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Re: Header??

To: Phil Bates <>,
Subject: Re: Header??
From: Larry Colen <>
Date: Tue, 28 Dec 1999 10:31:28 -0800
On Mon, Dec 27, 1999 at 11:14:47PM -0700, Phil Bates wrote:
> OK, while I have the engine and trans out to work on the transmission, I
> am considering putting a header on my '67 MGB.  Here is the thought
> process - I have a 3-main 1800 motor in my MGA with a header, and it
> seems to have a lot more power.  The gearing should be the same for both
Is that the only difference between the motors?  Same cylinder heads?
Pistons? Cam grinds? Is the 5-main an 18G or an 18V? How many miles are
on each motor? A well worn in motor will often make more power than a
tight new one (it's an old racing adage that motors make the most
power just before they grenade).

> (I did change the A's rear axle to an early MGB axle).  Anyone know of
> disadvantages of using a header on this car (other than cost) - I have
> heard the stock manifold is pretty good, but I think a header would be
> better.  I do expect that I'll always have a little less power in the B
> because of the 2 extra bearings, but it shouldn't be much different.
You lose a little to friction in the bearings, but I'd guess that one
would get a lot more safe RPM out of a 5 main than a 3 main. Since power
is torque * rpm, I'd guess (all things being equal) a 3 main would have 
more torque but a 5 main would have more power.

I do know that every few years I start itching for "easy horsepower"
and think of putting a header on my car.  I always get several 
knowledgable folks (Lawrie et. al.) saying that it isn't worth it,
that the headers don't give you anything but more mechanical headaches.

I've not seen any dyno charts or comparative lap times.


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