T500 porting

[tz375]

I recently finished a set of T/GT500 barrels for a guy in Canada for a speedy street bike, so I didn't want to go mad. Just raised and widened the exhaust and transfers and widened and lowered the intakes.

Even with a full range of air and electric tools it took a crap load of time. The biggest issue is the crappy shaped intake system with the S manifolds and exhaust ports that had been messed with plus they are cast in a tighter S than a 750.

Transfers were just as bad as a 750 but with less potential. I spent way too many hours working out the specs as well, but let's just say that the lift was way more than 2mm - closer to 5mm!!! Should be good for 55-60 at the rear wheel if the heads don't crack or melt.

Biggest risk was probably breaking through to the fins on the roof of the exhaust. This was a fast street tune not a race tune. How people do these things for the prices they do just amazes me.

Anyone else ported a 500 twin - Eric K of course.. ?

[titan performance]

Never attempted porting....but would be interested to know what increase in performance can be expected.

[ja-moo]

If I may ask, what timing spec did you go to? And how much did you raise the transfers?

[tz375]

If I may ask, what timing spec did you go to? And how much did you raise the transfers?

Not very wild. I raised the exhaust to where I thought it needed to be and allowed the right amount of blowdown to work with teh pipes that teh owner has.

[SpecialK]

TZ350,
I should start by introducing myself. I have been involved in racing/tuning 2T engines in both MX & Snowmobile Ice Oval racing at the National level since the late 60's. We were actually running "home-grown" expansion chambers back in 1967 on our Polaris Colt JLO 372cc sled while the factory riders were still running megaphones! Fun times. Recently, I have become involved with a friend of mine in Perth, WA building a Suzuki 1972 TR500 MotoGP bike for period specific racing down under. I have been tasked with developing the engine & exhaust package for the bike, and as part of our engine development work have ported 3 sets of T500 barrels with differing spec's to help us understand performance differences and applicability to different venues, so I might be able to answer some of your questions about the T500. It's great to hear that there's another adventurous soul out there trying to solve the puzzle known as the T500. It's apparent once you disassemble the top end that this was an early 2T design which really gets you scratching your head! Everything about the porting, ducting & Tx symmetry defies what we all now know about modern 2T design. But don't we love a challenge? Depending on the porting modifications desired, the amount of time required can fall into that category known as "Labor of Love". Again, depending on what the scope of the work is, either you will lose $ charging the customer so as not to lose him as a customer or hopefully you'll come across one with deep pockets! Getting to some of your comments, depending on how much you raise the Ex port, it's best to angle the top edge downward approx. 20 degrees so as not to penetrate through the casting. This will allow you to raise the timing edge as much as 6mm from stock. If you blow through, you can use Ali welding rod with arc low current (~40A) setting to fill the opening. The stock Ex port timing edge & side walls have no curvature (only 46mm wide chordal w/ a 6mm upper corner radius). As you widen the Ex port, it now needs to become more elliptical & ring friendly which is nothing new to you. Given this elliptical shape coupled with the raised Tx ports to +5mm (the factory TR500 specs never seemed to go beyond +3mm), you are potentially impacting your blowdown phase. Tx +5mm sounds aggressive having approx. 138 degree-plus Tx duration but I do not know anything about your design goals for your customer, Ex parameters, exhaust, etc. I recognize your username from this and other forums and believe I have read that you have access to both MOTA & EngMod2T software to help assist in timing and porting geometries. I can tell you that the Tx window leading flanks have a hook design that forces scavenging flow to wash along the back wall radius of the bore. Nowadays, the leading flank of the A-ports typically direct to a point approximately 30-50% between the center of the bore and the back wall ... leave them as is (haven't you spent enough time already! LOL). The Tx ducts are ugly & vertical with no shape ... a "relic" of a design from long, long ago. Be careful not to widen the asymmetrical Intake windows too much as there isn't alot of space between these edges and the piston Tx duct cutouts. I do not know if any of this helps you but if you have specific questions I'll do my best to share my experiences with you. Good luck with everything! PS. I would love to hear how your modelling turned out for ZunSpec4 with his new Tony Greene pipes!
SpecialK

[Zunspec4]

Hello SpecialK,

I would also like to know if tz375 was able to run his modelling software, and what it came up with, for the Tony Green pipes. I can't provide any info on the porting specifications being used on engine #1 as they have not yet been finished. When I get it all on the dyno I will be sure to provide as much knowledge as I can (or allowed too ) so you can add to your data. I think you describe the T500 engine very accurately viz: A successful development in 2-st design back in the day but pretty old hat now. Saying that, contemporary tuners developed the a/c T500 to 65-70 bhp. The works bikes even more, but they did use different/redesigned barrels etc.

Say hello to chrisK for me.

Cheers Geoff

[SpecialK]

Zunny,
I've been a fly on the wall for quite a while on this forum and others. It was time to chime in. ChrisK and myself are very envious of your TR500 build as we've been following your project for a while now. You're doing an amazing job and we thank you for sharing that with us. It wasn't clear to me if tz375 had access to your engine design to model the new pipes or not but ... I figured you two may have communicated outside this forum as many of "us tuners" have the tendency to keep things close to the vest. That being said, we hope you share your "seat of the pants" experience once you get your gem rolling. With as much modelling as I've put into our design utilizing MOTA, I do not know how well the software results will correlate to the actual dyno-confirmed performance. Time will tell. Take care.

