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  1. #1
    Join Date
    Oct 2018
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    Shipston-On-Stour
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    81

    K&N Stubstacks for Holleys

    Time on my hands, like all of us, so my mind has wondered on to 'what little tweaks could I do now'! Has anyone used K&N stubstacks to improve the airflow on their carbs? Also, has anyone removed the choke upstand? I was thinking of taking the plates out anyway as I never use the choke and then while looking at the stubstacks I saw they do one especially for carbs with choke upstand removed, which is obviously going to be better for airflow.

    I would be keen to hear anyones thoughts

    For information, I use 2 x Holley 600cfm's.
    Dax with 1964 Dual Quad 427 and Toploader box

  2. #2
    Join Date
    Sep 2010
    Location
    Nova Scotia
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    840
    I thought about those stubstacks for my twin Holley 600s, but didn't want to mill the choke horns off. Not sure why I thought that as I don't use a choke. With the choke plate removed it takes close to a minute before the engine will idle without feathering the throttle. Not much of a big deal.

    It does look like a stubstack could improve the airflow by about 5.8%



    What I did to improve airflow that helped dramatically was to install larger, freer flowing air-filters. My original Stelling & Hellings foam filters were small and very restrictive. Sort of like running with a choke that was partly on. "Maybe that helped with starting?" you ask. That 1 minute of feathering the throttle remained the same as far as I can tell.

    If you're interested, I posted about it here:

    http://www.cobraclub.com/forum/showthread.php?t=60734
    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

  3. #3
    Join Date
    Oct 2018
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    Shipston-On-Stour
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    81
    Thanks for that. I agree, I upgraded to a K&N high flow filter and found that much better. I run the big oval type covering both carbs.
    Interesting, your thoughts on milling the choke stack off were similar to mine. 6% better airflow is quite a lot though. I'm sure I read somewhere milling the choke off and adding a stubstack could get you 10 to 15% more HP. I might give it a go. The K&N ones are not expensive. Why not? I can't really understand why I have never done it in the past!!
    Dax with 1964 Dual Quad 427 and Toploader box

  4. #4
    Join Date
    Sep 2010
    Location
    Nova Scotia
    Posts
    840
    It has occurred to me that my engine (and likely yours) can't use the total of 1200 cfm available from the two 600s. If that's the case, and the air-filters aren't restricting anything, the stubstacks may not offer much improvement, if any at all. However I don't know the answer, so if you go ahead and do this, please post the results.
    John

    “A prudent person profits from personal experience, a wise one from the experience of others.”

  5. #5
    Join Date
    Jan 2006
    Location
    Chelmsford Essex
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    1,054
    I have taken out the choke plate as never need it and I have seen it improves flow. If you do remove it make sure you lock the choke off with a rod as it can come back on with vibration !
    Dax 351 Cleveland T5 2.88 PL

  6. #6
    Join Date
    Jan 2008
    Location
    Basingstoke
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    1,110
    Quote Originally Posted by Eggbert View Post
    It has occurred to me that my engine (and likely yours) can't use the total of 1200 cfm available from the two 600s. If that's the case, and the air-filters aren't restricting anything, the stubstacks may not offer much improvement, if any at all. However I don't know the answer, so if you go ahead and do this, please post the results.
    1200cfm of carb is, er, quite a lot... Based on this https://www.summitracing.com/newsand...cfm-calculator you'd need to be running a 540ci race cammed engine, revving to 7000 rpm to get the best out of those carbs.

    I'm running a single 600 edelbrock on a stock rover 4.6.. even a 500 is overkill for me. With too big a carb, the issue is not air volume its speed - the air doesn't flow fast enough due to the size of carb, so the fuel doesnt vapourise properly and bogging problems, bore wash etc becomes common. Top down air filter, stacks etc would help - air velocity & remove turbulence etc but

  7. #7
    Join Date
    Oct 2018
    Location
    Shipston-On-Stour
    Posts
    81
    You're right it is a lot. It does look good though! Although I won't win any prizes from Greta. They are two vacuum secondary carbs so effectively run at half that until the vacuum pulls in. It's a standard Ford set up from the good ole' 60's. Despite what the calculator says it runs really well. Not that I rev it to 7000 very often (!) and the current cam is fast road not full race. I did have it in full race configuration for many years with wild cam and two Holley 780's and revved it high and hard. It sounded absolutely amazing. I only dropped to current spec when I put the engine in the cobra. Over the years I have tried a single 4 barrel and various configurations but not found them significantly different and I really do like the 2 x 4 look, plus it is how my engine was originally configured so put it back that way with original heads and original manifold with the two carbs. Steve Hole of TKC came to see me a few weeks ago so all being well there will be an article on the engine, it's race history and current role in my cobra in an upcoming issue.
    Dax with 1964 Dual Quad 427 and Toploader box

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