Street Engine Ramblings



Street Engine Intake Ramblings

There are some things I see on the internet Mustang sites that I want to address, so I am going to do the best I can to give you some ideas about how you choose a head/cam/intake combination for a STREET car. Most of us fool ourselves into thinking we have a “street/strip” car when in fact 99% of our driving is done on the street or roads. That is the FIRST thing you need to think about really hard and be sure to know how you’re going to use the car. If you go to the track EVERY week, you may have a true street/strip car, but if you go once a month or less, you really have a street car that is run at the strip occasionally. Be honest with your self and think about how you will really use the car, not how you wish you could use the car. Is it daily transportation? If it is, put together a street engine, not a track engine.

What’s the difference? Primarily the RPM band that in which the engine makes power in my mind. There are no hard-and-fast rules, but most street engines make power below 6,000 rpm. Sure guys run engines on the street that can buzz to 7,000 rpm or more but they are not what I consider a true daily driver combination. Can it be, is it done? – Yes, should it be done? That’s entirely up to you but know what the true consequences are before you spend you hard earned money.

Driving a car that makes power in the 3,500+ rpm range can be hard to drive in traffic.

Now, my area of interest is intakes. I have some knowledge of heads and cams picked up over 40 years in this hobby, but my talent has always been on the intake path to the combustion chamber. For a street engine, I have always favored smaller intake cross sections than many people now think are optimum. Why? Because they will often make more average power in the idle~5,500 rpm band than the larger intakes – even on heads and can combinations that beg for more intake. One dyno comparison test was done by Richard Holdener and documented in the article “Super Intake Shootout”.

This engine was a Coast High Performance 347 with the following specifications:

•Block - 2-bolt 5.0

•Crank - Cast 3.40-inch 347-Coast High Performance

•Rods - 5.40-in. Steel H-Beam- (CHP)

•Pistons - Forged 10.5:1 5.0 Probe (11.5:1 with milled heads)

•Cam - XE 292R (Comp Cams)

•Lift - .621 in, .627 ex (.016, .018 lash)

•Duration - 254 in, 260 ex

•Lobe Center - 110

•Heads - AFR 185 (CNC ported & milled)

•Valves - 2.02-in, 1.60-ex

•Rockers - Comp Cams 1.6 ratio roller

•Intake - GT-40

•Throttle Body - 70 mm Accufab

•MAF - 77mm ProM (36 lb. calibration)

•Computer - EEC IV plus Ford Racing Extender

•Injectors - 36 lbs.-hr.

•Ignition – MSD

•Headers - 13/4-inch full length Hooker

•Water Pump - Electric CSI

•Timing - 34* Total

Clearly this was an engine that is more for the track than the street. Dyno tests were run on this engine with various intake combinations and I would like to show you some of the results that I have highlighted in graphic form. Dyno tests were run from 3,300 rpm to 6,600 rpm with GT40, Holley Systemax II, Trick Flow R and Victor EFI intakes. This power band clearly should tip the advantage to a larger cross section intake as most street engines operate at less than 3,000 rpm. So, how did things go for the GT40 that was clearly out-classed by the better intakes? We will see, but I need to add up front that the test results below are influenced by the longer duration cam that was used. This tends to help “restricted” intakes like the GT40 family intake on an engine that is a stroked small block as it allows more time for cylinder fill which the larger section intakes do not need. The larger cross section intakes tend to need less duration to fill the cylinder.

Let’s look at the Victor EFI and GT 40 torque curves

[pic]

The GT40 made much more torque & power below 5,500 rpm than the Victor. The green shaded area is the rpm that the GT40 made more torque than the Victor and the red shaded area is where the Victor produced more torque than the GT40. How could a little intake that flows 205-210cfm on a head that flows 260-270cfm and on a cam with an advertised duration of 292° out power the Victor? Because the GT40 intake’s smaller cross section was much more efficient at filling the cylinder in that rpm band. You can see that even if we averaged power to 6,500 rpm that the total area (average power) in red would still be less than the area in green.

How about the TFS-R intake and the GT40?

[pic]

Same thing, and the Holley Systemax II intake?

[pic]

Same results, but if you look closely you will see that the Holley did better than the other two intakes in average power production.

So, what happens if we run a similar test but use 302ci, AFR 165 heads, E303 cam and a ported Explorer intake. This cam is shorter in duration and the RPMII is a larger cross section intake. Here is a dyno of just that and had the ported Explorer intake changed out for an Edelbrock RPMII intake in the quest for more power through 6,000 rpm.

[pic]

Once again, the smaller intake but now ported makes more average power AND carries through 6,000 rpm right WITH the RPMII intake. This cam is not a “long” duration cam, but the heads used only needed the section that the ported intake provided. Porting the stock GT40 would have extended the rpm range advantage in the dyno tests in the 347 example above also.

Surprised? Don’t be – many guys are encouraged on the internet to use intakes that will lead to less average power right in the rpm band that will be used most on the street and occasionally on the track. It is AVERAGE torque/power that demonstrates a superior combination. The Engine Masters competition every year stresses this by taking torque and power into the calculation.

I have made my point and a case to consider smaller cross section intakes on street and even street/strip engines for best average power on a street or street/strip engine.

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