port timing and Camdens
07-17-08, 03:53 PM
#1
port timing and Camdens
Planning my next 4 port 13B here. It shall be compatible with a Camden. 
I've got a complete '76 Cosmo engine. Also some loose parts; a set of R5 side plates and '74-'75 boxed in MAZDA housings with a rotating assembly with 9.2 CR 3mm rotors. It is basically enough parts to build two engines. But which one should I choose for the Camden? The other is going into the GLC which will remain NA of course (can you imagine boosted? Eep!).
Knowns:
'76 Cosmo engine produced 110HP at 6000 and 117 torque at 4000
'74 REPU produced 110HP at 6000 and 120 torque at 4000
Both engines had emissions devices galore.
The Camden typically adds 30% more power so 110HP becomes about 143HP.
Unknowns:
143HP doesn't sound like much. Is the actual output affected largely by the pulley? I had this discussion with 84stock before and he suggested a -8 for the REPU since he thinks a -10 runs too hot and will cause detonation while towing. Also it runs out of breath too early, like at 6k. My friend has run a -10 for years with no problems. It had enough power to break them loose in gear in his 1st gens, and he'd take it up to 7k most of the time. I'd still like more power than 143 though, so that's what I'd like to discuss in this thread; the perfect setup for situation.
I've got a complete '76 Cosmo engine. Also some loose parts; a set of R5 side plates and '74-'75 boxed in MAZDA housings with a rotating assembly with 9.2 CR 3mm rotors. It is basically enough parts to build two engines. But which one should I choose for the Camden? The other is going into the GLC which will remain NA of course (can you imagine boosted? Eep!).
Knowns:
'76 Cosmo engine produced 110HP at 6000 and 117 torque at 4000
'74 REPU produced 110HP at 6000 and 120 torque at 4000
Both engines had emissions devices galore.
The Camden typically adds 30% more power so 110HP becomes about 143HP.
Unknowns:
143HP doesn't sound like much. Is the actual output affected largely by the pulley? I had this discussion with 84stock before and he suggested a -8 for the REPU since he thinks a -10 runs too hot and will cause detonation while towing. Also it runs out of breath too early, like at 6k. My friend has run a -10 for years with no problems. It had enough power to break them loose in gear in his 1st gens, and he'd take it up to 7k most of the time. I'd still like more power than 143 though, so that's what I'd like to discuss in this thread; the perfect setup for situation.
07-17-08, 03:58 PM
#2
Isn't towing essentially like adding a bunch of weight to your vehicle? It tkaes longer to accel and decel. The boost will help get it moving far more easily than NA.
It shouldn't detonate any more easily than when not towing if everything else is the same ie ambient temps, same octane fuel, ignition timing, etc. If coolant and oil temps are kept under control, which I suspect they will be with the large radiator and oil cooler REPUs come stock with, I don't forsee any problems using a -10. Do you guys? What's more, the early boosting potential of the -10 will work better with stock ports, since they tend to run out of breath around 6k NA as well.
Am I simplifiying things too much? Have I overlooked anything of great importance? I really hope not. If I haven't been clear enough on certain aspects of my project description so far, please let me know, ok?
I want to get this setup right from the start.
It shouldn't detonate any more easily than when not towing if everything else is the same ie ambient temps, same octane fuel, ignition timing, etc. If coolant and oil temps are kept under control, which I suspect they will be with the large radiator and oil cooler REPUs come stock with, I don't forsee any problems using a -10. Do you guys? What's more, the early boosting potential of the -10 will work better with stock ports, since they tend to run out of breath around 6k NA as well.
Am I simplifiying things too much? Have I overlooked anything of great importance? I really hope not.
If I haven't been clear enough on certain aspects of my project description so far, please let me know, ok?I want to get this setup right from the start.
07-17-08, 06:15 PM
#3
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towing just means you're at a higher load for longer time, which means more heat etc
i think a really nice exhaust system (right size, length etc) would make more hp than 143.
i think a really nice exhaust system (right size, length etc) would make more hp than 143.
07-18-08, 12:08 PM
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07-18-08, 07:41 PM
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07-18-08, 09:06 PM
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I wouldn't worry about the camden on the REPU. Its not like that chassis will tow a whole lot anyway. A good carb + good exaust should be enough. If you are going to beef up the rear end so you can tow stuff, I would be looking for power in other ways then a supercharger.
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07-19-08, 01:53 PM
#8
You've never towed anything with an REPU, have you. 
Towing a baja or a 1st gen is fine with these trucks, and that is all I'd ever want to tow. I just want more power without sacrificing driveability and low end. Tall order for some but I know the answer is out there. Just gotta find it.
