11-19-2007 12:09 PM #1
What is the right intake runner for a street car?
for a street car you need high torque at low RPMs, for a race car you need high power at high RPMs.
For high torque you need heads with a smaller intake runner volume to get a higher port velocity and better mixture of the fuel and air, but you don't want runners too big, they will kill the low end torque because of the loss of the above mentioned port velocity. For racing use you need a high volume of mixture, which is only obtainable by having big runners.
So, if I want to set up a street car, what kind of intake runner volume should my head have? What is big, what is small?
E.g. I am interested in buying World Sportsman 2 Heads, which have a 200 cc intake runner. What do you think about them?
If I want to run my car with LPG (propane butane), what do I have to consider when I choose heads? What is here the optimum of the intake runner for a street car?
What else is important? What kind of valves/valves seats do I need?
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Here is one formula I use.Originally Posted by James911
This is the amount of hp a given flow will support.
Flow at 28 inches of water X 2.06 = HP.
An example would be 270 X 2.06 =556 HP.
Most SBC 's seem to like around 180 cc port volume which would be enough to support 450+ hp.
At 400 HP and under I would try a 165 cc port volume.
Can you tell us more such as cam specs. and comp ratio etc.
Last edited by erik erikson; 11-19-2007 at 05:52 PM.
Any 180° intake is for street. The best one I've found is a GM 327 350 hp off the Corvette or Impalas
A 180* dual plane manifold similar to (but not necessarily this brand) Edelbrock Performer RPM. You will still have to do some more homework to determine what length/volume runners are needed for the way you want to drive the car. Usually the manufacturer can tell you which is the best based on a few parameters. For a Chebbie, lots of choices
I am now gone from this forum for now - finally have pulled the plug
Ok, but what is a small intake runner (170 cc?) and what is a big one (250cc?)??
What is the influence of the intake manifold in terms of power and torque?
How does a intake manifold influence port velocity and the mixture of the fuel and air?
I read, that World Sportsman II Heads have a similar port volume than that used in factory production heads and that they are good for low speed torque!
What is the intake runner volume, egg. of good old double humps?
It all depends on cubic inches. A 160cc runner would be good for a 327 sb but would choke a 400 sb. A 195cc for a 383 would kill low end torque for a 327.
There's no 12 step program for stupid!
and 200 cc on a 350?
For an all out 350 drag motor--yes. For a street thumper--no. I would try to stay around 170-180 for a 350, but it depends a lot on how much power you are making, whether you are running an automatic or manual transmission, etc. Everything is interdependent so you have to think of the combination when you consider individual parts.
There's no 12 step program for stupid!
The Sportsman II head is much larger than the old double hump heads.Originally Posted by James911
The old humpers where around 160 port volume.
Well said. Engine size, gear ratio, intended use, rpm range, vehicle weight, etc, all influence what size intake runner to use. Also, it's worth looking through some flow tests for heads. Some heads with a smaller runner size actually out-flow some with bigger runners, indicating better port velocity and cylinder filling potential.Originally Posted by rumrumm
I did had the 350hp 327 intake on a 400 and really love it. It had so much torque that nothing can out run it from red light to red light. And it also pick up the gas mileage very well in the city. It will run up to 85+ mph easy depending on what gear and transmisson. It will make good foot brake bracket on a 1/8 mile strip.