toopy
Club Member
It depends on the variant - 18RGs aren't homogenous as there are several versions as the applications and smog/emissions requirements evolved, and compression ratios were lowered with time. The early versions that are just called 18RG have 9.7:1 comp and run 140bhp on the Mikuni/Solex 40s. 18RGR - 9.2:1, 130bhp with air injection and EGR. 18RGRU and 18RGU, increasingly complex smog gear, non-rebuildable carbs, and power down to 125 and 120hp respectively. 18RGEU - 8.7:1, fuel injection, 120hp.
Basically, plan on rebuilding the engine and sprinkling fairy dust on it in the process! For example, my planned build will be:
Boring out to 2.2L, 92mm pistons (standards are 89)
High (11:1) comp pistons (RG heads can only be skimmed 1mm tops, so refacing is probably best and bump things with piston design and head gasket)
Rally cams, big valves, high rpm springs
Port job on the head (the one I've got is a Yamaha-made 18RGU head). The casting is really nice and will port very easily. The head has had new valve seats at some point which could be oversize as the ports at the seat end have been throat cut a few mil past the seats. This makes it perfect for blending the porting into those machined areas. There isn't much that can be done on the chambers as they are very smooth and bowl-like from the outset, just a bling polishing job.
Kameari valve guides to go with the port job and trimming to the guide bosses (similar to what I did to that Kameari SPL-style N42 head I'm making for Dixie).
44-45 carbs on Kameari/Harada intake with cable throttle.
Tubular manifold - I intend to have JP make one based on the TRD design for these cars; I have a copy of a TRD manifold for the 1600cc 2TG engine that can be used as a sample. It doesn't fit the 18RG, but the basic design is the same, so the aim will be something similar in appearance but with the right flange and bigger primary tubes.
In general, that and other related tweaks should get power up into the 160-180hp range. Which will be fine for what I want with the car, given it weighs 200kg less than a Z!
Of course, if you want 130-150ish, you don't need to go that far, just bigger carbs, maybe cams, etc.
I have to say Rich, the amount of research you put into these projects and the subsequent work that follows is pretty inspiring, i wish had the money, time and inclination to follow suit!