This is just one of those food-for-thought questions as our intakes can support something like 350HP at high RPM the way they are now. Not looking tio change them.

Anyway: I was thinking, ya dangerous I know, that said; the hump in the intake port is there help to atomize the fuel mix and should be left as is. With our intakes flowing much better than stock (higher velocites more cfm etc) would that change anything with respect to the need for the hump? When I built my turbo 86GT one of the many things I did was some head work: 5 angle valve job, better springs etc and some polishing etc. I left the hump almost stock, just polished it some.
Now for the real question; I have this design idea for a device that will let me put the injectors pertty much wherever I want on a custom intake and not need a solid fuel rail. If I made a new intake with the injectors on say the plenium shooting directly into the velocity stacks, or put them on the curve shooting into the strait section of the runners I think I could get rid of that hump and have more flow. We did something like that on my Son's 540HP+ 2ltr MR2. We put a 2nd set of higher flow injectors on the plenium like that. The engine would switch over (Electromotive management system) to them at 6K and stay with them on to the top of about 13k. We could not get good low rpm proformance with injectors rich enough for 13K, thus we went with the two sets. Anyway, think it would work, new injector locations and humpless ports?

I think the current engineering trend is to get the injector closer to the cylinder, not farther away. To the point that they're using direct injection in some of the newer cars. I can't see where injecting it further upstream would be good. Presents more time/opportunity for the fuel to fall out of the airstream (de-atomize?) Just my thought on the subject. It cost you nothing. Take it for what it's worth.

Regardless... I would leave the fin.
Various theories that I've heard say that it's supposed to divert the mixture around the valve stem, or up and into the bowl, where it'll have a straighter shot down through the valve.
It even mentions in the Chevrolet Power book that it needs to remain in place, even in a race-prepped motor.

Here's a pic of mine.


And a couple of pics of the lower intake, just for grins.

[This message has been edited by Raydar (edited 02-16-2008).]

Direct injection needs really good injectors and I think lots of fuel pressure. I know that you dont want the mist to form wet spots in the runners and such, why I said I would shoot it only into a strait pipe with a strait line right into the cylinder. Anyway, it was just a thought. Oh, check it out, new headers for my turbo
just made them. And thats an unfineshed intake and what the new ones will look like. That one is going to betig welded, no seams

Does anyone know of any other head with the shark fins? And if not, why?

quote Originally posted by Hudini: Does anyone know of any other head with the shark fins? And if not, why?

Very good question!

Yes, alot of the vette motors have the fins for one.
The fins are there specifically to INCREASE flow, not for mixing. the machinist I used has flow benched heads with and without them,
and on the vette heads the fin adds about 20% more flow over the same head with them removed.

they work for carbs too, as it is not a mixing thing for injection, but a aerodynamic adjustment that improves the flow.

Francis, the only way to know for sure is a dyno test with the heads as is and with the shark fin removed. Might make for more sales if you did some R&D.......

Funnycar head (3500 HP) With Sharkfins:

yes, the fins are to split the airflow to the sides of valves. instead of having it all crowd down the front, it is split and comes down both sides, and even around the back and, of course, NOT hitting the valve stem

think of it like the triangular peice on large ropes with hoops at the end. spreads the load, for more strength, keeps from binding on itself. in our case, spread the airstream for more overall flow. 2 flows @ 120, instead of 1 flow @ 200 (made up numbers)

edit: and - current injector placement says to point it at the back of the valve for best atomization. basicly - the hot hot valve instantly boils the fuel. there is nothing on the intake path hotter than the valve - and everything gets quickly cooler as you move away from the valve.

[This message has been edited by Pyrthian (edited 02-18-2008).]

quote Originally posted by kjelle69: Funnycar head (3500 HP) With Sharkfins:

Tonsils removed? Not unless you have to.

Seriously, if you have the engine on the pump, you aren't relying on naturally aspiration in your power band whether the fin is there or not, it is therefore probably not so clear cut as to relative benefit. Where it will show up big time is the idle to spool-up. Those rpms where the pump just isn't delivering. On that basis, I'd leave it in just for that factor alone.

Arn

quote Originally posted by Hudini: Francis, the only way to know for sure is a dyno test with the heads as is and with the shark fin removed. Might make for more sales if you did some R&D.......

LOL, would surely make for wallet stress!

The "fin" increases flow efficency. GM did extensive testing before finalizing the design.





The only time it would make sense to remove the fin is if you're using a big turbo or supercharger to just cram air into the cylinder but frankly, I don't think a 2.8 would hold up under that kind of scenario at all.

