18 degree heads
Safety Car
Joined: Feb 2000
Posts: 4,564
Likes: 109
From: Austin Texas
I am not saying a engine with heads like yours cannot make 750 HP, what I am pointing out is better flowing heads will make power more easily.
A rule of thumb is (intake flow X .256 X 8 = HP potential of a high performance street car), (intake flow x .280 x 8 = HP potential of a competition built engine designed for racing with limited on no street use), (intake flow x .311 x 8 = HP potential of an all out drag race engine, no compromises)
HP street (309 x .256 x 8) = 633 HP
Competition (309 x .280 x 8) = 692 HP
All out, no compromises (309 x .311 x 8) = 769 HP
These are rules of thumb and should only be used as that.
A rule of thumb is (intake flow X .256 X 8 = HP potential of a high performance street car), (intake flow x .280 x 8 = HP potential of a competition built engine designed for racing with limited on no street use), (intake flow x .311 x 8 = HP potential of an all out drag race engine, no compromises)
HP street (309 x .256 x 8) = 633 HP
Competition (309 x .280 x 8) = 692 HP
All out, no compromises (309 x .311 x 8) = 769 HP
These are rules of thumb and should only be used as that.
Thread Starter
Race Director
Joined: Feb 1999
Posts: 12,772
Likes: 17
From: Indianapolis IN
I am not saying a engine with heads like yours cannot make 750 HP, what I am pointing out is better flowing heads will make power more easily.
A rule of thumb is (intake flow X .256 X 8 = HP potential of a high performance street car), (intake flow x .280 x 8 = HP potential of a competition built engine designed for racing with limited on no street use), (intake flow x .311 x 8 = HP potential of an all out drag race engine, no compromises)
HP street (309 x .256 x 8) = 633 HP
Competition (309 x .280 x 8) = 692 HP
All out, no compromises (309 x .311 x 8) = 769 HP
These are rules of thumb and should only be used as that.
A rule of thumb is (intake flow X .256 X 8 = HP potential of a high performance street car), (intake flow x .280 x 8 = HP potential of a competition built engine designed for racing with limited on no street use), (intake flow x .311 x 8 = HP potential of an all out drag race engine, no compromises)
HP street (309 x .256 x 8) = 633 HP
Competition (309 x .280 x 8) = 692 HP
All out, no compromises (309 x .311 x 8) = 769 HP
These are rules of thumb and should only be used as that.
Racer
Joined: Oct 2007
Posts: 478
Likes: 1
"I am not sure what your goals are but your combination could benifit from a cam with a tighter lobe seperation and more duration. It will idle rougher but it will hit harder and make more power if the cam was changed."
You are correct it sure will. However I have rules I have to abide by and they are CARB for smog. Also looking over the dyno results at LS1 Tech I see many motors with just about the same camshaft and similar components making more power. I believe with the 18/15 degree heads you do not need the larger camshaft to make the same horsepower because the heads are more efficient.
I also agree that the LSX style intake runners are very good. I am thinking about emulating them or going to a somewhat straight runner and drop the length to 15-16" in length and utilize the 3rd harmonic wave. I will see what my dyno results will be with the intake manifold I have that is now under construction and go from there.
You are correct it sure will. However I have rules I have to abide by and they are CARB for smog. Also looking over the dyno results at LS1 Tech I see many motors with just about the same camshaft and similar components making more power. I believe with the 18/15 degree heads you do not need the larger camshaft to make the same horsepower because the heads are more efficient.
I also agree that the LSX style intake runners are very good. I am thinking about emulating them or going to a somewhat straight runner and drop the length to 15-16" in length and utilize the 3rd harmonic wave. I will see what my dyno results will be with the intake manifold I have that is now under construction and go from there.
Pro
Joined: Mar 2000
Posts: 658
Likes: 7
From: Perth Amboy New Jersey
Not too sure why you would WANT to go that route.
Your engine @ 7K RPM's NEEDS 1,758 CFM. That would be about 280 CFM per cylinder.
A set of Brodix 23 deg. T1 M2's like I have flow 309 CFM's.
To convert to 18 deg. heads?
Custom Intake
Custom Headers
Both will cost you a BUNCH of money.
