GSX 750 aircooled How Strong?

[ozkat]

1984 GSX750ES aircooled motor. Ive got a good one in the shed and was thinking about forcing lots of air(proberly about 15-30psi:D) into it, in my EFE style dragbike, while i get my proper race engine built. Are they a pretty sturdy motor or fragile?

[Zed14]

only one way to find out and you can do it on the cheap.

Generally pretty strong, but the boxes play up when pushed too hard. Defintely balance and weld the crank for drags

Put on the best cooler you can find!!!

[ozkat]

quote:Originally posted by Rexie

only one way to find out and you can do it on the cheap.
Yeah i know i can do it real cheap, but id prefer not to grenade it on the first pass. I was hoping for 180-200hp, im sure i can get that but im a bit concerned about the crank.

180-200 would bend the rods Oz, you'll need to go Carillo.

[Seven6]

Considering how many are still about with the same about abuse or more thrown at them..........I'm sure it will more than handle it

My '81 1100 of same breeding has sure copped alot ( minus the boost) and still fires up and runs like a demon!!!

Forced Induction section of the OSS site would be a place to start

[Benz]

Hey Shaynne, you can put whatever you want into one of those beasties, but there is an oil pressure problem with roll bearing bottom-ends. you will have to sort some kinda oil-pump, scavenger pump setup to keep the turbo alive. I've heard of guys just trusting their luck with the low oil pressure, but if you want any sort of reliability[you did say it's gonna dragrace right......], could end up with a nightmare setup, harder than a oilboiler rebuild.
I saw one of those motors motor in katana 750 dragbike up here, attached was a small supercharger, and a mechanical injection hangin off the side, ran comfortable high 8's. Only problem was he had the fuel shutoff too close to the belt, and when he reached for it, his fingers were dragged into the belt drive....not pretty.

Yeah the ones I've seen didn't have upgraded oil pumps, probably woulda solved a lot of their problems

[Seven6]

quote:Forced Induction section of the OSS site would be a place to start

Ah! see you already have:D

[ozkat]

Seven6... I just posted the very same question on OSS ;)
Benz... Im pretty sure the 750 ES ran a plain bearing crank, im not 100%sure tho. I do know that the blokes who turbo the 1100 aircooled motors install 750 oil pumps due to higher pressure, maybe thats pointing towards that they have a plain bearing crank.
Chalky... The gearbox isnt a problem, 99% of the 1100 dragbikes use the 750 gearbox with a few small mods because they are factory undercut and actually are a stronger box with the mods.

But they'll do their selectors if their's any appreciable wear on them, especially 2nd.

[ozkat]

quote:Originally posted by chalk10

But they'll do their selectors if their's any appreciable wear on them, especially 2nd.
Thats one of the mods Chalky ;)

[Hillsy]

Hey Ozkat - you're right. The 750's ran plain bearing cranks and hence, compared to the roller bearing 1100's, got the reputation of having a fragile bottom end. I guess if you're looking at cranking big horses out of one, they're not going to be as strong as the roller cranks.
Funny thing was I had a 750EF at the same time I had my 1100EFE - and I had no problems with the 750, but I had to rebuild the 1100 crank......

[megareg]

I spun bearings on 2 750 motors I had in my 750 Kat, the 750 motor is a plain bearing motor, in my opinion, they are a bit fragile, however, if you sort out the oil pressure with the correct clearances 'n' stuff... should be ok for a while... just wont last as long..

Cheers

[devo]

Aint that surprising [:0]
The GSX750 engine was notorious for spitting the #2 bigend BRG
lubrication not a strong point there.
What made it worse was people not changing oil regularly resulting
in loss of viscosity thus lack of oil pressure.
You will find Oz that the Drag Guys tend to go for a lot of GS750
stuff a fair bit more robust than the later 750 but just lacking
half the valves as the later GSX.
I reckon give it a miss unless you spent a small fortune on fixing
it wright up Mate.In which case it just aint worth it.
Infact if it is a runner I would build a nice display case for it
and stick it in a museum Buddy this that you may have could be
indeed a very rare find :D

[Benz]

Sorry Oz,
Obviously got confused between 750 and 1100........[^]
Oh well, you got good info from the rest of the panel:)

[Booster]

Stronger rods may not be hard to find, one option for a stroked or to decompress a busa is the falicon or carrillo efe rods , 2mm shorter, with a barrel spacer busa rods (that are commonly accepted as 350hp max)could be used on efe's
Don't know if that suits your motor but it may help someone.