VTR rods : how strong ?
 

As some may have heard before, I was planning to build a one of a kind VTR engine, but the information is scarce on internal components, specially the crank and rods. Since they endure pretty good beatings already at 55 hp/rod, I am wondering how far you can push the stock rods before they flex/bend/fail.
I'm curious if anyone here have heard of a VTR failed rod, is the RC51 have stouter rods ? It may not exist any aftermarket so I may place a special order at carrillo or eagle for a custom set. Pistons will have to go anyway for compression purpose. Next point that could fail, is the crank/bearings assembly, any failures there on the stock form ? It will receive ARP fasteners. Any infos on these engine weak links will be really appreciated.
Thanks

The crank is said to require modding for engines exceeding @ 130 hp. Not sure about the rest though

Crank and cases, since there will be more internal stresses and the swingarm is mounted to the cases.

I recall seeing a chap (on the VTR1000.org site) who had a special custom frame (made by Spondon if I remember correctly) and it had support for the swingarm built into it. You may want to look into doing something similar if tackling a high-hp adventure with the VTR

good luck and keep us posted :)

Thanks for replies, well it depends if the mods are RPM oriented, sadly the only way to know for sure will be to blow the engine, correct, blow again, sounds like fun :shock: .
The engine case and transmission was my second worry, well I will probably mount the induction system, tune it and run low pressures with the stock block. When done (should be next spring) I'll buy a used engine and rather modify the new one. So I'll have a functional induction to break in the engine as hard as I can drive it, then turn up the hp screw while fine tuning it.
That will take a while, but for now I'm building my asylum (garage) while I enjoy the bike in the stock form.

From what I understand, the stock rods are very strong, and when I say "very," I mean I have not a single number for you.

Say, is your tentative induction forced, perhaps? If so, which type?

Turbocharger, GT2052 - 727264 - 3 to be specific, I have been planning this for 7 months now, I plan on using Microsquirt (http://www.microsquirt.info/) as fuel management with 72 lb/min injectors. The makers changed the code of the ECU following a thread where I was underlining the complexity of putting a second pulse generator on the VTR crankcase, instead they made an offset for the second ignition trigger, this made a lot of V-twin owners happy, this mounted on an custom aluminium intake controlled by a single 60mm throttle body. First I figured to move the battery and put the turbo under the seat but after some thinking, I figured that the long travel of the rear cylinder exhaust to go to the front will bring the exhaust in sync (toward the ideal 1 pulse every 360 deg) instead to worsen the fire offset. There is no room anywhere for the turbo, the guy that put his radiator under the seat was really inspiring because if I could get rid of the radiators, I could hug the turbo high enough not to have to use a scavenge pump, as for the exhaust heat losses, I planned of running a 2.5 inch exhaust from the turbo with the rear runner going inside of it and switch to 2 inch after the runner turn toward the cylinder, it should keep the rear runner hotter and will help the bling factor.
I have somehow to figure out a way to put a EFI pump in the VTR tank, it may require to steam clean it and weld additional bung or maybe use a VFR tank. Most sensors will be GM units, MAP, IAT, Datsun TPS(240 SX throttle body), stock CTS, pulse generator.
The engine already have pretty low compression and mild cams that is the hot ticket for the turbo. But when the setup will be running, I will start to build a lower compression engine trough custom pistons. The cross beam pattern of the stock rods seem very stout, but some H beam rods could provide some margin if the crank can hold the additional downforce, as for the gearbox I hope it can handle some beating.
http://www.turbobygarrett.com/turbob...4_3_comp_e.gif

Are those injectors gonna be able to open and close fast enough? That's kinda huge. The turbo is pretty freakin big too. Turboing the hawk is a cool idea, but with such a low redline, why not go with a smaller turbo? More than like 5 lbs of boost would surely require mucho internal engine modding, and 5 lbs would still make the thing haul some serious arse.

Anyway, just to be clear, I'm not knocking your ideas or anything. Just tryin to get inside your head a bit. Obviously, you've looked into this for a while.

Yeah I have been recalculating the whole thing since I posted the post above and I changed the turbo (edited it). I have built an excel sheet based on Garrett site. The turbo I picked up first was good but I feel that I have to respect the torquey behavior of the VTR and get more midrange than high end.
I figured that the engine in the stock form should handle 8 to 10 psi using 94 octane gas, I will monitor knock so if I go to far it ain't gonna blow. I will start small and tune it using a wideband O2 sensor in small increments, riding a lot between the increases. I wanted the turbo to be good for a maximum of 180 hp(as the ultimate limit with built engine @ 19 psi) without sacrifying too much the low RPM band.
The injectors are no problems it's batch firing and microsquirt is very accurate. The idle may be a little lumpy with injectors that big but it will cure off idle.

At 72lb/min, that is about 10 gal of fuel a min?! right? Maybe I am confused. that would be huge, in my opinion. I know of cars running these injectors, but at 72 lb/hr and that is good for 1000hp in a v8. That is 125hp an injector/cylinder.

Let me know if I am crazy,
Bill

Lol you are not crazy, I was planning to use the injectors at a max rate of 80%, they should be good for 200 hp then, I don't want them to max out ever, because at that power and lean out destroy the engine in no time. And it adds some room to grow. I should be able to pull out of my project with 64 lb/h but it's really a motor safety issue, uh and I'm sitting on it lol
On the stock motor I aim for 140-150 hp max.
Note that my induction system will be usable for NA application, with smaller injectors like 42 lb/h
Edit : lol my bad I just realized that I wrote lb/min in fact it's lb/h, that makes you smarter than me lol

Talk to Revolution Racing in the UK. You may be able to source a Moriwaki crank from them, but only if you have a big bank account.

So aftermarkets exist for the SH, nice, on NA engines, the only way to increase power is to rev higher and increase displacement, so I guess that crank limitations are more of a RPM affair, I tried also to find people that used SH with nitrous to know what gives under abuse, given stock RPM.

Roger at Revolution Racing is the guru on these engines, and while what you say about NA engines being different to nitrous or forced induction is true, I still think he would be a very good point of reference for you.

Interestingly, some years ago B&M in the US found that supercharged engines often stressed bottom end components far less than NA engines producing similar power outputs. You may find a similar situation exists with the VTR, thereby limiting the modifications you require.

Just a thought, may not be correct with a turbo application.

This is correct, as RPM increase, the force applied on the rods is half the square of the RPM, the tensile force tend to stretch the rods until something give way, Superchargers and turbos(exhaust driven supercharger), are applying only downforce on the rods, the exhaust backpressure and intake charge pressure, can help a little and gain some RPM because of the cushion effect (residual cylinder pressure applied to the piston while the piston is approaching TDC, piston decelarating, tensile force on rod) since the RPM gains are on the short side, it stresses the engine on a downward way, the limitations become rod (flexing,bending, breaking) and (rod, crank) bearings load limitations. Nitrous is stressing the engine in a similar way, even if there less load from compression, no cushion effect since there is no more pressure than NA except at ignition, the oxygen/fuel % is greater and the cylinder pressure rise the same as SC or turbo, loading the rods/bearings. So a nitrous user could have found the limitations of the bottom end.

The cross pattern of the VTR rods is strong/lightwieght, this is essential to keep the piston/rod combo light in order to achieve the highest RPM possible, but they have a loading limitation, H-beam rods pattern are preferred for abuse(SC/turbo/nitrous)