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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 » Fri Feb 14, 2020 9:55 pm

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 » Wed Feb 19, 2020 1:33 am

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

Calypso
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Re: Suzuki F6A: 657 ccs of fury for a kei car

Post by Calypso » Wed Feb 19, 2020 8:28 am

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 » Wed Feb 19, 2020 9:33 am

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 » 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?

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

Post by burdickjp » Wed Feb 19, 2020 4:01 pm

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.

miniv8
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Re: Suzuki F6A: 657 ccs of fury for a kei car

Post by miniv8 » Thu Feb 20, 2020 5:24 pm

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 » Fri Feb 21, 2020 10:46 am

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 » Fri Feb 21, 2020 10:54 am

Interesting info .thanks. :D

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