I'm looking forward to this discussion.  We've had it a few times in the past.  Everyone on this page has their own idea.  Because all those measurements you show are, mostly, infinitely variable.  The one you picked is one that many use for street/track use.

Just remember Art Arfons used to drive the Green Monsters on the street.  (Allison V12 airplane engine)

First, a properly selected cam should ALWAYS be run straight up.  If you need to monkey with the cam timing you picked the wrong cam.  A lot is made of it, but in reality, moving the cam 1 degree moves the HP peak 100RPM.  You start to see what any kind of meaningful change is going to mean (e.g. a 500 RPM swing is going to require 5 degrees of timing change).  There may be forms of racing where this matters, but for the average guy it does not.

Second, if you are running EFI I would say a 108 LSA is too tight.  Generally EFI cams are ground on more like a 112 LSA.  They typically do not do well with a lot of overlap at idle.

Third, I would discuss everything you plan to do with the car and your power goal with a cam company and go with their recommendation.  We love to talk about this stuff, but the truth is we know enough to be dangerous.  The best of us here have build maybe a dozen or two engines over the years, whereas the cam companies have built thousands.

Lastly, I would stick with shorty headers.  Long tubes tend to have a real flat spot in the middle of the torque curve, which is where you need power the most on the street and autocross.  Long tubes are better for drag racing and all out power, but you want average torque. 
 

On race motors, there has always been a few more horsepower made on the dyno with an offset key on the cam drive. I have got really good at making offset keys. We never bother on street motors because it is a messy effort.. But, 2 or 5 HP more on a race car is a lot.

DC wrote:

On race motors, there has always been a few more horsepower made on the dyno with an offset key on the cam drive. I have got really good at making offset keys. We never bother on street motors because it is a messy effort.. But, 2 or 5 HP more on a race car is a lot.

True, but also moving peak torque can be as important as how much is made.  For example, if you were drag racing and you were crossing the finish in 3rd or 4th gear at the wrong RPM there would be benefit from moving where peak torque occurred.  Typically you want the engine smack back in peak torque after a shift, and want to cross the 1320 mark at the RPM where you'd shift again if not a little above.  If you were crossing at too low an RPM you could advance the cam and move peak torque down to raise your RPM at the end.  You don't want to add another shift, but you want to use all you can of each gear.  There's a vice versa scenario here too where retarding the cam would help.  Keep in mind this is for racing.  It probably makes no difference on the street

TKOPerformance wrote:

Lastly, I would stick with shorty headers.  Long tubes tend to have a real flat spot in the middle of the torque curve, which is where you need power the most on the street and autocross.  Long tubes are better for drag racing and all out power, but you want average torque. 
 

When I first started getting parts together for an engine update for my 66 I was planning on dropping in a refreshed mostly stock 5.0 but I've changed my mind about that. I think the shorties made sense for a setup like that. Another reason for going with the shorties was easier fit - I'm going to be using MustangSteve's cable clutch setup with the swap from C4 to T5 and have a Borgeson box installed.

That said everything I've read (and not just on the interwebs) suggests that well designed long tubes with appropriately sized primaries will positively impact torque across the curve and definitely pull more power. I am concerned that the small shorties I have will bottle neck the motor I'm building now.

McStang wrote:

TKOPerformance wrote:

Lastly, I would stick with shorty headers.  Long tubes tend to have a real flat spot in the middle of the torque curve, which is where you need power the most on the street and autocross.  Long tubes are better for drag racing and all out power, but you want average torque. 
 

When I first started getting parts together for an engine update for my 66 I was planning on dropping in a refreshed mostly stock 5.0 but I've changed my mind about that. I think the shorties made sense for a setup like that. Another reason for going with the shorties was easier fit - I'm going to be using MustangSteve's cable clutch setup with the swap from C4 to T5 and have a Borgeson box installed.

That said everything I've read (and not just on the interwebs) suggests that well designed long tubes with appropriately sized primaries will positively impact torque across the curve and definitely pull more power. I am concerned that the small shorties I have will bottle neck the motor I'm building now.

I'm hoping the headers aren't JBA.  If so they are going to hit the Borgeson box.  You will need to put a decent dent in one tube to get the clearance you need. 

My '89GT project started like yours as well, and now there's a 331 on a stand...

Best MustangSteve advice I can offer on this one…

“Listen to TKO”

Not a cam question butt....what size rings are you using in the pistons?
The thinner millimeter ring pack(used in newer engines are thinner than the old skool  ring pack.
Waaaaay less drag/friction. Should pick up power and rev quicker. Longivity/oil control should be the same or better as the old style.
6sally6

6sally6 wrote:

Not a cam question butt....what size rings are you using in the pistons?
The thinner millimeter ring pack(used in newer engines are thinner than the old skool ring pack.
Waaaaay less drag/friction. Should pick up power and rev quicker. Longivity/oil control should be the same or better as the old style.
6sally6

I've got a set of Hastings 'Made in USA' (wherever that is) 2M139 rings:
https://apacatalog.com/HastingsCatalog/Home/partdetail/296
Are these skinny enough!? Heh.
Edit: Pistons are Probe FPS forged also made in USA

Last edited by McStang (2/22/2022 10:03 PM)

5/64" is 1.98mm - that's pretty skinny. Seriously tho', I know they're talking about the darkside at the following link but quality of workmanship speaks to me and this kind of stuff prolly makes the biggest difference where the details add up.

Classic : https://www.youtube.com/watch?v=XdSUKSlUgUY

Last edited by McStang (2/23/2022 12:43 AM)