what I'm saying as from my point of view it looks fairly clear if it was read.

 

What I was getting at as a side point was that if you have specific questions relating to MAP based plenums then I'd recommend addressing them in another thread and not muddying up the water in the Carburetted Thread. Pointing out the differences of what works why in the two different systems is one thing, but starting to explain why each operates the way they do in the same thread will invariably lead to someone confusing statements about MAP based EFI Setups and Carburetted Setups.

 

Again, I don't know how much clearer I can be on the subject and why I said what I did. If you want clarifications on the statements (if required), I'd follow on in another thread, as I would hope this one could stay on the Carburetted setups, and not get muddied by talk on MAP.

[savageskaterkid]

That is what I was getting at for the longest time: The pressuirzation of the float bowl, even by a fraction of an inch of water will allow MUCH more fuel in to the circuit under boost situations (same as if you changed the float bowl level the same ammount on an N/A)

 

I'm still reading up on carbs, I'm fairly new to it, so I didn't understand some of the more technical things you were saying, but I'm desiphering it as I read it and its making more sence everytime. I've only talked to a few guys running turbo'd carbs, but they were all like SBC's with a single 4bbl and they were saying its a pain to tune at times for boost. But i guess with the plenum design on a triple setup helps to cure that?

[savageskaterkid]

 

The original poster has Megasquirt listed in his signature. It seems reasonable to assume he wanted to use the plenum with an EFI setup. He never said anything about carb'd applications, you brought them up. You made many negative statements about the cartech manifold that were unqualified as to which type of fuel delivery application you were referring to.

 

I'll update my signature

[Tony D]

I've only talked to a few guys running turbo'd carbs, but they were all like SBC's with a single 4bbl and they were saying its a pain to tune at times for boost. But i guess with the plenum design on a triple setup helps to cure that?

 

The difference is most guys with 4bbls that are blowing through them is that they make a 'pressure box' that equally pressurizes both the venturis and the float bowls. Many times it encloses the entire carburettor!

 

The design of the Mikuini (and the other horizontal carbs like Weber, dellorto, etc) is such that the float bowl can easily be pressurized separately. Some use a divided plenum, or like SHO showed, you can put a separate line, plug the normal breather port for the float bowl, and pressurize it from something added under the jet cover, or direct tapping to the float chamber. (Some Weber Guys will make a round 'standoff' for the jet cover, and put the boost in there, instead of through the front opening...that opening on the front is covered by their plenum, which only has the throttle bore openings in it.)

 

Most of the 4BBLs have simple tubes and they usually are right in the center of the throats, making it difficult to segregate. Sure, you can tap and plug them and then drill the bodies, but most guys just 'buy the big box' and go from there.

 

This is the same approach Cartech took when they designed their plenum---it pressurizes both chambers equally, so as a result you need MUCH larger jets in the main side than you would running any of the Japanese Boxes. We had a clubmember at GroupZ who had the full Cartech Setup and his jet sizes were MUCH larger than mine were. He also got fuel mileage that was in the very low teens. Granted he had a 3.0 and mine was only a 2.8, but the performance was equivalent when dynoed. Somewhere I have a video of him saying his jetting setup... I could find that, and then compare what was in my Solexes, as we both had 44's.

 

One of the things that impressed him about driving my car was the lack of the transitional popping. Same for another clubmember that had a 2X4 plenum, and was making somewhere north of 300HP on his 3.0 as well. No matter how they jetted it, they could not get rid of some transitional popping. I didn't know what they were talking about until I changed to the smaller 2X4 plenum without segregated float bowl pressurization.

 

Really, it's a twofold issue. Transitional drivability problems---which I link to the generic 'plenum style' not enriching the main circuit enough on-boost for transitional stability, and the Instant Boosting you get on the smaller plenum. What I found myself doing was driving with a much heavier foot simply to get the car from vacuum to +3psi boost so I didn't get t he popping. It was the worst from 0 to 1psi. My fuel mileage dropped (even with carbs) roughly 2mpg with the smaller plenum due to this driving technique.

 

What I'm getting at is it doesn't have to be that way, it can be a nice smooth drive where you aren't going to 25 and 30% throttle just to pass someone on the highway under normal speed conditions. And that kind of drivability really rewards you with fuel savings in a daily driver.

