Hello all. I am thinking of making a new intake manifold for my 350 Buick. I am good friends with the local shop owner and he said if I can come up with a design and materials he will help me build it. Here is my thoughts and than I need some help from an engineer or two out there. It seems like one of the problems with running bigger cams is the overlap. This overlap would be eliminated by having individual runners for each intake port. My idea would have 8 intake runners I would use 4 two barrel Weber carbs. That way it would be 1 bbl per intake port. We have looked at the base and feel a sheet of aluminum can be bent or welded to meet the needs here. We can weld in the water passages. For the intake runners we are thinking of bending some aluminum tubing and welding it to the intake plate. Mandrel bent tubes would keep the same I.D. so we would have any restrictions. We would weld a flange on to the end of two intake tubes to mount a Weber Carb to. We have even starting toying with the idea of how to make the one end of the tube more rectangular to match the intake port. All of the above said we are not Roads Scholars and need some help to come up with a good starting point for the length or volume of the intake runner. Anyone out there have a good idea of where to start? Thanks, Matt
I'd start by using auto cad to design the intake, thats what Mark did. The seperate runners are a good idea but you'll need some plenum volume before the runners in my opinion. marks intake has a large central plenum with thin dividing walls to direct the air/fuel to each cyl.
If you check out this months issue of Hot Rod magazine the is a article on intake manifolds that were dynoed and the ones that had 2 four barrel carbs on them did not have as much power as the single carb ones had. Just food for thought.
Yeah guy, that was a good article! My next custom intake will be a tunnel ram with front mounted throttle body and fuel rails for MPFI.
I am think that the starting point will be the I.D. and length of the TPI manifold. That is really what this would be except it would have a carb on the end. I got a friend in the parts business and he said this is how some of the be drag racers build manifolds. They take a 1/4" piece of aluminum for the base and the weld everything else up. He said he was at a customer that builds 502s for racing and they had a stake of manifolds that didn't get the HP they wanted. I realize there is some serious calculation here, but starting with the length and I.D. for a 5.7 liter TPI should at least get me to the ballpark. The linkage and tuning the carbs might be the more difficult item in the end. This isn't that radical. Aston Martin did it on their V8s in the '70s. Ferrari did it on their v12s. It will be fun trying.
Other intakes for inspiration: Go here: http://www.britishv8.org/Articles/Weber-Carburetor-Options.htm
I don't understand? Overlap is when the exhaust valve and the intake valve are open at the same time. How can the runner eliminate that?
It is the exhaust valve of a different piston I believe that causes the problem. Someone will have to correct this if it is wrong, but with longer duration cams the vacuum of one piston will draw some exhaust from another into the plenum. This can lead to rough idle. In a single runner design the exhaust from another cyclinder would not have any effect. It would allow you to run longer duration cams without the overlap issue. In essence your drag strip HP/Tq becomes more streetable. Supposely if you have the correct length of runner the echo of the sound wave will also draw in more air/fuel mixture. This is part of the complicated mathmatics for a big OEM. I like the looks of the side draft version above. In an article I read a shorter runner is better for torque and a longer runner is better for HP.
This is interesting. After thinking about it, I thought that was what you meant. I can see how at low RPMs you could get turbulence in the plenum from the overlap. I'm thinking that the idle would still be rough. I need to read up on this. :TU:
By all means try to get something built and i will pay for extra dyno time in taxas if you can send it to PAE asap for dyno testing.
to answer your question, found this for you Matt "B. General Rules For IM Designs and Complementary Parts 1. If you increase the plenum size (volume), the powerband is shifted up to a higher rpm. 2. Smaller plenums have lower to midrange rpm powerbands. 3. Large plenums prefer smaller diameter TB's and runners to maintain air flow velocity. 4. Small plenums prefer larger diameter TB's and runners to obtain more air flow capacity or air flow volume. 5. Tuning the runner length achieves the best air flow velocity for the powerband location you want. a) Longer runners have, on the plus side, more flow velocity which shifts the powerband gains to a lower rpm and has less reversion than shorter runners.... but on the downside, longer runners have less air flow capacity. b) If you need more air (capacity) to get into the engine , you must increase runner diameter . c) If you want a higher powerband location , you shorten the runner length. In the old Mopar Chrysler engines, Steve Magnante at Hot Rod magazine described a formula to obtain the best runner length (mind you on a carburated engine) based on your desired powerband location: N x L = 84,000 where N represents the desired engine rpm to tune for and L is the length in inches from the opening of the runner tube to the valve head. " Good link on manifolds here http://victorylibrary.com/mopar/intake-tech-c.htm
What you have in mind is an IR (Independent Runner) manifold. This is not at all like the pictured Edelbrock 4-two barrel manifold which uses a plenum. You are not re-inventing the wheel. Lots of IR manifolds have been built before. They're a friggin' nightmare. You have to buy four carbs--or two Holley 4-barrels set up for an IR manifold (all the throttles open simultaneously) Either way, you have high expense. The carbs are relatively huge in terms of airflow to supply the cylinder "on demand" with no plenum to dampen the intake pulses. (Think Japanese motorcycles--one cylinder, one carb throat, no interconnection on the intake manifold with other cylinders.) By the way--this does NOTHING for overlap issues. At low rpm, the mixture is diluted by exhaust gas, and the compression pressure is reduced. No intake manifold can fix that. Ram tuning works great. For about a three hundred rpm power band. You notice that Chrysler didn't continue using it...
That overlap thing, that's when both the intake and exhaust valves are open and it doesn't have much to do with the other cylinders. Don't confuse that with distribution problems where one cylinder will rob another of air/fuel mixture. On the exhaust side a decent set of headers will eliminate any issues you may have. Overlap is a function of the cam grind. To date the best way to deal with that problem for driveability is variable cam timing but it's not available for these engines. For your IR manifold you need to think more in terms of volume rather than just length. The other guidelines apply but volume is crucial. There are formulas out there for deciding what is optimal for your powerband. Personally I think a cross ram dual plenum injector intake would have a lot of potential. Jim
One Wikipedia there is a nice illustration. It is not accurate enough to show the exhaust vavle just off its seat during the initial intake stroke. http://en.wikipedia.org/wiki/Four-stroke_cycle The overlap of the exhaust valve and the intake valve are supposed to create a larger vacuum in the cyclinder than just the down stroke of the piston. By allowing the exhaust valve to be off its seat the goal is that the vacuum created by the exiting exhaust will help pull the fuel mixture into the cyclinder. If the pressure in the intake is greater than or equal to the pressure on the exhaust side this will work. If there is a lower pressure in the plenum than the exhaust will reverse direction. I believe what is happening at lower RPMs is there becomes lower pressure in the plenum. When this happens some of the exhaust gases are pulled back into the plenum. While an IR design does not eleminate overlap(that is a function of the cam) it can eliminate the ablity of the exhaust of one cyclinder having an effect on another.
