Inliners International Forums General Discussion Hi Performance Harper intake for Chevy 6

Does anyone have pictures of, or possibly describe the Harper progressive throttle setup. I have only heard of this setup with the split throttle shafts on the carbs so the inboard throttle plates open first and split the 2 barrel carbs into a set of primaries and a set of secondaries.

Since this would require linkage on both sides of the carbs, I am wondering how they were connected, There is a peice of the linkage that is part of the middle runner. I can see how this could be connected to the outboard side of the middle carb and that could run the scondaries.

Any decription or better yet pictures would be welcome. I doubt I would ever run this setup that way but if you think about maybe using a set of Stromberg 81 carbs on the Harper intake, the lower flow of the 81s might not overwhelm the engine.

Thanks for letting me day dream on my day off from work.

Not sure how it works.

I'd like to know more about this. Did it work really well or was it another idea that was more work than it was worth? What had to be done to the carbs? Beater

Panic - do you have a picture of the other side of the carbs? Since the front carb is not connected to the other carbs on that side they must be connected on the other side.

This is just hearsay ..... I have an Edmunds intake that uses these same type of carbs. My thought was to be able to set them up so one of the two barrels on each carb would be for cruising, but the other two barrels could be used to kick in with a "throttle stomp". I have been told this will not work because the size of the barrels will not allow a large enough volume of gas through them on to run with one barrel on each carb. If you think about it, however, unless it would work that way, what would be the point in running this type of carb?

Joe. I have searched for split throttle shafts and there is a little bit of info on the web. So it must have been done by some people. But using one barrel of two is no different than two of four. At least in my mind. Is that what you were thinking?

With that manifold (and other of same design such as Nicson) you have to run all 3 as primaries.
The problem isn't how much gas (it never is) but how much air, and 1 primary for each pair of cylinders (not 3 primaries for all 6 cylinders) works OK.
The total CFM on this has to be pretty big - much bigger than a 3 × 1 McGurk or Offy.

We have one we are still rebuilding, the 97s' throttle shaft is split in half between the butterflies and each side of the carb works seperately. So it works out it runs on a 3 bbl. carb set up then the other side kicks in progressively for a 6 bbl carb. The 97's are the only ones that have enough room between the butterflies to split them. Harper made these for a Chev's, GMC's, Buicks and Olds engines.

That could be a really interesting set up with a supercharger. Is the one you have for a GMC? It wouldn't be hard to adapt a Chevy to a GMC with a Harper.

I believe Gary Cope has most of the different intakes, he told us the story where he had tried to make a deal with Harper years ago and aggravated him so all the remaining intakes were sent to the scrap pile. The one we have is a Chevy but it would just take changing the balance tubes to switch engines. Here is one for a Buick,

Ok, I'm struggling to keep up here. How does the fuel enrichment (i.e. power valve) work in an application like this? Does it sense load (vacuum) from only one side of the carb only and react only to the booster on that side? Is the A/F ratio different from side to side? School me on how these type of carbs work.

On the flathead ford the Stromberg and Ford carbs worked like two single barrel carbs with right hand barrewl feeding cylinders 1-4-6-7 and the left barrel fed 5-8-3-2 with the cylinders starting at 1 thru 4 on the passenger side. There was no plenum to speak of. Multiple carbs can be adjusted for idle speed and mixture only and the accelorator pump has 2 or 3 adjustments with the shortest stroke for summer operation. Jetting is used to adjust WOT setting.

French, on the split throttle shaft carbs I believe that the linkage is such that no one barrel will ever be open far enough, by itself, to need the power valve open (still high enough manifold vacuum).

Or at least that's how I understand it.

Here is VanPelts' explanation which is a lot clearer than mine and has pictures . , http://www.vanpeltsales.com/FH_web/Flathead_trouble-carbs_34-38strom.htm

Jalop45 #4899

Do you have any pictures of the other side or a close up of how the linkage connects to the runner that seems to control everything (2nd from the right in your picture)

This is all I have in the compooter.,

I have never read of this sort of setup being used on anything other then a log manifold. As I understand the linkage - only the outer carbs have split throttle rods - the center is solid and is where the gas pedal bell crank is attached. This allows for attachment of an inner linkage and an outer linkage on either side of the center carb throttle rod - but these linkages are rigged to open at different progressive rates. The delay in opening on the outer carbs is typically accomplished with a slip-stop setup. A shorter distance on the inner linkage stop would cause the corresponding halves of the secondary carbs to begin to open. As travel continues the somewhat longer distance to the stops on the outer linkage would cause the other halves to open.

The setup pictured doesn't appear to be progressive/split at all. Only the center carb has a choke and there is a bell crank just behind it. This crank seems to act directly on the front carb throttle rod which in turn acts on the center carb and then back to the 3rd . . .