23 deg. intakes & headers?
LOTS of choices.
EASY decision...
Your engine @ 7K RPM's NEEDS 1,758 CFM. That would be about 280 CFM per cylinder.
A set of Brodix 23 deg. T1 M2's like I have flow 309 CFM's.
To convert to 18 deg. heads?
Custom Intake
Custom Headers
Both will cost you a BUNCH of money.
23 deg. intakes & headers?
LOTS of choices.
EASY decision...
Converting to a 18 degree set will only require custom piston, shaft rocker, offset lifter assembly and headers just like the ALLPRO. I know the AFR 245 looks good and AFR does deliver the flow they advertise but, 350 at .750 lift is a bit high for my taste on a street engine. There are off the shelf intakes, Edlebrock has 2 piece intakes that makes it easier for porting. There are plenty of used 18 degree parts to be had. I have a 15 degree head 434, I had my Miniram overhauled to work with the heads, since he wants to go with different intake, there are plenty to chose from.
Pro
Joined: Mar 2000
Posts: 658
Likes: 7
From: Perth Amboy New Jersey
"I am not sure what your goals are but your combination could benifit from a cam with a tighter lobe seperation and more duration. It will idle rougher but it will hit harder and make more power if the cam was changed."
You are correct it sure will. However I have rules I have to abide by and they are CARB for smog. Also looking over the dyno results at LS1 Tech I see many motors with just about the same camshaft and similar components making more power. I believe with the 18/15 degree heads you do not need the larger camshaft to make the same horsepower because the heads are more efficient.
I also agree that the LSX style intake runners are very good. I am thinking about emulating them or going to a somewhat straight runner and drop the length to 15-16" in length and utilize the 3rd harmonic wave. I will see what my dyno results will be with the intake manifold I have that is now under construction and go from there.
You are correct it sure will. However I have rules I have to abide by and they are CARB for smog. Also looking over the dyno results at LS1 Tech I see many motors with just about the same camshaft and similar components making more power. I believe with the 18/15 degree heads you do not need the larger camshaft to make the same horsepower because the heads are more efficient.
I also agree that the LSX style intake runners are very good. I am thinking about emulating them or going to a somewhat straight runner and drop the length to 15-16" in length and utilize the 3rd harmonic wave. I will see what my dyno results will be with the intake manifold I have that is now under construction and go from there.
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Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
"The AFR 235's flow in the 340cfm range, and the AFR 245's flow in the 350cfm range, both 18 degree territory."
I know what everyone is saying but I think there is more to this from my experiences. Comparing my motor to the LSX series I am down 30+ horsepower. Here are my stats.
1) 369cubes
2) 11.12:1 compression ratio
3) 280/280-233/233 camshaft on 113 LSA, .594" lift at valve.
4) AFR 210 heads modified by DR J., Flow 305cfm at .600" lift on his bench. Speed at the pushrod pinch is 315fps. 2.08/1.60 valves.
5.) Intake flows 336 cfm with maximum with max airspeed of 300fps at peak horsepower rpm of 6500rpm.
I know what everyone is saying but I think there is more to this from my experiences. Comparing my motor to the LSX series I am down 30+ horsepower. Here are my stats.
1) 369cubes
2) 11.12:1 compression ratio
3) 280/280-233/233 camshaft on 113 LSA, .594" lift at valve.
4) AFR 210 heads modified by DR J., Flow 305cfm at .600" lift on his bench. Speed at the pushrod pinch is 315fps. 2.08/1.60 valves.
5.) Intake flows 336 cfm with maximum with max airspeed of 300fps at peak horsepower rpm of 6500rpm.
Advanced
Joined: Jan 2012
Posts: 78
Likes: 0
18 &15 degree heads
18 &15 degree heads are plain more efficent in every way .Flow is not the only variable making h.p.And if your pulling a heavy sled around like corvette you should be aware of this.