The way I see things, at the moment, is I have two choices:
1. Stock ports and a -10
2. '74 spec ports and a -8
It would be nice if Atkins made a -9 pulley but what are you gonna do?
So we know heat will build the longer it boosts, and I'm not sure whether the current cooling system can keep up indefinitely. Probably not.
Towing is like accelerating in a really long quarter mile.
I'm kinda leaning towards '74 spec ports because the later port closing can take advantage of the greater cylinder filling that is available with an SC at low RPM (before the 'natural supercharging effect' kicks in at high intake velocities). The only downside is when it's off boost. However with a -10 it starts boosting very early in the RPM range. The only downside to the -10 is heat and when it runs out of breath kinda early in the RPM. However for a truck this might be an acceptible tradeoff. I just don't know.
I posted this in non tech so I could strike up a conversation without distracting the troubleshooters in the tech section. Sorry if it's too techy for this section.
Thinking more about my situation, if I were to go with stock ports and a -10 pulley, the low end torque would be perhaps noticeably better off boost, then it would kick in hard and fast, and then run itself out of breath at around 6k, which is basically where the stock ports run out of breath as well. This could potentially be very rewarding in a truck. However that stock 110HP at 6k isn't looking very good to me because I know that 143HP is all the Camden would do.
Yes, yes I know that with my direct fire ignition upgrade and a straight-through exhaust system, 110 NA would probably get raised to about 120 or so (that's nearly a 10% increase just in bolt ons!) but after those mods the only other option is an upgraded carb. However the low end driveability usually goes in the crapper to some extent.
You really can't beat the stock Hitachi for driveability. Seriously. A Holley just can't. A Weber makes you wait until 3 or 4k before it wakes up. An Edlebrock... not sure as I've never tried one NA before. A totally stock 6 port engine with fully functioning aux ports would be the ultimate setup for an REPU, but the complexity turns me off. A Sterlng Nikki would have great driveability yes but you're still limited to a 22mm venturi, which is what the stock '74-'76ish Hitachis had anyway. Plus it's a taller carb requiring the use of a 12A mani and a 13B width adaptor plate. I'll have to pass.
The 22mm carbs still had a strong enough vacuum signal for decent low end and enough flow for up to 6k at least (I'm talking 13B here), but NA rules still apply, so I'm still limited to whatever the engine can injest under normal atmospheric pressures.
As you can see my options are either go 6 port, which is more complex than I want to get with this project, or something not previously mentioned is a 3 rotor 12A because there's no replacement for displacement when you're talking NA, however the engine bay is short and I'd have trouble fitting a 15A or Renesis if I had access to either (wouldn't that be nice if I did?). A 16X is a pipe dream right now. A bigger carb isn't necessarily the answer because I lose the all important vacuum signal which is the key to good low end power. I guess I've pretty much talked myself into a corner and the only way out is boost.
Two flavors of boost: SC and turbo.
The turbo is an option I thought of briefly. I decided against it because my exhaust is already built, I don't have a turbo, again I didn't want to go EFI here, and also don't want to boost prep a carb+lock a dizzy etc.
Last but not least is the driveability difference between a turbo and an SC. The SC won because I wanted power right off of idle instead of waiting for a turbo to spool. Plus I didn't need 350HP at the expense of anything under 2000RPM or whatever. No jungle cats for me.
This brings me back to -10 vs -8 pulley sizing and stock ports or '74 spec. Let's talk about this.
Towing a baja or a 1st gen is fine with these trucks, and that is all I'd ever want to tow. I just want more power without sacrificing driveability and low end. Tall order for some but I know the answer is out there. Just gotta find it.
The way I see things, at the moment, is I have two choices:
1. Stock ports and a -10
2. '74 spec ports and a -8
It would be nice if Atkins made a -9 pulley but what are you gonna do?
So we know heat will build the longer it boosts, and I'm not sure whether the current cooling system can keep up indefinitely. Probably not.
Towing is like accelerating in a really long quarter mile.
I'm kinda leaning towards '74 spec ports because the later port closing can take advantage of the greater cylinder filling that is available with an SC at low RPM (before the 'natural supercharging effect' kicks in at high intake velocities). The only downside is when it's off boost. However with a -10 it starts boosting very early in the RPM range. The only downside to the -10 is heat and when it runs out of breath kinda early in the RPM. However for a truck this might be an acceptible tradeoff. I just don't know.
I posted this in non tech so I could strike up a conversation without distracting the troubleshooters in the tech section. Sorry if it's too techy for this section.
