GS450 Intake modification

GmanGS450

GmanGS450

Active Member
Another project is on the horizon.

2-1 intake with a VM32 for a 1982 GS450T, trying to maximize power out from a not-so-powerful engine. Using the metal foundations of old rubber manifolds as the starting point.

The design is complete and the material are purchased. Now to cut, weld, test.


But I have a question about the intake port on the GS450, What are the flat tabs on the intake. Everything I've learned in schools tells me that removing these will create a faster gas flow into the pump that is an IC engine. Creating more power!!!! The increase intake length and size will give the gas flow greater velocity into the cylinder, so removing these shouldn't be a problem.

OR WILL IT?
Do these create a some kind of mixture in the intake port? Are these totally necessary? Keeping in mind that I am not using a stock carb and will have the chance to tune the singe VM round Slide better than two cv's. Is this an attempt to get a better burn of fuel to reduce emissions back in the day? Reduce the HP to meet US requirements?

I have alot of questions so if someone could please help me out, it would be greatly appreciated.

Attached are pictures of what I'm talking about.
 

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Questionable. Two VM30s or two VM32s sounds about right for a 450, one seems pretty small. I think a VM38 would be about as small as you'd want to go on a two into one manifold, maybe even a VM40.
 
Sonreir said:
Questionable. Two VM30s or two VM32s sounds about right for a 450, one seems pretty small. I think a VM38 would be about as small as you'd want to go on a two into one manifold, maybe even a VM40.
Click to expand...

That was my thought, as well.
 
Someone here built a 2-1 using one stock CV carb and came out with comparable performance and better gas millage.http://nswroadandtrackbikes.com/forums/showthread.php?14088-GS450-Single-Carb

With a low restriction intake a vm32 should be able to flow enough, with the Opposing GS450 crank position. Its feeding a volume for two cylinders but only being drawn by one at a time. That time may be very very short, but its still there. Looks like its going to be an experiment.
 
GmanGS450 said:
Someone here built a 2-1 using one stock CV carb and came out with comparable performance and better gas millage.http://nswroadandtrackbikes.com/forums/showthread.php?14088-GS450-Single-Carb

With a low restriction intake a vm32 should be able to flow enough, with the Opposing GS450 crank position. Its feeding a volume for two cylinders but only being drawn by one at a time. That time may be very very short, but its still there. Looks like its going to be an experiment.
Click to expand...

I'm guessing his bike had problems to begin with. His claimed increase of 24km/liter of fuel consumption is just 56 miles per gallon. If he's getting 72% increase now, then he was at 33 mpg earlier, which is pretty darn poor for a four stroke 450cc bike.

Unless he posts a quantitative analysis of his power and fuel consumption, I still can't endorse this idea.
 
Iam looking into purchasing a VM38 for the project after some number crunching.

But no-one has answered my question about the tabs on the bottom of the intake.

With my idea of an extended intake track the fuel will have more time to atomize and flow faster into the intake, so removal should not be a big problem.

Initial media blast of parts is done, and the metal flanges look great, 1.5inch OD 16ga steel pipe is purchased and rough cut, now to find time to tack it up to the jiq and make sure its all square.

If anyone has a single VM38 they don't need I AM INTERESTED.

Thanks.
 
vm38 will be a bit big for the street go a 36mm it will give you way better driving characteristics
 
GmanGS450 said:
But no-one has answered my question about the tabs on the bottom of the intake.
Click to expand...

Not totally sure why they are there, but I would guess they might be there to create turbulence in the intake tract for better cylinder filling / combustion. Suzuki later on did the TSCC (Twin Swirl Combustion Chamber) which had ports linking the intake tracts between the cylinders which they claimed increased turbulance and efficiency in combustion. Yamaha also had the YICS system on their XJ bikes which was kinda the same thing.

Funny how no one uses that sort of stuff anymore ::)
 
It's not needed with fuel injection because the spray is so fine, nearly any amount of moving air is enough to keep the fuel in suspension.

Turbulence hurts air flow, so best to not have it unless it's needed.
 
hillsy said:
Not totally sure why they are there, but I would guess they might be there to create turbulence in the intake tract for better cylinder filling / combustion. Suzuki later on did the TSCC (Twin Swirl Combustion Chamber) which had ports linking the intake tracts between the cylinders which they claimed increased turbulance and efficiency in combustion. Yamaha also had the YICS system on their XJ bikes which was kinda the same thing.

