safe rpm question

[HobbyMan]

What is the max rpm one of these engines can handle before you start to destroy valves and such? I wonder because with a 750 FD mod and a turbocharger, how fast you you make an 11 go?

[trbig]

Not quite sure... it would depend on a lot of things like spring tension, mileage, and such. Just realize that it's a pretty fair bet that every one of them that you own has blown right past this "Safe Point!" ya lead-handed nut!!



Tod

[xschop]

yeah

I want to find out when I get my 80 head redid soon....Hey hobby, Do a search about using an inexpensive GM smog pump as a supercharger for a motorcycle, I had seen it before somewhere....I think that if one could redline the xs motor with the 750FD mod....165mph ???

[bikerphil]

rpm

These are old motors and I think even 8500 would be pushin' it.

[HobbyMan]

true true. can you see the gears in my head turning? I doub't I will ever be able to do this but I would like to ponder is some more. Would it be a safe bet to say that a stock engine should never go above 9k? At 9k and a 750 FD, what would your speed be?

[trbig]

I think someone else will chime in here with a scientific math formula, but my last outing at the Talihina rally with the 750/850 FD and 8k RPM, it was somewhere in the neighborhood of 140 if the tire is close to new.

You better get those wiggles outta your azz end (I'm talking about your bike ya freak!) if you are going to try that. All that schoolin' will go down the drain in a greasy smear mark! lol. Yeah I said greasy... I ate that military food too!


Tod

[HobbyMan]

I think I have it dialed in now but I am not sure yet. I think I am going to put some money into my rear shocks and play around with my front forks a little. You know, even with that wobble, I had your top end. I have gained a few pounds so maby one day we will be on an even playing field.

[Paintman]

RPM

LOL well if you increase spring pressure and with head work you can spin wm pretty hi but i use my CBR1000 when i wana realy fly 103 in first gear is a rush LOL
John

[HobbyMan]

So you say we can put heavier duty valve springs on to furthur max out rpms? Sounds like a good idea to try. Its too bad there isn't a good way to test this to see how far you can go without endangering a good engine.

[Paintman]

Rpm

well spring pressure will help reduce valve float at hi RPm teh bottom end on these engines is pretty tough in the 70"s when i was at honda school we built alot of Turbo bikes esp the CBX's and we ran them way past safe operating limits but they were also brand new bikes not 30 yrs old i anm building a hot rod out of my 80 i ahve i will bore do alot of head work new valves and it will be injected with a turbo al depends how much time and money you have.
John

[DiverRay]

Maximan put some aftermarket springs in his bike, and he could run it up to 9,500 RPM without any "float". I think he said it hit 10,000 RPM on one dyno test!
IIRC, the STANDARD with the 750FD should top out at 152 mph at redline. with the higher rate valve springs, you should be able to hit 160, if you dare!!!

[ccogswel]

At those type of rpm's I would also upgrade the rod bolts. I don't know what grade of bolts they used back in the day but to hit 10,000 rpm for a few seconds is one thing but to hold it for a few minutes is another. Things can come apart real quick. If you are going to go thru the trouble to replace the springs I would also find a good set of valve keepers to hold them together and I would also go ahead and check the rods. Maybe have them magnaflexed. I think that's what they call it. It checks them for cracks. I mean I don't know what you want out of your engine as you may or may not want to go this far into it. But if I wanted a high rpm motor I'd go thru it with a fine tooth comb.

Just thought I'd throw my 2 cents worth in.

[Pat Kelly]

"one time" after Igot my E running I took it to a special spot in the country.
Long straight road, slight downhill, tal wind, no side roads or farms for a couple of miles.
Took the bike to (according to the guages) 143 MPH @ 9,000 RPM. Bone skock 78 with 8,000 miles on it. (well, a small windscreen).

[AlanB]

Hi Pat,

My bike is an SG with a 17" wheel from a Euro "standard" swapped in.

It has run happily 500rpm into the red in top gear on the road for a few miles and on the dyno.......briefly!. the math for top speed is beyond me.......

AlanB

[Paintman]

RPM"s

when i build my next engine with the 1196 Kit i will have rods shot penned to help releive stress, then drill so they will accept ARP rod bolts,the valve springs will have a substanstialy higher spring rate and per pounds of holding force with new retainers. and everything will get balanced so at higher RPMs so nothing comes up and hits me in The A^&.The cams will be reprofiled by web cams and hopefully everything will work together nicely
John