Thinking more about my situation, if I were to go with stock ports and a -10 pulley, the low end torque would be perhaps noticeably better off boost, then it would kick in hard and fast, and then run itself out of breath at around 6k, which is basically where the stock ports run out of breath as well. This could potentially be very rewarding in a truck. However that stock 110HP at 6k isn't looking very good to me because I know that 143HP is all the Camden would do.
Yes, yes I know that with my direct fire ignition upgrade and a straight-through exhaust system, 110 NA would probably get raised to about 120 or so (that's nearly a 10% increase just in bolt ons!) but after those mods the only other option is an upgraded carb. However the low end driveability usually goes in the crapper to some extent.
You really can't beat the stock Hitachi for driveability. Seriously. A Holley just can't. A Weber makes you wait until 3 or 4k before it wakes up. An Edlebrock... not sure as I've never tried one NA before. A totally stock 6 port engine with fully functioning aux ports would be the ultimate setup for an REPU, but the complexity turns me off. A Sterlng Nikki would have great driveability yes but you're still limited to a 22mm venturi, which is what the stock '74-'76ish Hitachis had anyway. Plus it's a taller carb requiring the use of a 12A mani and a 13B width adaptor plate. I'll have to pass.
The 22mm carbs still had a strong enough vacuum signal for decent low end and enough flow for up to 6k at least (I'm talking 13B here), but NA rules still apply, so I'm still limited to whatever the engine can injest under normal atmospheric pressures.
As you can see my options are either go 6 port, which is more complex than I want to get with this project, or something not previously mentioned is a 3 rotor 12A because there's no replacement for displacement when you're talking NA, however the engine bay is short and I'd have trouble fitting a 15A or Renesis if I had access to either (wouldn't that be nice if I did?). A 16X is a pipe dream right now.
A bigger carb isn't necessarily the answer because I lose the all important vacuum signal which is the key to good low end power. I guess I've pretty much talked myself into a corner and the only way out is boost.Two flavors of boost: SC and turbo.
The turbo is an option I thought of briefly. I decided against it because my exhaust is already built, I don't have a turbo, again I didn't want to go EFI here, and also don't want to boost prep a carb+lock a dizzy etc.
Last but not least is the driveability difference between a turbo and an SC. The SC won because I wanted power right off of idle instead of waiting for a turbo to spool. Plus I didn't need 350HP at the expense of anything under 2000RPM or whatever. No jungle cats for me.
This brings me back to -10 vs -8 pulley sizing and stock ports or '74 spec. Let's talk about this.
07-19-08, 05:24 PM
#9
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actually positive manifold pressure fixes all the drivability issues with a high overlap intake port...
it'd be temping to go with something really odd, like a bridge port that closed early, and try and make big hp under 6k
it'd be temping to go with something really odd, like a bridge port that closed early, and try and make big hp under 6k
07-19-08, 08:40 PM
#10
Interesting idea, but at idle and part throttle cruise it actually pulls vacuum so I'm not sure I'd want to try it on this project. Maybe the next one I do as I may have access to a friend's 7" eventually. The one going on the REPU is a 5".
07-20-08, 02:38 PM
#11
I've communicated with 84stock over the months and here is what he had to say:
"I think it is ideally suited to a stockport engine. Intake ports can be opened up a bit as long as they do not open earlier. Exhaust can be streetported but i do not suggest a late closing. the camden produces great torque and response but porting is senseless since it cannot give anywhere near the potential of a turbo over 6000 rpm. I thought my bridgeport would scream with the camden compared to my streetported 6 port (same rotors). Not much difference though. I think the camden is best suited for a street-driven daily driver." dated 12-03-07
That sounds reasonable if a bit outdated by now. He has since blown up his bridged Camden setup and rebuilt it and the SC recently.
Here is what he has to say about pullies:
"I have had experience with the 6,7,8&10 pulleys. The 8 does provide a little earlier boost but at the expense of heat and detonation potential, not good if you wanna tow something. -10, way too much heat. I found best overall success with the -7 pulley and a goodyear gatorback belt. get the belt surface of the pulley sandblasted to reduce slippage. I am gonna modify the weights on a 12a dizzy for a test. You can port the 13b if you want, just do not open the intake earlier and do not let the exhaust close any later, this overlap is counterproductive. If you look at my bridgeport it opens late like a BDC bridgeport. I will soon be testing a carb spacer and a bigger carb as well. I am going with a 800 cfm spreadbore carb." dated 03-16-08
Since my rotors are 9.2 compression ratio, I believe a -8 will be fine for towing, especially with the large oil cooler and radiator of the REPU. I can also mod the thermostat for more flow and make sure the clutch fan is healthy; I want a mini hurricane under the hood.