Also, with this sort of dedicated trip one needs a power valve on every carb. With split throttle shafts the linkage would be further complicated since the primary halves would have to include the power valves.

regards,
stock49

As you can see, the bellcrank on the center carb doesn't do anything on the far side - the lever hole is empty.
I'm not convinced that this is how the links are supposed to be attached.
I've seen others (too small and grainy to post) which had a simple 1-2-3-pedal straight linkage with a sliding stop to the cross-over bellcrank (so it doesn't move until part-throttle) on the driver's side, and 1-bellcrank-3 on the far side, with shorter arms (for faster action) than the driver's side.

The explanation as we got it was all the carbs had split shafts otherwise the center carb would flood the center 2 cylinders and the balance tubes are not large enough to transfer enoug fuel mixture to the end cylinders. The complete running ones I have seen use one side for low end and the other side kicks in as one 3bbl carb for increased performance. These were not originally designed for street use but over the years were altered and adapted with whatever linkage and carbs that were available to make do.

Yes, the carbs are all identical as to jetting and also construction (split). The idle air & fuel passages on the (new) secondary side should be disabled, plugged etc. to increase vacuum and response through the primary side.
A similar manifold could be made for the Holley/Weber 5200 progressive 2 bbl. The orientation of the carbs doesn't matter since it all goes into the same runner, and the clocking can be whatever makes the linkage easiest.
A larger question is whether the individual carbs are big enough to supply what is in effect a 78.5" twin cylinder engine (235.5" ÷ 3). The 5200 is only 269 CFM @ 3.0" Hg., which is less than I'd like to see.
The (now obsolete) Holley 2305 split 2 bbl. is also a candidate at 351 CFM @ 3.0" Hg.

A note: Jaguar's experience with triple side-drafts has shown that the jetting should be slightly richer for the center carb than the end 2, because the irregular 240-480-240 intake stroke cycle actually pulls harder on the jet than the regular 360-360 interval of the center port.

Indeed. That is why my post suggests that the setup pictured is neither split nor progressive. That empty hole is where the gas pedal actuated bell crank on the engine (out of site below) attaches to the linkage. The verticle rod is not present.

If you look closely you will see that the visible bell crank is acting directly on the front carb. The rod attached on the back side of the front carb is in turn acting on the center carb which in turn acts on the rear carb via the linkage that is clearly visible in for foreground.

To jalopy's point - if one is going to have a progressive linkage on a 'dedicated' setup like the harper - all of the carbs would have to be progressive because there is no common log for sharing and the balance tube isn't enough. The linkage I've read about and described is thus suitable only for a log.

Curiously, in the setup pictured only the center carb has a choke . . .

Not sure I follow what you mean by 'cross over' with regard to the linkage.

I have a progressive Harper, the outboard side opens normally and the inboard side starts to open at part throttle, they reach WOT at the same time. I beleve the GMC and Chev manifolds were the same as they have both attachment features, just change the length of the idle balance tubes. I will try to get some pictures, and will bring it to the 2012 convention, if I still have it.

Tim

Compared to other tri-power setups of the time, was the split throttle shaft idea any better or offer any performance advantages over the traditional progressive or 1:1 linkage setups. Or was it more of an innovative idea that seemed to be trendy more than function.

Interesting. Very curious to see how this is accomplished.

Tim, Be careful what you bring. What comes to Nevada stays in Nevada. Seriously I'd like to have the chance to see this setup. Beater

I believe it was an innovative design that used a ram tube design that gave a better fuel distribution to each pair of cylinders that wasn't available using a log manifold. By splitting the throttle plates each barrel can be treated as a seperate carb. The same principal is used on some of the Pro Stock tunnel rams with split Dominator carbs.

The progressive feature made it possible to use much more CFM per carburetor without loss of response.
Other than not being as pretty, 3 × 1 CV carbs (SU, Stromberg/Zenith/keihin) will do the same thing at 1/2 the cost.

I think SU carbs are beautiful!

I agree, I was referring to the popular taste which regards a 97 as an icon.

I'll give you that - they're more tradional than SUs on American iron.

Isn't it interesting how we always come back to what we each perceive to be "pretty" and "traditional" when "functional" often falls by the way. This is one of the most interesting discussions I've seen in a while. This carb treatment is so vintage and purely mechanical yet very cutting edge for it's time. It is really interesting to think of how it would work on a Harper vs a log manifold. Also the use of other carbs in a similar set up interesting. I'd like to hear from folks who have used these. Beater

I'm still looking for detailed photos of the progressive linkage. I found these by going through old ebay auctions. This linkage is very different than the linkage I have on my non-prograssive intake, but very similar to the linkage on the buick intake that was posted.

On this picture it looks as there are adjustment screws of some sort.



Here you can see that the progressive set up uses both holes cast into the center runner to hold pivots and linkage. On the non-progressive setup the inside hole just has a plug filling the hole.



Any and all pictures or detail are welcome.

Thanks,