RZ HYBRID - Compression Ratio & Squish

[2Stroke_Hybrids(AU)]

Hello all,

I have a RZ Hybrid 399 YPVS, currently it's running 98 oct, 7.2 : 1 compression ratio, 1.6mm squish and from memory 24cc (maybe 26cc). The map is a safe map that came on the ignitec.

I've ran the bike on this set up for 20hrs now and want to tune it up at the start of the new year. (More comp, mapped to suit, 36 smarts carbs and longer k&n filters) The bike is running great and comes on the power nicely, but I don't feel like it's meeting the potential of what has gone it to the build.

I have a set of new inserts ready to be machined. The planned set up is 8.2 : 1 compression ratio, 1.0mm squish and 22cc.

Does this sound like a safe set up?

What octane should I run?

I don't have much knowledge in tuning, any help is appreciated.

ENGINE / ELECTRICAL :

PREMIX
PRO DESIGN COOLHEAD
PORTED YAMAHA RZ350 CYLINDERS
66MM MOTORRAD-RACING PISTONS
YAMAHA RZ350 BOTTOM END
4+ HOT RODS CRANK
BOYESEN REED BLOCK SPACERS
VFORCE4 REED BLOCKS
CHARIOT BILLET INTAKE
CHINGEL DUAL RACE TAP
PORTED KIEHIN 28 PWKS
UNI FILTER PODS
PETKU GP CUSTOM EXPANSIONS
DYNATEK HI PERFORMANCE COILS
TAYLOR HT LEADS
NGK IRIDIUM IX PLUGS
IGNITEC PROGRAMMABLE RACE CDI
RACER LOGIC QUICK SHIFTER
MOTOGADGET M-UNIT BLUE
MACDADDY RACING CLUTCH KIT
SUPERIOR SLEEVE BILLET CLUTCH
MACDADDY RACING PRO SHIFT KIT
VAPE ALTERNATOR KIT
MACDADDY BILLET WATER PUMP KIT
RD LC CRAZY OVERSIZE RADIATOR
CUSTOM HARNESS

[(F5)]

With 98 you should be able to run 12.5:1 safely, it's over square so I wouldn't push it much further. However you could skim to get down to 1mm which stops wasting that additional fuel and cools the piston better. Edit, I see that is your target. Looks like a racebike.

I run my 300 dirtbike at 13:1, but it doesn't rev high very often and you dont want to suppress revs. Hmm, I run my 496 RZ at 12.5, maybe you could approach 13 on 200cc cylinder. Depends how much you trust local petrol. Unless you can easily get AV gas.

I'd then measure the volume carefully with the head on using light oil 5w fork oil is ideal) and a burette which can be found online.

Tilt the engine to vertical and measure a few times until you are getting consistent results. If you take the oil to 2 turns up the threads from the bottom it accounts for the spark plug volume.

So that would be 198.3cc per cylinder at 66mm bore and 58 stroke yeah? So if you measure 18cc, then 198+18/18 =12:1 . On bare head that might be 22cc or whatever rather than 18 on the engine with a domed piston sticking in it.

If you really want to you can then measure the head by itself and do math during machining, but get the initial measurement correct.

Forget corrected ratios. No one really uses them. The pipes push mixture back in so the exhaust being open is mute, just as it is when valves open on a foul stroke.

I dont know what Taylor HT leads are, but if they are anything other than Copper, put then on your car and find some copper core leads.

Further, what revs do these pipes make peak power? Have you run it on the dyno yet? Seat of pants jetting is sometimes a ways out, but you then want to run a size safer out on the track as baseline.
Stinger sizes can get too small on oversized cylinder depending on how close they pushed them for std 350. Too big gives away power, but too small overheats pistons. They need to be matched to cylinder size and power output.

[2Stroke_Hybrids(AU)]

Hey mate,

The machining will be carried out by the same company that originally set up the bike. I just have to let them know the specs.

I'm looking for advice on how safe that set up would be or if I'm heading in the wrong direction. I was told that I would have to run octane booster or it would blow up.

The Taylor HT leads came as a package with the Dynatec Coils.

The bike hasn't had a proper run on the dyno, only used as a rolling road to set up the carbs. I believe the peak power on the pipes was at 10k, but that was on a stock 350, with vf4s and a ignitec.

Cheers

[(F5)]

I'm drunk so will try answer in the morning. YouTube how to measure compression. It's the most crucial measurement to get right. Easy as but needs care.

[kpke]

That sure is a hell of a build. Beautiful work.

I am unable to help with your questions but F5 or one of the other smart folks here should be able to answer them.

What is that tailpiece? Is it available for purchase?

Fuel tank is FZR or what is it?

[MK]

You plan to use a 26 (25?) mm exhaust port height with a +4 crank.
You did not mention whether you used a base spacer or machined the head to have the piston protrude 2 mm.

If it's the spacer solution, your exhaust timing is waaaay too high (some 206 deg), especially in combination with higher revving pipes.

