318 Cam Help

Comp Cams Choice

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DartGTDan

DartGTDan

'71 Dart GT Fan
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My engine builder has suggested the Comp Cams XE-250 or the XE-252. Since I'm cam "dumb" I would appreciate some guidance.

Some details about the car/engine to the best of my knowledge:
The machine shop performed an .030" over bore on the cylinders, polished the crank and added(?) hardened valve seats, using the stock valvetrain.
The car is my 1971 Dart GT 318, A904 automatic (factory stall torque convertor), Edelbrock LD4B intake, Edelbrock 1406 600 cfm carb, MP electronic ignition, Cloyes double roller timing chain/gears, factory exhaust manifolds with FlowMaster 40s & 2 1/4" pipes, 3.23:1 sure-grip (741) 8 3/4" rear end, 15" X 7" Rallyes wearing P245/60R15 tires (26.6" tall).

The car is a local ice cream parlor cruiser, with some 300-400 mile road trips planned this summer.

Help!
 
Either would be a good choice. They are close to a factory 340 cam and that is hard to beat really. The 318 runs darn good with it too.
 
Have you considered running the stock 318 2bblcam?
It will make fabulous low-rpm torque to go with those 3.23s, with the addition of nothing but a higher stall Convertor. I like the 2800; but for fuel economy, I would maybe choose a 2600. Cuz with your tires and gears, 65=2650 at zero slip, maybe 2730 tops, cruising at 3% slip. Naw, I'd still go with a 2800.
Here's the thing;
any cam with a later closing intake valve than the stocker, will loose low-rpm power, because of the loss of cylinder pressure. You are blessed with an already 9/1 compression engine, so yes you might be able to give some pressure away; but with just 3.23s in the back, I sure wouldn't do it.
IIRC the stock cam is 240/248/112 advertised; in at split overlap the Ica will be 50*
AS for the XE252H, the advertised on that is 252/252/110 and 206/[email protected] The Ica at split overlap comes to 56*
That's only 6 degrees difference, but the pressure, with no other changes, is predicted to fall from 157 to 149 psi, making your low rpm soft all the way to a breakeven point somewhere around 3000 or a lil higher. in your combo, 3000 is around 25mph at WOT.
You said;
DartGTDan said:
The car is a local ice cream parlor cruiser, with some 300-400 mile road trips planned this summer.
Click to expand...
So is losing bottom-end torque a good thing?
How much difference will it really make?
Well the Wallace predicts a P/V index of 131 with the factory cam, compared to 119 with the XE252. That is a loss of 6.3*, which will feel like a loss of 8.1% cubic inches. Making your 318 feel like a 289. read about P/V here; V/P Index Calculation
The only way around the pressure loss is to increase the Scr(Compression Ratio); but you didn't mention that.
Well there is a second way, which is to advance that XE252 cam 6 degrees to math the Ica of the stock Chrysler cam ; but this trades away power extraction to get compression, not really a good idea in a cruiser. To get the extraction back you would need a split pattern cam of about 6 more degrees duration on the power stroke. But I don't think anyone would grind you a funky cam like that.

The point is that the 2800TC will give your stock-cammed 318 a huge increase in bottom-end that no 252 cam can match.
Now, if you did both, lol, I would install that XE252H in a heartbeat or even any good used 360 2bbl cam...... which is also a 252, lol.
Happy hotRodding
 
What do YOU want? Do you want a noticeable lumpy idle? Do you want to melt tires? A little of both? Regardless of what anybody ELSE tells you, only you know what YOU want. Tell us what that is and we can help you make a better choice.
 
I ran a XE250H with a similar setup but with ported closed chamber truck heads & 2.92 gears.
Worked quite well for a cruiser - more grunt, fairly good fuel economy & good manners. If your compression ratio is reasonable the 252 is probably not a bad choice either with the 3.23 gears.
Plenty of choices from other manufactures too - just stay around that size and you will be fine.
If your going to put a lot of miles on it stick on the smaller side and you will be happier.
 
Without knowing the compression it would be hard to make a final decision. But if your somewhere around 9:1 I would go with a lunati 700 for a 318 if your compression is more than 9.5:1 id step up to the 701. Whatever you decide make sure you match your cam with the correct springs. With a stock convertor I wouldn't go any larger. Than the xe250 or the 701. Im running a 702 with about 10.5:1 and it needs more convertor.
 
