Dumb question

[mk028]

Let me start this off by saying I dont know jack about cars. What does it mean when I read that the 03/04 cobra's have a 4valve engine? what is the difference between the 03/04 cobras, 03/04 GT mustangs, the 05-07 mustang gt's, and the 07 shelby as far as valves are concerned? What does the number of valves have to do with your cars performace? Thank you for taking the time to explain this to me.

[AZSonicSnake]

96-04 cobras all came with 4 valve engines. the gt came with 2 valve modular motors from 96-04. 05+ gt's use a 3 valve motor. this relates to the amount of valves in the cylinder head, and more valves allow for more air to enter/exit the cylinder head during the cumbustion process.

[50 BMG]

What does it mean when I read that the 03/04 cobra's have a 4valve engine?

It means there are 4 valves to each piston. 2 intake, 2 exhaust. Most 4 valve engines are Dual OverHead Cam which means there are 2 cams in each head. There are a few pushrod 4 valve motors out there, but 99%+ of pushrod stuff is 2 valve per piston with the cam inside the block.

what is the difference between the 03/04 cobras, 03/04 GT mustangs, the 05-07 mustang gt's, and the 07 shelby as far as valves are concerned?

04 and eariler GT's with Single OverHead Cam engines have 2 valves per piston, and one overhead cam on each bank. 05+ GT's are the same except they have 3 valves per piston; 2 intake and 1 exhaust. The Ford GT and GT500 have the apex OHC heads. As far as the valves are concerned on those 2 cars, they can accept a bigger valve than any other current Ford OHC head resulting in increased airflow which means more horsepower.

What does the number of valves have to do with your cars performace?

Volumetric efficiency. 4V heads have a 90% VE on straight pump gas w/no other power adders. 2V heads have a 80-85% VE with the same parameters. When you increase the efficiency of your engine you make more horsepower. Increasing the VE on your engine is like removing weight from your car...you'll always want to do more.

In the case of Ford OHC engines, it also has to do with RPM's (which is addressed later on below). There are 4 ways an engine can make power:

1) VE
2) Forced Induction
3) Displacement
4) RPM's

We'll ignore the first 2 cause FI can be put on any engine and VE is easy to increase to small differences between engines if you know what your doing.

Which leaves displacement and RPM, which are the 2 main ways an engine makes power. Engines are essentially a giant airpump; the more air you can move the more power you make. CFM is one way to measure the output of an engine.

CFM is calculated by

CID (displacement) x RPM / 3456 = X

X is your CFM. You can then multiply X by your VE percentage (anything from .8 to .95) to get a more accurate CFM of your motor.

Now here is where the Ford SOHC vs DOHC thing comes into play. There is an old saying "There is no replacement for displacement." And it's true among engines of the exact same type with the exact same characterisitcs. But DOHC and SOHC are not the same...

The DOHC can spin at least 2000 more RPM's than a SOHC at the limits of the engine (11,500 RPM's for a DOHC vs ~9,200 RPM's for a SOHC). Understand you have more fingers on your hands than there are actual production based Ford OHC engines in existence actually turning that RPM. Neither engine can achieve a superior displacement over the other so that removes displacement from the equation. So the DOHC will make more power because it can flow more air due to higher potential RPM.

Among different types of engines, RPM's can replace displacement.

Take a 383 SBC with a 7500 RPM redline vs a 324 DOHC ford with a 9000 RPM redline.

The SBC has a CFM of 831. The DOHC Ford has a CFM of 843. Less cubes but more RPM resulted in more airflow; an effective replacement for displacement for different types of engines.

Multiply by the respective VE (.85 for the SBC, .9 for the DOHC Ford) and you get 706 and 758 respectively. Due to the increased efficiency, the DOHC Ford would only need to turn ~8400 RPM's to match the CFM of the 383 SBC at 7500 RPM's.

Now having said all that, I wish I could get my hands on one of the 7.3L DOHC mercedes engines in the Zonda F...

[AZSonicSnake]

^^^ dang. thats a good read right there. lots of kick arse information. thanks 50!

[mk028]

I cant thank you enough for taking the time to answer my question with as much detail as you did. I am trying to learn everything I can and I really appreciate it when people take the time and effort to give an answer with an explanation of the answer. Thank you 50 BMG........Mike
P.S. I would also like to thank Sonic for taking the time to give me an answer as well, thank you Sonic.......Mike

[Dalamar]

Great info BMG