I would have wanted to go with a -10 and stock ports, but I now feel the heat build up while towing would be too much. So how about this: I keep stock intake port timing but with smoothing and reduction of casting flash. Since my rotor housings have early opening and closing exhaust ports, this works in my favor; stock exhaust port timing but widened 2mm on each side for more flow. The overlap will be kept to a minimum, as 84stock recommends. It seems I could port to '74 spec (intake closing timing delayed slightly) but ultra low RPM and off-boost response would be weaker with only a little bit more high RPM power potential; I don't know whether I can justify '74 spec ports on this engine. Last but not least is a -8 pulley for towing and general purpose use.
A little more from 84stock concerning pullies:
"Great, I have used the 6,7,8 & 10. My buddy had the 10 on his and it basically wore out the teflon seals and caused a lot of heat. I tried it on mine for ***** & giggles. Huge immediate boost, almost needed a 3' pry bar to get the belt tight enough so it wouldn't squeal. The charger and air filter above got soooooo hot you couldn't even come close to touching them, it was that nasty. I like the 8 for stock ports and the 7 for a ported engine that's gonna rev a little higher. The 6 is good for fuel economy." dated 05-01-08
Ok, -8 it is. Mine has a -7 on it because it was originally on a streetported 4 port 13B in an RX-4. It had power up to about 8k but was gutless at low RPM. Anything below 3 or 4k was unpleasant considering the weight of the vehicle and the tall 3.636 geared diff. It also had a GSL-SE flywheel which was perfect in NA mode but felt way too heavy with the SC. Now that this same SC is in my 1st gen, it works a lot better. The engine is an Atkins 13B 4 port with unknown port timing (streetported I assume) and the -7 works for now. It had a light steel flywheel which was a major improvement over the GSL-SE flywheel, but it still felt a little heavy so I switched to an aluminum. It was the correct flywheel for this setup.
This is one subject where we differ. 84stock likes stock Mazda flywheels for better launches. I don't like them with Camdens because they feel so much heavier with the added drag and rotating mass/inertia of the SC. If you have enough power, launches aren't a big deal. Just keep wheelspin low and you're good.
The REPU is getting a light steel flyhweel and the Camden so it should feel more like a GSL-SE flywheel, which in a truck, is perfect. The rotors are the heavy '76-'78ish type so this will add some precious rotating weight too. Thanks for reading and please comment.
"I think it is ideally suited to a stockport engine. Intake ports can be opened up a bit as long as they do not open earlier. Exhaust can be streetported but i do not suggest a late closing. the camden produces great torque and response but porting is senseless since it cannot give anywhere near the potential of a turbo over 6000 rpm. I thought my bridgeport would scream with the camden compared to my streetported 6 port (same rotors). Not much difference though. I think the camden is best suited for a street-driven daily driver." dated 12-03-07
That sounds reasonable if a bit outdated by now. He has since blown up his bridged Camden setup and rebuilt it and the SC recently.
Here is what he has to say about pullies:
"I have had experience with the 6,7,8&10 pulleys. The 8 does provide a little earlier boost but at the expense of heat and detonation potential, not good if you wanna tow something. -10, way too much heat. I found best overall success with the -7 pulley and a goodyear gatorback belt. get the belt surface of the pulley sandblasted to reduce slippage. I am gonna modify the weights on a 12a dizzy for a test. You can port the 13b if you want, just do not open the intake earlier and do not let the exhaust close any later, this overlap is counterproductive. If you look at my bridgeport it opens late like a BDC bridgeport. I will soon be testing a carb spacer and a bigger carb as well. I am going with a 800 cfm spreadbore carb." dated 03-16-08
Since my rotors are 9.2 compression ratio, I believe a -8 will be fine for towing, especially with the large oil cooler and radiator of the REPU. I can also mod the thermostat for more flow and make sure the clutch fan is healthy; I want a mini hurricane under the hood.
I would have wanted to go with a -10 and stock ports, but I now feel the heat build up while towing would be too much. So how about this: I keep stock intake port timing but with smoothing and reduction of casting flash. Since my rotor housings have early opening and closing exhaust ports, this works in my favor; stock exhaust port timing but widened 2mm on each side for more flow. The overlap will be kept to a minimum, as 84stock recommends. It seems I could port to '74 spec (intake closing timing delayed slightly) but ultra low RPM and off-boost response would be weaker with only a little bit more high RPM power potential; I don't know whether I can justify '74 spec ports on this engine. Last but not least is a -8 pulley for towing and general purpose use.
