Results 1 to 28 of 28

Thread: Triple Carb Manifold Short or Long??

  1. #1
    Registered User
    Member ID
    CZCC-1316
    Join Date
    Oct 2001
    Location
    somewhere
    Posts
    2,495

    Default Triple Carb Manifold Short or Long??

    Ok I got a set of Triple Mikuni 44's recently see my gallery if you like. They came with what I believe is a short manifold so the runners look a little more bent than the long runners of a long manifold.

    I'm wondering what the opinion is on these manifolds and how the length affects performance. I would believe that the longer runners would increase the torque of the engine but the shorter runners look a little restrictive with the bend in them.

    However having read a few articles on porting and air turbulence this might be the aim of the short manifold. To slow the air just enough and reduce the turbulence before entering the combustion chamber.

    The manifold itself is a Mikuni item it actually has a Mikuni stamp on it.

    So what's the verdict what do the experts think?

  2. #2
    Registered User rzola's Avatar
    Member ID
    CZCC-1928
    Join Date
    Mar 2002
    Location
    St Clair Shores MI
    Posts
    41

    Default

    Longer runners give you peak torque a lower/mid RPMs. Short runners are for high RPM race engines. For a street car the longer set up may be better for drivability.......

  3. #3
    Registered User
    Member ID
    CZCC-5121
    Join Date
    Oct 2003
    Location
    Seattle, WA
    Posts
    2,362

    Default

    If you see the two side by side the short manifold has quite a sharp curve and funelling effect to it compared to a longer manifold. Based on this I chose to use a longer manifold, and so far I have told several race engine builders about my choice and they've all said the longer manifold works better. The problem is that you won't have as much room for an air cleaner, velocity stacks have to be shorter, and the linkage has to be adapted to work. If you're not racing just use the manifold you've got.

  4. #4
    Registered User Steve Parmley's Avatar
    Member ID
    CZCC-1154
    Join Date
    Jun 2001
    Location
    folsom ca
    Posts
    223

    Default

    Australians get more room for tripples and air cleaners with the brake booster and master cylinder on the other side of the engine bay.

    Here is a website with some Mikuni info and where I buy parts for my 44's. http://www.wolfcreekracing.com/carbid.html
    Last edited by Steve Parmley; 04-18-2006 at 04:13 PM.

  5. #5
    ++++++++ HS30-H's Avatar
    Member ID
    CZCC-2116
    Join Date
    May 2002
    Location
    London, England, UK.
    Posts
    3,023

    Default

    Gav,

    Steve has touched on something that you might not have thought of. The shape of your Mikuni inlet manifold might have a lot more to do with packaging issues, rather than being dictated purely by efficiency........

    Mikuni made some inlet manifolds that were expressly for the LHD market, and I believe that these placed the carbs higher in the vertical plain in order to give more clearance for a tubular exhaust manifold on an LHD car.

    I've also been told that some inlet manifolds for the L-series engined Skylines displayed these traits, because the Skyline engine bay was narrower than that of the Z.

    But I wouldn't worry about it if I were you.

  6. #6
    Registered User
    Member ID
    CZCC-5121
    Join Date
    Oct 2003
    Location
    Seattle, WA
    Posts
    2,362

    Default

    Quote Originally Posted by Steve Parmley
    Australians get more room for tripples and air cleaners with the brake booster and master cylinder on the other side of the engine bay.

    Here is a website with some Mikuni info and where I buy parts for my 44's. http://www.wolfcreekracing.com/carbid.html
    Actually with a Cannon manifold and Mikunis, my main issue was that the air cleaner just barely clears my strut tower bar clevis, which in my case is welded to the strut tower. Even if that weren't there, you still couldn't use a really long stack because there wouldn't be enough room between it and the strut tower to finagle a deeper air filter on there.

  7. #7
    Registered User
    Member ID
    CZCC-1316
    Join Date
    Oct 2001
    Location
    somewhere
    Posts
    2,495

    Default

    Well I did buy these from a guy in the US on ebay . So that might be part of the explanation. I've seen a few Canon manifolds around from time to time at a fairly cheap price. If I can get one cheap I might grab it just incase however as Alan said I don't think I'll stress too much over it for now.

