308 carb airbox restriction discovered

I reduced main jets back to 135's and reduced the air correction jets from 200 to 190 to richen things at the top end. It ran very well on Saturday. Very responsive.
Still trying to arrange another dyno session to verify the final A/F ratio. Previously it was about 12.3:1 with the 140 mains and 200 A/C jets.

 

For those who are interested...I just bought individual filters for each carb and will be testing the air temp around the filters. I realized that I have some Hobo Loggers (remote sensors for sampling temp, humidity, & light). I placed one on one of the filters last friday night and drove home from work (25 miles). Unfortunately, the vibration casued it to drop down in the valley between the intake manifolds. I'll tape it down next time. I'll report back as soon as I get some info.

Henry

 

Spasso: You're still running cats, right?

After I went to the individual filters on my 308 (mainly for the sound and the look) I added a 5" hose from the passenger side intake dumping out right at the intake.

Don't know if it will help (I have not noted any problems from hot air anyway) but assume it can't hurt...

Bill

 

Hi Bill,
No cats. ANSA sport exhaust.
Nothing wrong with the hose trick. I would do the same for what it's worth.

 

Then I will be very curious to see how the 135's show up on the dyno. I jumped directly from the stock 125's to 140's (staying with the stock tubes and AC jets, but bumping the idles up a size) when I went to the open filters and the test pipes in my '78... made a world of difference in the car, but at no time (other than a tad at idle) does it seem overly rich.

However, I have not done the dyno pulls and A/F measurements you have... just wondering if I might need to try at set of 135's myself...

Thanks!
Bill

 

Mine ran fine with 140's on my last dyno, it was just a little rich. I would like to get it back into the 13's.

Last year with 125's it ran 14.5:1 A/F ratio, just a bit lean.

 

Here's what I got. The outside temp was about 65 degrees. The car had sat for about an hour. I placed the sensor on the filter (about 74 degrees). Started the engine and begin driving (rose to about 79). Short drive about 3 miles (stablized about 69). Car sat for about 40 minutes (hot soak to about 110 then started to cool off). Started car and got on freeway 80mph (stablized around 70). Sensor fell onto the block (rose to about 165).

I'm going to try this again and see if these numbers are consistant.

Henry
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I am thinking that on cooler days the separate air filters wouldn't be an issue. When it is over 80 another story.

Curious to see.

 

Yeah, I'll see if I can sample a few more times during different temps. I would think that the temps would also rise during stop and go, but then I don't think losing a few hp from the temp would make a whole lot of difference.

 

The days have still been pretty cool here so I have only tested the engine bay temp once more. Once on the highway, it only seems to be about 10-15 degrees warmer than ambient. When things warm up, I'll try again.

I have been thinking lately about making my own airbox. Now that I have the individual filters, I was thinking of getting some sheet metal that would mount under the filters (like the stock airbox) and then bend up the sides to make a open top box. I could put some foam around the edges that would seal up on the bottom of the engine cover and then connect to the side opening. This way I would have the benefits of the cold air intake as well as the greater surface area of the individual filters.

Whatcha think?

 

Hey Boys,
I got the guts out of mine yesterday and then ran out of time so I haven't put it back together again. Man, there is a LOT of fiberglass in there. Looking at the airbox, at first I was thinking this was some kind of cheesy post-design "fixit" thing in order to reduce the intake sound to meet sound requirements. But the more I look at the airbox, that huge area below the snorkel seems like it was designed from the start to hold insulation. Perhaps the design was done to minimize some kind of resonance. I guess I'll find out! But there was no way air was getting around the obstruction to the rest of the filter. You can clearly see that the baffling comes right up to the filter so only a very small amount of the filter is getting any air. On top of that, the majority of the filter is clean except for the one "patch" where the air goes through it. I took a pretty good picture to illustrate it. I'll post it tomorrow. Can't wait to hear how it sounds!

Birdman

 

Take care of yourself over there, and don't forget to check six.

 

I know this thread has moved past the initial subject, but since I was slow to get my guts removed, I'm slow to report back.

Russ=genious!

DAMN! DAMN! What a sound! WOW! Impressions:

Passenger window down: So THIS is what a 308 is supposed to sound like! Yeah, an exotic. That's more like it! It's a bit louder, more mean sounding. It still makes the same sounds it always did, just better, and a little louder. It's not deafening or anything. In fact, the big difference seems to be when you get on the throttle. On a trailing throttle or cruising speed, the sound is only a little louder. With the window closed, the sound is not much different. (I haven't hit the highway yet, so maybe at highway speeds I'm wrong.) But when you nail it, holy **** what a sound! VROOOOM!

