Topic: Higher Rev;s combined Threads.

[Soos]

Hey all,



I have a cb650 crankshaft in the shop getting fitted with new crank bearings and rods from a suzuki GSXR1000.
The rods are redlined (for the GSXR) at about 12,000 RPM (?not 100% sure)

I know the GSXR used 73.4mm pistons, and I am going to be running 66mm (kz750) pistons.
Not sure the weights of the GSXR stock pistons but I think I will be moving lighter pistons overall.


From what I understand the connecting rods in the SOHC lineup was the weak link when it came to sky high RPM's.
These GSXR rods are WAY better that the cb650 stockers ever couls have hoped to be.


When thinking of upping the redline, should I consider using better wrist pins to support the added RPM's as well?
Ape has a nice set I've thought about as well.




l8r

[JohnG]

detonation is an enemy of connecting rods.

If you are going this far, new rod bolts should be considered.

For high RPMs, making sure your oil supply system works properly is worth considering. Providing enough oil at 8000 rpm is one thing; at 11,000 is another.

Valve springs??

Ignition??

[paulages]

bear in mind that your power will still drop off well below that redline without some serious head work. i'd guess that higher compression at peak power (which will be somewhere between 9,500-10K most likely) will more likely affect what abuse the rods will see, aside from potential stretch at high RPMs. i'd love to see you build an engine that will make power that high. IMO a 650 head with heavy porting could probably do it, but the two-valve valve train will probably still be a bottleneck as far as power production goes at 12K RPM.

for what it's worth, the guy who raced my cb550 racebike in the 70's and 80's says that he pulled to 12K all day long on shotpeened stock rods, and that the bottom end was "bulletproof." i think you'll be fine with these rods.

[Soos]

Porting is going to be another long project I think.

Paulages, didn't you go with oversized valves in your 550/650 head (shameless plug for a board member in 3... 2... 1...) by MRieck?


I've been thinking of running a size larger valves(even if I have to make them) as well as some serious porting.
Thankfully I have access to a home-brewed flowbench.


I would REALLY like to make power up to 11000-12000 and be safe up to 13000 if possible.
I just don't want to have all this time/$$/parts to destroy themselves.

And yes, conn rod bolts ARE being replaced.
Those $8.00 bolts(each bolt!) better be worth it!!.

It's costing me more for the bearings and conn rod bolts than the entire bill for my last overbore did(61mm).







l8r

[paulages]

Porting is going to be another long project I think.

Paulages, didn't you go with oversized valves in your 550/650 head (shameless plug for a board member in 3... 2... 1...) by MRieck?


I've been thinking of running a size larger valves(even if I have to make them) as well as some serious porting.
Thankfully I have access to a home-brewed flowbench.


I would REALLY like to make power up to 11000-12000 and be safe up to 13000 if possible.
I just don't want to have all this time/$$/parts to destroy themselves.

And yes, conn rod bolts ARE being replaced.
Those $8.00 bolts(each bolt!) better be worth it!!.

It's costing me more for the bearings and conn rod bolts than the entire bill for my last overbore did(61mm).







l8r

i didn't use larger than stock valves for a 650 head, but those are HUGE compared to a 550.

[kos]

It is all about airflow.


You will have to do a lot of documented port/flow work to have a head/cam combination to support 11,000 RPM.

BY documented....dyno tested after completing head with verification on flow bench.

KOS

[Soos]

I'm all about completely self done projects whenever possible.


The cam I am planning on having a 550 cam welded up and ground to the hottest profile I can get my hands on.
Thats one of the few high $$ Items I want dome by others.


Not sure on what all is going to be entailed with the headwork, or even if I will farm it out to someone else.
Depends on what I decide to do about the piston to head issue.




Anywhoo.....The $80 it costs for a dyno run would be 1/4 the cost of a re-weld/ground cam does.
If I knew someone I could get a few free dyno runs, or a discount... that would be another thing.
I'll spend money on parts.
 




l8r

[Bill/BentON Racing]

Yosh recommended shift pt was 11,500 rpm for Isle of Man TT cam,you could easily spin up to 13,000 rpm but power dropped off after 11,500.Bill

[turboguzzi]

Yosh recommended shift pt was 11,500 rpm for Isle of Man TT cam,you could easily spin up to 13,000 rpm but power dropped off after 11,500.Bill

Soos, and that's for a 500, a 650 is going to be more strangled for air at high revs.

