1979 1000 cylinder head question

[79gs1000l]

I have a 79 gs 1000 I got a lot of help with, when i installed some 33mm smoothbores, from you guys, they run good and i will be getting a vance and hines exhaust in a month or so. any way i had been toying around with the idea of putting an 1150 motor into my bike but have decided against doing so. My engine runs great starts easy my old bike will never compete with the newer bikes so i am going to get a newer bike some day and fix up my 1000 real nice. any way my question of the day is about the 79 cylinder head. from what i understand the 1980 had bigger carbs and intake runners so people like to put 80 heads on their pre-80 bikes. I was wondering if there is any difference in the valve sizes form 79 to 80. Could I have my existing head ported out to be as good or better than a head off a 1980 bike, i have been told that if the valves are the same size then i could make the 79 head just as good as the 80 head. what do you guys think?

 

[Paul]

Same size valves, but the later head had a larger casting so the ports could be opened up more.
Also the later head had an extra bolt at the front, to prevent leakage or distortion.
The later head was called the big-port head, but actually used the same size carbs and had the same size valves, so obviously had same size ports.
But they can be opened up, massive carbs fitted, huge valves installed!!
All at a cost of course.

 

[79gs1000l]

thanks for the info paul, if i am to understand you correctly, the only difference in the later head is the amount of material used, (bigger casting) so if i put on a stock head from a 1980 onto my 79 i would see no performance gains, aside from the extra bolt, since the ports were the same size. am I right in saying this? The way i see it in respect to what you have said, is that the later head is only better if you want to do some serious port work. Since i plan on riding mine only on the street i am not looking to kill my low end, i am merely looking for a noticable gain so here is my game plan tell me what you think. I currently have the bigger carbs and i love em, within a month i will have the vance and hines 4-1 street pipe. also i am running the pod air filters. within the next year i plan to have some head work done, apparently i would have the same results with either head seeing as i don't want to go to radical, and some mild street cams with the slotted cam sprockets, would the pressed crank be able to withstand that? has any body else who has done similar things been happy with the results and does any one know what kind of power increase these mods are worth?

 

[terry]

The later head was called the big-port head, but actually used the same size carbs and had the same size valves, so obviously had same size ports.

Hey Paul, I beg to differ there mate, the big port engines were fitted with either 34mm CV carbs or 33mm slide carbs (standard on the GS1000ST) as opposed to 26 or 28mm carbs (GS1000SN)

The valves were the same, but the ports were much bigger than the early 78/79 engines. I'm actually surprised to hear that someone fitted a set of 33mm carbs to a stock '79 head, without some major mods. The Wes Cooley Yoshimura bike only ran 29mm carbs, for pete's sake.

If I'm reading this right, there would be a 3.5mm "step" between the carb venturi and the port on an early head? Fit that late model head mate, at least your ports will be a closer match to your carbs, and there's got to be an improvement in performance straight away.

 

[cbxchris]

weld the crank...1000`s were probably the worst crank suzuki made that would twist....I know. I twisted one on a stocker. 8O

 

[saaz]

I have a 78 Gs1000 with a street ported head, can run 29mm smoothbores, but can't see how you would put 33mms on it as the intakes are not made for it. It works ok with 28mm carbs, don't really need much more for the street

 

[79gs1000l]

sorry i am so slow to respond but I have been out of town for a while, any way saaz yes it was a major pain getting the 33's into the carb boots, major. but they are in and run well, better than stock that is for sure. So it seems that the later model head is the way to go so I'll go for that and try to find one, my next question is probably quite obvious, anyone know where I can find one?
Also chris said that 28's are all you need for the street, then why did suzuki put on 34cv carbs in 1980, I am not questioning the validity of his statement but want to know if the cv carbs are less efficient then the slide carbs or how that all works.
And thanks terry for the information, and yes there is a big difference from the port to the carb, hence the quest for bigger ports. But my question still remains, could a 79 head be ported to be as good as a ported 80 head, or should i not even consider the 79 head and keep searching for the 80 head?

