Tunnel Rams & How They Increase Flow
Free flowing intakes allow engines that can take advantage of them more air flow. With the long large runners they let air slam into the cylinders. When the engine reaches the rpm in which the tunnel ram take effect the column of air on top of the valve keeps moving even if its closed. When the valve opens the air is force in by momentum and produces a ram effect. Giving them there name.
The more air that can be forced into the cylinder the more power can be made from the engine. When these engines reach there rpm range the power increase can be dramatic. Gaining many HP over a normal dual plane intake especially the OEM style intakes. Now this effect is also present on many single plain intakes. But with the tunnel rams the air charge can also be increased at lower rpm range. Giving them a large snap of torque along with massive boost in the top end.
The Straight Shot
You can see from the picture above that the intake runner is straight into the port and points air straight at the back of the valve. This allows the engine to take a big gulp of air each time the valve opens. Giving the engine more low speed tq and a lot more high rpm potential.
Now with that said you got to have an engine that can take advantage of the extra air flow. A low rpm stock engine would see little to no benefits. They would still get a little more air but since they will have compression lower than most performance engines they also don’t have a cam shaft large enough to reach rpm range where the additional air flow can be useful.
And of course it looks bad ass.
Tunnel rams with two carburetors also have some side effects you may not first think it means two 600 cfm carbs will produce 1200 cfm of air but with two carbs the vacuum signal is lower because the engine will see less vacuum at full throttle. A single carb will not have as much open area as two together. So if you run one large carb it will have more draw on it than two much smaller carbs. Now if those carbs are small and have a lesser vacuum signal they will also flow much less air in the end the engine wont be able to get as much air even though the amount of air available is greater. Since the vacuum signal is not as strong less air will be pulled thru the carbs.
Carb Size for Manifold Type
For this reason it is often suggested that larger carbs my be needed to run on dual tunnel rams. Often two 450 carbs are run but these can be much more restrictive. The smaller carbs may be easier to tune. May not get the air the engine may need to make max power. With two 600 cfm carbs these could hit the mark and more and let the engine breathe. Many small carb setups can in the end make less power than a single carb setup. For a strong engine that will flow massive air a good tunnel ram may use two 750 style carbs that will require some tricky tuning. But once tuned can run a lot better than small carb setups.
With max effort drag racing setups where the engine will operate in the high rpm range and make more power in that range. If you run these carbs on the street the car may need lots of tuning to bring things into focus. More power can be made with more air but if the vacuum signal is low this may not be an easy setup to get dialed in. Now once its dialed in it can make great power and run good with a large dual carb setup. These setups run great and produce good street power even if they few ft lbs less torque at lower rpms ranges. Once you stand on the throttle with a tuned tunnel ram can make more power over all and be very fun ride.