I've sort of been offhandedly thinking about this for a while, I'd like to build an engine using some motorbike carbies (ZX7R carbies with 38mm throats actually, I've had some in the shed for a while with this kind of thing in mind), and an L4, likely an L20B.

The goal of the engine would be to be fun, torquey, able to do the odd skid, do the odd slide, generally be fun in the front of a 200B sized car and be very tractable on the road (where it'd spend 99.9% of it's time).

I was thinking that in the interests of keeping the thing cheap that it wouldn't be made to rev to the moon, and it'd be biased towards midrange power, i'm guessing that this means less/no fancy headwork, no increasing valve sizes etc which would keep cost down. The motor would be entirely rebuilt, but the aim would be to do it at home, using as few expensive parts as possible, a machine shop would obviously have to do some of the work but preferably a minimal ammount.

So using an L20B as the basis I would add the following:
high comp pistons (standard crank and rods)
A87 head, perhaps ported a bit (will this really give you much gain for the outlay? Likewise is it worth doing anything with the valves?) Oh yeah my existing A87 head i ported the inlets out to match the twin SU manifold that is currently on there.
Midrange off the shelf rally cam of some kind
Extractors and 2 to 2.5" ish sized exhaust
ZX7R carbies and fed by an OEM ZX7R fuel pump (which is handily self regulating and externally mounted)
Bosch electronic ignition from a 910
Lightened flywheel

Is there anything else that could be added for relatively minimal cost that would boost the power by a meaningfull ammount? Z24 crank for example? Bore out the block? Starting to get too expensive doing that? Bang for the buck would be the goal. Is there anything on that list that isn't adding anything to the build or that is holding it back?

What do you reckon guys?

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good plugs, good leads, pull the belt driven fan off and use a thermofan, and run a fuel cooler

Well I'd run new NGK coppers and 8mm silicon leads, i don't know what you mean by 'good' plugs though?

I don't generally like thermos, would it not be better to simply replace the solid fan with a clutch one that bolts straight one (910 bluebird?)

Why run a fuel cooler? Does it get that hot that it needs it?

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Thermo fan is the way to go. Being electrically driven it uses less energy to power instead of being mechanically driven by the belt! And personally I reckon it sound cool sitting at the lights and instead of the standard fan whine, click and the thermo kicks in for 30 seconds then cuts out again. Giving you more time to listen to the L20 lump over!

if you could put a percentage of power/torque increase for removing the fan,what would it be??

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i can turn any hexagon into a perfect circle,pass me the multi-grips will you?

i would spend nearly all my money on the head work. This is what makes the power. The bottom end just holds it together. L series bottom ends are nearly indestructable so nearly standard is the go

Send the head away to mark banyard or similar and say you want him to make it good with 44mm inlets and 36mm exhaust valves. Get him to design you a cam. Steer away from the works cam profiles. Not many of the good l series these days are running them. Will cost you approx 1000-1500
Shneider does good cams

possibly use some 89mm flat top toyota 18r pistons/ standard rods and crank. Lighten the flywheel
with an open chamber head it should yeild around 10.5:1 which is a prefect street / weekend warrier comp ratio

twin 45mm webers would be the go but the moto carbies could work. Just hard to find jets for them and someone willing to tune.

with the above you would probably get >100kw at the wheels if mark did the head

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Circuit Race 1600 in the build

^ What he said

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1928 Model A CC Pickup

So it's all in the head ay? Interesting. Why 18R pistons and not something specifically for an L4?
I have a closed chamber head so that may not suit that well anyways though.

I still like engine fans with OEM shrouds for their efficiency. Although I don't imagine cooling will be a big deal on an engine like this though.

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Mate, go thermo. I did it on the CA20, it made warming up a million times better (now it gets to a good operating temperature, fast), and it makes it a sh*t load quieter under the bonnet.

Power difference wasn't too great, there was a bit more definately. Best part was the less intertia, it gave it a tad more up and go when you flicked the throttle.

Gains are minimal, but i'd never say that clutch fan is better. I hardly even use the thermo to be honest, only when i'm in traffic or in the drive through. (I have a manual switch) It's only a little single thermo fan too.