The throttle response is better. I'm definitely not imagining it. Just blipping the throttle in the driveway you can tell that the engine responds much more quickly to throttle input. It's finally breathing the way Enzo intended.

I only took a short drive around the block. I haven't really warmed the car up and revved so I can get an impression at high RPMs. We have an Fchat drive this weekend, will report back.

I got a few intake pops that I didn't have before. Might need to jet for this mod. It wouldn't surprise me. This must easily increase the useable surface area of the filter by a factor of 6. The engine is DEFINITELY getting more air.

One FChatter had reported not liking the sound so I had reservations about permanently gutting my airbox. When I pulled it out, only to see how much it was obviously restricting the carbs, there was no way I could leave it. They defintely threw some kind of quick band-aid solution on this thing to make it quieter. Poor Enzo. Must have killed him to have to do that to his beautiful creation to pass some silly noise spec.

This is a good, solid mod, easy and cheap as dirt. Can be done soup to nuts in a couple hours and 100% worth it. I give it the five shark thumbs up.

The magical 255 HP draws closer....

Birdman

 

I think that is a great idea. You could make it out of lightweight aluminum and powdercoat it wrinkle black. It would look cool! You could also duct in from both sides, assuming the oil cooler could live with half the airflow, not sure. (You would have to split the left intake between the airbox and oil cooler to do it I would think).

Either way, you get the benefits of both individual air filters and the cool air effect of the airbox. Not to mention, the nice weber sound ducted to your ears through the intake that you don't get with individual air filters.

If you are going to do that...wouldn't it theoretically be possible just to use a taller air filter that looks like the stock one? IMagine the stock air filter, twice as tall, with no top on the new airbox, sealing against some foam on the inside of the bonnet.

Birdman

 

Umm, I don't think it'd work out that way. The air flow will take the path of least resistance. With a partial vacuum on the inside of the air filter, and the filter's large surface area, I suspect that very little air would end up going thru the oil cooler. Not a good idea as these cars depend on the oil cooler as well as needing all the cooling they can get in general. Cooling is not as critical here in NE where we seldom see truly hot weather, but on a southern track in 90+ weather you don't want to loose any cooling capacity.

Maybe installing a suction fan on the oil cooler would compensate. Remember a nice thread a while back about someone installing one.

 

Let's not forget about engine roll....

 

Turn your idle screws out 1/2 a turn (unless it's on throttle and not during idle conditions).

 

OK, I finally bit! Gutted my airbox and I must admit (VERRRY SUBJECTIVELY) that the car is much happier. Somewhere around 4500RPM the difference becomes noticeable right to redline--definitely more air getting in there. As for the sound (noise?-not), excellent! More of a "ripping" sound but no noticeable resonance or vibration noted. There was a ton of insulation--what a shameful restriction to put in a high-performance car.

 

It was doing it at 4K RPM on a long right hand curve. I can't seem to reproduce it now, so I think it was a fuel starvation thing. I think I have a sticky float valve in one of my carbs. Not the first time this has happened.

Anyway, I doubt that there would be enough difference in flow at idle to change jets or idle mixture. (Remember that the mixture screw only affects the first progression hole, not the entire set of holes). I would think the only difference would be at high RPM.

Verell, I didn't think of that, True!

Don, I didn't think of that either.

Birdman

 

Heck, just make a cutout in the bonnet, install high rise intake horns or a ram air scoop like the F1 cars & it'll be a 'shaker'...

 

Here is the best pic I could get looking into the snorkel at the filter in place. The air cleaner section you can see is the only part getting air! That's not much air filter area for a 3 liter engine at 7K RPM!

Birdman
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Hey Henry,

Looks like great work on the temp issue. Do you by chance have a remote pressure sensor to finally deliver some hard data on air intake scoop/ram effectiveness.

Seems to me you could take readings inside the stock air cleaner with the pipe hooked up, maybe at 30, 60, 100mph and compare those to similar mph readings with the 4 filter set up in place and the sensor suspended inbetween the 4 filters.

Temp readings at the same mph points, with the two cleaner set ups would also be interesting.

Just a few questions I've been thinking about.

chris

 

I think the limiting factor here is going to be the space availability under the engine cover. I'll let you guys know what I come up with. Unfortunately, I'm in the middle of putting down wood flooring in the kitchen & dining room right now. I need to get all the house stuff done before our first bambino, due to arrive 8/20.