reduced stroke/displacement

[bobzdar]

I love my vmax but my first love has always been cars. I road race as a hobby and am considering building an SCCA D-sport racer, which is basically an unlimited class with 1 liter displacement limit.

I'm wondering if it's possible to get a vmax engine down to 1000cc by reducing the stroke - and if so how short on the stroke can you go. I'd like to run as small a stroke with as large a bore as possible to get to 1000cc and build the top end for 14-16k rpm limit if possible. The goal would be around 200hp at 16k rpms. I've already located a reverse rotating diff, so could bolt that directly to the trans case and have a nice compact V4 unit offset to the right to counterbalance my weight. Any ideas on how/if it's possible to de-stroke the engine?

I wouldn't be chopping my bike up to do it, but the engine has to come out anyway at some point for a 2nd gear fix so I could use it for mock-ups on the car. This would be a multi year project, but I'd like to start some planning now - the first hurdle is whether I can get the engine down to 1000cc and get compression to 12:1 or higher. Otherwise I'll have to go with an inline 4 sportbike engine.

 

[gennro]

Its possible but I would imagine it would cost more then its worth. You would be better off with a R1 engine or a GSXR 1000 engine.

 

[RaWarrior]

Yeah....unless you're dead set on being the oddball with a V4 Max motor, seems like a tremendous amount of effort and walking in "uncharted territory" when BMW makes a nice 1000cc motor, that puts out right about 200hp.

Would be an interesting build though....if you go through with it be sure to take pictures and record stuff....

 

[bobzdar]

Odd ball is fine/preferred with me. I could have 6 or 7k into the v4 for the price of stock r1/gsxr or bmw unit, so I'm curious on what can be done. I also plan to design and build the frame myself along with cfd derived bodywork, so this would be a multiple year project. I have 2 other race cars to play with on the track so I can take my time and do what I want with this.

 

[KJShover]

I like the way you think outside the box.

Falicon might be able to help you. I've ran a couple of thier supercranks in my old XS and dragbike. They are great people to deal with.

http://www.faliconcranks.com/

 

[satariel666]

Get busa rods which are 4,5mm shorter, shorten the cam chains, plane the block or heads, get destroked crank and you are done. Only 82cc by this but at least something for start.
Geting lowered pistons will aslo help you - one advantage besides all loses I can see here - you can rev that engine much higher.

 

[mattness]

i dunno if a stock vmax's valve springs can handle 16k. lets see what sean thinks. nothings official until sean posts

 

[gennro]

Oh yeah you will need to redo the whole valve train. The stock springs will not work. The stock shim over bucket setup will not work. Whole new cams will need to be designed also.

This will prolly end up costing well over 10 grand to make this work. Can it be done yes. Is it worth it no. You can pick up a R1 or GSXR 1000 engine off ebay for less 4000 dollars.

 

[one2dmax]

Length of the rod has no change to the displacement. It would kill compression though. We can get the rods/pistons required for the reduced stroke. We'll need to destroke it to 55mm which is 11mm shorter then stock. That with the 76mm stock bore would give you 998cc's and be an "oversquare" engine. Rod/stroke ratio would be plenty high.

We've considered doing this before but never tried it. I am not sure that you can reach your HP goals though? With a reworked set of heads it may be doable.

Sean

 

[SpecOps13]

As Sean said, reworked heads. Stock parts (Springs) will not hold up any where near the RPM you are trying to achieve... Bottom end, lots of money. Cool Idea though. Power from RPM rather than size. Wow, what a top end you could have. May want to go chain drive so you can adjust....

 

[Fastatv]

I would think this would be possible to accomplish in several ways. I've read the other posts and this may be a long shot but what if it were possible to reduce to 1000 cc'c by re-sleeving the cylinders and using a significanltly smaller dia piston. This may or may not require the enginnering of these parts as they may already exist...however lots of homework would be required. Anyway, neat idea...good luck

 

[gennro]

You would need to reduce the stroke to make those kind of rpm's. Reducing the bore would not work specially with stock rods would snap in half at 15krpm.

What would need to be done is.

New rods, crank, and pistons for the rotating assymbly. Also the cylinder jugs will need to be shaved down to match the new stroke. This will prolly be around 3 to 4 grand by it self.
The top end would need new valves, shimless shim buckets, newly designed cams to make power at the rpm. Ported and flowed heads. Prolly another 2 to 4 grand here.

Also taking into account the oiling system, cooling, etc. Who knows what else will break at those rpms.

Then you would need hours of dyno time to get everything dialed in then if something didn't work starting all over agian. Prolly around 2grand plus here.