 

Regardless, the 17mpg I was getting was 'acceptable' but when that dropped to 15 or lower on the same jetting it's when I started considering EFI. I can live with an occasional pop or sniffle from the carbs, such is the beast. But I had a 'driving circuit' south of my place in Corona that had a slight grade on it, and if I took it at highway speeds it would sneeze and cough the whole way. A larger jet would have solved it, but I didn't need them with the segregated plenums I had run, and that is what got me looking at 'why' instead of just throwing more fuel at it and saying 'it works good enough'...

 

4BBLs in a plenum (the big box that surrounds the whole carb, not just a 'top hat' style pressure apparatus) will be a PITA to get at anyway, just because you have to disassemble the box to get to the jets! And if it's not a mechanical secondary, then tuning the diaphragm and spring combination to open those secondaries would be something I would not choose to tackle. I don't even know if running non-mechanicals in a blowthrough ap would work. Most of my time with 4BBLs was in draw-through where they seemed as easy to tune as anything else running a 4BBL.

 

All that being said, there is another way to do it, and that is called "Modulator Rings"---basically you make a plate to fit over the main throttle bore that has a hole roughly the size of your main choke (say you are running 44PHH Mikuinis with a 32mm Choke--you make an 'orifice plate' of 32mm). This does the same thing, and could be done on a Cartech or other 'box style' plenum. Under normal aspiration, the orifice doesn't come into play, but during boost when air is being pushed through at a higher velocity the modulator ring (orifice plate) will act as a pre-venturi and make the main circuit tip-in much earlier through the same effect as the segregated plenum. This is how you did VW's. And with their pressure boxes it was easy enough to pop em off, and make the hole slightly larger to trim/tune the on-boost enrichment characteristics. The general rule of thumb is to start at main choke size and work up from there until you get the enrichment characteristics you want. I won't say it's an easy task... it's kind of a PITA if you ask me, but if you are running blowthrough carbs it will work to enrich you under boost without having to change to humongo jets that just make the car sloppy above 3000rpms without being under boost.

 

I hope this is making sense? There are a couple of ways to do it, IMO the easiest way is to either externally vent the float bowls like SHO diagrammed, or use one of the pre-designed boxes. Screwing with Modulator Rings was just something I wasn't willing to do on another vehicle at that point in time. Even with an external vent, you may well end up orificing the entrance of the plenum for more pressure differential. Sure...it's a restriction, but making ONE orifice is a heck of a lot easier than precisely trimming six modulator ring orifices to put back in between the plenum and the carbs!

[SHO-Z]

Here is a picture of my box and vent tubing for the floats.

 

 

I figure that I will loose about 1 PSI of boost through the intercooler and piping. I will be running a stock Subaru WRX intercooler, it should take care of 10 psi of boost. So will have to bleed off some of the excess pressure to the floats.

 

Tony D thanks for the input on jetting and on this entire thread it has been great reading and information.

[Careless]

that's the first time i've seen the swirl effect applied to a plenum.

something new!

 

*high 5*

[Xnke]

So what of this can i apply to an SU-carbed setup, Tony D? I have looked at the TBI conversions for the SU's, and eventually will go that route, but I don't even have a "car" yet. Still restoring the unibody...but I'm almost there. Early summer should see me ready to paint.

 

First things i can see here:

 

-Pressurize the float bowls via a tube off the plenum, needle valves to precisely adjust things.

 

-Separated plenum chambers, to help equalize boost pressure between the two carbs.

 

-get on boost at as low an RPM as possible, to lessen the effects of tip-in pops and snaps.

 

 

Probably could look at running a supercharger and eliminate much of the problems related to turbocharging, such as on-boost/off-boost situations. WIth a supercharger, shouldn't i be able to run +1 or +2 manifold PSI all the time?

[Tony D]

SU's are another bag of tricks altogether. I have heard of British Applications where they were used blow-through, but have never seen one firsthand.

 

All my experience with SU's has been drawthrough application on the Corvair. I would just run them N/A and save your money. I wouldn't want to tackle SU Blowthrough, at least on early carbs (pre 73) because I really don't know what the limits of the fuel feed tube are, and how the jet sealing area works under the various pressures. It is all 'sealable' through the use of clean air piping and drilling holes, etc...but that's a lot of work to go through when other alternatives are far more practical.

