Cathedral Port Vs. Rectangular Port
Registered User
Joined: Apr 2015
Posts: 5
Likes: 0
From: Greenville Michigan
I have been kicking around this same question Cathedral or Rectangular. I have a LQ4 in my 81 Trans Am and would like to get a little more HP out of it. It is a street car so I don't want to go nuts. It sounds like from this thread that I should port the 317 heads and swap the cam. I am running a LS6 intake and 1-7/8 headers 2-1/2" exhaust.
Do you think this would get me good street power and torque? If I wanted to take it to the track would I be able to hit it with a 150 to 200 shot of NOS?
Do you think this would get me good street power and torque? If I wanted to take it to the track would I be able to hit it with a 150 to 200 shot of NOS?
Mild work on the 317s and a cam should have the car flirting with needing a rollbar and a 200shot could have it flirting with a rollcage.....
Detail oriented folks will make a car like yours run 10s with portwork and a cam Most of us wont dial them in that perfectly though.
Detail oriented folks will make a car like yours run 10s with portwork and a cam Most of us wont dial them in that perfectly though.
Registered User
Joined: Apr 2015
Posts: 5
Likes: 0
From: Greenville Michigan
Thanks for the response!! this is what I was looking for. The car is in perfect shape and all original except for the drive train. I am going for the sleeper look that will turn heads when I unleash it on the street. I will never put a roll bar or cage in it, but 1 run down the track to get a time slip to be prod of would nice. I am running the 4l60E with a 2800 stall, 390 gears with an Auburn electric locker Any suggestions on the cam?
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo 2800 stall is going to make you keep the cam mild and not allow you to get the most of it at the track. Is it at least a 9.5" from a quality supplier like Yank, Vig, Circle D, Edge?
If you say 12" or something of suspect quality like TCI then that needs to be addressed before you look at a cam.
With a light car and 3.90s most quality 9.5" converters will drive wonderfully even up into the 32-3600stall range.
Would like to hear more about the electric locker, PM if you want
If you say 12" or something of suspect quality like TCI then that needs to be addressed before you look at a cam.
With a light car and 3.90s most quality 9.5" converters will drive wonderfully even up into the 32-3600stall range.
Would like to hear more about the electric locker, PM if you want
Registered User
Joined: Apr 2015
Posts: 5
Likes: 0
From: Greenville Michigan
It is a 9.5 custom built by a racing outfit out of Muskegon, MI can't remember the name, but it was built for my 383 SB with a nitro cam and FI, so I'm not opposed to changing it. I'm not looking to go real radical on the cam, just want it to sound a little more healthy like my 383 did and get a good power boost over stock. Some suggested a Howard cam similar to the GM hot cam I will see if I can get the specs.
Registered User
Joined: Apr 2015
Posts: 5
Likes: 0
From: Greenville Michigan
It is an electric locker from Aburn Gear called ECTED Max. I only use it when I do some serious burnouts or drag racing. I have a switch on the dash that applies 12V to the rear end to lock the spool. It works great never had the posi fail no mater how ruff I'm on it.
Launching!
Joined: Oct 2003
Posts: 267
Likes: 14
From: Chicago
I have a 383 stroked ls6, stock zo6 cam, 200 dollar bowl clean on my 317s, with 9.1 compression. Getting an f1 a soon..
However, just the motor dynoed 454 hp, with 494 ft lbs.
The ls7 427 crate has 505 hp, 470 ft lbs on 11.1 compression. Let's drop the compression 2 points on that motor and see.
Or If, I had 11.1, my 383 ls6 would be just about 500 hp, and have way more torque. If I had a 427 ls6, it would be close to 600 hp with 11.1. I don't know, I think the ls7 is kinda weak. Well, it's not, cam it..
But still, that motor has almost 50 cubes more. And it produced less torque .. How is that possible? The 427 should have like 525 to 550 ... But those square port heads, blead the torque, is my guess. They flow way to much.
Now stick a blower on rectangular port heads, they do come alive... Big time.
But the ls6 motors will still hold its own. I see some folks have 400 rw on their stock ls6 motors, with all bolt ons. Mean motor.. All time favorites..
Now you think this motor is bad. I dynoed my stock 340 sick pack, 1970 ta challenger motor. It made 412 hp, with 450 ftlbs. On a .474 inch stock cam... 10.1 motor. Factory TA fast burn small chamber heads.
Not bad for for 1970..
However, just the motor dynoed 454 hp, with 494 ft lbs.
The ls7 427 crate has 505 hp, 470 ft lbs on 11.1 compression. Let's drop the compression 2 points on that motor and see.
Or If, I had 11.1, my 383 ls6 would be just about 500 hp, and have way more torque. If I had a 427 ls6, it would be close to 600 hp with 11.1. I don't know, I think the ls7 is kinda weak. Well, it's not, cam it..
But still, that motor has almost 50 cubes more. And it produced less torque .. How is that possible? The 427 should have like 525 to 550 ... But those square port heads, blead the torque, is my guess. They flow way to much.
Now stick a blower on rectangular port heads, they do come alive... Big time.
But the ls6 motors will still hold its own. I see some folks have 400 rw on their stock ls6 motors, with all bolt ons. Mean motor.. All time favorites..
Now you think this motor is bad. I dynoed my stock 340 sick pack, 1970 ta challenger motor. It made 412 hp, with 450 ftlbs. On a .474 inch stock cam... 10.1 motor. Factory TA fast burn small chamber heads.
