Low Profile V-Stack Install Mods Update-308

I just finished the modification of an airbox and installation of Kermits Low Profile High Flow velocity stacks for my 308. Because the two banks of the engine are offset from each other resulting in an offset layout of the carburetors I had to modify two of the V-stacks to clear two of the corners of the stock airfilter element. The base of the new stacks are larger encroaching on the footprint of the air filter element in two places.

The interference takes place on the forward LH corner and the aft RH corner. I trimmed 1/4" from the overall length and recontoured the corner and lip.

Here is the thread and discussion on the airbox modifications to correct an engineered restriction that SUCKS horsepower.
Airbox Restriction Mods
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While the stock paper filter has a metal screen and is ungiving, a K&N air filter has no metal elements thus is more pliable and requires no machining of the low profile high flow stacks ('shorties').
Great job, DJ - I really like the custom snout.
Looking forward to your drive report - if it was like mine the differece is remarkable.
best
rt

 

Spasso,
You should approach this one variable at a time....first the modified air box, then add the short stacks, so you can tell us if the short stacks make a big difference!

(OK, now I'm being a pain, sorry)

We look forward to your drive report!!!

Birdman

 

You are absolurely correct. From a scientific standpoint that is exactly what I should have done.

Unfortunately the car is about 18" off the floor on jackstands while I do other work on the car, wheels and tires off to clean and wax the backsides, wash the suspension and inner fenders, repaired damaged coolant tube courtesy of the alternator pulley, pulled and rebuilt cooling fans, pulled grill to repair the gapping hole left by the old SuperFox radar, add drain tee to the heater hose below the steering rack, replace the thermoswitch in the bottom of the radiator while I was in there, oil change, top off transaxle and install sound system.

It takes a lot of work to put it in the air so I am making the most of it.

My guess is simply gutting the air box would make a LARGE difference. The only dirty part of the filter was right at the entrance to the snorkle so you can guess how much restriction was there at that part of the housing not to mention the reduced diameter of the inlet tract itself.

Don't forget, I'm talking about a '78 emissions box. I think the early boxes were better as is, less packing etc........

 

Spasso,
I was only razzing ya! I'm just glad that you are doing this experiment and saving us all having to experiment ourselves. Once you get it all figured out, I'll just do whatever works out best!

Too bad you don't love closer, you could use my lift. Since I got the lift, I simply can't imagine working on jack stands anymore! UGH!

("Jeez, I gotta bend over to reach that nut. Nah." (pushes buttton and car goes up another foot).

Birdman

 

I need a little razzing once in a while. I would love to have a fellow 308'r close by.

Actually I have a new lift, a new garage too but I can't use it during the winter due to it's unfinished state and freezing tempuratures. Summer yes.
The Project That Won't Die!

No electricity/light or insulation in the building so I am using my old setup in the basement. I pray this will be THE LAST TIME I have to jack this thing up by hand!

 

Thanks Russ,
The inside is shaped the same as the outside. It should flow pretty good. With the better breathing and change from 125 main jets to 135 main jets it ought to wake the Oldyellowone up a little.

 

Hey, hey.

This is a family site here...let's keep it clean

Really though, thanks to DJ & Russ for exploring these issues.

Henry

 

Spasso, nice mods. i believe my car wants 135's with the open individual air cleaners. i am very tempted to try the shorties also. guess i need to make up my mind to sell the GTB or keep tinkering and learning from it!

 

Russ is quite right in that they are a drop in with the K&N element.as that is what they were tested with. I cant help but wonder if the stock element couldn't be "coaxed" into conforming to the differances in corners tht is evidently the issue with yours. I would surmise that the inside radius is different in the MFG's elements. Sorry to see it caused any problems.
And Birdman, I agree completely that a more broken down, individual test procedeure would have been nice, without a doubt. As it was the dyno shop was threatening to put a time card up for me, and @$75.00 a pop, it gets expensive.
My observations are that the LPHF, and the air box rework were about an equal part of the increase in HP.
Kermit

 

Did you ever get dyno numbers for your throttle body bore-out mods on the QV/injected cars?

 

A '78 or '79, I'm told, is underjetted from the factory and would like at least 130 mains in an otherwise completely stock setup.

On my stock engine I removed the cats and went to the individual K&N's... they recommended 140 mains and .60 idles (up from .55) and that indeed feels spot-on. (And the sound is so much more exciting I'd have made these changes even if the performance had not also noticeably improved.)

Bill

 

Mike , One the 70mm TB's, I have two almost ready for dyno tune, and both are running 70mm TB's. I bought one of each, 4 valve and one two valve model from Bill @ Gt Car Parts so I would have one stock size ready to change out while on the rollers, for an acurate set of numbers on both. AND a set of KV's on Both that wil be getting the same before and after right then and there, as in both cases, the R&R time isn't much. Look to see it soon, as I want to get these sheets out for all to see!
For the record, the 4 valve is an '85 308, while the 2 valve is an 82 Mondial.

Bill you are in my experience right on the money on the jetting issue. The 308 I used to test had ported heads, etc, and was happiest with the jetting you use, although it was a tad on the lean side @ an average of 13.2 to 1 A/F ratio,across the board.Send me an E-mail@:
[email protected]
And I can send you the fuel curve readout from the roller runs if you wish.

