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HS8s?

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Nunyas

Nunyas

Yoda
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So yeah, I'm browsing eBay and I find a pair of HS8s. 2" barreles on these beasts. I don't know if I'll bid on these, but they look like they've been cleaned up pretty well. However, these look like they might have fittings that might be used for emissions. Would one of these be too big in a single carb use (ZS replacement use)? As far as I know if I were to employ one of these it'll be on an internally stock engine.

https://cgi.ebay.com/ebaymotors/SU-HS8-JA...1QQcmdZViewItem

First time I've seen an SU this large on eBay....
 
Installing too large a carb can flatten the high end of throttle response terribly. The engine can only take in so much fuel. Imagine huge butterflies opening up to allow fuel in. By the time they are 25% open, the engine is sucking as much fuel as it is capable already. Opening the throttle more will therefore do nothing as the engine can't take any more fuel no matter how open the butterflies get. I hope that made sense!
 
yup... totally makes sense... kind of sounds like how my car drives... anything beyond half throttle doesn't seem to make any difference...
 
Some competition MGB's were set up with a PAIR of 'em! Demand carbs can be tuned to accomodate many app's. I don't know if it's still available, but the book "Tuning SU Carburetters" put out by Speed Sport magazine in England is a good "primer" to peruse for solid info on adapting SU's to a specific purpose. A stronger piston spring will allow the piston to rise more slowly, making proper use of the vacuum demand in the intake. A proper profile needle is then all you'd need. Sounds simple enuff, huh? BWUHAAAHAAAAA!!!!!!

Seriously: a single HS8 would likely be a better induction device than that poxy ZS lump, ~IF~ you have good info on a basic starting setup and access to needles, springs, etc. BJ8 Healy's had THREE of them BadBoys bolted on 'em. Jag's as well. Not sure about the mechanical aspect tho: bolt pattern, intake opening diameter, etc. That may require some inventive engineering.
 
seller claims it's the same manifold bolt pattern as the HS6, which apparently is pretty similar to the ZS pattern.
 
eh... I finally noticed the seller's "Buy it Now" price, and that their reserve has not yet been met... and it looks like someone bought them before the auction ended... they were too steep for my blood. For the time being anyways.
 
Not to raise yer hopes but: I ~may~ have a set of HS6's from a B-series four-banger Volvo lyin' about... pack-rat that I am. I'll check after the sun's up so's I can get to my "shed". And YES I have TWO sheds... but me name ain't Jackson.

/ubbthreads/images/graemlins/smile.gif


1:30 PM UPDATE: Yup. HS6's; 1 5/8" diameter holes. I have taken photos of the pair, having cleaned up the one with a vacuum port just ahead of the throttle plate (assuming that'd be the one you'd want to fit). The jets were new (twenty years ago!), and I disassembled the dashpot/spring/piston and float chamber to make sure nothing had been ruined. SWMBO has the frellin' USB cable in HER car so I can't post the pix yet. They owe me twenty years' rent but they didn't take up much space and they didn't eat anything, so we should "talk" if you're interested /ubbthreads/images/graemlins/wink.gif
 
I would imagine the rest of the breathing track would need to be overhauled in order to make the most of such a carb... right?

I'm interested in tinkering with an HS6.. but with present season around the corner I think I may have to hold off til around Feb for fun stuff
 
The HS8 seems to have the same PATTERN, but I would suspect that it would require a different mainfold, as the overall size of the mounting flange is probably larger than a 6. Seems I ran across a website that showed actual sizes of the mounting flages with bolt patterns, and IIRC the 8 was just a larger versio of the 6.

Dr.E - sounds like the vacuum takeoff is in the proper location (at least looking at my ZS). Seems I bought an older set of 6's without the vacuum takeoff. I'll be interested in seeing your pics.

As for the other two needed ports on the carb (flametrap in put and float bowl vent), my 6's have a boss where the flametrame sould be and wouldn't take that much to tap one in. As for the float vent, an HS4 float bowl cover is the same size and could possible be interchanged. I don't have to worr about this as I'm not emissions equipped, but I did check this just out of curiosity. I'll prolly be modifying my carb for the vacuum take off and the flametramp vent sometime in the future. (or looking for another set of carbs to tinker with).

The SU tuning book (power tuning su's) does have some good info, especially on getting a better throttle response. I'd also recomend SU carburetters tuning tips & techniques.

-D.

BTW, After messing about more with tuning the 6 (various needle/spring/oil mods) I'm even more impressed with how much of a difference this carb makes. an 8 might even be too much. I can actually get instintanious throttle response, and the car seems even quicker =)
 
photo 1 attached
 
Photo 2
 
photo 3
 
Photo 4
 
Bolt pattern is 2-1/8" center-to-center, square.
 
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