Topgear A12 Turbo

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Club member Topgear turbo'd an A12 engine and it was a great learning experience. He went from 33 rear-wheel horsepower to 128. The short block was kept stock, but an A14 cylinder head with larger ports was used in the turbo version. The exhaust was 3" pipe and no muffler.

Overview

A12 turbo made 100kw rwhp on 12-13 lbs boost

• stock block except for new rings
• A14 head
• suck-through SU carburetor
• no intercooler

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• Before: 33 rwhp, about 60HP net at the flywheel (very typical for a stock A12 engine, which was factory rated at 69 HP)

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  Air-fuel ratio was extremely rich at 10.2-11.7. Optimum max power is around 12.5 for a naturally aspirated gasoline engine. Max economy is above 14.7:1.

• After: 128 rwhp

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  Air-fuel ratio was near perfect for a turbo engine (12.2) -- overly rich for max power with some cooling effect. Notice how flat the a/f curve is (lower lines).

Build

For more details, see Build Thread the Main Forum.

Carburetor was a Hitachi sidedraft at first (genuine factory Nissan carburetor of the SU type), perhaps from a P610 or a B210:
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But ended up using a larger Stromberg 1.75 (also of the SU type)

Turbo was one unit from a twin-turbo Subaru:
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Specs - First Turbo Engine (128 HP)

• Single turbo from Subaru B4 Twin-Turbo engine
• single Hitachi SU-type carb
• Stock A12 short block
• A14 cylinder head
• 3 inch exhaust, no muffler

Specs - First Turbo Engine (120 HP)

• TD04 Turbo
• single Stromberg CD SU-type carb
• Stock A12 short block
• A14 cylinder head
• 3 inch exhaust, no muffler

• I only spent $220 building it

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• the exhaust out of the turbo, it goes straight into 3" all the way out the side of the car with no muffler (straight out pipe)...
• My A12 turbo makes boost from about 2500rpm, but not good boost till 4000rpm, so as a daily road car it would be a little laggy and painful to drive....
• TD04 Turbo with a CD Stromberg and on initial driving makes 14-15lbs from about 2500-3000rpm onwards, and goes reasonably well...70KW atw (around 120 eng hp).
• I have an A12 Turbo Motor with a draw-through Stromberg carbie. I am using a TD04 off a Mitsubishi Lancer so ive been told(quiet small). The Motor received a gasket kit and set of rings (no bearings, it was a test project to see if it would work??).
• It makes 10lbs boost when reving it and makes 18lbs boost from around 3000rpm on.
• It was a stock cam and stock compression (9.0-1?), the motor is a fully stock A12 with an A14 head. After the thrashing it has received, it has reassured me the A-series motor is a bullet proof unit.
• It was built from 3 engines, Block from one motor, Pistons rods and 300,000k bearings from another, yes 300,000k old bearings. And A14 head obviously from another motor. It received a set of rings to seal compression, and a gasket kit. So it was a cheap slap together motor to see what would happen, and it worked exceptionally well
• Just ran premium unleaded (98), locked the weights in the dizzy and set it at around 17-18 degs and went from there...
• 25degrees btdc...
• stock, rings, head gasket etc.
• Its running 14lbs, it creeps up to around 15lbs from about 5500rpm onwards...It used to creep up to 18-19lbs before I retarded the timing...I think it would be fine as a street car, depending how you drive it... If you thrash it everywhere well then it wont last forever obviously. But If you drive like a normal car, and give it a small squirt every now and then it should be fine. Remember its not stressed when it not boosted...

Problem Solved

Due to not using a big enough radiator, it ran to 250+ deg F, blew a head gasket and was filling up with water. But on teardown the engine looked fine.

Lesson: Upgrade your radiator when making more 3x the horsepower. The extra heat has to go somewhere.

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