 

And the boost threshold point has nothing to do with tip-in pops, it's the combination of plenum sizing, engine draw, and compressor flow that causes the transitional popping issues. If you lag the compressor so much that the carburettors are on the 'main' circuit when boost comes on, then it won't be an issue. Though you limit your useable rpm range. The solexes run on the idle jets till almost 3000rpms, that is how they get such great fuel economy. On an SU, the fuel metering is totally different and much more complex in regards to spring weight versus vacuum exposed to suction piston weight compared to needle station height when coming on boost. Egads, my head is starting to hurt to see how that interaction would be attacked!

 

The 'problems' are not related to turbocharging, it's related to 'blow through turbocharging of solex style carburettors', it's not an issue with an EFI turbocharged application. Which was a point made early on in this discussion.

 

If you suck through a carb on a supercharger, you will have the same success as if you suck through a turbo.

 

And the reason I say 'early' SU's as an issue is they don't have an integral float bowl like the later carbs do. So that fuel transfer line just looks like a problem area, one crack or break when you are under boost and you are gushing fuel directly onto the exhausts. Not something I would look forward to during 'testing to failure' in the real world. Of course, dealing with a power valve under boost on the later carbs would present it's own issues, but it would seem like they are much easier to attack in a blowthrough application.

[savageskaterkid]

I was looking at the mikuni's last night and was wondering if there was a write-up or a picture that I could see that goes over pressurizing the floats?

[PanzerAce]

Well, I'm glad someone pointed me at this thread when I asked about a turbo/TT setup on a set of triple mikuni carbs.

 

Tony, it ok if I pick apart your brains through email?

[savageskaterkid]

Hey Tony D, do you have an inlet pipe for the SK compo turbo plenum for sale? Or a FPR that'll work with this setup?

[Tony D]

I have only the one FPR, and unfortunately for you, it's SO adjustable it works on EFI pressures as well!!!

 

Imagine that, I paid 12,000 Yen for that thing in 1987 (and think it's around 17000 yen today from what I recently saw) and never figured out what they were talking about in the (printend in japanese) instructions about the "EFI" section, because it showed two different possible ways to set it up---after some dorking around these past 30 days of unemployed freedom has revealed, the second setup was to allow the regulator to function at a base pressure of 3 Bar, instead of the way I was formerly running it around 0.3 bar!

 

Clever those japanese!

 

Panzer, I didn't blow you off, I just saw it, you can PM or e-mail me any time. Sorry I didn't see this post earlier.

 

The inlet pipe I have is on the front cover of the SK Comp Turbo Plenum I have---the P.O. welded it on in a sort of 'HKS Hybrid Inlet Setup' sort of way...

[PanzerAce]

I have only the one FPR, and unfortunately for you, it's SO adjustable it works on EFI pressures as well!!!

 

Imagine that, I paid 12,000 Yen for that thing in 1987 (and think it's around 17000 yen today from what I recently saw) and never figured out what they were talking about in the (printend in japanese) instructions about the "EFI" section, because it showed two different possible ways to set it up---after some dorking around these past 30 days of unemployed freedom has revealed, the second setup was to allow the regulator to function at a base pressure of 3 Bar, instead of the way I was formerly running it around 0.3 bar!

 

Clever those japanese!

 

Panzer, I didn't blow you off, I just saw it, you can PM or e-mail me any time. Sorry I didn't see this post earlier.

 

The inlet pipe I have is on the front cover of the SK Comp Turbo Plenum I have---the P.O. welded it on in a sort of 'HKS Hybrid Inlet Setup' sort of way...

 

Lol, np Tony, you mentioned in a PM you were out of work. Besides, I am as well, which means I don't have any money to spend on the car right now beyond a new set of tires

[DatsunD]

I wouldn't want to tackle SU Blowthrough, at least on early carbs (pre 73) because I really don't know what the limits of the fuel feed tube are, and how the jet sealing area works under the various pressures.

 

Maybe thats why i cant find anyone that has tried to blow thru weber dgv's?

[Tony D]

Maybe thats why i cant find anyone that has tried to blow thru weber dgv's?

Weber DGV's are no harder than dual quad holley's with vacum secondaries to set up. You simply convert the secondaries to mechanical operation...but like blowing through a four barrel: Why?

 

EFI is the way to go boys. Cheaper and Cheaper every day!