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Twin SU's - what cam and what head work for L20?
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Author:  datto_1600 [ Thu Jul 28, 2005 11:34 am ]
Post subject:  Twin SU's - what cam and what head work for L20?
I am building a L20 with stock crank, rods and pistons with a .5mm overbore so the block is almost completely stock. I am using an a87 closed chamber head and im not sure what i want to do to it. I was thinking larger valves, possible port and polish, stronger valve springs, new lash pads, and reground rockers with a performance cam. I have already purchased my twin flat top hitachi Su carbs off ebay and they're in the post, they are 1975 180b SSS ones.

The cam is the one i really don't know what i want... I want power from about 2500RPM towards 6-7000RPM with a reasonably rough idle - i like the rough idle but i dont want it to stall etc. What cam would you suggest? degrees? manufacturer? price?

So thats the cam and i was thinking about spending no more than $600 - $800 on the head... With the cam in mind and those twin carbs what do you think i could do to the head?

Cheers.

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Author:  lukey73 [ Thu Jul 28, 2005 11:52 am ]
Post subject: 
I would go a 72 or 74 degree cam, that way it will have a nice lumpy sounds and give good power. What diff are you using aswell ? These cams like to be in the rev range and having to high a diff ratio wont help.

I have 3.9 at them mo and am going down to a 4.6 when i get the money to buy one but soemthing like a 4.1 would be great for these.

If you can get a light port and polish done and bigger valves put it for your budget then do it.

Luke
Author:  jdmdatsun510 [ Thu Jul 28, 2005 3:34 pm ]
Post subject: 
lukey73 wrote:
I would go a 72 or 74 degree cam, that way it will have a nice lumpy sounds and give good power. What diff are you using aswell ? These cams like to be in the rev range and having to high a diff ratio wont help.

I have 3.9 at them mo and am going down to a 4.6 when i get the money to buy one but soemthing like a 4.1 would be great for these.

If you can get a light port and polish done and bigger valves put it for your budget then do it.

Luke
A 72-74 is WAY to much cam for "flat-top" 38mm SU's. It will run....like a bucket of p1ss. Get a Wade 25/65 Billet cam, should cost around $230 + $300 installation and tuning.

I have personally driven around a 25/65 38mm SU combo for the last 3 years and I can say with complete confidence that this is an excellent package.

Anything close to a 72-74+ will need bigger carbs. I'm not a big fan of the 40mm webers so go for something like twin 44mm SU's or a 45mm Weber.
Author:  Dave [ Thu Jul 28, 2005 9:12 pm ]
Post subject: 
Totally agree with Datsss73.

I had a 25/65 cam in an L18 with SU's. Fitted to my 1600, it was a really nice package. Also had a bit of work done on the ports and manifold, 280ZX inlet valves and flat top pistons.

The reason I liked it is hard to explain - it wasn't blindingly fast, but it just went beautifully. It pulled well, no bogging down at low rpm's, and revved pretty well. It did run out of steam at higher revs until I fitted custom needles to the SU's.

In contrast, a similar engine fitted to my other 1600 (an ex-rally car) but with a much more radical cam was a real pain to drive. It was probably quicker, but wouldn't pull below 3-4000 rpm. Stick with the head mods you've already got planned, keep the cam fairly mild and you won't be disappointed.

If you really want a more aggressive cam, you'll need the rest of the package to go with it (webbers, etc) and need to be prepared to put up with a loss of tractability.
Author:  fr3ak [ Fri Jul 29, 2005 6:38 pm ]
Post subject: 
I've got a 270' cam if you want. Will give you the power band you want and goes well with 180BSSS SU's.

Also fit an electric fan if you haven't already, makes it nicer to rev out.
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