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Author Topic: CR750 - Advice on racing frames and engines  (Read 1444 times)

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Offline HondaFreak

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CR750 - Advice on racing frames and engines
« on: July 10, 2015, 09:42:35 AM »
Hello All,

Having had 5 years at developing the 500/4, Mr Davies is thinking about building a CR750 to race in the CRMC series in the UK. As such it needs to be 1972 spec or earlier.
We would like some advice on eligible frames for racing (as far as we can see all the Egli, Rickman, Seeley frames are after 1972) and which are considered the best for handling and weight reduction?
Also, what is the bhp potential from a reliable, high output 750cc engine? I have seen 90bhp quoted for the CR using the Honda customer racing kit. Is this realistic at the back wheel?

Thanks in advance.

Peter Honda Freak Jones
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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: CR750 - Advice on racing frames and engines
« Reply #1 on: July 10, 2015, 12:02:51 PM »
Or more nowadays.
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As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline Sam Green Racing

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Re: CR750 - Advice on racing frames and engines
« Reply #2 on: July 10, 2015, 01:18:18 PM »
Check your PMs Peter.
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Offline SOHC4 Cafe Racer Fan

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Re: CR750 - Advice on racing frames and engines
« Reply #3 on: July 11, 2015, 05:47:20 PM »
I wonder if you could run a Drixton style frame, courtesy of CMR Racing Products in Canada.  Denis Curtis makes these for CB550s, and I bet he could make one to house a 750 motor.
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Offline HondaFreak

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Re: CR750 - Advice on racing frames and engines
« Reply #4 on: July 12, 2015, 10:57:30 AM »
JD has a Drixton frame from running 500T bikes. There are a few options. Build a CR750 with RSC style modified road frame, but in Reynolds tube. Take the 500/4 and bore it out to a higher cc, more like the CB500R that Honda developed. Try and find a pre73 race frame - Spondon, Dresda, Seeley etc - that we have evidence of racing in 72 or earlier.
We need to find the best balance of power, weight and handling to compete in the CRMC classes.
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Offline turboguzzi

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Re: CR750 - Advice on racing frames and engines
« Reply #5 on: July 12, 2015, 03:04:07 PM »
considering the experience you already have with the smaller sohc, i would seriously consider the CB500R way..... i published  most of the pictures from the motocilcismo story in the past and its proven to be from 1972.
10hp less than a full 750, but 40 kilos lighter is a no brainer IMHO. if honda built around a 500 to compete in the all japan 750 there must be a reason.
BTW, about half a year ago it was put up for sale..... have no idea where it ended up....
the key challenge will be the re-angling of the valves to allow the 64mm pisotns IMHO.
http://forums.sohc4.net/index.php/topic,37074.0.html


 
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Offline HondaFreak

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Re: CR750 - Advice on racing frames and engines
« Reply #6 on: July 16, 2015, 11:56:06 AM »
With regard to engines with 3v per cylinder, other than the 250n and 400n sohc twins, do you know any 4 cylinder bikes that Honda mass produced with a sohc and 3v per cylinder configuration?

I looked more closely at the CB500R details and it was ran as a 650 in 71 & 72 with an 8v head and one was prepared to the 75 Bol d'Or with a longer stroke 750cc engine and 12v head. So pre73 we could legitimately run a 650 at CRMC it seems.
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