Good on ya on the GSXR rods but from my experience, the small sohcs just dont go on making power after 10-11K. Heard that comment before building the motor and it turns out to be quite true.

Even if you just wanted a safety net of over-rev (quite useful) you'd still need to upgrade your valve gear first, After last racing season I did find some signs of valve float in my motor and that's with racing springs.  The two things that break engines are bent valves and snapped rods. you need to be safe with both.

[MRieck]

Yosh recommended shift pt was 11,500 rpm for Isle of Man TT cam,you could easily spin up to 13,000 rpm but power dropped off after 11,500.Bill

Soos, and that's for a 500, a 650 is going to be more strangled for air at high revs.

Good on ya on the GSXR rods but from my experience, the small sohcs just dont go on making power after 10-11K. Heard that comment before building the motor and it turns out to be quite true.

Even if you just wanted a safety net of over-rev (quite useful) you'd still need to upgrade your valve gear first, After last racing season I did find some signs of valve float in my motor and that's with racing springs.  The two things that break engines are bent valves and snapped rods. you need to be safe with both.

That goes for 750's as well and that is with a 34mm intake valve. The 550's need more valve but there is no room on the seat (unless you replace it). As kos said...you can fit a 35mm intake and back off the exhaust valve side and some more power will be had but still these things won't make power at 13,000 etc UNLESS you do serious work.

[Soos]

Makes me want to get new vlaves, springs.....



Hrmm having someone else kit up and port my head sounds more and more needed/wanted.

thnx all!


l8r

[MRieck]

Makes me want to get new vlaves, springs.....



Hrmm having someone else kit up and port my head sounds more and more needed/wanted.

thnx all!


l8r

Feel the Force  Soos.

[KB02]

Okay, so I kind of stole the title from another post...

not that I plan on visiting higher than 8 on the tach very often anyway, but since I have the APE racing springs in my 750, does that raise the redline in my engine? (New gauge faces still redline at the same point - no need for big booms if I'm just going to be road riding it, right?)

[w1sa]

OK,  I'll bite.
Heavier spring action on the valves, without other engine mods designed to deliver higher sustained power/revs, would not alone allow a meaningful (if any) increase in the original redline.
Heavier springs are designed and used to eliminate valve action bounce/float otherwise expected within the upper to maximum rev range of the engine builder/designer's intended use.

[bucky katt]

i imagine that lightening the valve train (rockers, retainers and locks) would have the same sort of effect that installing heavier springs in it if i understand my theories right. the added benefit of lightening valve train components over using a heavier spring is less wear on the cam, rockers, rocker shafts and valve stems, also would it not result in less parasitic losses?  please, if i'm mistaken i'd love to hear from some of our more experienced engine guys.

[mlinder]

The 750 (especially the 73 on) already has issues breathing well above 8k.
HD springs are there for when you do a bunch of other work to the engine, where you WILL be breathing better at high rpms, and your lift is higher because of a fat cam.
With the valves opening that much more at 3k more rpms, you need the heavier springs to get those valves closed on time.
The HD springs do cause wear faster.
Just no point in them without doing a lot of other work. You'll have faster cam lobe wear, faster tappet wear, and faster valve stem wear for an engine that doesn't make any more power than with stock springs, otherwise.

[Jerry Rxman Griffin aka MuthaF'er]

Stronger valve springs will help prevent this from happening when missing 1st to 2nd without untwisting your right hand. Stock 75 750F engine. Estimated 11K to 12K rpm with valve float. Valves aren't meant to remain intact when hitting the piston. Isn't that replacement a pretty sight?!

[mlinder]

If he's shifting at 8k max, though, Jerry, chances of hitting 12k are pretty slim.

[mlinder]

Some threads here do relate to HiPo applications, with good information regarding higher revving engines.
I'm going to combine them here.

[Soos]

Cool!


Unfortunately with higher revs a shorter life of the engine is somewhat inevitable.
The more I read this(and other threads) I feel I NEED to have my head done by someone else.

I have access to a homebrew flow bench, but what I want out of this next motor is (I believe) beyond my ability to do it properly.


thnx for the info all!!!





l8r

[kayaker43]

I always thought piston speed determined the mechanical redline for the most part, with valve float second. Stroke, rod length and RPM determine piston speed. Even changing rod length with no stroke change can have some effect due to angularity. Good ring design also contributes to the max safe piston speed which is where the rings float and lose their seal. Of course the valve train must also be capable of that RPM.