Pro
Joined: Mar 2000
Posts: 658
Likes: 7
From: Perth Amboy New Jersey
Burning Brakes
Joined: Aug 2000
Posts: 1,146
Likes: 2
From: Albuquerque NM
yeah but what most people dont realize is that most 18 degrees heas have way too big an intake port size for normal duty. If the port is too big, the flow will stall and you'll generate far to little dynamic pressure to effectively fill the cylinder...much less make effective vacuum.
just me but
a 355ci motor wants 165-195cc intake port size
a 383ci motor needs no more than 215cc
a 427-434 can take up to 250cc...i use a 227cc ported to 232ish
efficient heads mean that high mass flow for a small cross section...this is what AFR sells.
But when you need a sledge hammer....a 250-350cc port is needed to get the big flow numbers.
just me but
a 355ci motor wants 165-195cc intake port size
a 383ci motor needs no more than 215cc
a 427-434 can take up to 250cc...i use a 227cc ported to 232ish
efficient heads mean that high mass flow for a small cross section...this is what AFR sells.
But when you need a sledge hammer....a 250-350cc port is needed to get the big flow numbers.
Melting Slicks
Joined: May 2001
Posts: 3,270
Likes: 26
From: Winchester VA
Cruise-In V Veteran
yeah but what most people dont realize is that most 18 degrees heas have way too big an intake port size for normal duty. If the port is too big, the flow will stall and you'll generate far to little dynamic pressure to effectively fill the cylinder...much less make effective vacuum.
just me but
a 355ci motor wants 165-195cc intake port size
a 383ci motor needs no more than 215cc
a 427-434 can take up to 250cc...i use a 227cc ported to 232ish
efficient heads mean that high mass flow for a small cross section...this is what AFR sells.
But when you need a sledge hammer....a 250-350cc port is needed to get the big flow numbers.
just me but
a 355ci motor wants 165-195cc intake port size
a 383ci motor needs no more than 215cc
a 427-434 can take up to 250cc...i use a 227cc ported to 232ish
efficient heads mean that high mass flow for a small cross section...this is what AFR sells.
But when you need a sledge hammer....a 250-350cc port is needed to get the big flow numbers.
My 18 heads took a 1206 gasket and were probably 250-260cc. The other thing that effects the comparison is the relocated pushrod. The pinch reduces the measured volume of the 23 runner and not in a good way.
This effect is also seen in the 15 degree LS series. The LS6 at 346 cubes got a 210cc runner.
Need to consider varied runner design when comparing cc as a gauge of efficiency
Burning Brakes
Joined: Aug 2000
Posts: 1,146
Likes: 2
From: Albuquerque NM
runner design does have a lot to say (straight flow) about the potential pumping efficiency of the head. raised port heads (up to 1.5") are probably the most efficiency, followed by the cathedral ports of the Ls1/2. However, big port race heads will always want larger cubes or higher RPM range.
When I choose my final design (is it ever done?), i went with a best flowing intake and then port matched to the MRIII (1209?), Displacement and cam just set the TQ where ever thing works. Sadly the 18x head lost out because I already had the intake I was invested in.
Having said that, my offset rockers should have yielded more flow than the heads gave up.
When I choose my final design (is it ever done?), i went with a best flowing intake and then port matched to the MRIII (1209?), Displacement and cam just set the TQ where ever thing works. Sadly the 18x head lost out because I already had the intake I was invested in.
Having said that, my offset rockers should have yielded more flow than the heads gave up.
Melting Slicks
Joined: Dec 2008
Posts: 2,772
Likes: 64
From: Mystic CT
yeah but what most people dont realize is that most 18 degrees heas have way too big an intake port size for normal duty. If the port is too big, the flow will stall and you'll generate far to little dynamic pressure to effectively fill the cylinder...much less make effective vacuum.
just me but
a 355ci motor wants 165-195cc intake port size
a 383ci motor needs no more than 215cc
a 427-434 can take up to 250cc...i use a 227cc ported to 232ish
efficient heads mean that high mass flow for a small cross section...this is what AFR sells.
But when you need a sledge hammer....a 250-350cc port is needed to get the big flow numbers.
just me but
a 355ci motor wants 165-195cc intake port size
a 383ci motor needs no more than 215cc
a 427-434 can take up to 250cc...i use a 227cc ported to 232ish
efficient heads mean that high mass flow for a small cross section...this is what AFR sells.
But when you need a sledge hammer....a 250-350cc port is needed to get the big flow numbers.
OK rant over time to go back to work making HP.. Dave
