LQ4 Switching to Rectangular Port Heads?
Thread Starter
Teching In
Joined: Jan 2013
Posts: 30
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From: Saskatchewan, Canada
LQ4 Switching to Rectangular Port Heads? I have a rebuilt LQ4 engine in my '70 Firebird. It has a LS6 crank, floating connecting rods, flat top pistions, balanced rotating assembly, 799 heads, trunion kit for the rocker arms, hardened push rods, LS1 intake with a larger DBW TB off of a '05 sierra and a custom ground camshaft with the following specs:
ADV. DURATION INT:282.73
ADVERTISED DURATION EXH:286.97
INT DURATION @ .050":256.41
EXH DURATION @ .050":261.28
VALVE LIFT INT (IN.): 0.34677
VALVE LIFT EXH (IN.): 0.33988
VALVE LIFT INT (1.7R) : 0.589509"
VALVE LIFT EX (1.7R): 0.577796"
LOBE SEPERATION:?
INTAKE CENTERLINE:109.75
(Values taken from my cam card. Custom ground cam)
I have found a good deal on a holley mid ram w/ 102mm TB. It is however a rectangular port intake. I know my current intake doesnt flow very well and I have heard rectangular port heads will flow better than cathedral.
I was thinking of switching to a 821 or 823 head and running a DBW 102mm TB. Would that kind of investment be worth it?
The car currently makes 360.5HP@5550RPM and 386.2FTLBS@4700RPM on the chassis dyno. It just a TH400 car for now as well.
ADV. DURATION INT:282.73
ADVERTISED DURATION EXH:286.97
INT DURATION @ .050":256.41
EXH DURATION @ .050":261.28
VALVE LIFT INT (IN.): 0.34677
VALVE LIFT EXH (IN.): 0.33988
VALVE LIFT INT (1.7R) : 0.589509"
VALVE LIFT EX (1.7R): 0.577796"
LOBE SEPERATION:?
INTAKE CENTERLINE:109.75
(Values taken from my cam card. Custom ground cam)
I have found a good deal on a holley mid ram w/ 102mm TB. It is however a rectangular port intake. I know my current intake doesnt flow very well and I have heard rectangular port heads will flow better than cathedral.
I was thinking of switching to a 821 or 823 head and running a DBW 102mm TB. Would that kind of investment be worth it?
The car currently makes 360.5HP@5550RPM and 386.2FTLBS@4700RPM on the chassis dyno. It just a TH400 car for now as well.
Last edited by Offroadunleashed; Jan 23, 2021 at 09:11 AM.
TECH Senior Member
Joined: Jun 2016
Posts: 22,291
Likes: 3,616
From: Central Cal.
Uhhh.... .250 lift????
A wee bit low....
Edit- Just looked at cam specs- Intake cam lift is .34677
Exhaust cam lift is .33988
At 1.7 rocker ratio is - .589509 I
.577796 E
A wee bit low....
Edit- Just looked at cam specs- Intake cam lift is .34677
Exhaust cam lift is .33988
At 1.7 rocker ratio is - .589509 I
.577796 E
Last edited by G Atsma; Jan 17, 2021 at 08:00 PM.
Thread Starter
Teching In
Joined: Jan 2013
Posts: 30
Likes: 0
From: Saskatchewan, Canada
TECH Senior Member
Joined: Jun 2016
Posts: 22,291
Likes: 3,616
From: Central Cal.
Depends on how crisp you want your low end response. Rectangulars will give you some top end, but at the expense of some low end response. What will the main purpose of the car be?
