Cam and Valve questions with the Aussie 2V head

[MustangSix]

If piston to valve clearance is an issue, you have to flycut the pistons to add valve reliefs.

It''s funny how engines react to cam changes. Bigger is not necessarily better. I ran this combo thru EA 3.0:

200 ci
9.5 CR,
Aussie 2Vhead 1.75/1.4, 45% flow efficiency (lightly ported)
single plane manifold w/Holley 350
272 cam, 224 @ .050, 110 lobe separation, .480 lift
1.5" headers, duals

It turned 158 hp @ 5000 with 196 lb ft @ 3500. Sounds impressive. But at 1500 this engine makes less than 30 hp and doesn't make over 100 hp until nearly 3200. Estimated idle vacuum is 14.1". This will be a pig off the line when coupled to a stock converter that stalls at 1500.

Simply switching to a Comp 252 (206@.050, .425" lift) and no other changes yields 151 hp @ 4500 and 201 lb ft @ 2500. Not much difference in peak numbers. But at 1500 the little cam is making almost twice the hp and way more torque in a flatter curve than the big cam makes and is already over 100 hp at 2200. Idle vacuum goes up to 19.1". This would be one docile, but strong engine.

 

[Anonymous]

Jack,

What kind of numbers would I get with a 260?

 

[MustangSix]

About the same as the 272 at peak, but with a bit more at the bottom end.

In all the simulations I ran, until you get a head that can flow a lot more air (significant porting, webers, port EFI, other hacking, etc), the big cams don't do much. Kind of like making Carl Lewis run the 100 while breathing thru a straw. The potential is there, but the airflow is very restricted. One good example is Doug's engine with a 270-something cam. A fair runner with the YF, but took off like a rocket when the Holley 2bbl was bolted on.

Keep in mind that these are simulations. You may or may not get these numbers. The whole point is to make relative "what if" comparisons of different components. By doing this we can be pretty sure that the big cam is not the way to go for the gears you are using. Change gears, change converter and the cam assessment changes.

 

[Anonymous]

I think I might go with the 260 cam. I won't lose much performance. Plus, I can even pick some up when I get the tranny rebuilt. I can't change the gears right now cause my stang is a daily driver and a highway car for a 160 mile or so round trip every month from school to home and back.