  8. #8
    another classic car guy EricB's Avatar
    Member ID
    CZCC-1574
    Join Date
    Jan 2002
    Location
    SoCal
    Age
    44
    Posts
    904

    Default

    random related question...

    if you have a short manifold with long velocity stacks VS a long manifold with short velocity stacks such that the length from cylinder head to tip of velocity stack is the same on both setup...

    does it make any difference in performance?
    curious about that one...
    what do you all think?

    -e

  9. #9
    Registered User
    Member ID
    CZCC-5121
    Join Date
    Oct 2003
    Location
    Seattle, WA
    Posts
    2,362

    Default

    That's a good one Eric. I don't really know an answer other than to say that the closer the carbs are to the head the sharper the bends and the more severe the taper from carb outlet to the port size has to be.

    I've heard some really sketchy reasoning behind why having more air/fuel already mixed in the manifold was better, but they sounded so hokey to me at the time that I didn't commit them to memory.

  10. #10
    another classic car guy EricB's Avatar
    Member ID
    CZCC-1574
    Join Date
    Jan 2002
    Location
    SoCal
    Age
    44
    Posts
    904

    Default

    I remember talking about something related with Alan a while back when I was comparing just how short the S20 manifolds were (crossflow head of course) in comparison with our regular cylinder heads... In some of the period pics the camera angle of the pics is such that you could almost believe the carbs are bolted straight to the cylinder head hahahahahaha.... just kidding.

    -e
    Last edited by EricB; 04-19-2006 at 07:52 AM.

  11. #11
    Registered User
    Member ID
    CZCC-5121
    Join Date
    Oct 2003
    Location
    Seattle, WA
    Posts
    2,362

    Default

    Just took a look at one of Alan's photos. Judging by the perfectly straight intake runners I'm guessing Nissan designed the S20 head for Mikunis (duh!). Unfortunately this is not the case with our L engines, but I suspect that on the S20 you could put a very large stack on the end of the carb, and that might potentially enable you to get more air through the carb and into the engine.

  12. #12
    ++++++++ HS30-H's Avatar
    Member ID
    CZCC-2116
    Join Date
    May 2002
    Location
    London, England, UK.
    Posts
    3,023

    Default

    Quote Originally Posted by EricB
    In some of the period pics the camera angle of the pics is such that you could almost believe the carbs are bolted straight to the cylinder head hahahahahaha.... just kidding.
    -e
    Yeah, the inlet is pretty compact on the S20, especially when you consider that it is full of coolant passages too. See attached pic of an end-on view for comparison. The point ( in relation to Gav's question about his Mikuni L-series manifold ) is that there is not 'step' down from carb to head - it is just a ( short ) horizontal plane.

    Quote Originally Posted by jmortensen
    .....but I suspect that on the S20 you could put a very large stack on the end of the carb, and that might potentially enable you to get more air through the carb and into the engine.
    The stock airbox on the S20 ( and the remote filter - which was mounted in front of the radiator support panel ) was pretty big. The air box had integral airhorns for the stock 40PHH Mikunis, and these air horns were attached to the cover of the air box rather than its base plate. I think this was done to ease servicing; it would be a real struggle to get the air box cover over the stock airhorns.

    Nevertheless, I have had to address this issue with my project car's engine - as I am using Weber 45DCOEs instead of Mikuni 40PHHs. I reckon I can get the airbox cover over the 45mm high full-radius rampipes I hope to use, and will therefore be able to use the stock filter box too. It will be a tight fit, but I think it can be done. I think longer rampipes would be better, but for sure they won't fit under the modified stock airbox.

    The factory race cars were fitted with injection systems that used very long trumpets. The inlet manifolds for the ( sliding throttle ) injection system tipped the inlet UP at an angle - presumably for packaging reasons.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	15-04-06 010R.jpg 
Views:	375 
Size:	127.1 KB 
ID:	11976   Click image for larger version. 

Name:	15-04-06 007R.jpg 
Views:	887 
Size:	108.7 KB 
ID:	11977   Click image for larger version. 

