Too much duration?

[‘69_Sunfire_RR]

Hello all, got a cam question. So I bought my RR six months ago and I’ve decided to figure out what cam is in this 383, which I’ve experienced some poor performance. She’s been running kinda rich, and just no throttle response. Long story short I’ve torn the engine down to remove the cam because I found a broken valve spring, which certainly is a problem and may explain everything. First, dual valve springs on these heads. #3 exhaust valve spring broke. I’ve found an Erson HI FLOW 2-H grind. Lettering/ Numbers on the cam are B157S8; 108; 581; N. Looking around seems the HI FLOW 2-h grind in a Chrysler big block, advertised duration is 306/306, 235/235 @.050, .472/.472 lift. 108 degree lobe center. Power band: 3000-6000 RPM. So all of that said, too much for a mild street build? My 383 has forged flat tops, 10:1, stock heads, stock 2.08/1.74 valves, edelbrock performer 383 intake, Holley 650, HP manifolds, 2.5” through OEM style mufflers. 4-speed, 3.55’s.

 

[Russ69Runner]

No a broke exhaust spring is never good. At the most I would have a little hotter street cam so it would breath a little better. So the motor will ideal decent. Just my thought got a 383 my self. With 650 Holley. It was rebuilt before I got the car and it is 30 over. Seams to have a cam in it that is a little hotter. I will find out when removing it during the tear down process. Sure some of the other guys should give you some better info.

 

[‘69_Sunfire_RR]

Hey thank you. Good luck with your tear down. I’m just trying to figure this engine build out. It’s always interesting to see what others did when building an engine. I’m just puzzled by the advertised duration, seems a bit much but cams aren’t my strongest point. This engine was rebuilt before I bought the car and seems like a stock rebuild as it still had the stock iron manifold and a Holley 600 on it when I bought it. I added the performer 383 intake and the 650 Holley. I feel like it is simply overcammed given the near stock build, but it’s interesting someone would go to the trouble of installing this cam with 306 degrees advertised duration and dual valve springs without following through with a nice aftermarket dual plane performer RPM and a 750 Holley or similar, and headers, etc. I just want the engine to run as it should and not like the pig it had been. Sure the broken valve spring has to be the root cause for that or a strong factor. Reason I pulled the cam to check is because I found a dual valve spring broken. In my opinion, would take a lot to break one.. any advice here is greatly appreciated folks!

 

[quikbird]

One way to check the cam and see how it compares is to go someplace like comp cams and look at the list they have and see how far up or down the list you compare. The farther down the list, the more extreme the cam.

 

[quikbird]

Also check your compression. All the old stuff is notorious for being over hyped as to compression ratio etc. if you aren’t getting the comp you need, will run like a dog

 

[‘69_Sunfire_RR]

Agreed. I believe the duration or this cam is certainly affecting cylinder pressure at low RPM. Did a compression check and all 8 are consistent around 120 psi. Seems to me it should be at least 135 but I know the duration will lower that pressure. Thoughts? I’m close to just tearing it down completely and rebuilding.

 

[droptop]

Classic Chevy cam that just does not work in a Chrysler engine. To much lift and not enough separation. Hanging both valves open at the same time. I recommend the stock 69 440-6bbl cam. Slightly more lift than stock RR cam but will still have good vacuum at idle and good low end response with your relatively mild build.

 

[zupanj]

It is probably a combination of too much cam overlap and a low compression ratio. I had the same problem with a cam with 108 degree lobe separation and large overlap. I also had really low compression in the engine. It ran awful until I got to about 3500 rpm. I think I read at the time that it is hard to find replacement pistons that provide good compression and the compression ratio can be much lower than one would think. The 120 psi on the compression check is probably the result of too much overlap. You can't build much cylinder pressure. I would look at the pistons you have as well as the cam if you have the engine torn down.