If you haven't already butchered the cylinders, leave the port height at the stock 27mm (31K and 48H). Same applies for the transfer port heights.
Torque-wise less is more.
Some years ago I mangled that through several EngMod simulations and those who made the best power were always those with stock 31K port heights and no base plate.
What you should do is to match the lower transfer edges to the 2mm lower BDC of the piston. This is good for around 1.5-2 hp.
Leave the lower ex port height as is.

[(F5)]

1mm is safe if the heads are parallel to the piston, check with some thick solder to see that the ends aren't closer, if so machine squish ideally, or at least use the thinest measurement.

I dont care what the coils came with, check there is metal as a conductor in those leads. You will then need resistor plug caps and your plugs will have resistor in them. Ignitech dont like noise so above and dont mount too close to sparky bits then you should be fine there.

10k should be safe and allow some over rev if decent crank parts used in the assembly.

I did wonder how the stroke was adjusted but have no practical experience on using stock cylinders with +4. Everytime I've messed with stroke it has been the other direction for class regulations on small cc engines. But generally I just use a degree wheel and measure several times with adjustments to suit what durations I want/ can achieve with least port cuts to transfers.

[Yamavarna]

Beautiful build can we see more pictures of it?

[2Stroke_Hybrids(AU)]

That sure is a hell of a build. Beautiful work.

I am unable to help with your questions but F5 or one of the other smart folks here should be able to answer them.

What is that tailpiece? Is it available for purchase?

Fuel tank is FZR or what is it?

Thanks mate.

Tail is a modified 06 Yamaha R6 (fibreglass)

Tanks is a modified Honda VFR400 NC30

[2Stroke_Hybrids(AU)]

You plan to use a 26 (25?) mm exhaust port height with a +4 crank.
You did not mention whether you used a base spacer or machined the head to have the piston protrude 2 mm.

If it's the spacer solution, your exhaust timing is waaaay too high (some 206 deg), especially in combination with higher revving pipes.

If you haven't already butchered the cylinders, leave the port height at the stock 27mm (31K and 48H). Same applies for the transfer port heights.
Torque-wise less is more.
Some years ago I mangled that through several EngMod simulations and those who made the best power were always those with stock 31K port heights and no base plate.
What you should do is to match the lower transfer edges to the 2mm lower BDC of the piston. This is good for around 1.5-2 hp.
Leave the lower ex port height as is.

Hi mate,

Port height measurements are as pictured. Head / inserts have been machined to accept the piston.

[2Stroke_Hybrids(AU)]

1mm is safe if the heads are parallel to the piston, check with some thick solder to see that the ends aren't closer, if so machine squish ideally, or at least use the thinest measurement.

I dont care what the coils came with, check there is metal as a conductor in those leads. You will then need resistor plug caps and your plugs will have resistor in them. Ignitech dont like noise so above and dont mount too close to sparky bits then you should be fine there.

10k should be safe and allow some over rev if decent crank parts used in the assembly.

I did wonder how the stroke was adjusted but have no practical experience on using stock cylinders with +4. Everytime I've messed with stroke it has been the other direction for class regulations on small cc engines. But generally I just use a degree wheel and measure several times with adjustments to suit what durations I want/ can achieve with least port cuts to transfers.

Got you. The heads were machined and setup by a race shop using the complete engine, the squish was measured at 1.6mm. I will ask them how they it was measured.

The leads are "High conductive spiral wound core with stainless steel wire and fluorocarbon conductive material cover". They're supposed to be the business. Not some Chinese shite.

Longer rods make the piston protrude 2mm out of the cylinders. That is then accounted for when the dome inserts for the head are machined. Some people use a spacer base gasket, but that will mess with the port timings.

[2Stroke_Hybrids(AU)]

Beautiful build can we see more pictures of it?

Thanks and yes mate.

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[2Stroke_Hybrids(AU)]

I'm drunk so will try answer in the morning. YouTube how to measure compression. It's the most crucial measurement to get right. Easy as but needs care.

The compression has been measured by the race company that set the bike up. 7.2 : 1.

[(F5)]

7.2 will be a so called corrected compression ratio. The idea being that the exhaust port being open limits the compression stroke to only above the port. That may be apt for lawnmowers, but is 1970s thinking for anything with an expansion chamber. Also it might be calculated with the exhaust valve open or closed, but who cares? Try to find out what they measured in volume on the bike to get a full stroke compression value. Then you can estimate a reasonable change to optimise vs your fuel. I'm surprised they would have left it at 1.6mm especially on a race engine.

So if the port measurement is given, presumably there is then 2mm added to all those numbers if the piston encroaches out of the bores. Finding out what the genuine port timings would be good.

But it's not longer rods. It is the position of the Crankpin further out which allows the extra stroke. In this case the pin is 2mm closer to the circumference of the webs. 2mm up, and 2 down to give 4mm extra stroke. Longer rods are incidental but have other potential benefits, and may be required if the piston would collide with the webs for example.

[jerele]

Hello Martin.How was your experience using Engmod2T?.
Thank you very much