Name:	15-04-06 008R.jpg 
Views:	547 
Size:	98.0 KB 
ID:	11978  

  13. #13
    Registered User
    Member ID
    CZCC-5121
    Join Date
    Oct 2003
    Location
    Seattle, WA
    Posts
    2,362

    Default

    Some of the CP racers would mill their triple manifolds to angle the intake manifold up. Then they'd port the head to match. The idea is that the short side radius in the head is straightened this way, and it's done to improve flow rather than to stick a longer manifold or air horn on. There are pics of some of these manifolds in the How to Modify book.

  14. #14
    another classic car guy EricB's Avatar
    Member ID
    CZCC-1574
    Join Date
    Jan 2002
    Location
    SoCal
    Age
    44
    Posts
    904

    Default

    that's a great end-on pic Alan... really highlights the angle difference...

    jmortensen, if you mill the manifold to ease out that angle, then your carbs on the end of manifold are themselves even more tilted from an end-on view... I don't remember what the How To book said about those but doesn't that interfere to a certain extent with the way the float works inside the carbs??? or is it impervious to being tilted like that?

    -e

  15. #15
    Registered User byunique's Avatar
    Member ID
    CZCC-1108
    Join Date
    Mar 2001
    Location
    San Francisco, California, United States
    Posts
    158

    Default

    I was looking for this answer myself, but I was motivated to check into it because of a stumbling issue I ran into as I increased the venturi size. For some background, my Mikuni 44's came with the Mikuni manifold, but I later changed it to a Cannon (long) manifold since I was told the long manifold makes more power. I never tried the Mikuni manifold, and just sold it on Ebay.
    My motor is a pretty built 2.8, 9/1 compression, large cam, ported heads and I love to see power above 6500 rpms.

    As I increased the venturi size to a 37 or larger I started to run into a big stumble if I accelerated hard, and that would be right off the line or punching it down the freeway. I could tell that my motor was getting lean at those moments, (per mixture meter..) and despite what changes I made to acceleration pump, jet size, etc. the issue was always there. It would be milder with 34's but would get worse with the 37's. Of course, this hurt my top-end power and I was always yearning to go to 39's but the stumble would be ridiculous at that size.

    So, I had asked around about manifold length and was told a shorter manifold would help, but was never told it would cure the problem.

    I hunted around on Ebay, and found a SK/Sanyo manifold which looked just like the long run Cannon (mine was 5.5 inches btw), but it was a lot shorter (3.5 inches I think).

    see pics of shape/size
    http://www.brandonyu.com/gallery/mai...2_itemId=11681

    After getting it setup, I was amayzed. The flat spots that I had disappeared, and there was a much tighter feel to the engine. It felt much more torquey all around. It ran great with the 37's and then I upped from 37's to 39's, and the high rpm range was extended further, but this time without ANY hesitation off the line or midrange.

    I can basically roll on acceleration off a stop light and smoke the tires all the way across the intersection and pull strongly to 7000rpm. (a 4.44 helps with this too ) Yes, this basically cured my car of the huge flatspot and I was able to bump my timing a few degrees as well w/o pinging. The engine is no longer lean upon acceleration I believe it has to do with the velocity of the charge due to the shorter length. I also noticed the manifold is cut at a higher angle so, it tilts up more the Cannon, which also may help per the previous comment about that.

    Yeah, a long manifold may be good generally, but didn't help in my case with larger venturies! The car is night and day different My advice is get something straight, but shorter than the standard 5.5" Cannnon.
    Brandon Yu
    '73 240, stroked Rebello 3.0, ported N42, 44 Mikunis, Adj. Tokicos, 5 speed, Trust 10.8lb Fly., Centerforce Dual Friction, 4.44 Nissan Comp LSD, MSA Header, Autopower rollbar, 16 " Riken Mesh Wheels.

    sound of my Z

  16. #16
    Registered User Steve Parmley's Avatar
    Member ID
    CZCC-1154
    Join Date
    Jun 2001
    Location
    folsom ca
    Posts
    223

    Default

    When I talked to Dave Malvern several years ago he said he would get his race carbs level at all costs. He would remove as much vibration as possible by modyfing the Comp rubber isolaters and shield the carbs from the header heat. "No matter how much insulation you have now it is still not enough".

    I have the short manifold (can't help it I was born that way) and those funky white plastic isolaters with the carbs at an off angle and it has been fine even with quite a bit of autocrossing. That said, if you know anyone selling a Datsun Comp manifold let me know since I was told by a racer more torque is available with that manifold.