[Zunspec4]

Apologies to tz375 for the thread hi-jack

SpK - I can understand the keeping of hard gained knowledge close to your chest, my engine tuner is of the same mind. Where I can share experiences I will be happy to do so however. Sounds like both Chris and I are on similar paths, will be interesting to see how far we can go.

Cheers Geoff

[tz375]

Zunspec:
For some reason I didn't think I had all the info needed to run your numbers. I will look again and see what I have but I need your porting specs and pipe dimensions. Sorry to leave you hanging there.

SpecialK:
Lots of good stuff there thanks. You are right about the angled port roof and about the transfers. The "closer to 5mm than 2mm" reference was an oblique reference to the approach of just changing things 1mm or 2mm at a time. I cannot imagine what a 5mm rise in transfer timing would create on a street motor, but I'm pretty sure it would not be pretty.

On the 750s we regularly use a 3mm spacer plate plus an extra gasket to raise transfers by 3.5mm and then port the exhaust so they are closer to 7mm taller than stock, but this is just a little street motor, so that would be excessive. I know what late TR500 MK111 ports look like from one I restored years ago, and this is no TR500...

I did run the data with different spacer thicknesses to see what that did and the exhausts still needed to be raised enough to get blowdown into a useable range and by then the exhaust timing was excessive. I have some target numbers that work well as a starting point for Blowdown and exhaust port opening timing. Looking at exhaust pulse timing shows us that excessive transfer time allows too much back flow into the crankcase with most pipes.

So we go with more transfer width to get sufficient time area. It's always a balance.

You are right that the transfer outlets are old fashioned in that they are a single port with single stream, but the front edge is pointing just behind the mid bore point and that's about right for a simple design. We could do all sorts of things with auxiliary ports and boost ports, but they are not an available option.

Pipe design is a whole other subject. In this case the owner had some rather interesting pipes that MOTA seems to like a lot. Not very high revving pipe but a big fat plateau rather than a peak. I have no idea who designed or made them though.

I had the opportunity to purchase two barrels from a different bike a while ago that were ported by two top two stroke tuners and they both had very different approaches to making power. That was worth the price of admission to see and measure what they did and to then model them in MOTA and to then take different aspects of each design and "mix and match" them and to also look at the data versus the Bimotion target Time-area which really helps to identify bottlenecks and potential to make more power.

In those barrels one went with wide transfers and the other with tall transfers and similar time-area but different results and at different engine speeds. It is great to learn from the masters. I do this for fun for the challenge and the mental exercise. All good clean dirty fun.

As for DYNO HP, some things work on both Dyno and MOTA and some don't correlate as well.

[Zunspec4]

Hello tz375,

What dimension/measurements would you need to run my stuff through your software?. I have the Green pipe dimensions, posted on ChrisKs thread, do not have any porting numbers as the barrels are not yet with me. What porting measurements would be needed?, just curious really to see what a decent software app. comes up with.

The chap porting my barrels and preparing the rest of the engine is renown for producing a solid RIDEABLE engine, he does not just go for high bhp specifications. This is what I am after as to have the engine go south in the first race makes for a complete waste of a racing weekend (although you can then enjoy more than a few beers to drown your sorrows lol )

Cheers Geoff

[SpecialK]

Hello Zunspec4,
Seeing as tz735 is also chiming in on the modelling, I guess I can continue this topic within this thread. After all, any discussion about T500 porting for performance enhancement must include exhaust design. I can justify just about anything when I put my mind to it! Anyway, a few weeks back after you presented your new TG pipe dimensions, I took the liberty to model them via MOTA based on some assumptions I made. Because I already have T500 input files created for my T500 project, it was very easy to tweak these for yours. I ran a full series of different Ex timings assuming a 70% Ex width. Not knowing anything about how your motor is spec'd, my best guess is that these pipes will provide max BHP @ ~7500 RPM (Ex opens at 90 degrees (again this is one assumption)) and the curves support a powerband that is not peaky but rideable as to support your design goals. I'll get these charts right out to you later tonight. Should this be the wrong thread to present this, I apologize guys ...
Cheers,
Ken

[Zunspec4]

Hi SpK,

The peak power @~7500rpm is in line with what we are aiming for (~8000 rpm in our case). You can push the T500 engine ~10,000rpm with the appropriate bearings and porting/carbs but I don't think we will going that far even on the EVO engine#2.

Cheers Geoff

[Vintageman]

Suz had a performance bulletin for T500 I am sure they tested it too

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Sent scans to oldjapensesbikes (Ian) but can't find the link

I think it raise dEx 5mm lower intake 5 mm and shaved head 2.5mm. No change to Tranfers
I think it claimed ~8000 ish RPM

Me thinks that is radical for that air cooled engine. If you look at the T500 cyls there is no cooling fins where the L and R cyl butt. They can get away with this since they canted the ports and exhaust exit @ outside corners and there is some fin area for cooling. I also fooled with 70s twin sleds (Ski Doo - Rotax) and have similar approach with canted... you can only add some much HP before the piston simply melt.... not like GT750 which is liquid cooled

SpecialK, Vermont, I am in NH along the border VT ride more in VT then NH

[rngdng]

GEEZ you guys are makin' my head hurt!



Lane

[oldjapanesebikes]

Sent scans to oldjapensesbikes (Ian) but can't find the link

If we are talking about the same one - it was on eBay a couple of years ago I think ? You can find it at this link.