308 carb airbox restriction discovered

I always understood the length of the inlet pipe was important. Something to do with the negative pulse when the valve opens travelling up the inlet to the open end, to be reflected as a positive pulse back down the pipe, to arrive just as the valve is closing and cram an extra charge of mixture into the cylinder. Hence the complicated variable length inlets we see nowadays. Long pipes for low speed changing to short pipes at high speed. As Russ says, the short trumpets should move the power range to a slightly higher speed.

The airbox here might just be holding the air filter. I thought a Helmholz resonator was an altogether bigger volume, but then I might be talking cobblers....

 

"Simply put this short stack concept is nothing more than snake oil (no matter who made it) and it has no basis is engineering (Voodoo engineering? yes) and ZERO FACTUAL DATA to support the claims being made in this thread. Remember split fire plugs they didn’t do what they said they would (create HP) but they didn’t harm anything, what you are promoting creates real world changes that you know nothing about and may ultimately do the reverse of what you are promoting. You have changed intake runner length for possibly only a static HP gain. God only knows how lean the car will run at speed in the real world or for that matter how rich it will run with your jetting changes.

You may make a 1000hp on a dyno but it is static and front-end intake airflow modifications are anything but static!"
(posted by sloan)

The issues are simple yet the answers are lacking any real response to the questioning.

All this HP gain in a static Dyno test where there is NO AIRFLOW into the airbox, hell you could take off the top of the airbox and get a HP increase that’s a no brainer (and you would save $150) but what happens when you are now doing a 80 mph and air is being press into the airbox AND YOU HAVE SHORTEN THE INTAKE RUNNERS?
The 308 already has a short runner setup and now you are shortening even more which substantially limits the ability to absorb reversion as RPM's increase. Shorter runs limit the ability to reduce turbulence as well.

I am now repeating myself so lets again cut to the chase;

The theory is flawed with regards to the 308 as it has a short runner setup to start with.

The engineering is non existent especially now after the brilliant response ("defense") by the manufacture that shows that there is no engineering data to support such a set up on this car and no data that shows how it increases HP or torque under conditions outside of static (and his web site #'s contradict his posts). And there are so many conflicting results that God only knows what is real.

What is more amazing is that the manufacturer’s web site claims 12 HP gains with only a one up jet change on top of the stacks.
"We started @188 HP and as testing went on until we were finished at 200 HP we found the only change necessary was a main jet size one richer than we started with." (from the web site)

What is the HP Gain? Every post is different from the manufactures own web site even the manufacturer post #’s that different from his own web site Numbers and then Spasso says that you can have fluctuations of 5% per run, now 2% and next he’s not sure. (and then there is hankum who keeps talking about tagents and worms???)


I wrote my post so that those who might believe that these changes may be harmless and to show that those promoting them have no knowledge in what they are doing (outside of the snorkel restrictions).

SHORTENING OVERALL INTAKE RUNNER LEGNTH IS NOT SOMETHING ANYONE SHOULD DO WITHOUT TRUE KNOWLEDGE OF ITS OVERALL EFFECTS ON THE ENGINE. PROMOTING SUCH CHANGES WITHOUT KNOWLEDGE OF THE CONSEQUENCES is irresponsible.

There has been no response so far that addresses the legitimate issue’s that I raised. But yes the attacks keep coming.
Actually the responses I think prove my point no one has a clue about what these things really do in reality let alone on a dyno, everyone seems to be hypothesizing.

So if you want a 4 hp, or a 6 hp gain or a 9.4 hp gain or a 12 hp gain these stacks are the ticket but remember just stay on the dyno and don’t forget to make those few other changes as well. The dyno data supports all the #’s

Paul

 

paul, your killing me here! give me something tangable, something revealing, something that initiates or provocs the thought process. Ple-e-e-e-se

Thank you in advance

Gary

 

Just want to say thanks for all the ideas... got up the courage to do the air box mod and bump up the mains to 135 on my 1976 carb car....Tried it out using my Gtech toy...average over 10 runs..I'm almost 0.2sec faster from 0-60mph ..!! Very cool and it cost almost nothing. Now, if only I can master this 1st to 2nd gear shift, perhaps I'll crack 7 seconds some day...Wonder if a high flow filter will make a difference now that the air can actually circulate around the box..?? Thanks again....

 

The answers are there grass hopper. You just don't want to see them.

From whom? Not me, I gave up, You won. You were right. You have proven your case. Your knowledge is just too overwhelming for my meager "backyard" education. I couldn't possibly have a clue what short stacks do to the power band of an engine. I'm just too dumb. I'm sure you will straighten everybody out.

 

Even with the box, I found a 5 rwhp dyno difference between paper and K&N, so I'd guess 'yes'. You'll notice the sound change as well - it will sound like it's flowing.

