Engine upgrades: all comments welcome

[dassaur]

I’m glad I went a little smaller at 219/225.

Still has manners and low down torque

I'd be surprised if yours makes more low down torque than mine.
Do you know your intake valve closing timing? Mine's 39 ABDC @ .050

 

[RevNev]

I'd be surprised if yours makes more low down torque than mine.
Do you know your intake valve closing timing? Mine's 39 ABDC @ .050

An old race engine builder taught me in the late 70's before you fit a new camshaft, do a compression test on the engine. The reason he told me, is that increasing duration and closing the inlet vale later, reduces the engine's dynamic compression and it'll lose bottom end horsepower.

After fitting the new camshaft, compression test the engine again and it'll show less cranking pressure. Then what you do is keep machining 0.020" off the cylinder head until the cranking pressure is the same as it was with the stock camshaft.

It's "old school" engine trickery today, but it actually works to maintain optimum bottom end horsepower when changing to a bigger camshaft or increasing valve overlap!

 

[dassaur]

An old race engine builder taught me in the late 70's before you fit a new camshaft, do a compression test on the engine. The reason he told me, is that increasing duration and closing the inlet vale later, reduces the engine's dynamic compression and it'll lose bottom end horsepower.

After fitting the new camshaft, compression test the engine again and it'll show less cranking pressure. Then what you do is keep machining 0.020" off the cylinder head until the cranking pressure is the same as it was with the stock camshaft.

It's "old school" engine trickery today, but it actually works to maintain optimum bottom end horsepower when changing to a bigger camshaft or increasing valve overlap!

That's a great trick and it would work for cams like mine but as soon as you fit something 'big' in an LS gen 4 you will run into PTV issues on the intake with any milling.

I probabyl couldve milled down to 62cc or further but I left it at a safe 65cc

The guy who specced my cam reckons the DCR will be around 8.6:1 (in my limited understanding the DCR is taken to be compression in cylinder with piston at intake valve closing position vs static where it is at BDC)

 

[RevNev]

That's a great trick and it would work for cams like mine but as soon as you fit something 'big' in an LS gen 4 you will run into PTV issues on the intake with any milling.

I probabyl couldve milled down to 62cc or further but I left it at a safe 65cc

The guy who specced my cam reckons the DCR will be around 8.6:1 (in my limited understanding the DCR is taken to be compression in cylinder with piston at intake valve closing position vs static where it is at BDC)

Yes, dynamic compression is determined by the inlet valve closing position. You'll often see in camshaft listings it'll say, "needs comp" for a particular grind. Piston to valve clearance that wasn't so much of an issue in the older engines certainly needs to be physically measured.

 

[dassaur]

I wonder what DCR of a stock LS3 or L77 is.
In my case my static compression went from 10.4:1 to 11:1
Would be interesting to know stock cam DCR. According to wallace racing calculator, the DCR for LS3 stock is:
7.40:1

Alas I dont know cam specs of L77 @ 0.04 or 0.06

 

[RevNev]

I wonder what DCR of a stock LS3 or L77 is.
In my case my static compression went from 10.4:1 to 11:1
Would be interesting to know stock cam DCR. According to wallace racing calculator, the DCR for LS3 stock is:
7.40:1

Alas I dont know cam specs of L77 @ 0.04 or 0.06

You could measure the difference in DCR between camshafts but ultimately regardless of grind in a race engine application where they're subject to greater heat than on the road, any more static compression ratio than 10.5:1 with alloy heads is pushing it on 98 octane pump fuel.

 

[daves8]

I'd be surprised if yours makes more low down torque than mine.
Do you know your intake valve closing timing? Mine's 39 ABDC @ .050

Nope no idea, I’m not very tech.

I just know it hauls like a scalded cat down low, and has good manners

Enough for me!

 

[dassaur]

Nope no idea, I’m not very tech.

I just know it hauls like a scalded cat down low, and has good manners

Enough for me!

What were your specs again? I'm interested now in seeing!

Need intake, exhaust, lsa, and any advance. If you don't know advance, then intake centreline

 

[losh1971]

An old race engine builder taught me in the late 70's before you fit a new camshaft, do a compression test on the engine. The reason he told me, is that increasing duration and closing the inlet vale later, reduces the engine's dynamic compression and it'll lose bottom end horsepower.

Yes, but this means you can apply some FI without having too much comp, which then solves the bottom end problem.

A wise man once told me everything is better with boost.

 

[daves8]

What were your specs again? I'm interested now in seeing!

Need intake, exhaust, lsa, and any advance. If you don't know advance, then intake centreline

From memory

219/224/115 +2 advance, about 560 lift