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 Post subject: GT750 mild porting
PostPosted: Wed Dec 25, 2019 12:18 pm 
Around the block

Joined: Thu Dec 05, 2013 12:32 pm
Posts: 89
Country: Austria
Suzuki 2-Strokes: GT750
Hi forum members, Merry Christmas!

I have almost completed building another engine from my spares. Barrels have already been bored and honed to 71mm, new pistons, head skimmed by 1mm. I am going to use this engine in my BIMOTA-replica with JEMCO pipes and VM34 aftermarket carbs, Accent ignition. I am after a streetable engine characteristics still strong enough off idle to not need too much clutch when pulling away, but like 15HP more at high RPM.

Now I need to decide on porting. It is a M/A/B cylinder with 40mm exhaust port; I lean towards a 37-38mm exhaust port, widen it to 48mm. Now, do I need to raise the transfers by the same 2-3mm? I assume so, since this is the same when using spacers below the barrel.
I dont want a spacer plate since it is one extra gasket face with a risk of leakage.
I have filled the step in the intake floors with Devcon but will not alter intake timing.

Any feedback to my plan?

PS: I currently run a TR750 spec engine in that bike but it does not match my riding style with this bike. Too little low RPM performance, and a pain in low-speed hairpins

 Post subject: Re: GT750 mild porting
PostPosted: Tue Dec 31, 2019 1:36 pm 
Moto GP
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Joined: Mon Nov 03, 2008 10:47 am
Posts: 6087
Location: Illinois
For a mild hop up over stock, you could leave the transfer heights, but it's best to clean them up and get them all the same if you can. If you are in the transfers you can widen them a little and again match them to each other.

You could also clean up the intakes which are generally very lumpy and inconsistent.

Raising teh exhaust port reduces effective compression at lower revs, so make sure the CR is high enough. You can take at least 1mm off the head or barrel and you should have a nice smooth motor. Won't have that huge 2 stroke rush though. It won't make much HP below 3,000, but should be pretty useful around town

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