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Suzuki F6A: 657 ccs of fury for a kei car

General engine tech -- Drag Racing to Circle Track

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burdickjp
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Suzuki F6A: 657 ccs of fury for a kei car

Post by burdickjp »

I recently picked up a potent drink in a small cup: a Suzuki Cappuccino. This was a car sold in Japan in the early '90s as a 2 seat sports car that fit their Kei car tax bracket.
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Part of this class of cars is an engine capacity less than 660 ccs and less than 67 horsepower. In this case the engine is Suzuki's F6A. The F-series was Suzuki's first 4-stroke automobile engine. This one is a 3 cylinder with dual overhead cams and an IHI RHB31 turbocharger. The smallest turbocharger I've ever seen.
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This DOHC head uses cam boxes. The cams fit through from the back of the head with a plate holding thrust loads:
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Those cams act on rockers which pivot on lash adjusters:
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I did some investigating to determine the rocker ratio:
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When the valve is closed the rocker ratio is about 1:1. At the other end of its travel it's about 2:1 (2 mm of valve lift for 1 mm of cam lift).

So I'm looking forward to working on some cams for this application. The travel limit of the lash adjuster will determine the smallest base circle my cams can be. I'm considering replacing the hydraulic lash adjusters with shims, or making them from scratch.

The variable rocker ratio should be able to compensate for a fast cam ramp. Considering the way the camshafts fit in the cam boxes, there's a limit to the size of the cam nose. More similar to how a pushrod camshaft fits in the block than what I'm used to.
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Am I thinking about these cams correctly? Is there anything further I should consider?

I can't describe how excited I am to be working on this. It's been a while since I've dug my teeth into an engine like this.
BLSTIC
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Re: Suzuki F6A: 657 ccs of fury for a kei car

Post by BLSTIC »

So you say the travel of the lifter limits the smallest bcd? Is that purely a limit when you're installing the cam and not a limit during operation?

Can you fit the cam boxes with the cam already installed? Or hold the valves open during assembly, allowing the cam follower to not interfere with larger lobes and a higher lifter?

Also that intake port looks like it could be made to conform to Toyota's new high tumble way of thinking. Wouldn't do overlap charge robbing much good with big overlap but they claim it resists detonation and improves burn speed if pump gas is a thing you have to use
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Re: Suzuki F6A: 657 ccs of fury for a kei car

Post by Calypso »

Curious why focus on cams initially, when it's a turbo car?
burdickjp
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Re: Suzuki F6A: 657 ccs of fury for a kei car

Post by burdickjp »

BLSTIC wrote: Wed Feb 19, 2020 1:33 am Can you fit the cam boxes with the cam already installed?
The order of assembly is installing cams into boxes and then boxes onto head.
BLSTIC wrote: Wed Feb 19, 2020 1:33 am Is that purely a limit when you're installing the cam and not a limit during operation?
The lifter has a mechanical maximum that it can extend. This would represent the minimum base circle the cam can be.
Calypso wrote: Wed Feb 19, 2020 8:28 am Curious why focus on cams initially, when it's a turbo car?
Cams are the heart of the whole operation. I am spec'ing a turbocharger as well. This engine came apart before the turbo arrived, so this is what I'm digging into right now.
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Re: Suzuki F6A: 657 ccs of fury for a kei car

Post by BLSTIC »

So is it possible to raise oil gallery 8 and space the lifter body 9 up a mm or two?
burdickjp
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Re: Suzuki F6A: 657 ccs of fury for a kei car

Post by burdickjp »

BLSTIC wrote: Wed Feb 19, 2020 1:13 pm So is it possible to raise oil gallery 8 and space the lifter body 9 up a mm or two?
I'm going to measure that relationship on this cylinder head. If my reading of some of the Japanese aftermarket companies is correct, via Google Translate and Microsoft Translate, then they reduce the base circle of the cam and then install a shim under the lash adjuster.

The nose radius on that lash adjuster is a cool 8 mm if I'm reading correctly. I could manufacture some mechanical lash adjusters as well.
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Re: Suzuki F6A: 657 ccs of fury for a kei car

Post by miniv8 »

Thanks for sharing. it's fun to see something so different.
burdickjp
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Re: Suzuki F6A: 657 ccs of fury for a kei car

Post by burdickjp »

Image

I had a friend grab a scan of the head using a Hexagon arm.
Brucedg
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Re: Suzuki F6A: 657 ccs of fury for a kei car

Post by Brucedg »

Interesting info .thanks. :D
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Re: Suzuki F6A: 657 ccs of fury for a kei car

Post by englertracing »

This screams to dump the original engine for a 1000cc + sport bike engine...
An s1000rr makes 200hp..... And doesnt sound like a forklift
burdickjp
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Re: Suzuki F6A: 657 ccs of fury for a kei car

Post by burdickjp »

englertracing wrote: Sat Feb 22, 2020 9:35 pm This screams to dump the original engine for a 1000cc + sport bike engine...
An s1000rr makes 200hp..... And doesnt sound like a forklift
If I put any other engine in this, it'll be a Suzuki K-series. The K6A was used in the EA21R, the revised Cappuccino. It's all-aluminum with a much more modern head. Other versions of the K were larger in displacement, or 4 cylinders. I intend on doing that eventually, but for now I'll play with the F6A.
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Re: Suzuki F6A: 657 ccs of fury for a kei car

Post by Calypso »

Any updates on this?

What are your plans in the exhaust side, with manifolding and the turbo.
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Re: Suzuki F6A: 657 ccs of fury for a kei car

Post by BLSTIC »

I'm also curious about the manifold design. It will be interesting to see exactly what design and measurements work on a 3 cylinder car with such tiny cylinders.

Also what duration cams are you thinking of running? I've been reading about blowdown interference and it's a concern on most engines, but perhaps not on a three-pot unless your cams are quite long duration.
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Re: Suzuki F6A: 657 ccs of fury for a kei car

Post by Calypso »

BLSTIC wrote: Thu Apr 16, 2020 1:13 am I've been reading about blowdown interference and it's a concern on most engines, but perhaps not on a three-pot unless your cams are quite long duration.
3-cylinder engines should work very well with short exhaust manifolds, because the firing events are spaced much further apart. Current OEM solutions have in most cases manifolds integrated into heads, which will reduce heat losses and enhance pulse conversion. However, Nissan 400hp 1.5L DIG-T R still has an exhaust manifold, albeit short, so it seems that in high HP applications it will still be beneficial to have separate, more direct outer exhaust ports.
I'm tempted to build turbocharged 1L Daihatsu/Toyota 1KR-FE, which is modern, lightweight (69kg with accessories), cheap and available, and put it into a light chassis...
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Re: Suzuki F6A: 657 ccs of fury for a kei car

Post by BLSTIC »

I've driven one of those. It was not-quite adequate in a 900kg car. I mean if I didn't live in a hilly city it would have been fine, or if it had boost. But there was a 1.3 K3-VE option available in that car, and that K3 was available turbocharged in other vehicles, so I would have been mad to turbo the 1KR at the time when combining factory parts could get between double and triple its output before modification. It did allow for a really tight turning circle though (the four cylinder models would do a 3 point turn on a 2 lane road, the 3 cylinder could nearly do it in a double carport)
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