Gary and Ham
Good points and questions all round. I'm still learning and experimenting (what fun) which is how the airbox obstruction was found in the first place.
From a Ducati Website:
Quote:
The air in the plenum is also considered "free air." That is, its already passed through the air runners and filters so it can be supplied to the engine without any flow restriction. If you use the auto industry's standard calculation of air required for "nil" vacuum restriction within the air intake system, you should have at least 130% of engine capacity in available air volume between the throttle butterflies and the air filter element.
UNQUOTE

I believe most of what we are seeing is the plenum effect of the airbox and it's ability to provide a ready fill of air to the throats. In the original 3 liter application, that volume would be 3.9 liters, or about a gallon between the butterflies and the airfilter. Probably pretty close. The ability to fill that plenum space easily through aggregate vacuum across a wide filter area is one thing this thread is all about.

Also, something I connect in my mind as a factor is functional air velocity and columnization in the inlet tract, which I was taught was a function of both venturi size and inlet tract length - velocity being inversly proportional to choke size and directly proportional to inlet track length. And this velocity manifests itself to the driver as throttle response and low end filling. So, signifigant reduction in length of the track could reduce velocity which would reduce throttle response. Likewise, a smaller venturi will increase velocity and improve response.

It's been pointed out in many Alfa threads that Webers are sensitive to the volume of air above the air horn - i.e . more space the easier for air to smoothly flow in due to less sharp angles, i.e. straight fluid resistance. I've seen this myself in comparative back to back dynos of open airboxes versus airboxes without filter elements. The open horns were about 8 hp in my application as I remember.

So, things we are balancing here in this thread are the resistance to cool air flow from the scoop to the air filter, available filter area to fill the plenum, aggregate vacuum providing a better flow across a filter element (single large vs individual air filters), space above the air horn to allow good inlet flow angles and columnization, and matching pulse frequency to inlet tract length to rpm power range.

Something to think about.

 

Now we're getting somewhere! Exactly my point--why would I (or anyone) spend hundreds or thousands of dollars on a 25-year-old Ferrari (or anything else) in dyno time, parts, etc, to gain 10 or 15 or maybe 20HP when atmospheric conditions alone can give or take 5% or more...or does that, too, not conform with all the experts' opinions??? Maybe "density altitude" is a myth also. Bottom line-if it feels good, go for it. Just don't try to convince me that your opinion is fact without science to back it up.

 

Steve,
How did you like the sound??

Birdman

 

The discussion has long since departed that aspect of the controversy. All opinions and speculations have been retracted so why are you dragging this out?

For the sake of solid information why don't we quit whipping a dead horse and listen to the contributions made by the other people willing investigate the issue objectively. I believe Russ' analysis is with merit and supported by hard data as well. A great learning experience.

At the risk of repeating myself,
Finding and removing a factory designed and installed obstruction (including limited clearance at the top of the velocity stacks) in the induction system isn't seat-of-the-pants as much as simple logic. The engine needs air to run. The more the better. Once the available supply is increased then the fuel delivery can be increased to take advantage of the plentiful air supply. The result MORE POWER!. Not IF but MORE.

If you don't like the proposed modifications or disagree with them, great! Don't do them!

 

I don't think I understand your point.
Is it "since the car will have good days and bad days, no point in making a change that can't overcome atmospheric conditions"?
So the only changes that should be made are those that are 50hp or more?
I really don't understand either (1) your statement of exactly your point because the interpretation I offered above is unfathomable or (2) your point of view. If I live in Colorado, I'd might as well still hotrod my car if I'm not satisfied with its performance, because that Porsche next to me is breathing the same air I am. The Ferrari F1 team downloads optimized programming into their ECU before the race based on the ambient conditions, no reason the rest of us shouldn't try to extract all we can regardless of the conditions, too. We're just not likely to change jets every day before driving... :O

 

I love the sound...louder and throatier than before, yet far from overwhelming..I find it quite exhilarating...nothing at all like the riced out hondas around around here that sound like they're being chased by swarms of bumblebees...I've ridden a Harley for many years because it felt special..same great feeling with the Ferrari..it's special..!!!! I think it likes being able to breath better....By the way those fuse boxes made a huge difference...especially in terms of enjoyability.....

 

No one is trying to "convince" you of anything, the whole point of this site is an information exchange. You can take or leave what you like, everyone on this thread has been pretty clear on what is fact, and what is opinion/conjecture. If you don't like it, skip the thread and move on.

People spend the money and time on 25 yo Ferraris because that is what a Ferrari does to you..makes you passionate for the car, the history and the performance.

 

Now this is interesting, I am also like you going to give it a go just removing the sound deadening and bumping up the jets. If it gets me a bit more pep for next to nothing then I am happy. Out of interest how much was the Gtech toy and are you happy with it? I would love to actually know how fast my cars and motorbikes really are.

On another note it seems to me that a lot of people are very interested in this airbox subject. Surely with all the great minds around it must be simple to build and market maybe a more efficient carbon fiber box or fiberglass box for a reasonable price???

