Hypothetical question about cam rpm range and seat of the pants feel

[Crockett85]

Hello everyone,

Lets assume hypothetically that I have a 4000# B-body with a mostly stock 383 (ie 906 heads, performer intake, 650 spread-bore, electronic ignition, and factory HP manifold), 4-speed, and 3.55 rear gear. My driving is mainly street cruising, occasionally opening the throttle, and driving on twisty mountain roads. The only missing piece is the cam.

Now lets say that I have narrowed my cam choices down to two. One cam has an rpm range of 1000-5000. The other cam's rpm range is 1500-5500. If I went with the latter cam, would there be a noticeable loss of torque from 1000-1500?

From past experience driving 4 cylinders with 5 speeds, I could usually coast in gear down to 1000 before the engine starts rattling. If I needed to start from a stop light or accelerate, my rpm would need to be least 1500. Would a big 383 behave the same way?

Thanks!

 

[Jcharger]

I suggest putting more details about the specific cams you have in mind.

My guess is if you put specific information about the cams, you will get specific information from those who know.

I am not an expert on the best ones. I used a lunati 60302 (now 1230702) on a 383 and liked it, but do not know if that is one you have narrowed to.

Regarding starting off, I usually start off with more than 1000 RPM and try not to run at too low RPM. I actually prefer ~2000 RPM as my lower limit for running. It will run lower than that, just don't like to run there.

 

[Mike67]

I think anything that's says idle -5000 is vague... If you have it narrowed down to 2, post the specs to get more guidance from the experts here....IJMO, but I think with that gear and a 4 speed there are many cams out there that can meet your needs and really make you "feel it" and still have great street manners....

 

[Lionized]

Short answer is no.

 

[Crockett85]

At first, I was considering the following two cams:

Lunati 60301: http://www.lunatipower.com/CamSpecCard.aspx?partNumber=60301
Lunati 60302: http://www.lunatipower.com/CamSpecCard.aspx?partNumber=60302

However, I also found this one from Crane: Part #680101
Int/Exh Dur @ 50 thou: 214/225
Lobe Separation Angle: 115
RPM Range: 1400-5000
Gross Int/Exh Lift: .447/.464

Likewise, I am thinking of keeping the static compression around 9:1 so that I can run on 91 octane at any rpm without worrying about pre-ignition or detonation issues.

 

[Jcharger]

I reread your earlier post. I don't think you will notice a significant difference at low RPM (between 1000 and. 1500) between those cams. Given that you have 3.55 gears and a manual I would go with the 60302. I think that the 60302 will work well with the 383 from a torque standpoint. I switched from the 1970 magnum cam to the 60302 and it woke the car up nicely. See what others say.

I am going to go out on a limb, but I think the 9:1 target would be good with pump gas to deal with detonation (probably 9.5:1), but also see what others say.

 

[Crockett85]

I reread your earlier post. I don't think you will notice a significant difference at low RPM (between 1000 and. 1500) between those cams. Given that you have 3.55 gears and a manual I would go with the 60302. I think that the 60302 will work well with the 383 from a torque standpoint. I switched from the 1970 magnum cam to the 60302 and it woke the car up nicely. See what others say.

I am going to go out on a limb, but I think the 9:1 target would be good with pump gas to deal with detonation (probably 9.5:1), but also see what others say.

Thanks for the feedback jcharger! The 60302 cam is looking pretty good. It's awesome if it can give a good step up in power from the factory cam without having to go more radical. I don't mind a tiny bit of lope, but I don't care for the choppy idle at all.

I know piston choice, cylinder head chamber, and quench are factors in preventing detonation. However, I think that is over my head.

 

[Cranky]

With cams, you can make an engine with 8-1 comp ping or you can run an engine with 11-1 on pump gas with a cam that doesn't build a lot of cylinder pressure down low so it doesn't ping....so, static compression isn't the only thing to think about when building an engine. I like to shoot for 9.5 to 10 with iron head mild build engines then go look at what's available in cams that are made for Mopars. Mopars have a larger diameter lifter so you can play a better game with cams than with most off the shelf cams that are designed for GM etc. If I can't find what fits the combo I'm working with, then I'll go for a custom grind. I dunno man....it takes some time to learn and understand what effects a cam will do for a particular combo (the whole car is in the equation) and I found it better to just find someone that really knows cams and has the experience (Mopar experience) to help you select what you want or need but imo, I've never liked cams with a late opening and a late closing intake valve.

