First off you'll need to lose the idea of 200rwhp (147rwkw) from a 2.0L l-series. While possible from an FJ20, it'd be very peaky and better suited to a close ratio gearbox and a race circuit. Not a rally stage. A Honda F20c makes 130ish rwkw, and that's a good shooting point for a flexible 4v engine.
Thing is for a rally engine, especially tarmac, is that it needs to be flexible with a wide spead of torque. Even more so if you're stuck with the stock 3.7 diff and 4 speed. If you get an L-series to 200-210BHP that would be a good shooting point. 220-230BHP for an FJ20. And whatever gets to the wheels, gets to the wheels.
A last gasp screamer is out of place on rally stages, because it's too hard to keep the engine up there, what you really need is good pulling from low to medium speed corners at medium RPM.
If you use the FJ you get the extra gear, but it's an overdrive which is still of no use, unless you can shorten the diff ratio, 4.4:1 would be perfect. Food for thought, in my caldina on the many, many nights thrashing in the Adelaide hills and up and down Mt. Hotham/ Falls Creek. I very, very rarely get out of third gear. Having a flexible motor that you can leave in gear will lower your stage time, because every time you change gear you lose time. + More gear changes = more chances to miss gears especially as you get tired. I'd often leave my car in second or 3rd on the limiter for almost 2 seconds between corners because it's faster then changing up and then having to change back, being able to use all of the rev range is vital in a rally engine with a H-pattern box.
You need Power under the curve.
Personally I'd stick with an L20, Flat top pistons, Works 74 cam, 41cc Closed chamber A87 head ported on a CNC with chambers done, 86mm flat top pistons, 1mm HG, 0 deck height, Light weight Flywheel billet flywheel, 102-Race fuel, Big inlet valves,
Keihin FCR39 or 41 or Mikuni RS40 mm Flat slide carburettors (these are smooth bore and have no chokes, very popular in Japan in place of more traditional DCOE carburettors.)
That combo will yield 11.5:1 static compression, which should be fine on race fuel. If that doesn't get you a very usable 210BHP on the engine dyno I'll be a monkey's uncle. and you'll definitely have change out of $15k. Note the same could be done on an L16 and then you're in the 1600cc class
I'd advise against over-boring the L18 to 2L, because you lose torque with the shorter stroke. With the cash you save using an L20 you, can splurge more on chassis development/handling which will pay dividends on the clock far more than a few extra ponies at the top end.
The big ticket items are the carburettors (~$1000 for new Mikuni RS40's,) the CNC porting, inlet manifold though a DCOE manifold can be adapted easily, tuning. You wont need forged pistons, quality replacement L28 flat-tops (with valve notches) will be fine and stock rods with some love (shot peened + balanced) will be more than up to the task. No need for MLS head gasket. Dry sump for a few extra KW, but I'd say hardly worth the expense.
Test with both 4-1 and 4-2-1 extractors and evaluate what's better for your purpose. + heat wrap the extractors and install a heat shield.
High compression FJ20's are getting expensive to build, due to availability of blocks/heads, high comp pistons, appropriate camshafts/cam gears, valve springs... You also run into the age old problem of space between Cylinder no.4's inlet trumpet and the clutch/brake master cylinders. the 510 engine bay isn't large and I'd see this being a problem needing to be solved. Also consider that Carbie FJ20's aren't entirely street legal (removal of EFI and all) so you 'may' need to trailer between stages
The FJ20's are also heavier than the L-Series.
Regards
Jordan.
Edit: I see you're looking to use the RB25 box? I'd seriously reconsider this. Given the low torque (relatively speaking of an NA2.0L vs say a turbo 2.5L) I can't think of any reason to lug around the extra mass of an RB25 gearbox, they're really heavy. I've been putting 250RWkW through my CA18 gearbox on the circuit and it's holding together. Remember you're not going to be clutch kicking, drifting, abusing the gearbox. You'll probably have 205/50R15 tyres, your car will weigh 1-Tonne and change wet with drivers you don't need that gear box. A smart person would use an SR20 6-speed (where 5th is already 1:1
) and lock out 6th gear to keep it legal (if you have to.) Newer, cheaper, lighter and more than strong enough to handle an NA2.0L.
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