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Twin hs2 alloy inlet manifold

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Twin hs2 alloy inlet manifold

Postby H » Thu 17th Aug 2006, 09:33pm

Hi!

I've been reading topics about twin hs2's. Almost everybody is saying that twin hs2's standard inlet manifold is junk but it is easy to modify it to flow better.

What kind of mods you are talking about? I have two of them. It would be interesting to compare to result within original and modified one. Thanks beforehand.

H
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RE: Twin hs2 alloy inlet manifold

Postby Dogmatix » Fri 18th Aug 2006, 12:29am

Save up and get a maniflow!
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RE: Twin hs2 alloy inlet manifold

Postby chunkyjh » Fri 18th Aug 2006, 09:40am

you need to get yourself "tuning the a series engine" by david vizard. in it he says that the sharp edge at the top edge of the intake just infront of the balance pipe causes serious restrictions so filing this off to a large radius helps no-end. You need to read it yourself really. theres 33 pages on intake manifolds alone! but yeah Dogmatix is right, maniflow is a good option!
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RE: Twin hs2 alloy inlet manifold

Postby Mister_D » Fri 18th Aug 2006, 04:43pm

The modification is basically to do with rounding off edges especially on the balance tube.
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RE: Twin hs2 alloy inlet manifold

Postby royallingham » Sat 19th Aug 2006, 07:26pm

It can be done - takes a lot longer than V suggests - but you have nothing to lose, so go for it. basically - you are aiming for a nice smoothflow from the carb to the head - with the haed end enlarged to match the ports in the head. The upper flange where the balance pipe joins has to be filed away almost to nothing - to ease the flow of any gas try to enter the head from the balance pipe. Some folks completely block off the balance pipe with'plastic metal' - which then allows completely smooth transition from carb to head - not tried this myself - but I understand it works well. I have - dim and distant past - made a steel twin manifold for 1.5" carbs with no balance pipe - and it worked v well indeed. After all - Weber manifold has no balance pipe.
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RE: Twin hs2 alloy inlet manifold

Postby H » Thu 14th Sep 2006, 06:36pm

I read Vizard. I'm more muddled than I normally am. Vizard says that twins are totally crap and standard alloy inlet is even more junk. VS1 inlet Vizard is introducing uses balance pipe as a extra feeding port to another carb. Others block balance pipe totally. Both works fine???

What to do? Smooth transition to balance pipe or blocking it totally. I really don't know. Vizard su mods were very interesting. May I try to do throttle shaft mods next winter. Have You lads tried them?
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RE: Twin hs2 alloy inlet manifold

Postby Random_Nonsense » Thu 14th Sep 2006, 06:46pm

Dont bother with the carb mods. Just fit bigger ones if you need to

Regarding flowing the manifolds, I could do it for you for £30 if you like!
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RE: Twin hs2 alloy inlet manifold

Postby royallingham » Thu 14th Sep 2006, 09:00pm

You only block off the cross pipe (or make a manifold with no cross pipe) if the twin carbs are each big enough to feed the port adequately. This is what a weber does - it's not magic, just common sense. Twin 1.25" carbs are a waste of time - go for twin 1.5 or 1.75 carbs . I have modded the standard inlet manifold for use with twin 1.5" carbs - took 'a while' - but I think I have done a good job! Not tried it on the car yet. Easiest and best really is big single 1.75" HIF 44 on MG Metro (or similar) alloy inlet manifold.
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RE: Twin hs2 alloy inlet manifold

Postby Random_Nonsense » Thu 14th Sep 2006, 09:04pm

1.25s arent a waste of time if they are the right size for the application.

Its incredibly tricky to get an undersize OR oversize carb fuelling properly
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RE: Twin hs2 alloy inlet manifold

Postby royallingham » Thu 14th Sep 2006, 09:11pm

They are ok for 850 - and just about ok for a mild 998. Otherwise - go bigger!
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Postby craig1010cc » Fri 15th Sep 2006, 10:04am

You confuse me Roy, why would a set of twin HS2's be only any good on a mild 998? They where after all fitted to 1275 S's from the factory and made a heathy 65-70 BHP (can't remeber the book figure and cant be arsed to look) and thats with a pretty restictive looking filter system. As discussed else where, to get 65-70 BHP from a 998 is quiet a high state of tune.

Also, you keep insisting that all twin SU's are rubbish, but now your building a set of big twins? Why don't you upgrade to a HS8 or go for a webber?

Personally i like twins, they look good and I personally believe that I wont lose performance over the single HIFF44 that is on there at the min but I accept that they need more work to keep them in tune and if I do lose a brwak or 2, then so be it.

But back to the original question, if your going to the trouble of fitting twins, fit a decent exhaust as well and get it booked into a rolling road afterwards to get it set up properly.
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Postby brant_richard » Fri 15th Sep 2006, 12:55pm

Roy just likes causing arguments. :wink:

As for the carb debate I have a set of 1.25 SUs that I'm about to bolt onto my 998 which is in a fairly mild state of tune. When we sell the big car, however, and Alfie gets a cash injection I'm fitting twin 1.5s to the more powerfull engine I'm building as I understand they'll be more suitable for the higher power output.

