Diff Between 18 And 23 Degree Heads
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Instructor
Joined: Sep 2003
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From: Apple Valley MN
Diff Between 18 And 23 Degree Heads
Could someone inform me about the differences between 18 and 23 degree heads. Does one make more power than the other.??? Im shopping around for heads to go on my new motor with the procharger. Ill be lurking around 
Race Director
Joined: Dec 1999
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valve angle (18 vs 23 deg) port height, basically the 18 degree valve has the port aiming down at the valve from a "higher" plane meaning the port makes less of a bend down to the valve. The 18 degree head has more flow potential.
Instructor
Joined: Aug 2004
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From: Roskilde
Originally Posted by supervett77
Could someone inform me about the differences between 18 and 23 degree heads. Does one make more power than the other.??? Im shopping around for heads to go on my new motor with the procharger. Ill be lurking around
Thread Starter
Instructor
Joined: Sep 2003
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From: Apple Valley MN
what do you mean compensating for inefficient head design? You want better heads so you can get better flow for boosted applications right. I wonder if the 383 stroker could make up for that loss in lower rpm torque. I didnt' even know they had 15 degree heads. It sounds like if i go lower in degrees i will loose more low end power. What rpm range is an 18 degree good for? That might help me a little
Thread Starter
Instructor
Joined: Sep 2003
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From: Apple Valley MN
So basically If i get 18 degree heads im bolting on a lot more hp than i would with 23 degree fastburn heads. The setup that will be built is SRP dished pistons 8.5 to 1 383 stroke, my camshaft specs are .540 , and .550
with about 240degrees of duration at .50. It is hydralic roller cam. The procharger is coming to my house on a preset 12psi at 6200 rpm. I have a feeling 18 degrees make power at like 7000 rpm not 6400. Im not sure the cam would be matched to 18 degree heads. What would happen if i did have them ?
with about 240degrees of duration at .50. It is hydralic roller cam. The procharger is coming to my house on a preset 12psi at 6200 rpm. I have a feeling 18 degrees make power at like 7000 rpm not 6400. Im not sure the cam would be matched to 18 degree heads. What would happen if i did have them ?
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Instructor
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From: Plano Texas
Originally Posted by mensch53
I would say the difference is about 5 degrees 
Sorry...had to be said
Sorry...had to be said
The difference IS about 5, but only in METRIC degrees . . . . pretty much everyone here knows THAT!!
Le Mans Master
Joined: Feb 1999
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From: Park Ridge IL
I used 18* heads on my TT SBC427. You will need shaft mounted rockers and offset lifters and pistons designed for 18* heads as mentioned. Most 15* heads utilize the same valvetrain components and piston designs as 18* heads. You'll also need an intake manifold design for 18* heads due to the difference intake face angle and raised ports. The exhaust ports are also raised, and some 18* heads have different header bolt layouts (standrd,Stahl, Reher-Morrison, or two, etc) so the headers may have to be changed or modified.
The reason most 18* cylinder heads give up some low end torque compared to conventional 23* heads is due to the fact that 18* heads are intended for racing use and almost always feature larger intake port size (volume and cross-section) than 23* heads intended for street/hiperformance use. You can get smaller port 18* heads, but they are still at least 235cc or so. The Dart 18* CNC heads I ran were 257cc, but on a 427 ci engine with a 4" stroke, low end torque was overabundent.
I have additional details on my website at
http://www.twinturbocorvettes.com/19...nderheads.html
The reason most 18* cylinder heads give up some low end torque compared to conventional 23* heads is due to the fact that 18* heads are intended for racing use and almost always feature larger intake port size (volume and cross-section) than 23* heads intended for street/hiperformance use. You can get smaller port 18* heads, but they are still at least 235cc or so. The Dart 18* CNC heads I ran were 257cc, but on a 427 ci engine with a 4" stroke, low end torque was overabundent.
I have additional details on my website at
http://www.twinturbocorvettes.com/19...nderheads.html
Last edited by Monty; Mar 7, 2006 at 06:24 PM.
