Don't tune GSX400 engine, it will overheat?

[HugoW]

Hi,

I'm looking into programmable EFI and ignition for my 1984 GSX400e engine. I read on this forum I should stay away from tuning / increasing heat as these engines are air cooled and prone to head cracking. Adding the EFI and ignition won't add a huge amount of power, but some anyway and the part-load advance I can program into the ignition, adding efficiency, will all add heat. I can find very little on this forum about adding power to these engines. Is there anyone who can share from experience the problems or safe-zone to tune? I consider to add an oil cooler but I fear that will not make a huge difference.

Any input from experience is welcome,
Cheers,

Hugo

 

[Guest]

These engines pull hard up to 10.000 rpm and then hit the restriction of the carbs and air box. With fuel injection they would probably go to 12 but that's probably not a good idea. The advance is already at 40 degrees from 4,000 up so increasing that would get you nowhere; there just won't be any more low end torque.

The 'restriction' is in the intake port angle which goes around a right angle bend, and the rather small intake port diameter in comparison to the two valve 400s. But meddling with this design would probably only add flow at very high rpm and make it run weaker in the midrange. Unless you're making a track bike, stock is pretty much going to give more overall power. Larger ports reduce intake velocity which can end up losing power, especially if the port isn't very straight.

I have toyed with the idea of removing most of the web in the exhaust port between the exhaust valves. It's elegant, and probably increases flow slightly, but it also absorbs heat from the exhaust and expands, cracking the head. The only heat path for this web is out the top into the cam box - you can see the toasted oil area under the rocker - which the later oil cooled engines attempted to flood with oil. Simply cooling the existing oil supply will help, but there isn't enough flow volume to deal with the heat. Having essentially no room for fins on top of the combustion chamber doesn't help either. Four valve heads pretty much go with water cooling.

The simplest fix is to just swap your cylinders and head for a 450 one and then consider using the 500 pistons and maybe the carbs as well. The peak power is pretty much equal, but there's a whole lot more low end and midrange torque. The difference in finning over the combustion chamber is huge. There's also far better parts availability for pistons and rings.

I'm not quite sure why Suzuki went to the 4 valve head. Cleaner combustion, screw adjust valves, but mostly just peak power and the TSCC hype to compete with Honda's three valve 400. But unless you're restricted to 400cc for legal reasons I'd just look for a 450 head and cylinders in the US.

 

[Nessism]

There is a long thread in the archives were a member increased the displacement of his GSX400 and installed larger valves. You might want to look up that thread and review.

Adding EFI and a different ignition system would be very costly. I suspect you would have to spend far more than the bike is worth to add these features.

EDIT: here is the thread mentioned above...http://www.thegsresources.com/_foru...mendations-boring-ballancing&highlight=GSX400

 

[HugoW]

Thanks for the input. Let me share a bit more of my ideas. The EFI / Iginition module is to be a homebrew item based on the Teensy (Arduino-like, but faster) development board. I hope not to change anything to the mechanics of the motor. It will get better intake and exhaust flow by replacing the stock intake and exhaust, which will not add a huge amount of horses. I'd like to add manifold vacuum advance to make the part load run better, leaner. more efficient. The project is developing the EFI / Ignition, not really adding power or performance. I was warned on another subforum here that increasing advance at part load will make the engine run hotter, since there will be a more efficient burn. And that these air cooled machines don't like that.

I do consider making a water cooled cylinder block. I's not a very complex item which can easily be made from sheet metal and tubing. Fitting that with an electric cooling pump, small radiator and a soft copper head gasket would certainly keep things cooler. But that would be a fairly major step...

Hugo

 

[GregT]

The problem per se is not specifically heat but a design fault which is aggravated by more heat.
John Park has suggested the reasons and i agree with what he's said.

If you wanted a bike specifically to play with electronic ignitions, the GSX400 would not be my first choice....
The 2V 450 head is one which will respond to advance curve changes - generally positively.

 

[Chuck78]

Remember all air cooled engines need a little bit richer mixture than water cooled, as they run slightly hott er to begin with, & the incoming air fuel mixture helps cool the top of the piston as well as the chamber. There are no fins to help cool the tops of the chambers much.

Yoshimura drilled the tops of the chambers on the much more stout gs750 and gs1000 2v heads quite a lot to increase cooling surface area. They also media blasted the head's surface with a particular grit of bladting media to leave a rough texture to give more surface area than a smooth texture would provide, & then I believe used some type of Gun-Kote coating to further aid in cooling over standard engine paint (not sure how this last part aided in cooling, will have to read up - a vintage magazine Yoshi article or 3 mentioned these techniques.

Drilling the 400 8 valve head for more cooling area may create more areas for them to crack, however.... I have heard of these heads cracking, but not sure where the cracks tend to be.

Also, leaning out more at part throttle isn't as major of a concern as leaning out at 3/4 throttle or more under load at rpm... that situation will generate some serious heat.

Test it out before with an infrared thermometer, & test it out after under the same outdoor Temps and engine warmup times.

 

[Chuck78]

Pops Yoshimura cylinder head cooling mod...

This creates more surface area, hence more air can get to it to cool it.

I would not recommend doing this on the 400 8 valve head until you determine where the common areas of cracking are located. Maybe John would be able to tell you that better. I have never even had my hands on a 4 valve per cylinder engine, so I could not tell you even if there is room to do this type of mod on those engines, but I suspect something could be snuck in there

 

[Chuck78]

Another one... pardon my french!

 

[Chuck78]

I don't believe that making basic modifications will make the engine run substantially hotter as long as you keep the AFR's in check where they need to be (low 13's is the highest I'd go,substantially more rich like 11:1 is needed often on startup and shortly thereafter. The issue would be lessened especially if you run an oil cooler, & swap to a Polaris #4012941 ebay'd $45 used series-regulating SH775 regulator-rectifier and an LED headlight (the SH775 being a mod ALL stock GS's really desperately need anyway, the stock r-r is garbage, a time bomb - and may overcharge eventually and fry your fancy efi controller). Your engine oil temps will drop drastically from both the oil cooler and the series regulating charging systed, both of which will help it cool a lot better.