The Edelbrock 650 with Camden SC thread

[Jeff20B]

Hey everyone!

The time has come to discuss my next supercharger project.

Parts list:

•Edelbrock 650 Performer Series with electric choke (1406)
•Edelbrock calibration kit (metering rods and springs)
•5" Camden SC ('05 model)
•RB collected header
•narrow band AF guage
•Carter fuel pump
•Holley fuel pressure reg

Gonna boost the REPU!

Just a small question about compressions ratios. The stock early 13B rotating assemblies of REPUs were 9.2:1 CR. I also have access to an S4 T2 assembly which I think is 8.6 CR. Which assembly would do me best for towing and off-boost performance, such as under vacuum conditions and low end torque since it is a truck?

Oh and for RotaryDave, the SC curently has a -7 pulley, but is going to get a -10. I'd like to know whether the T2 assembly ought to be used. Will it be beneficial or a bad idea? Thanks!

[TheDriver216]

the 9.2's would be good.. but the rotors alone are 1.5 pounds heavier(according to mazdatrix).. so you will probally get better response from the lighter rotating assembly but might lose a little from the lower CR, but you will get it spinning faster.

[Rogue_Wulff]

The 9.2CR would give better power off-boost, but would be a limiting factor in how much boost and timing you could run.
The S4 rotors have lower CR, but they also have 2mm apex seals.

In my opinion, stick with the early rotating assembly. For towing/hauling, you're not gonna be looking for peak power/boost on the top end, but rather a decent improvement in the mid-range, which is where the engine will be running ~90% of the time.

[Jeff20B]

I forgot to mention the rotors are milled out for 3mm apex seals.

[Whizbang]

actually a heavier rotor might be nicer for a truck since the engine will keep more momentum

[Jeff20B]

Perhaps you guys are right. A heavier rotating assembly would be best for the truck. I'll keep the T2 assembly for something else.

[Rotarydave]

Jeff, why not just go with a S4 NA set? they have the same CR and are a little bit lighter than those of GSL-SE, much lighter than that of the REPU, afterall what flywheel are you using, I would much rather use a heavier flywheel which will not have any non rotational movement than in my rotor set which even though it is a rotary does have some off center movement. I have great response from mine and I am using a set of S4 NA rotors I have put in excess of 10lbs boost to it and have had some issues with detonation until i got my timing and ignition right. The set up you are talking about should be good for right at 240-250 lbs of torque and a max of 285hp. (talking out of my butt cause i have no paper in front of me and my memory is drug impaired) Oh Apex seals mine is using standard atkins 2 piece 2mm ones i had no problem with them. If you were going to race it then i would worry about making them 3mm.

As for the turbo rotors don't use them unless you want to move the power band in the engine up to the higher rpm range. But for towing I would want my torque to stay in the lower range about 3k

[Rotarydave]

Originally Posted by Rogue_Wulff

The 9.2CR would give better power off-boost, but would be a limiting factor in how much boost and timing you could run.
The S4 rotors have lower CR, but they also have 2mm apex seals.

In my opinion, stick with the early rotating assembly. For towing/hauling, you're not gonna be looking for peak power/boost on the top end, but rather a decent improvement in the mid-range, which is where the engine will be running ~90% of the time.

Great ideas and right on track.... but with him running the 5 inch charger and a -10 pulley his max boost should only be in the 10-12lbs range and it (blower) will start to cavitate( read stop boosting) about 9k rpm so with the setup he is using the turbo rotors really don't make any sense, he does have the option of going to a -11 pulley for more boost but then the blower will cavitate much quicker like down in the late 6-7k range. Also the -11 is special order item not recommended in most cases by camden/atkins. I did use one for a little while but lost so much Rpm range it wasn't worth the power increase.

I only like using the turbo rotors if you are using the bigger blower but then you really need to be in a racing application to get the max benefit.

[Jeff20B]

Thanks Dave. Now that you mention it, I do have an S4 NA set with 2mm apex seals. What if I used it? I like your reasoning. As for torque and HP numbers, did you mean 145-150 foot pounds and 185HP? Sounds a bit more reasonable. That would be great in the truck with the driveability of the SC and response of the S4 set.

My apex seals are also standard Atkins 2 piece 2mm ones.

My flywheel choices are Racing Beat light steel and stock S4 NA (N326). I have the proper S4 rear counterweight so I can use either flywheel.