A little more from 84stock concerning pullies:
"Great, I have used the 6,7,8 & 10. My buddy had the 10 on his and it basically wore out the teflon seals and caused a lot of heat. I tried it on mine for ***** & giggles. Huge immediate boost, almost needed a 3' pry bar to get the belt tight enough so it wouldn't squeal. The charger and air filter above got soooooo hot you couldn't even come close to touching them, it was that nasty. I like the 8 for stock ports and the 7 for a ported engine that's gonna rev a little higher. The 6 is good for fuel economy." dated 05-01-08
Ok, -8 it is. Mine has a -7 on it because it was originally on a streetported 4 port 13B in an RX-4. It had power up to about 8k but was gutless at low RPM. Anything below 3 or 4k was unpleasant considering the weight of the vehicle and the tall 3.636 geared diff. It also had a GSL-SE flywheel which was perfect in NA mode but felt way too heavy with the SC. Now that this same SC is in my 1st gen, it works a lot better. The engine is an Atkins 13B 4 port with unknown port timing (streetported I assume) and the -7 works for now. It had a light steel flywheel which was a major improvement over the GSL-SE flywheel, but it still felt a little heavy so I switched to an aluminum. It was the correct flywheel for this setup.
This is one subject where we differ. 84stock likes stock Mazda flywheels for better launches. I don't like them with Camdens because they feel so much heavier with the added drag and rotating mass/inertia of the SC. If you have enough power, launches aren't a big deal. Just keep wheelspin low and you're good.
The REPU is getting a light steel flyhweel and the Camden so it should feel more like a GSL-SE flywheel, which in a truck, is perfect. The rotors are the heavy '76-'78ish type so this will add some precious rotating weight too.
Thanks for reading and please comment.
07-21-08, 01:41 PM
#12
Cliff notes from above are:
I've decided to go with a -8 pulley.
Still deciding between stock intakes and '74 spec. I'll probably compromise and just smooth the stock ports to remove casting flash and the sharp 90° edges while leaving actual port timing stock. I need more data before a decision can be made. At least intake opening timing will remain stock for as little overlap as possible with 4 port plates. Only JC Cosmo primaries open later.
Exhaust ports of US-spec '70s 13B rotor housings and 1st gen 12As open early and close early. This early closing is good for reducing overlap, which is important on this project, so I'll leave exhaust port timing alone. I can widen the ports to about 2mm on each side (this matches T2 spec) for a little more flow. I won't open them any sooner since they already open earlier than MFR or GSL-SE ports. j9fd3s knows what I'm talking about.
I've decided to go with a -8 pulley.
Still deciding between stock intakes and '74 spec. I'll probably compromise and just smooth the stock ports to remove casting flash and the sharp 90° edges while leaving actual port timing stock. I need more data before a decision can be made. At least intake opening timing will remain stock for as little overlap as possible with 4 port plates. Only JC Cosmo primaries open later.
Exhaust ports of US-spec '70s 13B rotor housings and 1st gen 12As open early and close early. This early closing is good for reducing overlap, which is important on this project, so I'll leave exhaust port timing alone. I can widen the ports to about 2mm on each side (this matches T2 spec) for a little more flow. I won't open them any sooner since they already open earlier than MFR or GSL-SE ports.
j9fd3s knows what I'm talking about.
07-22-08, 02:52 PM
#17
I wonder where 84stock is. I want him to critique my pulley choice. I also look forward to his thoughts on port timing. It comes down to stock vs '74 spec intakes. As for exhaust ports I'm pretty set on widening the ports without changing actual timing.
There is also the flywheel choice, rotor weight and compression, ways to reduce heat build up etc.
Anyone else care to comment?
There is also the flywheel choice, rotor weight and compression, ways to reduce heat build up etc.
Anyone else care to comment?
07-22-08, 03:42 PM
#18
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good choice on going with the 8 the 10 is rewarding right away but everything gets so hot and you can feel the power deminishing at 5800-6000. the #8 made for easier launches things stayed cooler and it kept 8psi to 8000
I cant comment on the port timing as I dont have alot of knowledge in that but i have a 1/2 bridge with a big street port on the primarys and I had great low end power with both pullies. with the #8 I could smoke 1st and 2nd and get a healthy healthy long chirp out of third. That was right after the camden got rebuilt
My rotors are 12aT rotors and I have a light weight flywheel everything seemed to work together very well. Felt very fast
I cant comment on the port timing as I dont have alot of knowledge in that but i have a 1/2 bridge with a big street port on the primarys and I had great low end power with both pullies. with the #8 I could smoke 1st and 2nd and get a healthy healthy long chirp out of third. That was right after the camden got rebuilt
My rotors are 12aT rotors and I have a light weight flywheel everything seemed to work together very well. Felt very fast