hunt2elk
Well-Known Member
What else would you look at?
Cam selection ideas
- Thread starter hunt2elk
- Start date
What else would you look at?
Mebsuta
Well-Known Member
I want to say 130 psi is probably pretty good for low compression piston kb-162 with open chamber heads. My ancient Chilton book says 68-69 383HP is 150 psi. Original 383 hp pistons have greater compression height than KB-162. Mine is like 140-145 with RR cam, rebuilt many years ago with pistons available back then, with same compression height as original. I use blue Fel Pro head gasket and early 70s open chamber heads.
I have 68 RR 4-spd with 3.91. Long time ago when motor was rebuilt, used Isky 270 Mega Cam with 108 LSA, .465 lift, and something like [email protected] duration. I had a little mismatch going on with cast iron exhaust manifolds, Torker single plane intake, and 28-inch tires(275/60/15). At that time I also had 906 heads on it.
I made the following changes pretty much together: dual plane intake (cast iron and later Edelbrock Performer), factory RR cam Rusty talked about, put 4-into-1 headers back on, and went to 26-inch and now 27-inch tires. I was happier after that. The Isky cam sounded mean but it was just not that responsive for me at the time, the way everything was set up. I had 12-13 inches manifold vacuum with the Isky, have 16 inches with the RR cam.
I always think mine can run better and I spend hours and hours with Desktop Dyno, but it doesn't mean too much because all the cam people measure seat-to-seat timing differently, so I don't know.
Long long time ago, rode in and drove 71 383 RR that was pretty much stock except headers. It still had 346 heads. That car would not shred tires, but it would accelerate and leap into the next gear. It was so much fun and it could be scary.
I have 68 RR 4-spd with 3.91. Long time ago when motor was rebuilt, used Isky 270 Mega Cam with 108 LSA, .465 lift, and something like [email protected] duration. I had a little mismatch going on with cast iron exhaust manifolds, Torker single plane intake, and 28-inch tires(275/60/15). At that time I also had 906 heads on it.
I made the following changes pretty much together: dual plane intake (cast iron and later Edelbrock Performer), factory RR cam Rusty talked about, put 4-into-1 headers back on, and went to 26-inch and now 27-inch tires. I was happier after that. The Isky cam sounded mean but it was just not that responsive for me at the time, the way everything was set up. I had 12-13 inches manifold vacuum with the Isky, have 16 inches with the RR cam.
I always think mine can run better and I spend hours and hours with Desktop Dyno, but it doesn't mean too much because all the cam people measure seat-to-seat timing differently, so I don't know.
Long long time ago, rode in and drove 71 383 RR that was pretty much stock except headers. It still had 346 heads. That car would not shred tires, but it would accelerate and leap into the next gear. It was so much fun and it could be scary.
Meep-Meep
дворянин
Your problem is the 108 LS cam and the 130-ish PSI of cylinder pressure. I'll agree you probably have 8.5:1 - 9.0:1 CR and things would improve greatly with a different cam.
The important factor that drives cylinder pressure is the point at which the intake valve closes. Overlap has nothing to do with it. You want to balance the static compression ratio with a cam that will provide proper cylinder pressure, and done right you will have a very enjoyable engine. From my own experience an engine with a CR in the 8's will be pretty darn happy with 195-160 PSI of cranking pressure.
For tuning the power band a cam with a wider LS angle will make for a better street cam but produce a lower peak torque. I think a 110-112 LS cam is pure magic for a daily driver street car, where a 108 will come on like a two stroke. The Road Runner cam is good but if you want a little more mid range punch tighten up the LS angle just a bit and pop in some 3.55's. Also don't forget to free up the exhaust (if you haven't already done so). This one mod will be the most important one you can make, even before changing intake manifolds (stock iron vs. Eddy perf vs. similar dual plane design) or cam. A radical intake change like an individual runner type or some other tuned runner design will be a notable improvement but those aren't common.
The important factor that drives cylinder pressure is the point at which the intake valve closes. Overlap has nothing to do with it. You want to balance the static compression ratio with a cam that will provide proper cylinder pressure, and done right you will have a very enjoyable engine. From my own experience an engine with a CR in the 8's will be pretty darn happy with 195-160 PSI of cranking pressure.
For tuning the power band a cam with a wider LS angle will make for a better street cam but produce a lower peak torque. I think a 110-112 LS cam is pure magic for a daily driver street car, where a 108 will come on like a two stroke. The Road Runner cam is good but if you want a little more mid range punch tighten up the LS angle just a bit and pop in some 3.55's. Also don't forget to free up the exhaust (if you haven't already done so). This one mod will be the most important one you can make, even before changing intake manifolds (stock iron vs. Eddy perf vs. similar dual plane design) or cam. A radical intake change like an individual runner type or some other tuned runner design will be a notable improvement but those aren't common.