    Jon, my large ITG filter is a problem with Vacuum booster when I position the engine back to the firewall which is legal in XP SCCA auto-x or in FP if you run under the GT-2 in excess rule with accompanying weight penalty.

  17. #17
    Registered User
    Member ID
    CZCC-5121
    Join Date
    Oct 2003
    Location
    Seattle, WA
    Posts
    2,362

    Default

    Quote Originally Posted by byunique
    I was looking for this answer myself, but I was motivated to check into it because of a stumbling issue I ran into as I increased the venturi size. For some background, my Mikuni 44's came with the Mikuni manifold, but I later changed it to a Cannon (long) manifold since I was told the long manifold makes more power. I never tried the Mikuni manifold, and just sold it on Ebay.
    My motor is a pretty built 2.8, 9/1 compression, large cam, ported heads and I love to see power above 6500 rpms.

    As I increased the venturi size to a 37 or larger I started to run into a big stumble if I accelerated hard, and that would be right off the line or punching it down the freeway. I could tell that my motor was getting lean at those moments, (per mixture meter..) and despite what changes I made to acceleration pump, jet size, etc. the issue was always there. It would be milder with 34's but would get worse with the 37's. Of course, this hurt my top-end power and I was always yearning to go to 39's but the stumble would be ridiculous at that size.

    So, I had asked around about manifold length and was told a shorter manifold would help, but was never told it would cure the problem.

    I hunted around on Ebay, and found a SK/Sanyo manifold which looked just like the long run Cannon (mine was 5.5 inches btw), but it was a lot shorter (3.5 inches I think).

    see pics of shape/size
    http://www.brandonyu.com/gallery/mai...2_itemId=11681

    After getting it setup, I was amayzed. The flat spots that I had disappeared, and there was a much tighter feel to the engine. It felt much more torquey all around. It ran great with the 37's and then I upped from 37's to 39's, and the high rpm range was extended further, but this time without ANY hesitation off the line or midrange.

    I can basically roll on acceleration off a stop light and smoke the tires all the way across the intersection and pull strongly to 7000rpm. (a 4.44 helps with this too ) Yes, this basically cured my car of the huge flatspot and I was able to bump my timing a few degrees as well w/o pinging. The engine is no longer lean upon acceleration I believe it has to do with the velocity of the charge due to the shorter length. I also noticed the manifold is cut at a higher angle so, it tilts up more the Cannon, which also may help per the previous comment about that.

    Yeah, a long manifold may be good generally, but didn't help in my case with larger venturies! The car is night and day different My advice is get something straight, but shorter than the standard 5.5" Cannnon.
    Hmm... interesting. I have the stumble too with 37mm chokes on 44mm Mikunis, but I was able to *almost* completely eliminate it through jetting. Kept going bigger and bigger and bigger on the pilot. Bigger I went, the less it stumbled. I tried bigger pump nozzles, but that didn't have anywhere near the beneficial effect of the bigger pilots. Your comment makes me want to try a different manifold and see the difference though. Malvern was one of the people who told me the manifold choice was the right one, the other was Rebello FWIW.

  18. #18
    Registered User
    Member ID
    CZCC-5121
    Join Date
    Oct 2003
    Location
    Seattle, WA
    Posts
    2,362

    Default

    I guess another idea would be to put an airbox on and see what difference that makes. In my non-engineer mind that would kinda group the vacuum from all the runners to get a more steady stream of air moving.

  19. #19
    another classic car guy EricB's Avatar
    Member ID
    CZCC-1574
    Join Date
    Jan 2002
    Location
    SoCal
    Age
    44
    Posts
    904

    Default

    hmmmm very interesting indeed...
    i also went to bigger pilots to cure a cough/spit problem i had when i accelerated just so... actually was jon's advice i followed... sure i did notice my MPG take a small hit and it runs pretty fat at idle but hey can't win all the battles right? my venturis are still the stock size my 44s came with - never changed them... all of this is very interesting... Brandon thanks for sharing your impressions...

    -e

  20. #20
    Registered User
    Member ID
    CZCC-5121
    Join Date
    Oct 2003
    Location
    Seattle, WA
    Posts
    2,362

    Default

    What manifold are you running Eric?