Not bad for for 1970..
Last edited by stage274; Jun 17, 2015 at 05:35 AM.
Launching!
Joined: Oct 2003
Posts: 267
Likes: 14
From: Chicago
Yeah... Sure buddy..
Soon I will have 850 rw, with an f1a at 20 lbs on that same 383... Rectangular port heads are not the best even though they flow, is the point.
I am a Muscle car fanatic. But always hated old Chevy engines. I mean, I would take a 70 427, or a 454. But their motors performed the worst out of the big 3. And worse than Pontiac and olds and Buick. There is no way, a square port 454 will beat a Buick 455, or a poncho 455...
454 head flowed more always... But a Buick 455 or poncho would destroy it, making world turning torque...
Soon I will have 850 rw, with an f1a at 20 lbs on that same 383... Rectangular port heads are not the best even though they flow, is the point.
I am a Muscle car fanatic. But always hated old Chevy engines. I mean, I would take a 70 427, or a 454. But their motors performed the worst out of the big 3. And worse than Pontiac and olds and Buick. There is no way, a square port 454 will beat a Buick 455, or a poncho 455...
454 head flowed more always... But a Buick 455 or poncho would destroy it, making world turning torque...
Last edited by stage274; Jun 17, 2015 at 12:56 PM.
Launching!
Joined: Oct 2003
Posts: 267
Likes: 14
From: Chicago
http://image.gmhightechperformance.c...g_camshaft.jpg.
Not very impressive for such big cubes, not at all..
But to be fair, I did see some making huge power...
Not very impressive for such big cubes, not at all..
But to be fair, I did see some making huge power...
340 6 pack stock only run 99 MPH or so in the 1/4 mile....So, that HP number seems awfully suspect to me. Anyways, the original LT-1 solid lifter 11:1 370HP 350 is the best small block IMO of any of the "old school" muscle car engines...My old man had a 71 Corvette with that motor that was a beast and sounded ungodly 
LT-1s also typically trapped higher in the quarter mile...100+MPH
Worst performing my azz....Lol
LT-1s also typically trapped higher in the quarter mile...100+MPHWorst performing my azz....Lol
Launching!
Joined: Oct 2003
Posts: 267
Likes: 14
From: Chicago
Now, we can take an expample from one of my old cars, an 89 turbo ta... Put a small, te 44 on it, and 18 pounds of boost. You will be making 400 plus rear wheel, but 600 plus ftlbs... Those heads flowed like 190 cfm... There was not a zo6 that could touch that car. Everybody thought is was a 305 ta to boot.
That was one of the most potent cars, that ever left GM. And was the biggest sleeper of all time in my opinion.
I can't wait for the twin turbo ctsv.. I know, people would opt for the ls7 in the ctsv, but not me.. That twin turbo model that is coming out, is going to be a killer.
That was one of the most potent cars, that ever left GM. And was the biggest sleeper of all time in my opinion.
I can't wait for the twin turbo ctsv.. I know, people would opt for the ls7 in the ctsv, but not me.. That twin turbo model that is coming out, is going to be a killer.
Launching!
Joined: Oct 2003
Posts: 267
Likes: 14
From: Chicago
340 6 pack stock only run 99 MPH or so in the 1/4 mile....So, that HP number seems awfully suspect to me. Anyways, the original LT-1 solid lifter 11:1 370HP 350 is the best small block IMO of any of the "old school" muscle car engines...My old man had a 71 Corvette with that motor that was a beast and sounded ungodly LT-1s also typically trapped higher in the quarter mile...100+MPH
Worst performing my azz....Lol
LT-1s also typically trapped higher in the quarter mile...100+MPHWorst performing my azz....Lol
1250 cfm is the carburation man.. The motor, has been blue printed, only... There are many 340 6 pack 4 speeds, running fast, like 11.50s.. A few years ago, a guy running stock class, got tens, out of his 340 Ta.
I know they are advertised 275 hp... But a blue printed motor is where it's at... I said I used a stock cam, well I did, from a regular 4 barrel, 340, .474 lift. The actual cam specs for the 340 6 pack was .424. They detuned them. I was not going to use that cam.
The dz 302 made over 400 hp also, with the daul carbs... 400 hp is not hard to get. But what I was impressed with is the tourqe it made..
The ta heads, are the best small block heads to come from mopar, special heads, special trans am series x block...
The turbo TA was one of the quickest cars GM ever built.
The 370hp 350 was in a corvette much lighter than any mopar it would have faced. The Chevy small block won lots of races due to weight, not output. Otherwise, we wouldn't be putting LS's into older cars.
A 340 six pack putting down 400+? At the crank MAYBE.
Now, back to the thread. Square port heads are great when the engine is drawing 300+ cfm. Most of the time, your engine isn't breathing that hard, so port velocity becomes more important than total flow capability. This is what gives air momentum to continue filling cylinders past TDC. Also the reason cathedrals can tolerate bigger cams
The 370hp 350 was in a corvette much lighter than any mopar it would have faced. The Chevy small block won lots of races due to weight, not output. Otherwise, we wouldn't be putting LS's into older cars.
A 340 six pack putting down 400+? At the crank MAYBE.
Now, back to the thread. Square port heads are great when the engine is drawing 300+ cfm. Most of the time, your engine isn't breathing that hard, so port velocity becomes more important than total flow capability. This is what gives air momentum to continue filling cylinders past TDC. Also the reason cathedrals can tolerate bigger cams