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gs1000 cylinder head which to use?

  • Thread starter Thread starter chandler
  • Start date Start date
C

chandler

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hello had this post in the preformance section had no replies figured i would post it here .
i am getting ready to do the top end on my 1979 gs1000 .
it has the small port head with the 26 VM mikunis with a stage 3 jet kit kerker header dyna iggy and K and N filter pods. i just got a reworked head from a 1981 gs1000g with the large ports all ready shimmed and ready to bolt on .
i also have a set of 34 mikuni cv carbs ready to go.
How much of a performance gain will i see if i were to use the big port head and 34 carbs . i plan on upgrading cams in the not to distant future what would be a good cam to start with ?
which setup would be better.
this is the first big 4 cylinder 4 stroke i have owned i have mostly built and raced 2strokes
any info appreciated
steve
 
Where is Ray and JD? Selling tickets to this thread. anyone for popcorn?
 
chandler said:
hello had this post in the preformance section had no replies figured i would post it here .
i am getting ready to do the top end on my 1979 gs1000 .
it has the small port head with the 26 VM mikunis with a stage 3 jet kit kerker header dyna iggy and K and N filter pods. i just got a reworked head from a 1981 gs1000g with the large ports all ready shimmed and ready to bolt on .
i also have a set of 34 mikuni cv carbs ready to go.
How much of a performance gain will i see if i were to use the big port head and 34 carbs . i plan on upgrading cams in the not to distant future what would be a good cam to start with ?
which setup would be better.
this is the first big 4 cylinder 4 stroke i have owned i have mostly built and raced 2strokes
any info appreciated
steve
Click to expand...


the cv's can be a pain to tune with pods smoothbores are so much better
just the cv's and big port head i doubt will give you much gain
check the hp figures for 78 model with 26mm carbs and 80 model with cv's

ozman
 
Last edited:
I'm lucky to have three GS 1000s in my stable with 3 different carb setups:cool:
A std GS 1000 EC with VM 26s and the small head ports,
A std GS 1000 ST with the VM 30 carbs and the wide head ports.
A std GS 1000 ET with the BS 34 carbs and the wide head ports.
The ST has also the special cams that came with that model.
The seat of the pants differences are as follows:
The VM 26 bike runs like an electric engine: you twist the throttle and the power just flows without any peak or trough. A pure delight for a cool ride:)
The VM 30 bike with the special cams doesn't flow as nicely but it really goes when higher up in the rev range. A delight for the spirited canyon roads:D
The BS 34 bike with pods ( very difficult to get right) does a bit of both: very smooth power delivery ( when you finally get it right) and significantly more power than the VM 26 and probably on par with the VM 30s.
A big advantage however: you don't have this heavy throttle action required by the other carb setups:rolleyes:
My preferred day to day ride;)
 
Ther will be little, of any, gain from the original set up to BPH and 34s

Now, header, 33 SB carbs and a cam - that will get you some more oomph
 
thanks guys for your replies :) i may go ahead with the bph and find a nice set of 33s like i said i do have a really nice kerker with the competition baffle and a dyna iggy on it .
what cam should i get they seem to be kinda hard to find i know there are web cams but not sure of much else
i am not trying to build a race bike i already have one of them i just want some more kick LOL but still enjoy taking it on the nice road trip :)
 
sharpy said:
Where is Ray and JD? Selling tickets to this thread. anyone for popcorn?
Click to expand...

Ooooh, you're evil Sharpy....

I'll buy in though...given that both heads use the same size valves, the difference is gas speed. The big port head has a larger volume hence a slower gas speed so responds to throttle less well than the small port.

Horses for courses, road use or tight tracks,small port head. Drag and all out race, big port plus cams and carbs...
 
I prefer the larger port head it will flow better. As far as which carbs to use the intake port size is the deciding factor for this. Measure the intake port with the rubber manifold off and then you want your carbs to be between 1 and 3mm larger than the intake port. I set most of my motors with the carbs 2mm larger than the intake port. Never use carbs that are smaller than the intake port or the intake charge will expand in the port and lose its velocity. Ok now for cam selection first you need to decide what you want to use the bike for and how is the head set up. Is it all stock or does it have any work done to it? If it has stock valve springs I would not go any bigger than a set of drop ins. .020 more lift than the stock cams should be ok with the stock springs.
 
thanks for the info guys will go with the big port head and see how it runs i will be post up some pic when i get started thanks again
 
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