Power loss at air filter

I am now noticing typically 10+ hp rwhp loss using a K&N filter with a stock 308 Ferrari airbox as compared to open carb trumpets on back to back same day chassis dyno runs. Paper filters are a little more yet by my dyno comparisons. The back-to-back loss has varied on different days with different jetting/advance/exhaust, with as much as 20 hp this week. Is this everyone else's experience?
I know the advantages of cool air from the scoop, but am really considering a different filtering system. My hyper experienced racing dyno tech said it was time for the hole saw. I have seen some 308 racers with separate carb foam air cleaners.
Has anyone used aftermarket or custom air cleaners with success over the stock box?
Any advice cheerfully considered.
thanks
rt

Russ, I think this offers us the opportunity to put our collective minds together,
and design a better box!

My thoughts include not just feeding cold air from the right side scoop, but the left side scoop as well.
Maybe a carbon fiber box, with Dzus fasteners for easy removal of the top, for quick access to the carbs and easy removal of the individual K&N filter elements.

Hi Russ,

Have you tried adding a spacer to the lid of the stock air box to raise it up a little farther away from the stacks to see if it is too close to the stacks causing the HP loss?

JRV
Many thanks. Actually, I think you are exactly right at one reason for the power loss. While the K&N showed a loss of say 10 hp over open trumpets, I did a dyno run with a closed airbox and NO airfilter and lost 5 hp. The diffulty is the runners sit higher than stock, and the top of the airbox cannot be raised anymore. One idea was to run with NO airbox lid and let the bonnet act as the top of the airbox giving the maximum area possible and use seperate domed racing foam air cleaners for each carb mounted inside the topless airbox.

I have driven aound with open trumpets and NO airbox, and doggone it did feel peppier. I know Superformance and Pierce Manifolds sell trumpets with screens. Man, that would look cool - perhaps this cold air thing is over rated. Perhaps not. In a mis-spent youth I had an Alfa 1750 with twin 40DCOEs with wire air screen trumpets that I would cover with KMart baby socks that worked pretty well - and holy #$%@ what a sound. Perhaps an answer would be to run the screened trumpets in a topless airbox sealing against the bonnet like a 250 SWB comp.

Philip Airey has given me the specs on the 308GT4 LeMans Airbox from the racing car. Will look that over also.

May just have to bite the bullet on this one for engine protection.
best
rt

After plowing through the dyno graphs and other filter options, I think 10 hp or so is just going to be the "cost of doing business". I am vertically challenged spacewise and really do not want to modify my bonnet. I would like to keep the stock cold air ram (minimal as it may be). Interesting to note that, using formula numbers, even if my temperature delta was 48 (e.g. 70 ambient, 118 underhood) degrees, that would only be a 4 hp penalty assuming minimal resistance individual carb air filters. From a cost effectiveness standpoint, making another airbox wouldn't buy me that much on a street use car.

I do jet the carbs on the use of my car, which is on the street with a filter. However, as the graphs in previous dyno runs have shown, the hp output does not change much at all for this engine under a fairly wide AF range of low 12s to low 14s (I've never gone above 14.5). My current jetting (40DCNF-12/36/140/190/55/F24*) on the chassis dyno will keep me pretty much between 14 - 13 under full load in 4th gear with a K&N air filter from 3000 tip-in to 8000 rpm (I have seen 3.2 Kjet dynos that hold the A/F at 14.5 or so the entire range under load, which is pretty impressive). On a recent trip between DC and Newport News, she got about 17 mpg cruising at 70 mph (+/- 10!) which I think is probably ok. She may be a bit rich at cruise as the family behind said it 'smelled' (and was loud, but not as loud as with the tubi). This mpg is almost what she got with the Kjet (closer to 20). Probably closer would be a 145/50 combo to correct for a possible cruise richness, but will need to buy one of those cool A/F doofers Pelican sells when I get resettled.

So after it's all said and done, I'm pretty happy with the 20+ or so rwhp, reliability and DIY service improvement with the current set up. I've yet really to experiment with the advance as I am in the middle of a move, but will next do runs to max advance of 32 (stock), 34 and 36 degrees once I find a dyno in San Antonio; am still waiting on the cams after some tumultuous grinding events; Will look at rejetting when they go in whenever that works out (if ever).

I will also pass on that, thank God above, the nuts that hold the airhorns on are magnetic - ask me how I know.

best to all
Russ

* after many $$ dyno runs; donations accepted for passing these settings on.

About the HP loss. Have you tried using a vacum guage around your intake system? IE before and after the air cleaner/with/without top?

I have a 81 308 gtb/i and am about to test various points to see what the various restrictions are. Did you do this with the K-jet before installing the webbers?

I'm all for keeping the standard airbox..... the trumpets do run rather close to the airbox lid but while spacers and a little modification might help, depending on how much clearance there is, there's not much that can be done there.

What I do wonder about is removing the restriction from the cold air entry to the airbox. i.e. grinding off the welds and removing the silencer type tubes and all the sound deadening material. Has anyone experimented with this? Any useful conclusions?

OK
I've had it with this hp loss at the airbox & filter. Best I've read, the hp loss due to the heated engine compartment doesn't even come close to what I'm losing now. Part of the loss I've figured out is to some flow/pressure variations inside the box itself, perhaps some reversion. Came down from an open top max rwhp of 238 SAE hp (flywheel 290) on STOCK fi cams, so want to recover some of that.

Time to radically experiment.
That's right - I'm going to sinful meshed trumpets with a bit longer velocity stack (better midrange response) - may keep the airbox with the lid off to nullify the plenum effect, but still maintain a cool air source. Will run foam covers on them when I go on a trip.
Even if I break even on power, it'll be much easier to work on, look pretty wild and no doubt sound wilder. And I can always go back to what I have now.

Did I memtion working on Ferraris is fun? It really is.

best
rt