Just because it will hold together at 13K doesn't mean it will make power there, that's all about breathing. Modern bikes have crazy short strokes, many light valves and lots of valve area.

[Ecosse]

totally out of my league here but what are thoughts on extrude honing? does anyone do it in the bike world... or anymore?

[Soos]

Thats something I have had interest about in the past, hard to find places that can.
A few race shops I have called have it, but it ain't cheap.


But does sound interesting.




l8r

[Soos]

I always thought piston speed determined the mechanical redline for the most part,

 Good ring design also contributes to the max safe piston speed which is where the rings float and lose their seal. Of course the valve train must also be capable of that RPM.

Just because it will hold together at 13K doesn't mean it will make power there, that's all about breathing. Modern bikes have crazy short strokes, many light valves and lots of valve area.

I'm running the same stroke a suzuki GSXR 1000 does (roughly).
Head design on the 650 is (for the SOHC's) the best design I have seen (from where I see it)
It's nothing compared to the capabilities of a modern DOHC motor.
Nowhere near the valve area, nor liquid cooled.
And probably nowhere the aggressive profile possible due to the beter cooling ability of those motors as well.




However, I think the 650 head can be made to get some serious power, given all the accompanying parts(cam/pistons/carbs/rods/valves) can handle it as well.



l8r

[Jerry Rxman Griffin aka MuthaF'er]

If he's shifting at 8k max, though, Jerry, chances of hitting 12k are pretty slim.

You're sure right about that. I was probably TRYING to shift somewhere north of 9000 when I missed 2nd and the tach needle went ballistic. Main thing I was trying to allude to was this is one very expensive thing stronger springs will prevent if he misses a shift at higher rpms. I don't think stronger springs will do much for a stock engine unless you miss a power shift above 9000 as I did.

[Soos]

I SOOOOOO miss my rev limiter the dyna2000 unit I was running(before it fried)!!!!!!!!!!!!


The safety factor of high RPM shifting was AWESOME!
Seriously looking into one for my daily rider.




l8r

[mlinder]

If he's shifting at 8k max, though, Jerry, chances of hitting 12k are pretty slim.

You're sure right about that. I was probably TRYING to shift somewhere north of 9000 when I missed 2nd and the tach needle went ballistic. Main thing I was trying to allude to was this is one very expensive thing stronger springs will prevent if he misses a shift at higher rpms. I don't think stronger springs will do much for a stock engine unless you miss a power shift above 9000 as I did.

I was somewhere above 9k at wot when my clutch slipped. 15k at least. Somethign broke, still haven't looked at what, though. It did get me home, though, an hour at 70mph. I'm guessing the spring itself broke.

[KB02]

Mike did Stage II porting on my head and I am running a webcam 41a grind Cam. I also running stock rods so I know that 12k would be a bad idea.  But, yeah, the incidental missed shift is basically why I am wondering.

[mlinder]

I may be wrong, but it is my opinion that the cb750 bottom end (as well as the 650/550/500s) are fine with frequent forrays into the 11k plus area.
Doesn't mean you'll make power there, though.

[MRieck]

I may be wrong, but it is my opinion that the cb750 bottom end (as well as the 650/550/500s) are fine with frequent forrays into the 11k plus area.
Doesn't mean you'll make power there, though.

That's for sure

[turboguzzi]

If my electronic GSXR tacho is anything to go by (I expect it to be way more precise than a stock mechanical), I often go into 12K in my 500, with some 13K peaks,

that said, you can see how power falls down after the peak (its about 10.5K in rpms). 

therefore, I can hardly believe that a 750 will peak at more than 10K, 9K would be more likely, just to put numbers in the right proportion. Maybe Kos can confirm :-)

Sure, stronger rods are always nice but I rather stop the engine from hitting 15K with the preset 13.5K limiter of my GSXR ignition. Whatever you do to a sohc valve train, you will never match the GSXR valve float ceiling: dohc, bucket followers, small ti valves vs. big valves and springs that need to return valves AND rockers.

 

[mec]

@TG:
do you use stock conrods in your 500?

mec

[turboguzzi]

MEC, I am on shot-peened stock rods

BTW, had a look at your old dyno charts and you seemed to peak HP at 8800 right?

TG

[mec]

that´s right.
1000ccm engine power peak at 8865rpm
stock 836 engine at 8048rpm

mec