  21. #21
    Registered User byunique's Avatar
    Member ID
    CZCC-1108
    Join Date
    Mar 2001
    Location
    San Francisco, California, United States
    Posts
    158

    Default

    Glad I can share my experience with this EricB. The first time I really thought this would work is when I saw a car that Scott Performance had put together and it was at the Motorsport Show '05. It was a Cannon Manifold, but it was cut shorter, and thats what prompted me to do it.

    http://www.brandonyu.com/gallery/mai...2_itemId=11813

    I thought about cutting mine up, but it would be quite $$$ . So, I am really glad I found that manifold on Ebay. I don't think the short straight shot manifolds are plentiful.
    Brandon Yu
    '73 240, stroked Rebello 3.0, ported N42, 44 Mikunis, Adj. Tokicos, 5 speed, Trust 10.8lb Fly., Centerforce Dual Friction, 4.44 Nissan Comp LSD, MSA Header, Autopower rollbar, 16 " Riken Mesh Wheels.

    sound of my Z

  22. #22
    another classic car guy EricB's Avatar
    Member ID
    CZCC-1574
    Join Date
    Jan 2002
    Location
    SoCal
    Age
    44
    Posts
    904

    Default

    you know i'm not quite sure...
    i just landed in tokyo last night and am still all out of sorts...
    hmmm either i have a TWM or a Mikuni manifold - I honestly don't remember right now... sorry...

    -e

  23. #23
    WESTCOASTZRACER ron carter's Avatar
    Member ID
    CZCC-932
    Join Date
    Sep 2000
    Location
    Sunny Oceanside, CA, USA
    Age
    53
    Posts
    1,105

    Default

    I have run the Mikuni Manifold on my old street car and it always went like heck from idle all the way to redline. That being said, On my BRE Z I run the Nissan Comp / Interpart manifold on the race car which is a balance between the Mikuni and the Cannon and it works very well...no flat spots and good top RPM.

    The rule of thumb I always heard was Mikuni Manifold for the street. Cannon for Auto-X (better torque). Nissan comp for roadracing.

  24. #24
    Registered User
    Member ID
    CZCC-18002
    Join Date
    Oct 2008
    Location
    Baltimore
    Age
    43
    Posts
    16

    Default

    Has anyone ever mounted the long runner Mikuni Manifold in their car? Do you have any pictures.

    As best as I could tell, there were only two people in the thread who have even seen one of these manifolds in person (Ron Carter; though I think I may have misread, and Gav240z, who found one on eBay). I have seen hundreds of Cannon long runner manifolds, and a few other brands as well, but I have never seen another Mikuni stamped long runner intake manifold.

    I have always understood that the short runner Mikuni manifold was only intended to allow clearance between the carbs and the brake master cylinder (when used with brake master vac).

  25. #25

  26. #26
    Registered User
    Member ID
    CZCC-18002
    Join Date
    Oct 2008
    Location
    Baltimore
    Age
    43
    Posts
    16

    Default

    Gav240z, you said Mikuni was stamped into the manifold. Did you mean it was part of the casting?
    Last edited by cafebaltimore; 11-17-2008 at 04:33 PM.

  27. #27
    Registered User
    Member ID
    CZCC-21527
    Join Date
    May 2010
    Location
    Mississippi
    Age
    32
    Posts
    1

    Default

    To bring up a old post. I am trying really hard to find out who made my manifold. I just received it and still have to clean it. No pics yet. All i know about it is that it's short like the Minkuni manifold, but says London on it. no other markings. No balance tube "molded" into the casting either.

  28. #28
    Registered User byunique's Avatar
    Member ID
    CZCC-1108
    Join Date
    Mar 2001
    Location
    San Francisco, California, United States
    Posts
    158

    Default

    thats interesting... London
    Brandon Yu
    '73 240, stroked Rebello 3.0, ported N42, 44 Mikunis, Adj. Tokicos, 5 speed, Trust 10.8lb Fly., Centerforce Dual Friction, 4.44 Nissan Comp LSD, MSA Header, Autopower rollbar, 16 " Riken Mesh Wheels.

    sound of my Z

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •