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 honestly) and be sure to figure out 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 cam combinations that beg for more intake. One dyno comparison test was done by Richard Holdener and documented in the Muscle Mustang and Fast Ford 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 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?

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

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?

Same thing, and the Holley Systemax II intake?

Same results, but if you look closely you will see that the Holley did better than the other two intakes in average power production.  Look at the graphs again and you will see that even if we had averaged to power up to 6,600 rpm that the area in green would still be larger and so average power would still be higher for the GT40.  Since many of us run stock computers with a 6,250 rpm rev-limiter, we could not turn that many rpms anyway.

Now that you have seen the graphs, lets take a look at the numbers when placed into an Excel spreadsheet….

If you choose a 3,300-5,500 or a 3,300-6,000 rpm band, the diminutive little GT40 stomped the larger intakes on a combo that clearly seems to want a larger intake for operation below 6,000 rpm.

So, what happens if we run a similar test but use a 302-306ci engine with AFR 165 heads, an E303 cam and a ported Explorer style intake? Here is a dyno of just such a combination that had the ported Explorer intake changed out for an Edelbrock RPMII intake in the quest for more power through 6,000 rpm.

Once again, the smaller intake (but now ported) makes more average power through 5,200 rpm AND carries power through 6,000 rpm right WITH the RPMII intake. Porting the stock GT40 lower intake would have extended the rpm range advantage in the dyno tests on the 347 combination above also.

How about a combo with Twisted Wedge heads and a nice Anderson Ford Motorsport cam with a STOCK Explorer intake and a Track Heat intake?

Here is an interesting test done with a Performer/RPM ported lower running both the Performer upper and the RPM I upper in the same dyno session.  Most People would think the Performer would loose power on the top end to the shorter RPM upper right?



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. Moving to an intake that can make more peak power often means the losses in the low-mid range power offset the peak gains.  It is AVERAGE torque/power that demonstrates a superior combination. The Engine Masters competition every year stresses this by taking torque AND power into consideration for the calculation of a winner.

If you are going to build a combo that makes power in an rpm band that is 1,000 rpm higher (4,500-7,000+), then by all means take a fresh look at the numbers and you will find that the other intakes are the cat’s meow for such a combination, but most of the guy’s combinations I see posted in signatures on the net do not fall into this group. Here is one quick example of a higher rpm power dyno comparison.

On this race engine, you cam see that the longer Holley makes more mid-range power but the shorter runner Victor carries power further up the rpm range and is more desirable for this application. 

I hope I have made my point and a case for smaller cross section intakes on street and even street/strip engines for best average power. Don’t be mislead by the peak number worshipers – average power is where it’s at.

Tom