 

For those of you who have just tuned in:

So far in this thread, we have seen that there probably can be recaptured rwhp (10 - 12+) from removing the very flow restrictive sound deadening mesh and packing in late 308 GTB airboxes. This hp gain is added to further perhaps on the top end by using shorter velocity stacks (although disputed - see below).

The sound deadening mesh with it's fiberglass packing is easy to remove, and several FChatters have already done so. Spasso, a well known Tech Section overachiever, even brilliantly built a beautiful air snout extension ( http://ferrarichat.com/forum/showthread.php?t=50136 ) to further promote cool airflow. His initial driving impressions did indicate a possible secondary lean situation with the stock jetting that was addressed by richening the carb jetting (see below). He described 'running out of umph up high, which would be consistant as that is where the flow improvement would be most notable. His subsequent dynos showed a hp increase over one a year prior. Steve 308 showed a decreased 0- 60 time after the airbox modification.

With the removal of the sound deadening material, the Weber induction sound is much more pronounced, over the stock box, but not as loud or raw as the individual carb filters. Important to note that one FChatter removed the insulation and then found the intake noise too loud for his tastes, and will be reverting to a muffled box.

Webers are well known sensitive to the amount of air above the air horns. Shorter velocity stacks act to increase this area allowing greater high end air flow, possibly at the possible subjective cost of a little lower end umph. Dynos were posted suggesting around a 5 - 6 rwhp improvement.

With the increased airflow comes the possibility that the carburators will need to be richened, probably by going to 135 - 140 main jets at a minimum. The proceedure to do this is documented here:
http://ferrarichat.com/forum/showth...g+weber+jetting
I personally would add a richer (smaller, e.g. 190) air correction jet for the top end where the flow difference will be most pronounced.

The proper re-jetting of the carburretors to take advantage of the increased air flow was discussed at length. Corraborating a previous experiences, Spasso now found almost 10 hp over a previous year's dyno from now using the airbox and short stack mod, but needed to increase his Weber main jets to 140 to cover fuel availability for increased flow. This gave an air fuel (A/F) ratio in the 12s, while best power is in the low 13s. He is now looking at going to a 135 main and a richer air correction jet (200 to 190) to approximate an A/F in the low 13s and ensure fuel availability in the high rpm band.

The most often recurring side discussion seems to focus on some folks doubting any real gain from the mods, or even if they are worth it. Several have pointed out what they feel are serious flaws in the measurement of the results. The word 'science' was even used. Very emotional positions ( about an airbox!) were arduously presented on both sides much too long to be recounted and inflammatory remarks made.

My take as thread starter: Bottom line is it's just a car, nothing is for sure, pay your money and decide for yourself what you think weighing the data and arguments. It's all about having fun with these wonderfully passionate automobiles anyway. Ironically, the most vehement disputer has the most modified and beautiful carb 3.0 qv project around.

Based on what I have seen on my own dynos and experience with this modification combined with others, I personally feel that there is definitely demonstrable better airflow (and some more power) from the airbox modification and shorter velocity stacks, and a more beautiful passionate sound of the unmuffled Webers. Some would disagree, and I'm no expert, but this is what it looks like to my best judgement.

best to all
rt

 

Russ,
Said like a true diplomat!! Great synopsis...

Regards,
Dave

 

"Porting is not worth the time and money when you can get more out of tuning and at a lower cost" - A guy whose never ported or seen the results from porting.

 

And for the next Ferrari high-flow cool air mod 'at the touch of a button...':

http://www.andylaurence.co.uk/full.pl?image=CRW_9268_JFR.JPG

Happy Easter!
rt

 

Wow, what a cool spoiler that guy has! Where do you buy one of those?

 

I'd just like to say thanks to RT and Spasso et al. I've been reading this thread from the start and have been inspired, I removed the fiberglass wadding from my airbox and have been amazed at what a glorious sound has been released, so much so that I no longer have a desire to upgrade to a sports exhaust! For the time being anyway.

I have also stripped and cleaned my carbs, something I wouldn't have had the confidence to do without this post.

Its because of posts like these that I decided to subscribe to this site.

Cheers
Scotty

 

Hey Birdman,

Buy a 308GT4 (or Mondial by the looks of the photo), pull on the engine cover latch, drive at high speed and in the rear view mirror you will see the automatic nature of that spoiler. (I did it by mistake once , never thought of it a s a feature until now). It helps to have the lower air baffle in place, it acts as a scoop to get cool air into the engine bay from below the car.

Yet another reason why 308GT4's rock!

Gerrit
http://dino308gt4.com

 

Didn't you know your MondialQV already had one - LOL!!!!!

 

I guess TECHNICALLY the 308 has one too....it's just "oversized"!

 

Scotty
How terrific! I'm glad you took the plunge and are happy with the results. Also, don't be shy about posting pics of your own 'Canterbury Tale'! We're all in this together and would love to see your version.

The sound difference is really amazing, isn't it? More than I would have ever predicted.

best
rt

 

For the person asking what the timing was during the last dyno pull on my car, +6 degrees static timing as illustrated in the Workshop Manual

 

Thanks for remembering!