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Modifying a stock intake manifold-questions

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Mgnostic Matt Kirk
Vernon, North Texas, USA   USA
1959 Austin-Healey Bugeye Sprite
1979 MG MGB "Killer Bee"
I have been studying a spare intake manifold from a midget. The transfer passage has a huge, relatively speaking, opening that spans the entire port. In reading a couple of years worth of posts I have seen mention of a manifold that has a small passage opening, the practice of rounding the cylinder head side if the intake to smooth flow and even the idea of epoxying over the passage. It seems like it would be reasonable easy to cover or reduce the opening with a small passage to maintain the crossover function. How often is this done and is it practical/useful for a street driven car? My engine is a mostly stock 948 with a mild street cam.

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Speedracer Platinum Member Hap Waldrop
Greenville, SC, USA   USA
1967 MG MGB Racecar "The Biscuit"
Matt I am quite someone has modified the square-ish roof intake to imitate the one with the round holes, it could be done with epoxy putty and then finish with a liquid epoxy, I have done my fair share of intake epoxy work on intakes. I n fact Jeff S at Advanced Distributor modded a MGB intake (same square hole leading into the balance tube) to only have a small hole in it. However it may just be easier to get a intake with the round holes, they are not that rare, we only used those on the SCCA limited prep 1275 engine. Also on race engine we have blocked off the balance tube entirely before. I don't know on street driven 948 street engine, that is it is going to make a hug difference, but you car did come originally with a intake that had the small round holes, the square-ish roof intakes cam along later with the smog 1275s.



Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com


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AN5L8016 Avatar
AN5L8016 Mark Haynes
Nederland, Colorado, USA   USA
As Hap says you may be looking at a later 1275 intake, and the one on the car may be an earlier 9CG or 9CC intake it shard to tell from the outside unless you have the casting numbers. David Vizard's book has a number of tips to increase flow in the stock induction system, including radiusing the edge of the balance tube where it intersects the runners.



'58 Bugeye
'05 Mini Cooper S

Mgnostic Matt Kirk
Vernon, North Texas, USA   USA
1959 Austin-Healey Bugeye Sprite
1979 MG MGB "Killer Bee"
Thanks for the responses. My car currently has the stock carbs and intake mounted. My parts stash includes a set of HS-2 carbs and intake from a 1098. I've always heard that these are a good upgrade. Since it is an easily reversible swap I thought I would give it a try and while cleaning up the manifold I noticed the large crossover tube. I have the Vizard book and have seen the bit about radiusing the the edge of the tube. Since the book is about making power he moves on to single carb manifolds pretty quickly. I am somewhat limited in terms of working with what I've got and a desire to maintain the twin carb configuration. Before I did anything to the manifold I thought I would see what the knowledge base here had to say.

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AN5L8016 Avatar
AN5L8016 Mark Haynes
Nederland, Colorado, USA   USA
My BE with its H1 SUs runs great, especially down at your elevation. IF you try to update the carbs (I've got a pair sitting and waiting myself), be sure to change out the manifold gasket, as the gasket takes a set and if you don't put the new manifold on EXACTLY where the old one was on an old gasket, you'll get vacuum leaks. Ask me how I know this...eye rolling smiley



'58 Bugeye
'05 Mini Cooper S

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