 

[‘69_Sunfire_RR]

It is probably a combination of too much cam overlap and a low compression ratio. I had the same problem with a cam with 108 degree lobe separation and large overlap. I also had really low compression in the engine. It ran awful until I got to about 3500 rpm. I think I read at the time that it is hard to find replacement pistons that provide good compression and the compression ratio can be much lower than one would think. The 120 psi on the compression check is probably the result of too much overlap. You can't build much cylinder pressure. I would look at the pistons you have as well as the cam if you have the engine torn down.

Thank you for your advice here. I’ve got it down to a long block at present so I think you’re right. May as well take the heads off now and take a look around. I intend to replace the cam anyway. What would you all recommend for a good all around streetable combo? Forged flat tops and a close to original grind, IE the Mopar Roadrunner can? Or something a little more aggressive. I’d like a good streetable 400-450 hp. This is a cruiser and I’d like it to be streetable with an attitude. Like I said I’m running stock manifolds, a performer 383 intake and 650 Holley. I’m considering a performer RPM, Holley 750, and headers along with new mufflers, perhaps flowmaster.

 

[zupanj]

My experience has been too long ago for me to offer much in the line of advice as I ended up going another route, installing a hemi. I would spend some time doing piston research before making any decisions. It seems like Moparts had a line of discussion maybe ten years ago but I couldn't turn up anything in a search. I would talk to several piston manufacturers as they should be able to help tell you to have a reasonable compression level. I would also talk to the cam company I plan to use. Personally I have not been impressed talking to Comp Cams techs though they seem to be an extremely popular choice. Hughes seems a popular choice for Mopar guys.

 

[Russ69Runner]

All I know is to much lob on the cam and the valve will hit the Piston before it close's. This is not a good thing. Valve need's to close before the piston starts on its way up to get full compression on the cylinder. That is what I call duration. Amount of time valve is open. So I am sure I will be corrected if I am wrong.

 

[BioMedTechGuy]

Dwane Porter, Jim at Racer Brown, Engle and a very few others for advice on Mopars.
Hughes should be ok too.
Too much duration on the cam you have IMO.

 

[Coyote]

All the cam grinders have a tech line to help in your choice. With the stick you can go a little more cam than an auto with a stock converter.
With a pretty much stock build I wouldn’t go more than 230 degrees at .050. Lobe separation about 110-112 degrees and lift no more than .480 at the valve.
Of cource there are lots of choices and lots of cam grinders. You pays your money and hope you get what you want! Good luck!

Ps. If .472 lift is breaking springs you may want to go a little less lift!

 

[Russ69Runner]

A nice street cam is what we use to put in our cars. If you search the web you can find out what some people have done to get more horse power out of the old girl. I was reading on one site they got about 456 HP out of a 383 with cam new intake and bigger carb. Open plane in take. Yes I am also looking what to do when I get to the motor. Have fun that is what part of working on the runner is all about.

 

[BioMedTechGuy]

My 440+6 definitely has a hydraulic Purple Stripe cam in it, but I am not certain which one. I and others suspect it is the 292°/.509 because of the way it runs and sounds.
Whatever it is, it will be until my next engine build.
I did replace the lifters, locks and retainers with CompCams items, and breathed new life into it with a set of CompCams springs as the ones in it were way down on pressure both open and closed.

 

[Russ69Runner]

Sounds like you doing a good job. I got a 383 to do. Might be asking questions here also.

 

[ACME A12]

A question of this nature will garner you a 100 different answers from 100 different people, all with varying degrees of accuracy. Send a PM to IQ52 and ask him to make a cam recommendation for you. He's not on here a lot, which is why I suggest a PM, but he will be able to help you zero in on EXACTLY what you need after answering a few questions that will surely be forthcoming. He is the owner of LaRoy Engines in Challis, Idaho. They competed in the AMSOIL/Mopar Muscle Engine Challenge numerous times. Cut through all the opinions of the hobbyists (myself included) and ask a Pro.