How much does 59cc CC make up for bigger/slower ports?
02-19-2006, 03:14 PM
#1
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How much does 59cc CC make up for bigger/slower ports? I'm trying to work out which heads ($$/power) to mate with which cam for 425+ rwtq on 2000 TransAm 346, without spending $2500 on AFR's or ETP's. Last dyno (Mustang) was 336rwhp/345rwtq with just about all bolt-ons, except pulley. So I'm looking for the head/cam/intake combo to add 80 rwtq, or as close to it as possible keeping the 346 displacement. (I know, 
)
The question is, do the 59cc combustion chambers make up for the lower velocity of 220cc+ intake ports on LS6 or Patriot heads? What are the trade offs between Combustion Chamber cc's and port volume where velocity at low revs (and therefore power) is concerned? And will the 59cc chamber make 11:1 even with say 225cc intake runners, and how important is CR vs port velocity.
To help the process, I was looking at mating the heads with a TSP 233/239, .595"/.603" 112. I was hoping the aggressive Comp lobes will develop power quickly and the exhaust duration and lift would make a tall, flat torque curve. I'd like to bring the torque curve up as early as possible.
... or should I just wait a couple of months for Patriot's Predator heads?
) The question is, do the 59cc combustion chambers make up for the lower velocity of 220cc+ intake ports on LS6 or Patriot heads? What are the trade offs between Combustion Chamber cc's and port volume where velocity at low revs (and therefore power) is concerned? And will the 59cc chamber make 11:1 even with say 225cc intake runners, and how important is CR vs port velocity.
To help the process, I was looking at mating the heads with a TSP 233/239, .595"/.603" 112. I was hoping the aggressive Comp lobes will develop power quickly and the exhaust duration and lift would make a tall, flat torque curve. I'd like to bring the torque curve up as early as possible.
... or should I just wait a couple of months for Patriot's Predator heads?
Last edited by FUN LS1; 02-19-2006 at 03:22 PM.
02-19-2006, 05:54 PM
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And will the 59cc chamber make 11:1 even with say 225cc intake runners, and how important is CR vs port velocity.
02-19-2006, 08:05 PM
#4
Originally Posted by 67camaro
intake runner size does not affect compression ratio.
Last edited by Rescue Ranger; 02-20-2006 at 11:10 AM.
02-19-2006, 10:16 PM
#5
Originally Posted by Rescue Ranger
how so? how does a 59cc chamber make 11:1 compression; what would a 63cc chamber make? How can you make 10.5:1 compression on 59cc heads?
FUN LS1 - your either gonna spend 2500 bucks now, or 2500+ bucks later to achieve your goal.
a good set of heads, kooks/qtp's, fast 90/90, ect.
check the rwtq thread in the dyno section and you'll see that 425rwtq+ n/a 346's arent all that common. i've got about a dozen or so dyno graphs of 425+rwtq setups and none of them are using budget heads. most are AFR 205's' or extensively ported 243's.
02-19-2006, 10:28 PM
#6
Combustion chamber and intake runner are NOT the same thing. Most people call the intake runner the port, so I will do so from this point forward.
Higher compression will bring overall power up, but if you compare a large intake runner port (230+) vs a 205-215 at the same combustion chamber size, you'd give up torque with the larger heads. If you compare the high compression, large port to a low compression, small port, you're not comparing them equally.
And the other main argument of the smaller port heads is throttle response. As far as the higher velocity giving better throttle crispness, this may be true if compared apples to apples with the same smallish cam on both engines. However, most people like cams in the 230+ duration for whatever reason (but usually more horsepower and top end for the same price as a smaller cam). But since camshafts have more to do with the driving characteristics of the car (idle, low speed smoothness, throttle response), a large cam takes away some of the small port advantage.
In your case, the fast ramp rates of the XE-R on the TSP cam will make for good drivability, but the small port heads would supposedly compliment them and reduce any low end softness (although to be honest, I've never actually seen this), but I doubt they'd give much back in throttle crispness, because of the lowered vacuum your engine will produce due to the cam.
Therefore, most of the heads out there will "feel" the same. Once you break, say, 5000 RPM, the torque advantage goes to the higher flowing head, regardless of runner port size (but once again, I've never seen a real advantage one way or the other below 5000--but most people that buy more expensive heads put more expensive intake manifolds, headers, bolt-ons, and use thinner gaskets for quench to make better overall power, because they have more money to properly "set up" the car).