JazzMan

The only time it would make sense to remove the fin is if you're using a big turbo or supercharger to just cram air into the cylinder but frankly, I don't think a 2.8 would hold up under that kind of scenario at all.

JazzMan[/QUOTE]

On that topic Jazz, what is the 2.8s weakness besides the knid of small oil passages on the crank, (that can be drilled larger on the crank anyway) is it the the bottom end, Does it need 4-bolt mains to handle say 15lbs of boost and higher? Not that I'm thinking about jacking mine above the 10 or so I now have with 9.3:1 or so comp, just curi.

I know one guy Francis, who was running about 15 psi on a stock (but rebuilt) bottom end. His problem wasn't the bottom end, it was head gaskets.

Arn

Dont we already get fuel pooling with the batch fire on the injectors? worst case the injector fires 2 times with the valve closed and a third when it opens, this HAS to create pooled fuel in the heads.

Even the 7730 ECM upgrade still has us stuck with batch fire on the injectors. I think that one of the steps to go with your modification idea is to find a ECM that will allow sequential fire of the injectors.

quote Originally posted by Francis T: The only time it would make sense to remove the fin is if you're using a big turbo or supercharger to just cram air into the cylinder but frankly, I don't think a 2.8 would hold up under that kind of scenario at all. JazzMan

On that topic Jazz, what is the 2.8s weakness besides the knid of small oil passages on the crank, (that can be drilled larger on the crank anyway) is it the the bottom end, Does it need 4-bolt mains to handle say 15lbs of boost and higher? Not that I'm thinking about jacking mine above the 10 or so I now have with 9.3:1 or so comp, just curi.
[/QUOTE]

The problem with bottom end oiling is that there isn't a dedicated oil supply gallery for the mains. The oil supply for the bottom end is siphoned off of the cam bearing supply, that means that as the cam bearings wear more flow goes out the increased clearances and less volume makes it to the mains. GM addressed this somewhat by adding lead-in grooves on the main bearings in '87 and their 60° V6 racing program recommended using small block Chevy cam bearings (which fit just fine and are much wider) to protect oil flow to the bottom end. Ultimately they fixed the problem with the 3.4 by adding a third oil gallery for the bottom end.

JazzMan

The problem with bottom end oiling is that there isn't a dedicated oil supply gallery for the mains. The oil supply for the bottom end is siphoned off of the cam bearing supply, that means that as the cam bearings wear more flow goes out the increased clearances and less volume makes it to the mains. GM addressed this somewhat by adding lead-in grooves on the main bearings in '87 and their 60° V6 racing program recommended using small block Chevy cam bearings (which fit just fine and are much wider) to protect oil flow to the bottom end. Ultimately they fixed the problem with the 3.4 by adding a third oil gallery for the bottom end.

JazzMan

Thanks for into. With an 86 block is it worth then to mod the oil pan for another quart or two? Been thinking about doing that for a while now.

Doubt it will affect longevity unless you're driving in such a manner that the oil pickup is being uncovered, and outside of a racetrack or off-road course that doesn't seem likely. At that point a dry-sump system would be the way to go, but the bearing oil supply problem can only really be fixed by going to a 3.4 block. Now, for a street-driven and light-performance setup I'd be perfectly fine with the 2.8/3.1 block (they're the same block) with the SBC cam bearings and the crank with lead-in grooves.

JazzMan

quote Originally posted by JazzMan: Doubt it will affect longevity unless you're driving in such a manner that the oil pickup is being uncovered, and outside of a racetrack or off-road course that doesn't seem likely. At that point a dry-sump system would be the way to go, but the bearing oil supply problem can only really be fixed by going to a 3.4 block. Now, for a street-driven and light-performance setup I'd be perfectly fine with the 2.8/3.1 block (they're the same block) with the SBC cam bearings and the crank with lead-in grooves. JazzMan

BTW: lead-in gooves, I'm thinking you're talking about cambering (or slotting) the oil hole at the center of the bearings to widen the oil footprint?

Dang, thought I had a picture up. They are shallow grooves ground into the crank main journals that wrap around from the oil hole about 30° more or less. As the crank turns the slot catches the bearing oil groove and allows oil flow to the rods sooner on each rotation. It was a running change by GM starting in '87. In the performance book there's a diagram and details on grinding that slot into earlier cranks.

JazzMan

One must remember that in the upper RPMs a SFI ECU reverts to batch fire as a fail-safe...

quote Originally posted by timgray: Even the 7730 ECM upgrade still has us stuck with batch fire on the injectors. I think that one of the steps to go with your modification idea is to find a ECM that will allow sequential fire of the injectors.