 

[Anonymous]

Also chris said that 28's are all you need for the street, then why did suzuki put on 34cv carbs in 1980, I am not questioning the validity of his statement but want to know if the cv carbs are less efficient then the slide carbs or how that all works.

What I've heard is that, because the CV carbs have a butterfly valve in addition to the slide, it's necessary to increase the size of the bore to compensate (because the valve effectively decreases the size of the bore).

As I understand it, 28 mm slide carbs are roughly equivalent to 34 mm CV carbs -- in terms of the amount of fuel-air delivered to the engine.

If you're looking to tune the bike, you might be best to stick with the old head/slide carbs, because they're supposedly easier to tune. Someone posted this link a while back:

http://www.f6rider.com/VRCC/tech/carb101.htm

Good luck!

Michael

 

[terry]

.
And thanks terry for the information, and yes there is a big difference from the port to the carb, hence the quest for bigger ports. But my question still remains, could a 79 head be ported to be as good as a ported 80 head, or should i not even consider the 79 head and keep searching for the 80 head?

Mate, the "Big Port Head" is definately the way to go. CV carbs aren't quite as efficient as slide carbs, but the advantage of CV's for me is the lighter throttle and smoother acceleration. CV's lose a little to slide carbs in mid range and top end, but I still prefer them.

The advantage though, of the big port head in your case, is that the ports will almost exactly match your carbs, so there is no "step" that will affect the gas flow, as it does now. I think you'll be happily surprised with the difference it'll make to your engine.

And of course as Paul said, there is plenty of "meat" on the big port head casting to take the ports out to accept larger carbs again. But without any other mods, early 36mm GSXR 750 carbs will go straight on, and apparently these are just as desirable nowadays as your 33mm "smoothies", looking at how hard it is to obtain a good used set.

Any head from a 1980-82 GS1000, or any of the GS1100 (2 valve) models will fit, I nearly bought one on ebay for less than 50 dollars for my '79 GS1000S, but living here in Australia, shipping is a major concern. Anyway, I hope this helps mate!

 

[Anonymous]

I have a big port head with 36mm Mikuni RS flatslides. The power gain at the top end with these is amazing. The good news is that RS carbs are relatively efficient at small throttle openings, so you've almost got the best of both worlds. Because of their design, the flatslides have a fairly high depression in the venturi through most of their operating range, making them draw fuel well at low throttle settings. In the mid 80's when they came out, they were remarkable for this characteristic, at a time when equivalent roundslide smoothbores such as mik 33's, Keihins CR's and Amals were a bit flat unless WFO.

The early smaller port head can be opened up to accept the bigger carbs such as gsxr carbs or GS(X)1150 carbs using the appropriate rubbers. I'm not sure about carb spacing, but that can often be adjusted.

If you can find a big port head, get it if for no other reason than you can fit a whole range of carbs from later bikes, or aftermarket stuff. This will give you either more power, or at least a lighter throttle! Modern carbs like Bandit 38mm CV's will just slip on and they are awesome.

 

[terry]

If you can find a big port head, get it if for no other reason than you can fit a whole range of carbs from later bikes, or aftermarket stuff. This will give you either more power, or at least a lighter throttle! Modern carbs like Bandit 38mm CV's will just slip on and they are awesome.

Hey Martin, how do the RS36 carbs from the early GSXR's compare to the 38mm Bandit carbs? I'm picking up a set of RS36's this weekend to go on the engine with the yoshi 1100 kit and stage 2 cams, and I'll fit the Dyna3 Ignition and Dyna coils etc at the same time. The carbs are only on loan for the time being though, so I've still got the opportunity to source some Bandit carbs if they're a better choice? Cheers mate.

 

[Anonymous]

Terry, the RS36's I've got are not from an early gixxer, they're the aftermarket ones. They're very similar though...
I would say the Bandit carbs give slightly less ultimate power, but are more useable 90% of the time. Especially at the bottom end. having said that I love my flatslides and don't find them a problem.

 

[79gs1000l]

Thanks for all of the good tips and the lesson on the difference between cv carbs and the slide carbs. I am now officially in the market for a "big port" head. If any of you come across one please let me know.... cause I want one real bad! :lol: