Small port 308 engine

I haven't the lift curve data to map the catcam lobe agression but the curves give the impression of where things start and finish. The intake is based around the 40 DCNF and 34 chokes.
I decided not to go the catcam route based on the loss of significant lower speed Hp in a 9.6 CR motor. The absolute numbers are to be regarded with caution.

The first graph 308 crank euro has the labels swapped, The green Hp and dark blue Tq are indeed the the catcam combination!

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Thought I should put this with the other graphs.

QV London have a road cam with a 10.2mm lift, used with standard springs and shim on bucket (SOB) but a shorter duration than the catcam sport. It is a billet cam made by Kent cams in the UK and would be a sensible choice for most 308 owners if they were buying camshafts for some reason. The graph is based on a 9.5 CR engine. Perhaps some losses below 6K but strong upper range. You could ask them for the real data if needed.
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Thanks Rob, Given that most of us spend a lot more time below 6000rpm, I would rather have the milder cams. I can get some euro 208 cams and I've heard you can switch inlet and exhaust cams so what combination do you think would work for a faster road setup (I can change the cam timing and carbs to match, plus port match etc. (if that will help but it sounds like reversion may be more of a problem than flow.)

 

Derek,

Attached graph is the difference in the euro 208 vs 308 intake when used with the 308 euro exhaust.330 lift in the 2.95 stroke motor. Otherwise the "348" sim graphs give an indication of the bottom end losses.
I am currently using the 208 inlet & 308 exhaust cams and don't feel reversion is a real issue. Pay attention to intake valve edge margin/sharpness and round off the exhaust valves chamber face to aid in that issue.

Do you already have the euro 308 intake or exhaust cams ?
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Rob,

I'm a relative novice on the porting so would appreciate an explanation of the "intake valve edge margin/sharpness". I understand the "round off the exhaust valves chamber face."

I only have the crappy N. America '79 cams (217/.305 and 212/.300) but had read somewhere you could use inlet cams for exhaust in case the 217/.305 works for exhaust. I may just keep a look out for some euro 308 cams. Do you know the 208 cam specs?

 

Unfortunately you can't swap the intake cam for the exhaust.
The 208 exhaust cam is the same as the 212/.300 you have already. I did a sim a while ago showing gains below 5.5 k but losses above this when used with the euro intake. The car felt just like the sim predicted. I will plot one for your engine combo later.
The valve nomenclature is around the vale margin thickness which can be reduced with flat or conical grinding to a sharp edge, The reality is to not round the edge like the exhaust or you can narrow the margin to .040 with a 70 back cut from the chamber face of the valve ( Guy Croft mod for some of the hemi fiat engines). I will see if I can find a picture.

Texture seems a reasonable thing for these DCNF engines.

PipeMax Creator Larry Meaux on Race Engine Head Porting | Hot Rod Engine Tech

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Here are the effects of matching the 208/308 euro intake cams with the US/208 exhaust cams as well as US intake with US exhaust. These are for the 348 crank with 10.5 CR and wildly optimistic VE numbers.

The trends seem valid. The second graph is with the 208 intake/exhaust camshafts timed to 100/102 to help the higher RPM with the subsequent lower torque loss visible.

With respect to the intake valves, it is a 30 degree to the vertical cut on the chamber face of the valve rather than the standard 45 deburing bevel that acts as the anti reversion edge as detailed in Guy Crofts books.
If the 208 intake cams are cheaply available then I think they are a good alternative for a motor used to a 7k rev range.

Cheers
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Great stuff there. I have nothing but high praises for the cat cams as long as higher compression of at least 10:1 is run. I saw 274bhp at the wheels with my 3.4 motor, which translates to about 330bhp at the crank. Very friendly to street drive as well

 

John, do you have their mildest cams (around 10.5mm lift?) Rob's simulations suggest you give up a bit at the lower rpms where the car spends more time in traffic.

 

John,
The fact your heads could flow to that sort of horsepower is very encouraging! With a larger capacity engine the Catcam or QV camshafts are impressive. It's really just a budget and setup issue, shim on or shim under bucket deal. I installed the springs and Ti retainers in preparation for catcams and supertech followers but am not yet sure I will now go that way with my "standard engine".
Derek,
There is only perhaps 600 rpm difference between the catcam output and the euro cam outputs in the lower rev range at WOT. The bigger differences from the catcam to euro were when the euro cams were timed for maximum torque but not higher rpm.

The following graphs may show it better
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