This is a street car, I am not much of a racer. This is a journey for me, and I enjoy the trip. So please humor me.

I have a pair of grand national turbos. And they made a nice 245hp at 4400rpm with 231ci.

So to define my new peak RPM I use the formula : (231*4400)/(355/2) = 5726 rpm (5700 RPM for my purposes)

Defining Torque at the GN peak power
T = 5252*HP/RPM
T = 5252*245/4400
T= 292 Ft-Lbs of Torque

HP = T*RPM/5252
HP = 292*5700/5252
HP = 316.9

Its a twin setup so 316.9*2 = 633.8hp Not to shabby for a mild street car.

So we have now defined peak RPM, and HP goals.

A compcams replacement camshaft for a grand national is 258/258 with an LSA of 110.

The Dynamic Compression ratio for a grand national is 6.85:1

The sweet spot for the intake closing would be 68.5 ABDC


If we compare the stroke to the duration of the camshaft.
258/3.4(GN stroke)*3.48(355 stroke) = 264.01

To get an comparable dynamic compression ratio similiar to a GN I would need an intake centerline of 116.

Until I get some flow numbers I cannot adequately define my exhaust lobe, and vicariously my lobe seperation angle.

But for the sake of arguement an exhaust lobe with the same duration as the intake will be used. Which will require an LSA of 114.

So given the cammotion cam lobes they have the cam would be 265(208)/265(208) with an LSA of 114 and 2 degrees of retard ground in.
The rest of the motor as it sits now.

Speed pro 21cc forged dish pistons
Eagle H-beam rods 5.7"
No crank yet
Custom billet aluminum oil pan
Titan speed engineering oil pump
Superflowheads that have been port matched and the throat areas cleaned up
OE roller block
OE roller lifters
Weiand Xcelerator intake
Holley 750 that I am home modifying

Just my thoughts and home layman engineering. It will be fun to see how it works out.

 

My exhaust duration will be determined by the formula

eD * eF = iF*iD*.77

iD=264

 

WAY over my naturally aspirated head, man, WAY over....

 

Where's TT? On Holiday?

 

I approach things slightly different.

I think most people would want me to have a 276/276 with a 114 LSA and 4 degrees of advance ground into it.

Given what superflowheads advertises their flow numbers for comparison as 238 and 191.

So eD*191=238*265*.77

So in theory my exhaust lobe would be 254 degrees of duration. That is entirely dependant of course on actual flow numbers.

Long durations have lots of overlap. The GN had 38 degrees of overlap. I want to get under that.