Airhorn lenght.

[kokkolanpoika]

I have got 5.2litre RV8 and car is Rover SD1. I´m fitting Jenvey throttle bodies in it.

Problem is airhorn/bonnet clearance. Airhorn is 40mm long +19mm spacer top of the throttle body. So i measure that i have got only 20mm clearance with airhorn top and bonnet with 1&2 cylinder. So i cannot fit any type of filter or airbox without change airhorn´s to approx 19mm long. Or make scoop/power bulge to bonnet.

So question is. Is 19mm long airhorn to short for RV8 witch will rev approx 6300rpm max? If i use 19mm long airhorn, then i can use 2x big air filters or make deep airbox. Power output "hope" with throttle bodies approx 360-370hp

Total lenght of inlet manifold/head mounting face to air horn top is approx 250mm. And i measure STD 3.9 V8 manifold inc 45mm trumpets, lenght is approx same.

So any experience/dyno testing to recon air horn lenght. Local Jenvey dealers say´s that try to stay with 40mm air horn. Usually always better than short airhorn.

Or any idieas how to make nice scoop/power bulge to SD1 bonnet.

[topcatcustom]

Hi Timo, I'd have thought that the radius of the lip around the entry to the TB's is more important, your 250mm length means that the extra 20-40mm on the top won't have a massive effect, so I'd go for shorter ones with a really good 180° 1/4" radius around the top, this should smooth out the flow a treat.

Dont take my advise for gospel but thats what I'd try! What are you doing for filter?

[kiwicar]

Hi Timo
It is a case of what you want to achieve, if you have a gap of 1.5 X the trumpet diamiter or greater between the top of the trumpet and the underside of the bonnet, or any flat plate, say an air box it is effectivly infinatly far away as far as tuning is concerned, less than that then it will reflect pulses back into the inlet tract at different points in the rev range. If you are thinking about the length of a feed into a common plenum then you need to work on whole number multipels of the inlet length for everything to reinforce any shock wave tuning, for straight forward ram tuning then it is a case of try it and see, sorry can't advise further.
for bonnet scoops and bulges, have a look at Perrys MGB pictures!
Best regards
Mike