I have a thing about being able to control everything, when I drive I'm often checking temp, oil pressure, revs, speed, etc etc. So being able to have the thermo fan available makes it great when you want the engine to warm up, or when you want it to cool down. With a clutch fan, there's a wooshy noise that's always on, there's less room in the engine bay, there's a prolonged warm up period because the cold water is being cooled again once it is pumped from the motor.

The only time i've had trouble overheating was when I was away from the car and had it idling (there was a problem so it was idling fast - 1500RPM), and it had been idling for a good 7 mins or so without the thermo fan on. But if i'd have had it on, there would have been no issues.

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910 S3 Bluebird - FJ20ET, E85, IRS, 5 Speed, 4.4 LSD
910 S3 TRX - RB25DET, Coilovers, S13 Front end, Power Steering
RA23 Celica - 18RG, Twin 40mm Webers, Coilovers, rolling on SSR mesh 15x7 0s.

I've had a fair few drift cars now, so i've had a bit of a play with cooling. Only had thermos in the first one (an S12, used twin Camry thermos on it, they worked decently enough) Naturally they all had clutch engine fans in them origianlly, not solidly mounted ones. It's mostly down to the shrouding on OEM fans being ALOT better but also I think down to the fact the most engine fans are just physically much larger than any thermo.
The S12 fans worked well, they had a nice double shroud from Toyota so that helped alot i think, as for my two S13s and C32...would never even consider going to aftermarket thermos on them...maybe an RB25 fan which is a minor upgrade.

I think i'll just stick with engine fans, clutched ones if i can . But it's probably a moot point, an L20B on the street is never going to need the cooling my SRs have needed on the track haha.

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i have herd of people useing air cooled VW pistons in there L4 back in the day to eliminate heat issues plus apparently they give pretty reliable compression, most of that come from the book called, "How to hot rod and race your datsun". fortunantly i memorised about 90% of the book because i was reading nearly 3 weeks straight, unfortunantly it was destroyed in the qld floods.

18r pistons are used because they are flat top and if i remember right around 88.5-89mm with the right pin height. No standard datsun piston is as large with a flat top.max 280z flat tops are 87mm from memory.
18r pistons are really cheap aswell. and make your engine about 2.1 litre

If you used your closed chamber head with these flat tops you would have like 11-12:1 comp. Way too high for street engine.

the other option is to use your closed chamber head and fit 1mm oversize l18 pistons. This will achieve around 10.5:1 aswell. But the engine will only be 2 litres.

just remember, the head is where you want to be spending 90% of your money

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Circuit Race 1600 in the build

v-dub has air cooled pistons??

cross drilled & slotted just like rotors

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Driving takes three abilities: Accelerating, braking, and turning.
More power only helps acceleration.
Lower weight helps all three.

Oh really? I thought there'd be an off the shelf piston available to do the job.
But i DO like cheap.
Well i actually have a U67 open chamber head in the shed, that could do the job. Will it be detonation prone with the open chamber and such though, or is that a relatively minor thing?
Do you have to fly cut flat tops to clear the valves?

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According to Precision Engine Parts Australia parts database;

Toyota 18R pistons have a pin hieght of 39.75mm
Datsun L20B pistons have a pin hieght of 38.1mm

so 18R piston would need 1.65mm machined off the crown or they will hit the cylinder head.

Standard 18R bore size is 88mm & are available up to 0.060" oversize making for a 89.5mm bore/piston.

Assuming the pistons can be adequately machined, and the L20B bores can be opened up (safely) to this size, which is a 0.180" over size, this would make for a pretty decent combination.

I have spent hours looking, and I can't find anyone who still makes forged pistons off the shelf, to suit an L20B. You can have them custom made, at about $1200 a set. Without going to that extreme, you're limited to "hyper" style cast pistons. So you would definitely need to keep rpm under 7500 or it is highly likely the rod will seperate from the piston.
I haven't researched the 18R pistons (other than through Presicions), but I would bet they will be the same deal.