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Discussion Starter · #1 ·
I’m in the process of building an engine for my Gen 3 and I’m trying to get as much out of the engine as I possibly can naturally aspirated before we put it together and put it in the bike. Here’s what I’ve got so far:

Carpenter Racing Head and Cam package
Marine 4mm stroker crankshaft
JE 3x4 pistons at 13.5:1 compression
Carrillo Connecting Rods
Full bolt ons and gearing
Bike will be tuned on e85 (still deciding which, not pump e85 though for sure)

I’ve been trying to find info on running 1mm oversized intake valves and also info on getting my throttle bodies bored out a little more. The bike is mainly street ridden but it’s not the kind of riding where I’m out putting around in bumper to bumper traffic so I can go a little more extreme than the normal street setup.

Is it worth the money to go oversized valves? What kind of gains can I expect?
At what point are the factory throttle bodies limiting?

I found a place online than can bore them out about 3-4mm larger but I couldn’t find any concrete info on whether I was wasting my time or should I try to switch to aftermarket throttles?

Any info is appreciated. Thanks for looking
 

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I’m in the process of building an engine for my Gen 3 and I’m trying to get as much out of the engine as I possibly can naturally aspirated before we put it together and put it in the bike. Here’s what I’ve got so far:

Carpenter Racing Head and Cam package
Marine 4mm stroker crankshaft
JE 3x4 pistons at 13.5:1 compression
Carrillo Connecting Rods
Full bolt ons and gearing
Bike will be tuned on e85 (still deciding which, not pump e85 though for sure)

I’ve been trying to find info on running 1mm oversized intake valves and also info on getting my throttle bodies bored out a little more. The bike is mainly street ridden but it’s not the kind of riding where I’m out putting around in bumper to bumper traffic so I can go a little more extreme than the normal street setup.

Is it worth the money to go oversized valves? What kind of gains can I expect?
At what point are the factory throttle bodies limiting?

I found a place online than can bore them out about 3-4mm larger but I couldn’t find any concrete info on whether I was wasting my time or should I try to switch to aftermarket throttles?

Any info is appreciated. Thanks for looking
Is that place you found online Max Bore by chance?
 

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Carpenter does do a +1mm valve cut, you can then use the G1 valves which are 1mm larger the downside there is the inlet valves are the older steel ones and heavier, wether or not carpenter has done this you'll have to ask him, he tends to talk riddles and mis quotes sometimes. You would be better off using G4 throttle bodies but you may find it hard to blend those in if its already been ported for the stock throttle bodies.
 

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Discussion Starter · #7 ·
Carpenter does do a +1mm valve cut, you can then use the G1 valves which are 1mm larger the downside there is the inlet valves are the older steel ones and heavier, wether or not carpenter has done this you'll have to ask him, he tends to talk riddles and mis quotes sometimes. You would be better off using G4 throttle bodies but you may find it hard to blend those in if its already been ported for the stock throttle bodies.
I’d be fine with upgrading to a stainless set of that was an option but I have heard of using the g1 valves before. Guess I need to call Bob up and see what they can do for me.

Next question though, as I said I already have my pistons done. Is it possible to have someone machine the piston for the OS valve now? Didn’t really plan to take it this far originally so I didn’t consider having it made like so but if I could have someone do the machining, I’m all in.
 

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I’d be fine with upgrading to a stainless set of that was an option but I have heard of using the g1 valves before. Guess I need to call Bob up and see what they can do for me.

Next question though, as I said I already have my pistons done. Is it possible to have someone machine the piston for the OS valve now? Didn’t really plan to take it this far originally so I didn’t consider having it made like so but if I could have someone do the machining, I’m all in.
As Gaz said mate those pistons are good for a +1mm valve i have a the same pistons in a stroker with +1mm valves no problem. But if your going to use stainless valves your going to have to really be careful with your valve to piston measurements, the valve base is very deep and could be hard to get good numbers on the cams.
 

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good point, stainless valves have thick margins, also more than just reseating them with new 45. they must be sunk back in head close to original valve installed height for ptv clereance that means the chamber now needs unshrouding for the larger valves to flow properly. dont think u will gain much over the valves u have now. as far as tb's gen 1 are most cluttered, gen 2 up throat dimensions different, main throttle blade milled down, they are fine, will make great street torque/accleration. cooper perf does all my machine work, he built a gen 1 3x4 2 years ago with stk tb's, that bike ran close to 170 mph in the 1/4 so tb[s not limiting factor on that bike. remove secondary rods, epoxy holes, good to go on street engine.
 

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Discussion Starter · #11 ·
Thanks for all the info guys. Hard to get info like these on the crappy Facebook groups everyone uses these days.
 
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