Hi i am currently running an HS4 carb on my 998cc engine, i am looking to tune up the engine as part of my ongoing project and was wondering if someone would be kind enough to summarize the advantages of either replacing this carb with a HIf38 or changing to a twin carb set up (Twin HS4). I have done a search but with some people changing to twins and some to Hif38 i am sort of getting lost amongst all the information.
Thanks Aaron
Twin Carbs Or Hif38
Started by
ad53ggz
, Dec 05 2007 07:36 PM
6 replies to this topic
#2
jim295
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Speeding Along Now
Posted 05 December 2007 - 07:48 PM
From what i have gathered reading around on forums and from looking at other sources (vizard etc.) HIF 38 is basically a more modern version of the HS4 so still 1.5" carb... bit more complicated but i think that is because it can 'possibly' - if you want it to - give a better mpg than the HS4?... Shoot me down if im wrong here...
The twins on a 998 that you most likely are thinking of would be twin HS2s as in 2x 1.25inch carbs, twin HS4s (2x1.5") would be overkill as a 998 cant possibly need that much fuelling (unless its mental..)
Pros and cons...
Performance wise...
Twins can make for a torquey engine as its like a carb per inlet so it kicks in that bit better on lower down the rev range... (i understand)
hif 38 just like a hs4 for flow rates (well enough not to notice it unless your going mental on a flow bench) so effectively the same carb...
Price wise...
twins (HS2s) would be more to buy and install unless you get a bargain somewhere.. all in looking at around 150 for carbs and heat shield might get manifold as well for that price but itd have to be a good find... getting it tuned would be more of a hassle as they need to be balanced for fuel and air into the cylinders... so would cost more to get it tuned in and as good practice that should be done for summer and winter... (or so ive heard)
hif38 can be picked up fairly cheaply...(cheaper than twins anyway) maybe 30 quid for a decent one? getting it tuned should be fairly cheap aswell as less fiddling for the man to do..
If you havent got it already buy the yellow book called 'Tuning the A series engine' by David Vizard... then turn to page 73... all your questions will be answered just be prepared to not understand whats going on until youve read it about 5 times(unless your an engineer)
*edit*
also for a 998 hs4s are good up to 60 bhp easy and there are routes you can go down to mod your existing one... again the vizard book has it all in...
The twins on a 998 that you most likely are thinking of would be twin HS2s as in 2x 1.25inch carbs, twin HS4s (2x1.5") would be overkill as a 998 cant possibly need that much fuelling (unless its mental..)
Pros and cons...
Performance wise...
Twins can make for a torquey engine as its like a carb per inlet so it kicks in that bit better on lower down the rev range... (i understand)
hif 38 just like a hs4 for flow rates (well enough not to notice it unless your going mental on a flow bench) so effectively the same carb...
Price wise...
twins (HS2s) would be more to buy and install unless you get a bargain somewhere.. all in looking at around 150 for carbs and heat shield might get manifold as well for that price but itd have to be a good find... getting it tuned would be more of a hassle as they need to be balanced for fuel and air into the cylinders... so would cost more to get it tuned in and as good practice that should be done for summer and winter... (or so ive heard)
hif38 can be picked up fairly cheaply...(cheaper than twins anyway) maybe 30 quid for a decent one? getting it tuned should be fairly cheap aswell as less fiddling for the man to do..
If you havent got it already buy the yellow book called 'Tuning the A series engine' by David Vizard... then turn to page 73... all your questions will be answered just be prepared to not understand whats going on until youve read it about 5 times(unless your an engineer)
*edit*
also for a 998 hs4s are good up to 60 bhp easy and there are routes you can go down to mod your existing one... again the vizard book has it all in...
Edited by jim295, 05 December 2007 - 07:54 PM.
#3
alexcrosse
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Up Into Fourth
Posted 05 December 2007 - 08:06 PM
woudlnt u want twin HS2's? HS4's will be overkill for a 998 surely.
You will get alot more response and torque from twins, well worth the expense. You do have to make sure there balanced etc though.
Id go twins, well, id go weber, but i suggest you go twins
You will get alot more response and torque from twins, well worth the expense. You do have to make sure there balanced etc though.
Id go twins, well, id go weber, but i suggest you go twins
#4
ad53ggz
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Speeding Along Now
Posted 05 December 2007 - 08:42 PM
Thanks for the reply's i will have to get that book! Tempted to go down the twin HS2 route then i am planning to do a fair bit to the engine stage 3 cylinder head etc. Thanks for the replies now lets go get that book....
#5
blue redtop
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Camshaft & Stage Two Head
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Posted 05 December 2007 - 08:52 PM
ive got twins half fitted. so far the cost is.
carbs 50 quid
new springs and needle's for my engine 20 quid
manifold and heat shield 20 quid
then theres the setting up ive got
air balancer 20 quid
colour tune 15 quid.
if you know what your doing you can get them set up very very close to perfect with the correct gear.
i had a hs4 before i started changing them,
ill let you know if i feel much difference when i fit them on saturday.
carbs 50 quid
new springs and needle's for my engine 20 quid
manifold and heat shield 20 quid
then theres the setting up ive got
air balancer 20 quid
colour tune 15 quid.
if you know what your doing you can get them set up very very close to perfect with the correct gear.
i had a hs4 before i started changing them,
ill let you know if i feel much difference when i fit them on saturday.
#6
ad53ggz
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Posted 05 December 2007 - 09:06 PM
ill let you know if i feel much difference when i fit them on saturday.
That would be great its a work in progress and taking engine out her hopefully on Sat. to start work properly. Should be fun!
#7
blue redtop
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Camshaft & Stage Two Head
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Posted 05 December 2007 - 09:09 PM
ill let you know if i feel much difference when i fit them on saturday.
That would be great its a work in progress and taking engine out her hopefully on Sat. to start work properly. Should be fun!
if your putting on a stage 3 head and modding the engine i would ask the tec guy's on hear with years of experience of what carbs to fit.
i know that twin hs4 carbs will kill a 998 engine but if your changing heads cams ect ect it might not.
just thought i would mention that.
happy playing.
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