I don't think that it's that you can't get the power out of the smaller carbs (as the Cooper S proved) but I think you need to have them rather well set up to get it whereas the larger 1.5s on a highly tuned 998 will put more fuel in to begin with.

I think. :?
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Postby H » Fri 15th Sep 2006, 02:34pm

Thanks all for advises. Thank you for generous offer Random Nonsense but I have to have something to do in long winter evenings. So I smooth all the edges, maybe that is the best alternative, including entrance to balance pipe.

So nobody haven't tried shaft mods?
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Postby Random_Nonsense » Fri 15th Sep 2006, 03:02pm

No point in modifying a carb. It will never out flow a larger one.
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Postby HairyMonk » Fri 15th Sep 2006, 10:19pm

if you look through the carb section of vizards how to modify you mini there is a chart which gives the approximate power ranges the carbs are good for, twin 1 1/4 inch are good up to about 70hp before starting to restrict the engine. small twins will also give better low down power and increase low end torque. dont forget to put ram pipes on with a good filter
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Postby MiniCooper1460 » Wed 20th Sep 2006, 12:43pm

Twin HS2 are ok until 95bhp if you have the correct manifold, air filters and needles: Keith Calver said me this recently.
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Postby royallingham » Wed 20th Sep 2006, 01:13pm

KC !! The twin 1.25 carbs were fine on the 970/1071 S - the 1071 made 70 bhp - same setup on the 1275 made 75. This was done to try to limit warranty claims. Standard upgrade was to stick on twin 1.5s - made 85/90 bhp depending if the head got a seeing too at the same time.
I had twin 1.25s on my 1275 engine - it went well enough. Changed to a 44HIF - it went much better.
I DO like twin 1.5s on a good manifold - used them on my 998 racer and on my 1275 Rally Elf S. But the big single SU is so much easier. I just shudder at the daft prices twin 1.25" SUs seem to fetch on ebay - if you have a set by all means use them - just don't pay over the odds for them.
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Postby Jimmyarm81 » Wed 20th Sep 2006, 01:26pm

So nobody haven't tried shaft mods?


I tied a bow round mine for missus's birthday, does that count ?
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Postby H » Wed 20th Sep 2006, 07:27pm

I paid 30 pounds for twin hs2's, 57 pounds for full rebuild kit and heat shield 18 pounds.

I also have twin hs4's without manifold and heat shield in rather bad condition. They need total rebuild. Full rebuild kits cost quite a lot for hs4's. I paid them approx 40 pounds. I got bigger twins in barter.
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Postby royallingham » Wed 20th Sep 2006, 08:22pm

And I bought an excellent HIF44 at the weekend in perfect order for £5 !!
Yes - I have modified my shaft (!) and the throttle plate and put a large 'bell mouth' on the carb. It all helps a bit - but if you can just fit a bigger carb (ie 44 instead of 38) then that's a lot easier.
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Postby midgetracer » Wed 20th Sep 2006, 10:27pm

Just found this forum.
I race a Midget (Iknow it's not a mini before anyone has a go but the engine is virtually the same) with twin 1.25 SU's, modded head with standard size valves, 296 sp, 1330. Gives about 83bhp @ the wheels. Carbs are fully modified as Vizard with KC bellmouths and on a standard inlet manifold. That has been modded and dowled to the head, with the balance bar reamed out - pulls a bit from the "other" carb is the theory. Therefore, shows that you don't necessary need a bigger carb set-up if you spend time with a dremel!
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Postby H » Fri 22nd Sep 2006, 06:40am

What kind of air filters you use with your twin hs2's? I have old school pancakes which are not so good. To be precise those pancekes are terrible. It's impossible to fit ram pipes inside of them, they are very shallow and filter material is not so good.

Any suggestions? K&N makes very good but expensive alternatives according to my knowledge. Which one to choose?
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Postby Jimmyarm81 » Fri 22nd Sep 2006, 10:35am

Any suggestions? K&N makes very good but expensive alternatives according to my knowledge. Which one to choose?


Have a look in the bible, there is a big ol' chapter on filters :D
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Postby HairyMonk » Fri 22nd Sep 2006, 09:50pm

K&N last forever, a good investment will save money over time on engine rebuilds and replacement filters, look an sounds beaut aswell :rock:
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Postby siryun » Sat 23rd Sep 2006, 11:07am

what kinda intrigues me is WHY a 1.25 inch is too small.

for instance a Mugen MF408S Engine (4 liter NA) will produce about 440 KW sucking through two 33.4mm restrictor plates. (a tad over the troath diameter of a HS2)

I know common knowledge suggest that twin HS2's will feed about 70 BHP (50 KW) but shurely it must be possible to get around 90 to 100 BHP wich selected carb mods and proper rampipes.
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