Exhausts, trumpets, air boxes and power
I did some rolling road testing with the Minari Club over the weekend. Below is a summary of the results
1. Maniflow crossover exhaust manifold on standard 16v engine gave 4 bhp increase over std Alfa manifold, peaking 300rpm lower. Improved power from 3300 rpm up to 6350 rpm (peak) with a max gain of 10 bhp at 5200 rpm.
2. Torque for same arrangement as above. 5 lb/ft peak improvement 100 rpm lower at 4640 rpm. Improved torque from 3200 to 6200 rpm with a max gain of 10 lb/ft at 5200 rpm. The 'plateau' section of the torque curve using the Alfa manifold was about 500 rpm longer than the Maniflow one.
The induction system on the above was std Alfa throttle bodies and a std Alfa airbox leading to a CDA filter cone filter box with a 100mm convoluted tube leading to the air intake in the bonnet. See pic.
3. Swap intake for 60mm long Delorto trumpets. Lots of nice noise! Loss of power and torque everywhere until 6300 (where the airbox system was tailing off). Torque hopeless from 3000 - 4500 rpm with about a 10lb/ft loss.
4. Swap 60mm trumpets for 25mm trumpets. Exactly the same result in both power and torque as the 60mm ones. The lines on the graph were ptreet much identical.
Conclusion - unless you want the noise, stick with the std airbox. Mr Alfa didn't do a bad job after all!!
We ran a Minari with a completely std 1.7 8v hydraulic engine with Maniflow exhaust with about 100,000 miles under it's belt. Peak power was 104bhp at 5700 but with a virtually flat torque curve all the way from 2500 to 6000rpm.
Another Minari with a race tuned 16v unit gave 175bhp at nearly 8000 rpm but was producing less power and torque than the 8v engine above until 5200rpm Above 5200rpm the output really took off and held well over 8000rpm.
Great for a race track - crap on the road!
Interesting results and a bit of a rethink on my part on the value of trumpets!
Last edited by markp2; 19-04-10 at 20:59.