 

[bobzdar]

I would think this would be possible to accomplish in several ways. I've read the other posts and this may be a long shot but what if it were possible to reduce to 1000 cc'c by re-sleeving the cylinders and using a significanltly smaller dia piston. This may or may not require the enginnering of these parts as they may already exist...however lots of homework would be required. Anyway, neat idea...good luck

I don't want to reduce the bore as it reduces breathing which will hurt power. Keep the bore the same and you can make the same power, just at a higher rpm (valvetrain needs to be beefed up to support it). To get to 200hp, I'd have to increase breathing as well, but this would be done in stages (bottom end first, then top end).

I had planned that most of the money would be in the top end if there was a way to get the stroke down, which sounds like there is. The major concern is getting the compression up over stock even with the reduced stroke. If I can get compression up to 12:1 and get the stock valvetrain to work at 11k rpm (will better springs get me there?), it should be good for around 165hp - or around what a higher compression stock engine with the usual jetting and exhaust mods puts out. The last 30-40hp would have to come from a complete top end redo, porting, larger cams, lighter valves and better springs to try to get it to 14k rpm to make use of the better air flow.

It would be easier to buy an inline 4 and slap it in with a chain, but not necessarily cheaper and for sure not as much fun . I'm an engineer so it's not as much fun for me to do stuff that's already been done - hence why I want to build my own car.

 

[bobzdar]

Length of the rod has no change to the displacement. It would kill compression though. We can get the rods/pistons required for the reduced stroke. We'll need to destroke it to 55mm which is 11mm shorter then stock. That with the 76mm stock bore would give you 998cc's and be an "oversquare" engine. Rod/stroke ratio would be plenty high.

We've considered doing this before but never tried it. I am not sure that you can reach your HP goals though? With a reworked set of heads it may be doable.

Sean

This is what I was after, would it be rods from another bike with smaller journal diameter and then offset grind the crank? Let me know what you had in mind. Head work probably would be after I had the bottom end together and some testing - then porting, cams, complete rework of the valvetrain etc.

 

[satariel666]

i dunno if a stock vmax's valve springs can handle 16k. lets see what sean thinks. nothings official until sean posts

You just offended everybody - I feel like a dumb ass now!
The fact you dont know something doent mean someone is at the same level :smileystooges:

Length of the rod has no change to the displacement. It would kill compression though. We can get the rods/pistons required for the reduced stroke. We'll need to destroke it to 55mm which is 11mm shorter then stock. That with the 76mm stock bore would give you 998cc's and be an "oversquare" engine. Rod/stroke ratio would be plenty high.

We've considered doing this before but never tried it. I am not sure that you can reach your HP goals though? With a reworked set of heads it may be doable.

Sean

The stroke/bore ratio may be one concern - Im afraid this could change the torque curve dramaticly and would need completly redesigned crank and flywheel.

 

[satariel666]

This is what I was after, would it be rods from another bike with smaller journal diameter and then offset grind the crank? Let me know what you had in mind. Head work probably would be after I had the bottom end together and some testing - then porting, cams, complete rework of the valvetrain etc.

The main goal to reach that high rpm is mainly around valve springs and rod lenght - everything else is around cosmetical things.
After reducing rod lenght you need to match the crank rotation mases.


You dont need to invest 100 grands on this like some says...
I've seen some stock v-maxes reving over 12k and they running till today LOL

 

[mattness]

dude you flame almost all my posts i dont know what i ever did to you but relax. with several hundred viewers some people just dont know. it makes a good read and starts a discussion. take a chill pill man i dont even know you

 

[satariel666]

dude you flame almost all my posts i dont know what i ever did to you but relax. with several hundred viewers some people just dont know. it makes a good read and starts a discussion. take a chill pill man i dont even know you

dude, I was kidding...

 

[Rusty McNeil]

I love the concept and don't see why it can't be done............I love high revving engines...destroked a few SBC's back in the day...............Large Journal (cast) 327 Crank in 350block...Would easily rev to 8000 and never had a problem with them.....Low end torque DID suffer....................But dang they were fun and made plenty of power up top......did it mostly just to be different...

It will cetainly change the characteristics of engine driveabilty

..Hopefully the oiling system would keep up........other than that I would think it would just be a matter of getting the right crank, rod, piston combo to keep the compression up....Probably need shim under buckets lifters for that kind of RPM???

 

[one2dmax]

The vmax rod is already very long compared to other engines. We looked at the Busa rods which are the same (more or less) except for rod length. They have plenty of them out there pushing 300+ hp and have held up.

BUT, you'll be better off getting a custom rod like Carrillo ($1200) or our Muscle Rod ($750 - normal length and would need to see if we can keep that price on custom length). Then the HD springs ($150) and shim under buckets ($300 ish). Custom Pistons ($700ish). Custom Cams $750.

Crank Stroke/Balance work with lightened balanced flywheel - $1500. BUT, we'd want to destroke the crank before ordering anything else since I don't know how far you can cut into it before you weaken it around the oiling passage (or expose a passage).

Sean