Funny how no one uses that sort of stuff anymore ::)
Click to expand...

i'm not entirely sure what tabs youre talking about, but i'm not sure about youre idea of lengthening the tracts....and it goes back to what hillsy said...turbulence. increased intake velocity is good to a degree, but it also destroys turbulence, especially at atmospheric pressure levels. a longer tract at lower pressure will (i surmise) give the charge time to actually slow down, leading to less atomization. i might be way off base, but these are things to think about
 
i see what youre talking about now. if it were me i'd leave them. they are probably there for low-speed throttle response. Kevin Cameron wrote a great column on this. Carbuerated smaller displacement four strokes have issues with low speed throttle response if they are equipped with large carbuerators, which they often were to get good peak power numbers. Honda's fix was to use an egg-shaped intake port, meaning it was more restricted when the slide is low in the carb body, providing a faux venturi and keeping intake velocities up enough to provide good low-end response. these tabs may have been suzukis fix to the same issue.
if nothing else you can leave them for now and take them down incrementally while tuning.
 
Sonreir said:
It's not needed with fuel injection because the spray is so fine, nearly any amount of moving air is enough to keep the fuel in suspension.

Turbulence hurts air flow, so best to not have it unless it's needed.
Click to expand...

Fuel injection mist is certainly finer than what you can get out of a carb, but more importantly it only gets shot in as the intake valve opens, so it doesn't have to draw the fuel up through the carb - hence it's increased efficiency.

As for turbulence hurting airflow, well yes that true if you are talking about a totally linear situation, but with an ICE intake we're talking about flowing through an inlet port and valve then the mix stops in the combustion chamber. It's a bit more complex than just simply moving air volume through a pipe. Turbulence can be beneficial in this scenario.
 
i agree on the turbulence issue. more is better (provided velocities stay up) because youre going to loose some by the time it makes it to the CC.
And concerning fuel atomization, i've always read that carbs actually do a considerably better job at atomization. the inability to meter fuel consumption to the gnats-assed efficiency the way you can with injection is why carbs are largely a thing of the past. perhaps new injectors do a better job.
 
Not looking to start a pissing match, but injection is only times to the intake valves in sequential port fuel injection. With multiport fuel injection, it is not. The increased efficiency has to do with better atomization (sorry, Zook) and better metering.

I'll stand by my turbulence statement, though. There's a very good reason why intake porting involves removing casting marks, shaping valve guides, etc. There's no way to remove turbulence completely, but it should be limited as much as possible until the mixture is inside the combustion chamber. After that, turbulence is good.
 
All FI / intake lengthening discussions aside........

When I had my GS450 engine apart, I noticed the same lip inside the head. After looking at a GS500 intake port and realizing it did NOT have that lip, I cut it out. Sometime between 1979 and 1989, Suzuki figured that lip wasn't needed. So I ran with it.
 
I was considering a single carb for my Suzuki GS300 as well. I think a similar sized smaller carb would give better low and mid range response, perhaps at the expense of top end power. The reason being is that both cylinders would draw from a plenum as opposed to an individual runner scheme as the stock set up is. Building an intake would be easy enough for anyone with fab skills.

The "OneBigThing" that kept me from going this way is the "odd fire" arrangement the 300 has. Is the 450 the same way? One cylinder fires, half a revolution later, the second cylinder. A revolution and a half later, the first cylinder fires again. Zero, 180, 540. My fear was that one cylinder would run fat, and the other lean.
 
Honda 350, 360 are all like that too...called a 180 degree engine. That's why Honda's sound different then Triumph's. The later CM series honda went to the 360 degree engine, both cylinders going up and down together.

360 degree engines tend to vibrate a little more. The 180 is in balance vertically, but has what is called a rocking couple, as the space between the cylinders mean the balancing isn't exactly perfect.
 
I knew I had read this, and. Yes, not looking to start a pissing match, but from whath I consider the horses mouth:

Cycle World, August, 1995, in Kevin Cameron's article "Virtual Reality", "Injected fuel is less well atomized than carbureted fuel because carbs bleed air into the fuel stream, breaking it up finely. To counteract this, injected fuel must be given extra time in which to break up and evaporate".

Like I say, I'm not looking to argue, but when I found my source I had to post it.
 
1 carb per cylinder is better.period
that is if you want any kind of performance
i dont know why anybody would waste their time,if it was a good thing it would be done from the factory,and or used on race/performance machines, it very rarely is....
much more productive to use what has been proven best and fine tune that ;)
your mile-age may vary,pun intended
 
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