Mebsuta
Well-Known Member
Well here is one that looks similar to RR cam but with 112 LSA.
http://www.summitracing.com/parts/sum-k6400
It has crossed my mind to try one just to see what would happen, but that's a lot of work and I always think "not today."
http://www.summitracing.com/parts/sum-k6400
It has crossed my mind to try one just to see what would happen, but that's a lot of work and I always think "not today."
MikeyT
Well-Known Member
I really like the comp extreme energy 268 cam. Nice lope, good vacuum for brakes and worked well in my mildly built 440. The 440 was 9.5 comp with aluminum heads, so about like 8.5:1.
However, if you really want the best for it. My suggestion would be contact Dwayne Porter and talk to him. He will make a good suggestion or build you a custom one and I promise 100% you will be very happy you did. Plus he great guy to talk too.
Mike
However, if you really want the best for it. My suggestion would be contact Dwayne Porter and talk to him. He will make a good suggestion or build you a custom one and I promise 100% you will be very happy you did. Plus he great guy to talk too.
Mike
hunt2elk
Well-Known Member
I never even thought the pistons may be a big part of the problem. I had told the builder (if that is what I should refer to him as) to rebuild it close to factory specs but with a slightly lumpy sounding cam. It never dawned on me that he used low compression pistons. So what you guys are thinking is that if I do anything at all I should change the pistons along with the cam? On this car at this time I really want to keep the stock intake and exhaust and will build my Charger with some more snort. I realize headers are the first thing to change to help with hp, but how do the guys running F.A.S.T. get so much power with stock hp exhaust manifolds?
BeastlyBirdie
Well-Known Member
Cam and pistons aside, as plenty of people on here have given some great options, I would do two things. Get a Holley. Vacuum secondary. Imho, they have much better throttle response, and they aren't a carter. The second is add an H-pipe of smaller diameter. I've forgotten which gas law it follows, Dalton, Boyle, etc, but it will help get the gases out, since you don't want to run headers.
lewtot184
Well-Known Member
130psi blow is too low for that short cam. i think compression may be 8.5:1 (and no quench) and the cam may not be in correctly (are there multiple keyways on the timing set?). the 108lsa and short duration, cam should have 2 to 4 degrees of advance, should build more cylinder pressure. was the cam degreed in? these types of problems are difficult to diagnose on the internet. simply milling the heads and using a steel shim gasket will get the compression up.
how about the dampner? is TDC mark accurate? what about fuel delivery? are you using one of those stock replacement 3-5lb pumps that didn't work 50 yrs ago and are probably worse today? do you have a cellulose fuel filter on the suction side of the pump? i can't believe the people who do this and swear by it! the 750 edelbrock is a better suited carb. the 600 is too small.
what about wheels and tires on the back? do you run large diameter wide tires on heavy wheels? 383's don't make a lot of torque and won't accelerate heavy wheels and tires quickly.
i played with a couple of 383's with the 1.86 compression distance pistons and they were real turds. drove o.k but no power. do some checking before you spend money on another cam. if you end up thinking you have to have another cam i'd recommend a mopar 272-.455 or a comp cams magnum replacement #21-305-4. good luck!
hunt2elk
Well-Known Member
We did take the front apart and checked the TDC marking and the degreeing of the cam. There is only 1 keyway on the gears. After all the measuring and calculating, it was found that the cam is degreed at 108 - so '0' I am assuming. Yes to the stock replacement fuel pump and the tires are 275/60/15 - 28 inches tall. Yeah, I don't want to throw money at the problem without knowing if it will help. Maybe I should just start over with a better builder.
Meep-Meep
дворянин
You can make an 8.5:1 engine work. Just put in a cam DESIGNED for low compression. It will run like a stock motor but it will run well. If you want a powerhouse on pump gas, then throw one more point of compression at it and run a 112 LS cam with a slightly later intake closing point. Some say headers can be worth +/- 25 HP at high RPM. If you want to run stock manifolds then run a larger exhaust tube with the H pipe. Manifolds won't kill your build but I think if you don't plan the cam carefully you can kill it easily. A buddy back in the 80's ran a 67 Formula S 383 Barracuda with stock manifolds and a hemi grind cam. Car went mid to high 13's at Fremont and with N2O it ran a best of 11.84 @ 120. To free up the exhaust he just had some water pipe cutouts with a threaded cap about 2.5" dia just behind the front wheel. My guess on the FAST guys and success with manifolds is the cam. They are probably all running some 500 plus cube engines with low overlap cams (wide LSA's) so intake and exhaust tuning might be less sensitive than engines built with a high overlap cam.