Do you think I should use the stock flywheel (I think it's 24 pounds) since it's a truck? Or will it slow down the response of the SC a lot? I only ask this because I'm used to driving this S4 engine with an aluminum flywheel with SC and in NA mode in my 1st gen and it's a little light in the bottom end when NA but still very driveable thanks to the low weight of the car.

Back when I tried the 5" and the 7" on this engine in the 1st gen, the superchargers caused the rotating assembly to feel a whole lot heavier than it really is. I actually started originally with a light steel flywheel but switched to aluminum precisely because the light steel felt heavier than I wanted.

I realize with a truck's added weight there will be compromises, but that's all I want it to be; a compromise. I don't want to return to the days of driving around something that feels like a 30 pound flywheel, which I'm affraid might happen if I use the 24 pound stock flywheel (this happened in my brother's RX-4 with GSL-SE assembly, GSL-SE flywheel and my 5" SC. With SC it felt like it had the old stock 30 pound flywheel, but in NA mode it felt lighter and much better). The 30 pounder is too extreme for daily driving, and only basically useful when hauling a large load or towing. Aluminum would probably be fairly useless for the same (opposite) reasons, even if adding an SC would help by adding rotational mass and all that, possibly making it feel more like a light steel in NA mode.

Instead I want a compromise that will drive like it has a light steel flywheel with an SC, or a 26/27 pound GSL-SE while NA. But then again since it is a truck, I'm willing to bend a little and accept the 24 pound FC flywheel with an SC, but I'd like some feedback as to how it drives.

84stock has an S4 engine with a 7" SC and stock 24 pound flywheel in his 1st gen, and he actually endorses it because it gives him a better launch.

I think I'll leave it at that and move on to the pressure plate and clutch disc. I have a Racing Beat street strip pressure plate in 225mm and two choices for clutch discs. 225mm HD and stock '83-'92 Exedy/Daikin. I like the thought of using the SS p-plate in the truck because it's similar in grip rate to the stock REPU type. I also have a stock aftermarket Daikin pressure plate in great shape if I want to use it.

As for the discs, I like how the OEM REPU disc has some buffer zone with center springs and marcels, like the Exedy disc. The HD disc lacks marcels so I'm a little paranoid about using it.

Like you said, if I'm racing I should go with 3mm apex seals. Well, I'm not racing, so maybe I can get away with the Exedy disc and save the HD disc for another project I have in mind (which will actually need it).

[Jeff20B]

I've given it some thought and if I juggle a few other things around, I can use an HD disc in the REPU.

I had my doubts (fears) about using an HD disc in the truck due to the potential for shuddering while towing, well, launching basically, as occours in my friend's REPU. Dave gave me advice about using a solid tranny mount and maybe a torque brace to help minimize the effect. I have access to competition motor mounts so I'll try those first.

Another problem is the grabbiness and the general dislike for slippage these HD discs exhibit. They are somewhere between a stock disc with marcells and a 6 puck. You can slip an HD disc for as long as you need and it will take the abuse, but they're not as friendly as a stock disc. Puck, no. Well, 6 puck maybe.

Now that that's out of the way I feel I should mention how the old REPU setup handled. The disc was almost gone. Friction point at the top of the pedal travel, disc was 6.99mm thickness uncompressed. I don't know how thin it became installed. The nice thing about HD discs is you get what you get. If it measures 7.33mm, as mine does, it stays that way. Thinner than I'd want, but if you guys think it'll work ok in towing situations, I'll go for it.

Oh one more thing about this clutch issue. My old REPU setup, with its very thin disc, was as grabby as any HD disc I'd ever driven, and even more so than the current setup in my 1st gen RX-7. Man, you blip the throttle just so you could let the clutch out and it wouldn't shudder or bog, but you had to have the right technique. The stock REPU 30 pound flywheel helped in that regard because its extra inertia carried you through while 'finding' the friction point; it turned out my slave cylinder was leaking too, causing the friction point to wander a bit.

Ok, enough of my boring stories. I think I will go with this list of clutch parts:

•Stock FC N326 24 pound flywheel (recently resurfaced at Atkins; this is not a plug; I'm telling it like it is, as the engine was built by them)
•Racing Beat Heavy Duty (HD) clutch disc in 225mm
•Daikin pressure plate in 225mm
•new slave cylinder for 79-80 with rod swapped for old style which is longer for the ribcase style trannies by maybe 10mm