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Location:
Camden
Registered:
May 2002
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18RG Version
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Tue, 01 April 2003 12:14
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Ive searched and read past posts on this topic and it seems as though other ppl are after similar info. So just as a suggestion, if anyone out there has all the serial number listings and version type and all that kinda info, ya recken ya could make an article up??? Anyway....
Ive got an 18RG with a yamaha head with serial # 11111 - 88250. If anyone could help me out and tell me what version ive got, compression ratio and just stuff like that.
Also, ive managed to scam an injection manifold planning for a turbo setup. Im just a bit concerned with the compression ratio. What is a suitable ratio for turbo and how could get this engine to a suitable ratio. Do ya get lover compression pistons or make up a spacer or sumfin similar???
Any info would be appreciated!
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Location:
Brisbane
Registered:
May 2002
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Re: 18RG Version
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Tue, 01 April 2003 14:13
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The ideal compression ratio depends on a lot of things, but generally speaking you want it somewhere between 8.0:1 and 9.0:1. I'd aim for higher compression on a street engine as this gives better off-boost response and quicker spooling. If possible you should get your hands on an 18R-GU as this has an ideal 8.7:1 compression ratio from the factory.
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Toymods Social Secretary
Location:
Sydney
Registered:
July 2002
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Re: 18RG Version
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Wed, 02 April 2003 01:31
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The head NO# you are listing there is from the earlish model 18R-GU. This motor was supplied with 8.7:1 compression pistons and slightly bigger valves than the earliest 18R-G (88250 has 45/37mm valves), and is single valve sprung.
This is all stock parts of course. IF the motor has been rebuilt by someone with a bit of knowledge of the 18R-G's back in its day, then its possible that the 9.7:1 pistons have been installed as this was a common upgrade when rebuilding. Only way i can think to check is to crack off the head and see if the pistons have HUGE domes or not.
My personal preference for heads, and what is commonly accepted as the best head to work with, is either the 11111-88253 or 11111-88270 heads (from late model 18R-GU and 18R-GEU respectively). These are preferable for working since they have double sprung valve stems, the best head flow, the most meat for porting and the biggest valves.
If you want i have a complete 18R-GU (11111-88253) motor at home without intake side of things 
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Location:
Canberra
Registered:
August 2002
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Re: 18RG Version
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Wed, 02 April 2003 02:25
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where bouts is this serial number located?
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Location:
Camden
Registered:
May 2002
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18RG Version
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Wed, 02 April 2003 12:47
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If this is the version (18RGU) i should be looking for, how much ya want for it?????
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Location:
adelaide
Registered:
May 2002
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Re: 18RG Version
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Wed, 02 April 2003 13:38
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| alwaysRA23 wrote on Wed, 02 April 2003 11:55 |
where bouts is this serial number located?
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If you are refering to the 11111-882xx head serial number, it is embossed(?) on the front end/face of the head, just more to the exhaust side. Just above and to the left of the timing cover-plate at the motor from the front.
It is in fairly large numbers so it should be fairly easy to find on even the grubbiest of yamaha heads.
It is also in the same spot as the yamaha logo but on the exhaust side, not intake.
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Toymods Social Secretary
Location:
Sydney
Registered:
July 2002
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Re: 18RG Version
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Thu, 03 April 2003 05:24
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if you are looking to work the motor - then the 11111-88253 motor is a good one to start with, since it already has the best head flow of all the 18R-G's, biggest valves and 8.7:1 compression pistons (although the 18R-GEU had 8.3:1).
However, my motor is a little tired - it has some small oil leaks (timing chain tensioner), makes a bit of smoke, and seems just a bit old and worn (still goes like the clappers though!). But nothing a good rebuild wont fix, which is what you would be doing anyway were you to have a turbo application for the motor.
Im still undecided about selling it. Gimme a week or two to think
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