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Toymods Social Secretary
Location:
Sydney
Registered:
July 2002
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Re: 18R-GU specs
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Wed, 07 May 2003 13:56
 
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Well well well..  what have we here... 18R-GU head information!! :)
Ok, here is the information i found about some of the variant 18R-G heads that were produced. I got this from the Yahoo Celica Group i think.
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> 88250:
> - 49657 single spring early rgu single dump ex ok head small studs on ex
> - 52978 same as above
> 88253:
> - 73086 double spring late rgu good head to start with large studs on ex
duel dump man
> - 62744 single late rgu still good head may be small stud ex should be
single dump
> - 81784 double spring late also
> - 87278 double spring late also
> 88270: these are ale efi heads all double springs alll good heads these
are the ones you use
> - 35140 biggest ports biggest valves no smog ports best casting
> - 08037
> - 49383 very late head newest ive seen
> ?:
> - 81225 same as above double late rgu if the head is a 11111-88253 not a
11111-88270
> 88253 88270s would be the heads of choice since these need very little
work from the factory these willl make lots of power with little porting
they will make a lot more power with a lot of porting the castings are a lot
thicker around the ports so there is a lot of room
the 88250s can be made good but the ex studs should be changed up to 10mm
ones for best sealing
all of these engines should have 8.5s to 1 but the efi 88270 heads they
should have 8.3 to 1
just be glad you dont have any of those 11111-88230 or 88210 heads they are
good paper weights
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Also a good point to note that ALL Toyota twincam heads were made by Yamaha. Its a common misconception that simply because Yamaha started embossing their twincam head on Toyota motors with "Yamaha" that all of a sudden Yamaha started making twincam heads. This is far from the truth. ALL Toyota twincam heads are of Yamaha design and make.
AS for the Motor's specifications, most of the specs from the "Green Book" as i like to call it are still applicable to the 88250 variant 18R-GU, the major difference between this model and the earlier ones is the pistons (went from 9.7:1 down to 8.7:1 compression ratio) and the valve sizes went up to 45/37mm in the 88250 head (not sure what they are stock in the earlier models, but i know its smaller) and the camshafts have a shorter duration to make up for the newly introducted emissions laws.... as was the reason for most of the modifications.
I have also heard that the 18R-GU came about in the introduction of unleaded fuel in Japan... but either way, the U still stands for Japanese variant emission control.
A couple of specs:
Cylinder Bore: 88.50-88.55mm wear limit: 0.2mm
Stroke: 80mm
88250 intake valve face size: 45mm
88250 exhaust valve face size: 37mm
cam specs...? i know the earlier cams had longer duration - visibly longer!
Air flow figures... no idea... except that from the green book the manifold vacuum at idle is: 380mm of Hg (mercury).. and i forget what that equates to in HPa or PSI
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