Btw, unless you have pistons that have a reverse dome on them, you don't have any quench to speak of with the 906 heads and especially so if they are stock and have never been milled. Even with the factory steel shim .020 gaskets, you're looking at .100 to .110 piston to head quench side clearance.

 

[moper]

Granted it's an E body, but I built a 383 years ago that is the numbers matching engine for a '70 RT, 3.91, stick car. It's 9.8:1 static compression, 906 heads completely redone for performance, KB hyper flat top pistons, the block was blueprinted, and I ran the XE268 Comp Cam, Street Dominator intake, Holley 3310. It will idle at 750rpm, and it pulls from 1K without a problem in 4th. I'd do that again in a heartbeat.

 

[Mike67]

You can always call Hughes, they will ask everything from your first borns weight to how old you were when you lost your last tooth....but they will make their best recommendation based on all of your componenants/ expectations....

 

[Crockett85]

I have seen a lot of threads on here about folks having to modify the 906 heads to get the results they want. From what I can see, .040 is the magic number for piston to head clearance. The most common way I see people doing this is by shaving the block to zero deck and adding a .040 gasket.

I agree with you on letting pros handle this task. I'm just fascinated by this kind of stuff. I realize that the more I read into this, the less I know lol

 

[Crockett85]

Granted it's an E body, but I built a 383 years ago that is the numbers matching engine for a '70 RT, 3.91, stick car. It's 9.8:1 static compression, 906 heads completely redone for performance, KB hyper flat top pistons, the block was blueprinted, and I ran the XE268 Comp Cam, Street Dominator intake, Holley 3310. It will idle at 750rpm, and it pulls from 1K without a problem in 4th. I'd do that again in a heartbeat.

That is cool how you can pull from 1000 rpm. I'm sure those 3.91 gears helped a lot. The rpm on the highway must have been brutal though. If I tried that in a 4 cylinder, the engine would rattle until it threw a rod lol

 

[Dennis H]

Got a Comp Cam. 9.5:1. 91 pump. Love to loaf along light throttle @ 900 RPM. No balk or buck. Any gear. TKO 5. Dyno says it stops pulling at 4850. Don't care.

 

[747mopar]

I'll answer by telling you even a cam with a range of 1,800-5,800 rpm is very well mannered mind you it's in a 456 stroker. I'm running a 6 speed standard and the 1,800 rpm is no issue whatsoever, keeping it in the meat of rpm range just feels natural and is very enjoyable to cruise as well.

 

[moper]

Well, there's not much difference between a 3.91 and a 3.55 ratio: about 300rpm at 60mph and cruising a little below 3K with 15" wheels and stock size tires. This car was "as ordered" as he's the 2nd owner and he's had it for decades so no major changes...

Not sure what you had for issues with 4cylinders and 5sps. My Neon was great and would pull from under 1500 in 5th. Not well or hard, but it wouldn't buck or shudder.

Some facts...
There are no flat top pistons for the 383 that allow for static compression over 9:1 without replacing the heads with milled closed chambered units, or milling the block's decks to get it. You can run a domed piston if you want to, but you're limited by the pistons if you want to upgrade later.
There are no quench dome designs at all for them. So again unless you replace the heads and blueprint the block - no quench benefits are possible either.
When running factory exhaust manifolds and looking for real power, the LSA of a cam is more important to a cam choice than duration at .050", and much more important than lift. IMO, Comp sort of missed the boat on that part with the smaller XE grinds but they were probably looking more for carrying the rpm band higher than maximizing the torque under the curve.
Unless you are running a camshaft that is designed for midrange and upper rpm power curves that really depend on pushing the envelope in regard to lifter/lobe relationships the ".904 lifter" claims are a bunch of crap used to sway the ignorant consumer. Lobe designs don't know what engine family they are in, and fast rates of lift and closure cause a lot more problems than present benefits, even with the wider lifter base. This is especially true for street (read that as relatively low peak rpm & lots of very low load & idle time) engines.

