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Fiat Coupe 16 VT trackday-cruiser

Posted: Tue Jun 12, 2018 9:06 pm
by TurboB
This is my Fiat Coupe 16vt trackday car in action about 10 years ago at Gellerasen Raceway.
Dead reliable and viritually indestructible.
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A year later at Anderstorp Raceway during the last pass of the day it started to rain at the far end of the track. It looked dry but wasn't so I just slid, at a considerble speed, straigt over the edge of the first hard banked curve into an ocean of hydrograins (LECA pellets) which filled up everywhere including the cambelt drive.
Crank sprocket + cambelt + pellets = No good
IMG_0794sm.jpg (103.75 KiB) Viewed 315 times

Finally the time has come to put the car together which leads to two question.

1. At what angle is inlet and exhaust valve located in the 16v head? My intention is to make a jigg to place the head in but find it difficult to accuately measure the angle. I don't like to wiggle the head around in the press on temprary blocks when depressing the valve springs without being sure the valve face rests absolutely flat on support.

2. How much difference in valve weight is acceptable for a straight replacement? The new exhaust valves are 3 grams heavier(55) and inlet valve 1,5 grams heavier(63). Although the engine is largly unmodified, my redesigned intake ducting allows for a much broader powerband and it gladly revs to 6500. Will I risk running into problems using OE springs?
IMG_6966 (Large).JPG
Not pretty but very effective
IMG_6966 (Large).JPG (121.63 KiB) Viewed 315 times

Re: Fiat Coupe 16 VT trackday-cruiser

Posted: Wed Jun 13, 2018 10:32 am
by Guy Croft
I think the valve angles are 23.5 deg inlet and 22.0 deg ex

The change in valve weight is insignificant although I would recommend the use of GC valve springs.


Re: Fiat Coupe 16 VT trackday-cruiser

Posted: Wed Jun 20, 2018 5:23 pm
by TurboB
It's easy to understand the physical behavior of mass and velocity but it takes someone with knowledge and real experience to give a valid answer to "how much is much?". Thanks a lot.

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You have done some testing in the past on the Kappa straight intake manifold comparing it with the standard Integrale/Coupe. Knowing how even small changes to the inlet side can make a big difference in performance in these engines I am interested in your opinion on these two manifolds. Silver is standard Fiat Coupe 16vt, black is Lancia Dedra 16v NA.
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Apart from a different throttle body angle the Dedra plenum has larger volume. Runners has 20 pct larger cross sectional area (41 vs 37,5 mm inner diameter) and the radius from plenum into the runners are about twice that of the turbo unit. Little bit difficult to take good pictures. Am I right to go with the Dedra plenum for my 16vt?
IMG_0095small.jpg (264.76 KiB) Viewed 231 times
In the "swan neck" part, the Dedra unit has injectors placed much further back (55mm). Angular difference is about 15 degrees but both seem to spray at the same area into the head. Some enlarging of the mouth is required to match the head but there is no hump for the nozzle as in the turbo unit. Is this injector placement, for some reason, unsuitable for a turbo engine?
IMG_0098small.jpg (323.63 KiB) Viewed 231 times
There is enough material on all parts to allow size matching so I can chose any combination.

Re: Fiat Coupe 16 VT trackday-cruiser

Posted: Fri Jun 22, 2018 1:17 pm
by TurboB
I just checked a Fiat Coupe 16V NA plenum and it is exactly the same as Dedra. So the question is: - why does the designer want the injector placed much closer to the head in the turbo engine than in the NA head?

Re: Fiat Coupe 16 VT trackday-cruiser

Posted: Sat Jun 23, 2018 6:12 pm
by Guy Croft
I doubt there is an exciting explanation for this to be honest,