| Author | Message | ||
| Russ Gould (Russ)
New member Username: Russ Post Number: 30 Registered: 2-2003 |
I don't know whether it's just the psychological effect of the louder intake roar, but it seems to go better. Then again I changed the idle mixture settings at the same time. Hans says he actually tested for ram air effect with a manometer and there is none. That is intuitively right given the position of the scoop. So the question is how much hotter is the intake air? I don't know the answer but the car does not run any hotter. There is plenty of air circulating back there, I suspect the air is sucked up from under and out of the vents on the lid. I didn't blank off the scoop, just left it open. K&N's are supposed to breathe better than any other filters..and I suspect there are more square inches per carb with this setup. BTW the velocity stacks are still in there. You need to save the aluminum pillars from the old airbox to mount them. There is about an inch clearance between the vel stacks and the covers. | ||
| "The Don" (Mlemus)
Advanced Member Username: Mlemus Post Number: 4903 Registered: 8-2002 |
Russ, did your performance go down due to the intakes sucking in engine heat? M | ||
| Russ Gould (Russ)
New member Username: Russ Post Number: 28 Registered: 2-2003 |
Try this!  | ||
| Dave Helms (Davehelms)
New member Username: Davehelms Post Number: 11 Registered: 5-2003 |
The issues I have are with the screens, and the stack shape. The stock 308 stack is of a parabolic shape, with a 180 degree lip, that has been proven to be far and above the best shape for high flow rates. The stacks you have in the picture will with out a doubt drastically reduce the effective flow rates compared to the OE units. The screens (per the dyno test) were shown to have a great effect on the flow of air as well, not to mention they are only good for keeping small animals and golf balls out of the engine. The fuel stand off is directly effected by the cam profile and the rpm, and will happen at some rpm through out the useable rpm range. The fire I spoke of happened with std. 128c (250 inside plug) cams, which were nothing to write home about for performance. Try setting a light behind the stacks on any 308, and slowly raise the rpm. Hint, DONT smoke! The stock air box and stack assys on the 308 are an exceptionally well designed combination right out of the box, although a pain to work with, granted. The only mod that I have considered is to drill large (2") holes on the vertical side of the box across form the intake, and filter them. My thought was the air flow from the intake NACA duct might be stalling out due to the limited amount of air being drawn into the engine compared to the air flow at speed across the duct. We sold the 308GT4 race car before I ever got around to yarn tufting it to watch the air flow at speed, and test the idea, but Formula Atlantic cars have been using this design concept for many years now. | ||
| Andy Falsetta (Tuttebenne)
Junior Member Username: Tuttebenne Post Number: 126 Registered: 3-2003 |
Wouldn't the carbs need to be re-jetted to run with velocity stacks and no filter. A couple of years ago I had taken the filter out of the airbox on my carb 308 and drove it on a test run. The sound of the air being pulled into the eight throats, coupled with the sound of the exhaust was addictive - but the power was definitely down - leading me to believe the mixture had leaned out due to the increased airflow. Any thoughts? | ||
| Andrew A. Illes (Andyilles)
New member Username: Andyilles Post Number: 27 Registered: 10-2002 |
Screened or foamed stacks on a stock cammed/timed 308 shouldn't really raise a fire issue. There's not enough overlap to produce standoff like Dave mentions about his Hart. Now, if you have P-6 cams, or crank in some overlap with stock cams.. different story! Question for Dave.. don't you get standoff at idle and low speed, not high? Craig's comments about stack heighth and needing to tune the intake/exhaust as a unit is dead-oh right. On an unmodified 308 with stock exhaust, the stock tubes are well tuned. The Michelotto cars, at least the 6 that Charles Pozi campaigned, used stock air boxes. Heated intake air isn't really as much of an issue with 308s because of the "trunk lid" vents. Though I sure agree about all those bits and pieces to take the airbox off, you do get a definite ram effect with the stock Ferrari setup, and I'd bet you'd lose power going to just stacks. But damn.. they sure do look cool, huh? | ||
