What cam- for a blown lump?

[JP.]

It seems that nobody has experiance with the RV8 Supercharger/Turbo cam.
Its also hard to compare one engine to another. It only can be done if engine's are build to the same specs if there's any real improvemend between a standard cam and this Blower/Turbo cam.

In my opinion there's a difference in a Supercharged engine and a Turbocharged engine. So there must be a difference between a Supercharger cam and a turbo cam.
A turbocharged engine comes on boost on a given rpm while a supercharghed engine is always blowing even while you'll see no boost on the gauge. If you'll hit the throtlle on a supercharged engine there's instand boost, it doesn't matter which rpm range, even from low down.

We drive a Supercharged 3.5 with Merlin heads.
Normaly on a 3.5 you can't run Merlin heads but as the supercharger is always pumping air it will work perfect.
Running Merlin Heads on a 3.5 with Turbo won't work until the Turbo comes on spool.

We have the Viper Hurricane cam cause it was allready in before the supercharger came up. By its dyno graphics it showed a nice rpm range in we like the engine to perform.
Before the supercharger came up we where not satisfiet with the Viper Hurricane cam and always thought that the Kent Hi Torque was better for our aplication.

So hence for you the question what do you want, and in which rpm range.

The real improvemend lies not in the cam, its in the heads. Changing over from standard heads to Merlin heads was 45 rearwheel horsepower improvemend in our aplication with no other modifications.
In my opinion : The cam only gives you horsepower in a specific rpm range.

[topcatcustom]

Thanks guys, I am going to mildly port the heads as budget is a bit of an issue in this build- and it isn't going to be an out n out muscle motor (though I'm sure it will be plenty enough for me whatever happens!)
I think by the time I use comp. head gaskets and have removed some material from the combustion chamber in the heads I will be left with (very big guess) 8.75:1 (?) So will be looking at running around 7psi boost.
Want to keep things well in range of 'normal' running use so that nothing is too stressed thus not producing as much power as I could but keeping reliablility (as much as possible!)
Like I say its going to be pushing well over 200 horses (I hope) so would rather have less to worry about and more fun than every available horse!

[kiwicar]

in that case I would go for one of the "standard" cams or somthing pretty close. Probably one of the injection cams.
Mike

[topcatcustom]

Thanks, with the option of uprating the heads in the future to make the most of it would I loose any power by using the SC cam in the meantime? (So dont have to do another rebuild when I swap the heads)

[chodjinn]

just buy a higher torque one then you wont have to worry about upgrading later.

[topcatcustom]

Higher torque cam? What is the exhaust duration usually like on these? Also forgot to mention I may want to add a small (75) NOS shot to the system (to cool the charge + the obvious)- would the longer exhaust duration of the SC cam be beneficial for this?

[chodjinn]

yes, although i have no idea about exhaust stuff. I've got a custom high torque cam in my twin turbo motor, and yes i realise the difference between SC and TC, but both instances would benefit from more low down torque (esp. the turbo route which obviosuly requires time to spool, where as SC has power constantly) as both instances you don't need to rev the b0ll0cks off the motor to get peak power.

Personally, I have read a LOT on turbo/supercharging and camshafts and I've still not found a single convincing arguement to point me in the right direction. Its hard to find conclusive evidence on the net, most of it is 'my mate did this' or 'my mate ran this cam spec and this happened' but there never is any consistency.

Some people say zero overlap, some dont. Some say longer exhaust duration, some equal. There is so much ambiguity (IMO only, dont flame me for that!) that I think it's best to get a cam for the whole engine (if you see what I mean) such as high torque.

You can never have enough torque mate. You could have 800 bhp, but without decent torque its all useless and wasted (see group B rally cars vs. WRC rally cars as an example)

[topcatcustom]

I am most definately looking for torque well down as I want to use as much of the standard valve gear as possible including hydraulic lifters which means keeping the peak power well under 5800 (so I understand)

[chodjinn]

Found the spec of my cam. Its somewhere between a Piper 255 and 270 I believe.

Problem is I have two quotes of the spec for it!

1. Rev range 1000-5500rpm, peak torque 2000-4500 rpm. , duration 264 degrees, lift 0.44".

2. The other quote give it 262 degrees and .433" lift (so there's not much in it but you get the idea).

Hope that helps. And customs cams are not that expensive to get done, speak to Pipe they are good value and helpful.

[Rossco]

Plenty of exhaust duration and preferably one with more than 112 LSA

Try looking at some of the Voodo or Crower cams