Thus, price and flycutting become factors. I know a small port low compression head is not going to out perform a large port, high compression head. And you know what you've been looking at and whether your cam will fit.
Whatever you do, you should match the compression to the cam. And, I can't think of a cam that couldn't use more compression.
Higher compression will bring overall power up, but if you compare a large intake runner port (230+) vs a 205-215 at the same combustion chamber size, you'd give up torque with the larger heads. If you compare the high compression, large port to a low compression, small port, you're not comparing them equally.
And the other main argument of the smaller port heads is throttle response. As far as the higher velocity giving better throttle crispness, this may be true if compared apples to apples with the same smallish cam on both engines. However, most people like cams in the 230+ duration for whatever reason (but usually more horsepower and top end for the same price as a smaller cam). But since camshafts have more to do with the driving characteristics of the car (idle, low speed smoothness, throttle response), a large cam takes away some of the small port advantage.
In your case, the fast ramp rates of the XE-R on the TSP cam will make for good drivability, but the small port heads would supposedly compliment them and reduce any low end softness (although to be honest, I've never actually seen this), but I doubt they'd give much back in throttle crispness, because of the lowered vacuum your engine will produce due to the cam.
Therefore, most of the heads out there will "feel" the same. Once you break, say, 5000 RPM, the torque advantage goes to the higher flowing head, regardless of runner port size (but once again, I've never seen a real advantage one way or the other below 5000--but most people that buy more expensive heads put more expensive intake manifolds, headers, bolt-ons, and use thinner gaskets for quench to make better overall power, because they have more money to properly "set up" the car).
Thus, price and flycutting become factors. I know a small port low compression head is not going to out perform a large port, high compression head. And you know what you've been looking at and whether your cam will fit.
Whatever you do, you should match the compression to the cam. And, I can't think of a cam that couldn't use more compression.
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02-20-2006, 11:09 AM
#8
Originally Posted by jrp
read what he wrote. he stated intake runner volume has no effect on compression, and he would be correct.
02-20-2006, 11:35 AM
#9
The combustion chamber is the "D" shaped area that the valves sit against and where the fuel is burned at the top of the cylinder. Therefore, its size in cc matters for the combustion process. The intake runner is the tube that the valves open into that leads into the cylinder to let in or let out the contents of the cylinder, so it has no affect on the combustion process.
02-20-2006, 12:15 PM
#10
Higher compression would certainly help get a little "snap" back in the throttle from a bigger, lazier port design but what your not taking into consideration is the extra snap and low speed grunt the smaller, more efficient port design would respond to the same change (a bump in static CR)....
Just something else to consider....
Tony M.
Just something else to consider....
Tony M.
02-20-2006, 12:22 PM
#11
This is my advice, been there done that. 59cc will REALLY wake up your throttle response between 2k-4k if you intend to run a cam larger than 230. Ive driven cars that felt stock, OR SLOWER until 3500-4500 because of the size of the cam. I wouldnt consider anything else since Ive driven both. My .02 
03-20-2006, 12:44 PM
#13
A friend of mine has an 04 GTO with HPE-S cam, 1 3/4" longtubes, LS-6 stock heads, FAST 90/90, K&N Intake and a Borla Catback and he is making 427rwhp and 388rwtq. He still has some tuning to do to it as well.
03-20-2006, 02:57 PM
#14
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Thanks, guys.I've been reffered to a guy who hand ports and builds LS1 heads for $1700 + your old heads. He comes highly recommended and is supposedly good at custom porting for your application. I'm just about convinced I'd be better off (for the $$) getting a great port job on LS1 heads than CnC'd 243's or even the CnC'd LS1's that are listed at $900 but really end up being $1500 when you add the stuff you need like dual springs, etc.
Given the above, How much can you mill the 241's and still get a 233/239 (with stock 2.0 valves, but I can choose others) to fit without flycutting? Or if I used a cam with a little less intake duration, how much can/should the 241's be milled to improve quench, and which gaskets work best?
BTW - I understand the difference between the combustion chamber and the ports
, thanks anyway. I wasn't sure whether port velocity could make a difference on CR, and got my answer on that plus a lot of great info on port volume vs velocity and where it affects you most. 