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BN1 - Question about cold air box

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matt78

Senior Member
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Hello.

My BN1 seems to be equipped with 2 cabs H6 (I think - couldn't find a number), with separate filters from later versions (AH 6 cyl.).
I intend to install a cold air box (100M type) that I saw on pictures, but when looking under the bonnet, I wonder how it could be fitted, because there is a very short distance left between the front carb's filter and the bodywork...
Maybe I'm wrong, and the 2 SU carbs aren't H6 ones and their intake ducts are too much long ?
If not, how did you manage to get the air box fitted ?

Matt
 
The factory 100Ms had the bracket that supports the shroud bent outwards a couple inches so the cold air box would fit (it's one of the ways to identify a 'factory' 100M). I have a 100M and, if it wasn't for 'authenticity,' I'd remove the CAB--it was missing when we bought the car--and install some good aftermarket air filters. The CAB is a PITA to get on and off, and you pretty much have to remove it to do any work on the carbs. I corresponded with a guy who raced a 100 way back when, and he claimed the car developed more power with velocity stacks than the CAB.

BTW, you can determine the carb type/size by measuring the opening; the carb number designates the diameter of the throats in quarter-inches. So, an H6, or HS6, has a one-and-a-half-inch throat diameter, HD8s have a two-inch diameter, etc.
 
Last edited:
Bob, Slight correction - the numbers are the multiples of 1/8" plus 1". Examples:
H4 = 4 x .125 + 1 = 1.5"
H6 = 6 x .125 + 1 = 1.75"
HD8 = 8 x .125 + 1 = 2.0"

Dave
 
red57 said:
Bob, Slight correction - the numbers are the multiples of 1/8" plus 1". Examples:
H4 = 4 x .125 + 1 = 1.5"
H6 = 6 x .125 + 1 = 1.75"
HD8 = 8 x .125 + 1 = 2.0"

Dave
Click to expand...

Thanks for the correction. I was wondering how an H4 could have a one-inch dia. throat.
 
OK, I better understand the trick !
Your comment about efficiency combined with this packaging constraint - Idon't want to modify anything on the body - are going to help me saving money...
I'll check the carbs' type following your indication.
Thank you for your information.

Matt
 
Matt, the quickest way to determine if you have the standard 100's H4 or the 100M's H6 is to look at the mounting flanges. The H4 has 2 mounting holes, top center and bottom center. The H6 has four, one at each corner. They cannot be interchanged on the same manifold.
 
CraigC said:
Matt, the quickest way to determine if you have the standard 100's H4 or the 100M's H6 is to look at the mounting flanges. The H4 has 2 mounting holes, top center and bottom center. The H6 has four, one at each corner. They cannot be interchanged on the same manifold.
Click to expand...

Yes, you are right. Mine have 4 mounting holes, so for sure are not 100's, but I wondered if they were H6, HD6 or HD8... especially regarding their overall size, due to my potential packaging issue with a cold air box. At the moment, following the advices I got, this is no more an issue :joyous:

Matt
 
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