Carbs on a Fiat SOHC 1300cc engine

Non-engine, eg: aerodynamics, gearboxes, brakes, suspension
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Joined: September 13th, 2006, 1:41 pm
Location: Ireland

Carbs on a Fiat SOHC 1300cc engine

Post by podd37 » July 7th, 2010, 3:29 pm

Before I go on the following engine was built several years ago and bought recently. I have no issues with anyone regarding it, just a few questions!

I have a 1300 sohc, with 1500 size valves, properly ported etc head (built by a respected tuner but not GC) and a standard 128 coupe cam. Rolling road supported (but I cannot verify) output with this set-up using a modified Weber 34 DMTR carburetor on a manifold that is matching the ports and a standard (but matches the exhaust ports too) Fiat 128 Coupe exhaust manifold is just over 100 bhp at the flywheel.

I recently ran this motor up on rollers with twin 40dcoe's, and a 4-2-1 manifold and we could only get 88 bhp at the flywheel.

Could the carbs be too big? Everything else seems ok with the engine, smoke free, revs reasonably well, good compression etc. Whats puzzling me is that we got 93bhp on a standard 1300 small valve head with the same ancillaries on the same rollers.

Any ideas?

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