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Fiat 130TC cam timing and adjustments

Posted: July 26th, 2006, 3:56 pm
by dafnos
Hi to all!

I have some questions regarding cam timing and adjustments that you can do to take the best results from your engine and fit your needs.

With long duration cams e.g 40/80 80/40 we know that the inlet valve closes long after btc so the piston has less stroke to compress; that means less static compression ratio that not helpful to acceleration at low rpm but offers more at high rpm.

So if we advance the cam deg. and give some more equal lift, the "poor" torque low rpm will be benefit from that? If we use higher compression pistons it will help the situation?
With that adjustment how does it influence the high rpm band?
What cam duration is more efficient for drag race? Considering that the engine is going to built for drag racing.

Posted: August 15th, 2006, 7:16 pm
by vcg
40/80 cams are not generally considered long duration cams, they are stage 1 or mildy modified engine cams. Dyno tests I have done in the past convinced me that against popular belief its better to retard the exhaust cam than to advance the intake. Both ways you increase the overlap, but messing with exhaust is more efficient than messing with intake (you can split the overlap gain desired of course by both advancing the in and retarding the ex, but again just retarding the ex proved better). But this is all general stuff, what is your specific case with your car to see if we can help in particular?

thank you,

Posted: August 15th, 2006, 9:44 pm
by dafnos
Vasili geia sou!
Vasili hi!

The car runs on Alquati 494 cams 80/40 40/80 12.25 lift, as Guy told me they are long sircuit race cams and very difficult - almost impossible to run properly on a road car without very specific and detailed job from a race engine builder...and he is right...
The car run on 45 DCOEs, high compression pistons, ported and polished head but the header is the standard 4-2-1 with 2 silencers... (wrong header? )
I advanced the inlet cam and retarded the exhaust cam and at tdc I have an equal lift of 5mm, when I drove the car I saw big diference at low rpm but it still lacks power and when I accelerate hard from 2000-3000 it chokes.
By the way I'm from cyprus.

Posted: August 15th, 2006, 10:11 pm
by vcg
Yeia sou koumpare!

I am confused here, if you advanced the intake and retarded the exhaust, then you increased overlap.

Please give me more info:

engine size:?
piston dome height:?
head valve sizes in/ex:?
carb barrel size:?
carb venturi size:?
is the head ported:?
header pipes outside diameter:?

Also give me as much info on the cams as possible.