 

I tried "racking" the element to get around the two prominent corners but it caused a bad fit around the top. The element is a Baldwin and may be thicker than the OEM and/or the K&N though I am not sure. It most definately is not very flexible.

I wonder if this 1976 box has different clearances.....................

It was no big deal to shave the ends and recontour. The filter just drops in without being preloaded, just like it was planned that way.

You may get a chance to see/hear it this Saturday when I do my shakedown run.

 

Mine had 125's, no cats and ANSA exhaust, around 14.5:1 A/F ratio on the dyno last year. LEAN!
I went to 135 mains. Stock style element. It may still be a bit lean but then I won't be loading up or fouling plugs in town either.

 

Hey, that's why NGK makes the BP5ES!

 

I know you know this, but in town you'll rarely be on the main circuit and the classically rich Weber idle circuit (intentional for smooth transitions) is the 'usual suspect' for plugs fouling. As example, using my handy dandy portable LM-1 A/F meter, much of my around town and highway A/F (less than 3500 rpm is still mostly on idle circuit) is in the A/F 12s. An MSD or hot coil in addition to Dave's NGKs helps keeps plugs clean for sure!

Wcelliot, I may be wrong in your application, but .6 idles in my experience are quite overrich for a 40DCNF 308 with stock cams, although they will be no lean flat spot in transition - that's for sure! I definitely do agree with 140 mains, and these have been the favorites among many threads in the past. Indeed, 140s also work well on 3.2 liters!

For A/F ratios, very high 12s or low 13s are what I was taught was best for power, but my dyno experience shows the 308 tolerates quite a bit of variance with similar output. As to A/F 14+ in real world operation, I was so impressed by a stock Bosch Kjet 328GTS dyno which at wide open throttle (WOT) nailed the A/F at 14.5 the entire run delivering rated output and meeting emissions. While K-jet is certainly not the best system for performance max power and response, it is mightily impressive for accurate fuel delivery and emissions!

Just my experience.

 

The car came stock with 55 idles and 125 mains... you're saying that you'd leave the idles alone even after going to 140 mains?

Bill

 

Yes - the idles are only working below 3500 rpm or so; The 140 mains take over after that where your power band is. So when you punch it at around 3500 - 4000, after the the accels fire for about 3 - 4 seconds bringing you above 4K the mains are going to be full in in the low 13s/ high 12s giving max WOT power.
And you'll still have that famous Ferrari fuel economy down low!

best
rt

 

Without wishing to divert this thread, what do you see Russ?
On the street, I usually get 10 - 11 mpg. May get more on longer trips, but I don't tend to do these (it gets trailered). Track about 5 - 6 mpg at best.
Philip

 

Man, I must be losing it. Yes I knew that. Just not thinking.

One question I've been pondering is if my emulsion tubes are going to work with the change from 125 to 135 mains. They are F36 tubes.

I have no idea what my idle jets are but I think I'll leave them alone. I know how to "work around" flatspots

 

Another data point....my '77 was popping through the carbs and not idling well, even after cleaning the .55's and synching. A switch to .60 idles completely cured it and the car runs SO much better. I'll stick with the .60's and let the small animals in my wake go running for clean air!

However I have 135 mains on mine (with Ansa exhaust). Should I up them to 140's once I clean the obstructing crapola out of my airbox?

"Fuel Wastin" Birdman

P.S. DJ, nice garage! I found the old thread. How is the floor holding up on top of the foam? Any cracks?

 

I would run what you have. Don't change a thing. Take it out and run it for 100 miles or so. Blow the crap out of it, bring it home and pull some spark plugs and see what color they are. Personally I try to run just a little lean. The engine runs cleaner and the oil doesn't become contaminated as quickly as an engine on the rich side, (like my 240Z with triple 40 DCOE Webers).

The foam is super high density and does not crush easily, even from boot heels. I do have some cracking but it is from running the hot water heat at too high a tempurature initially. I started out at 100 degrees at first. I turned it down to 60 and that seems to work okay. I'll just shoot some polymer caulk in the cracks and drive on. It's a working shop and not a show place so I am not worried too much about asthetics.

 

Philip - Depending on driving, usually wag about 14 - 15 - I remember it being the same as my 4wd Dakota truck.

Birdman - Agree would stick with 135 mains for now. What the 60 idles probably cleared up was the fact that your previous all marked 55s may not all have been functioning as 55s.... Not uncommon I'm told by Pierce.

DJ - the F36s will work just fine with 135s or 140s - have done this myself. For the injection guys here, what DJ is talking about in 'working around' flatspots due to transient leanness is application of the Weber magic cure-all - the accellerator pump...

And to just hijack and taunt just a little, spoke to Laurie today and will be looking at intakes with 234 degrees @ .050 and .381 (stock 220@ .050 with .342). Gotta take advantage of the carbs.....

best
rt

 

The best I have ever gotten in my 308 was about 14 mpg, all freeway driving at legal speeds, 50 to 60 mph.

When out with the club and trying to keep up, 9 mpg.