| Hans E. Hansen (4re_gt4)
Intermediate Member Username: 4re_gt4 Post Number: 1277 Registered: 4-2002 |
A year or so ago, I was contemplating the same thing. Temporary filtered stacks for those times that you are doing lots of fiddling with the engine. I never came up with any idea that I liked, however. | ||
| JohnR. (Rivee)
Junior Member Username: Rivee Post Number: 205 Registered: 1-2002 |
The reason for wanting these is that every time I go to work on anything in the engine compartment I have to remove 16 nuts, washers, and brass sleeves (the ones that get dropped into the carb. throats when removing the air box) so I thought if I had these stacks with filters, I could work on things a lot easier and leave these on temporarily while fiddleing around with the engine. | ||
| Craig Dewey (Craigfl)
Member Username: Craigfl Post Number: 595 Registered: 1-2001 |
While what Dave said is true for the Brian Hart engine, because he measured it, velocity stacks are resonant(tuned) devices. Length affects at what RPM the extra power will be -- the shorter they are the higher the rpm HP boost. As with most resonant device, it causes the hp peak to be in a narrower band, which means that if the length for the stacks doesn't match the rest of the engine tuning you may seem to actually lose hp. If you experiment with the length, you should find that the overall hp will increase but will be in a narrower band. It is also possible to stagger the resonance so that even though the peak hp is less, the hp band may actually widen and give you better drivability. It just depends what you're looking for. | ||
| Dave Helms (Davehelms)
New member Username: Davehelms Post Number: 9 Registered: 5-2003 |
Thougths to ponder: Just got a Hart Big Valve twin cam Lotus engine off the dyno last week. Screens on the stacks dropped 17 HP off the peak of 189 @ 8200 RPM with no screens. Stacks of the shape shown will be good for an additional 20 to 30 HP loss at about 7000 RPM as well. Foam socks on the stacks caused a fire that took the paint off the hood of the TdF we campained some years back due to them retaining the fuel stand off comming out of the stacks at high RPM. Try reving the 308 with just the stacks on and watch how much fuel goes UP, not down! Sure do look nice just the same. | ||
| Ben Millermon (Brainsboy)
Member Username: Brainsboy Post Number: 308 Registered: 5-2001 |
Food for thought, I dont have a photo, but about a year ago I was eating at Bennigans and ordered the chicken fingers. When it came they had two stainless cups one for barbque sause and one for mustard sauce. Turns out I couldnt eat it all, so my wife(really x wife now) put it in a to go box along with the 2 stainless cups, which I didnt know at the time. When I got home I noticed the two cups, ... with plans to return them, they got placed inside a cupboard where I forgot about them. Now that I saw this post, the photo reminded me of it. The 2 cups look just like a velocity stack its just missing the screen and needs the bottoms cut out. I guess if I eat there 4 more times I will have a complete set | ||
| Philip Airey (Pma1010)
Junior Member Username: Pma1010 Post Number: 234 Registered: 7-2002 |
Visual appeal of the v stacks is undisputed. The issues of advisability (getting more dirt into the engine) and functionality (heat) have been discussed before. The HP losses due to increased heat (versus the stock "ram" box) were reported to be significant. Anyone know what the Michellotto GT4/GTBs did? LFSC has a 308 they campaigned in GT2. I know they relocated the oil cooler to the front of the car and plumbed both the passenger and the driver side air intakes to the (carb) intake area. | ||
| Matt Morgan (Kermit)
Junior Member Username: Kermit Post Number: 131 Registered: 8-2001 |
John, I'd be concerned with underhood heat with this settup. Just a thought... Kermit | ||
| JohnR. (Rivee)
Junior Member Username: Rivee Post Number: 204 Registered: 1-2002 |
Here's a better picture  | ||
| JohnR. (Rivee)
Junior Member Username: Rivee Post Number: 203 Registered: 1-2002 |
Where can one get velocity stacks with foam or some air cleaning element and screen for a 308? Simular to these pics.  |