black64
Well-Known Member
I used a lunati cam in my 383 a few years back it was advertised 284 duration and .484 lift it responded well with a 750 cfm edelbrock performer carb and intake, 10:1 compression, 906 heads, hooker headers, X pipe and 2 1/2 inch exhaust. When I first put the car together I had stock exhaust manifolds and convertor the car did not respond well until I put a 2800 stall convertor, headers and free flowing exhaust. You have a 4 speed so that is a good thing but a better exhaust would help you. 383 like higher rpms to make power so cam power range is important like mine was 1800 to 6200 range yet it still needed the higher stall convertor to perform well out of the hole. The voodoo lunati cams are improvements over the older cam grinds out there and they have a nice cam for 9:1 compression mopar engines.
RustyRatRod
Well-Known Member
Keep in mind too, since you have a 4 speed, you don't have the torque multiplication of a converter. Don't get too crazy if you do a recam because you could lose some bottom end torque....even with a 3.91.
Garys1969RR
Well-Known Member
A friend once had a 65 Fury convertible 2 door with a 383 Commando. 330 horse power. This was in 1967! Boy would that thing fly! Made me want a 383 Road Runner, and launched my Mopar quest for power. Now I know that came with closed chamber 516 heads, and 10 to 1 C/R. Also pistons that came close to the deck surface. Prob .020" down. And with .020 steel shim head gaskets, had excellent squish and quench. This I believe, is essential to getting these motors to run well. Meep Meep is running a 440 with the 915 heads, bigger valves, and a mild cam. That thing runs high 12s with a cast iron intake! 67 Satellite. My best running motors have had .035 to .040 quench. Took a long time and alot of motors to learn this. The keys are (1)Airflow,(2) squish, (3)compression. If you have a healthy amount of those then it will perform well with most cams. If you dont have those key factors, then it just aint gonna have the throttle response and torque, no matter what cam you use. Although some cams will perform better than others. Good luck!
- - - Updated - - -
The KB 162 has a C/H of 1.908" , which puts it at .024" below the deck on a blueprinted engine. And with closed chamber heads gives a C/R of around 9.5 to 1. With quench
- - - Updated - - -
The KB 162 has a C/H of 1.908" , which puts it at .024" below the deck on a blueprinted engine. And with closed chamber heads gives a C/R of around 9.5 to 1. With quench
hunt2elk
Well-Known Member
So if this motor has a 9.5 to 1 CR, am I right in thinking that the pistons should be able to be left alone?
Garys1969RR
Well-Known Member
We need to know the casting number on your cyl heads. This is found on top of the cyl head intake runner.Your pistons should be ok, according to the KB website. But according to the C/R Calculator, you will be at about 8 to 1 C/R. Thats with 88 cc heads such as the 906 or 452. If you go to a closed chamber head of 80 cc, such as the 516 or 915, with a .020 head gasket you will be looking at 8.9 to 1. Thats because the KB pistons have 8 cc valve notches in them. The original 383 pistons had no valve reliefs, so you had a little more C?R with the stock pistons.
- - - Updated - - -
This low C/R is probably 1 reason the motor is sluggish. Going to a closed chamber head with a Mopar .020" thick head gasket should help alot.
hunt2elk
Well-Known Member
My heads are the factory 906's
Mebsuta
Well-Known Member
lewtot184
Well-Known Member
'915 heads with a steel shim gasket will not only increase compression but will also create a much better quench. a simple pocket port and back cut on the valves will increase power. compression and quench will both add power. get a carter 6903 pump (mancini has them) and make sure you have an unrestricted 3/8" fuel line from the tank with a 3/8" pick-up in the tank.
a bob k. cam was suggested. these cams are engles. i like engles! if an engle is desired i'd suggest a ep-43hyd intake lobe and a ep-46hyd exhaust lobe with 112lsa. any lift at the valve exceeding .490" should have the retainer to guide clearance looked at. all this assumes your using stamped steel rockers.
also, i'd suggest shucking those big heavy tires. a 275-60x15 tire with a steel wheel will weigh about 20lbs heavier than the stock wheel and tire. multiply that by 2 and you can imagine the heavy flywheel effect on an engine that struggles to produce torque.
a bob k. cam was suggested. these cams are engles. i like engles! if an engle is desired i'd suggest a ep-43hyd intake lobe and a ep-46hyd exhaust lobe with 112lsa. any lift at the valve exceeding .490" should have the retainer to guide clearance looked at. all this assumes your using stamped steel rockers.
also, i'd suggest shucking those big heavy tires. a 275-60x15 tire with a steel wheel will weigh about 20lbs heavier than the stock wheel and tire. multiply that by 2 and you can imagine the heavy flywheel effect on an engine that struggles to produce torque.
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