 

[Crockett85]

Well, there's not much difference between a 3.91 and a 3.55 ratio: about 300rpm at 60mph and cruising a little below 3K with 15" wheels and stock size tires. This car was "as ordered" as he's the 2nd owner and he's had it for decades so no major changes...

Not sure what you had for issues with 4cylinders and 5sps. My Neon was great and would pull from under 1500 in 5th. Not well or hard, but it wouldn't buck or shudder.

Some facts...
There are no flat top pistons for the 383 that allow for static compression over 9:1 without replacing the heads with milled closed chambered units, or milling the block's decks to get it. You can run a domed piston if you want to, but you're limited by the pistons if you want to upgrade later.
There are no quench dome designs at all for them. So again unless you replace the heads and blueprint the block - no quench benefits are possible either.
When running factory exhaust manifolds and looking for real power, the LSA of a cam is more important to a cam choice than duration at .050", and much more important than lift. IMO, Comp sort of missed the boat on that part with the smaller XE grinds but they were probably looking more for carrying the rpm band higher than maximizing the torque under the curve.
Unless you are running a camshaft that is designed for midrange and upper rpm power curves that really depend on pushing the envelope in regard to lifter/lobe relationships the ".904 lifter" claims are a bunch of crap used to sway the ignorant consumer. Lobe designs don't know what engine family they are in, and fast rates of lift and closure cause a lot more problems than present benefits, even with the wider lifter base. This is especially true for street (read that as relatively low peak rpm & lots of very low load & idle time) engines.

I agree with you about the comp xe cams. Yes they make all that power, but I know I will be paying for it somewhere down the line. I can picture in my mind how those aggressive ramps would put a lot of stress on flat tappet lifters. I assume that is when roller lifters come into the picture?

Regarding LSA, While there are a couple of comp cams that interest me, all their cams have a 110 LSA. Not sure how much of a difference 2 degrees would make. All I know is that narrow = peakier powerband and wide = broader powerband. That is why I picked those particular cams.

I am starting to wonder if using the stealth heads from 440 Source would make things easier. The only reason I mentioned 906 heads was because I love the stock look of the 383 HP. Can I use the original valve covers with the stealth heads if I stick with the factory 1.5 rockers?

 

[moper]

Stealths are almost perfect match for stock iron. I built one with them that one Stock Appearing at Carlisle... but makes about 160% the horsepower. You will want to make sure you measure for the correct pushrods though to maintain the right preload.
On the LSA - yeah, Comp seams to have blown it IMO making them all 110°. But to be honest, I don't think it's a huge difference when you're talking about a conservative cam choice anyway.

 

[OntarioBeeper]

Thanks for the feedback jcharger! The 60302 cam is looking pretty good. It's awesome if it can give a good step up in power from the factory cam without having to go more radical. I don't mind a tiny bit of lope, but I don't care for the choppy idle at all.

I know piston choice, cylinder head chamber, and quench are factors in preventing detonation. However, I think that is over my head.

I read everything I could find on cams for my type of driving which sounds just like yours, then ordered the 60302 and rpm heads for my 383 4 speed. Haven't installed yet but the Lunati sounded just right for me. Good luck with it. Bill

 

[Crockett85]

I read everything I could find on cams for my type of driving which sounds just like yours, then ordered the 60302 and rpm heads for my 383 4 speed. Haven't installed yet but the Lunati sounded just right for me. Good luck with it. Bill

There are a couple of videos on youtube of a red 66 Charger 383 with the 60302. The idle sounds so nice! Let me know how it works out for you.

 

[Crockett85]

Stealths are almost perfect match for stock iron. I built one with them that one Stock Appearing at Carlisle... but makes about 160% the horsepower. You will want to make sure you measure for the correct pushrods though to maintain the right preload.
On the LSA - yeah, Comp seams to have blown it IMO making them all 110°. But to be honest, I don't think it's a huge difference when you're talking about a conservative cam choice anyway.

Yeah it seems that going with the stealths would be a win-win for me...I get a stock appearing engine that runs more efficiently due to the aluminum and closed chambers. However, I have read that the quality control on these heads can be questionable. What kind of things do I need to out for after receiving them?...or is this a job best left to a machinist?