Last edited:
AJ/FormS said:
Have you considered running the stock 318 2bblcam?
It will make fabulous low-rpm torque to go with those 3.23s, with the addition of nothing but a higher stall Convertor. I like the 2800; but for fuel economy, I would maybe choose a 2600. Cuz with your tires and gears, 65=2650 at zero slip, maybe 2730 tops, cruising at 3% slip. Naw, I'd still go with a 2800.
Here's the thing;
any cam with a later closing intake valve than the stocker, will loose low-rpm power, because of the loss of cylinder pressure. You are blessed with an already 9/1 compression engine, so yes you might be able to give some pressure away; but with just 3.23s in the back, I sure wouldn't do it.
IIRC the stock cam is 240/248/112 advertised; in at split overlap the Ica will be 50*
AS for the XE252H, the advertised on that is 252/252/110 and 206/[email protected] The Ica at split overlap comes to 56*
That's only 6 degrees difference, but the pressure, with no other changes, is predicted to fall from 157 to 149 psi, making your low rpm soft all the way to a breakeven point somewhere around 3000 or a lil higher. in your combo, 3000 is around 25mph at WOT.
You said;

So is losing bottom-end torque a good thing?
How much difference will it really make?
Well the Wallace predicts a P/V index of 131 with the factory cam, compared to 119 with the XE252. That is a loss of 6.3*, which will feel like a loss of 8.1% cubic inches. Making your 318 feel like a 289. read about P/V here; V/P Index Calculation
The only way around the pressure loss is to increase the Scr(Compression Ratio); but you didn't mention that.
Well there is a second way, which is to advance that XE252 cam 6 degrees to math the Ica of the stock Chrysler cam ; but this trades away power extraction to get compression, not really a good idea in a cruiser. To get the extraction back you would need a split pattern cam of about 6 more degrees duration on the power stroke. But I don't think anyone would grind you a funky cam like that.

The point is that the 2800TC will give your stock-cammed 318 a huge increase in bottom-end that no 252 cam can match.
Now, if you did both, lol, I would install that XE252H in a heartbeat or even any good used 360 2bbl cam...... which is also a 252, lol.
Happy hotRodding
Click to expand...
AJ/FormS said:
Have you considered running the stock 318 2bblcam?
It will make fabulous low-rpm torque to go with those 3.23s, with the addition of nothing but a higher stall Convertor. I like the 2800; but for fuel economy, I would maybe choose a 2600. Cuz with your tires and gears, 65=2650 at zero slip, maybe 2730 tops, cruising at 3% slip. Naw, I'd still go with a 2800.
Here's the thing;
any cam with a later closing intake valve than the stocker, will loose low-rpm power, because of the loss of cylinder pressure. You are blessed with an already 9/1 compression engine, so yes you might be able to give some pressure away; but with just 3.23s in the back, I sure wouldn't do it.
IIRC the stock cam is 240/248/112 advertised; in at split overlap the Ica will be 50*
AS for the XE252H, the advertised on that is 252/252/110 and 206/[email protected] The Ica at split overlap comes to 56*
That's only 6 degrees difference, but the pressure, with no other changes, is predicted to fall from 157 to 149 psi, making your low rpm soft all the way to a breakeven point somewhere around 3000 or a lil higher. in your combo, 3000 is around 25mph at WOT.
You said;

So is losing bottom-end torque a good thing?
How much difference will it really make?
Well the Wallace predicts a P/V index of 131 with the factory cam, compared to 119 with the XE252. That is a loss of 6.3*, which will feel like a loss of 8.1% cubic inches. Making your 318 feel like a 289. read about P/V here; V/P Index Calculation
The only way around the pressure loss is to increase the Scr(Compression Ratio); but you didn't mention that.
Well there is a second way, which is to advance that XE252 cam 6 degrees to math the Ica of the stock Chrysler cam ; but this trades away power extraction to get compression, not really a good idea in a cruiser. To get the extraction back you would need a split pattern cam of about 6 more degrees duration on the power stroke. But I don't think anyone would grind you a funky cam like that.

The point is that the 2800TC will give your stock-cammed 318 a huge increase in bottom-end that no 252 cam can match.
Now, if you did both, lol, I would install that XE252H in a heartbeat or even any good used 360 2bbl cam...... which is also a 252, lol.
Happy hotRodding
Click to expand...
I have a question about the use of the factory 318 cam. Is it true that one of the problems with the 318 is it's "lazy" camshaft ? Would the 3.23's and a 2,800 rpm stall converter really make that much difference? I like this forum, always learning something new.
 
AJ/FormS said:
Have you considered running the stock 318 2bblcam?
It will make fabulous low-rpm torque to go with those 3.23s, with the addition of nothing but a higher stall Convertor. I like the 2800; but for fuel economy, I would maybe choose a 2600. Cuz with your tires and gears, 65=2650 at zero slip, maybe 2730 tops, cruising at 3% slip. Naw, I'd still go with a 2800.
Here's the thing;
any cam with a later closing intake valve than the stocker, will loose low-rpm power, because of the loss of cylinder pressure. You are blessed with an already 9/1 compression engine, so yes you might be able to give some pressure away; but with just 3.23s in the back, I sure wouldn't do it.
IIRC the stock cam is 240/248/112 advertised; in at split overlap the Ica will be 50*
AS for the XE252H, the advertised on that is 252/252/110 and 206/[email protected] The Ica at split overlap comes to 56*
That's only 6 degrees difference, but the pressure, with no other changes, is predicted to fall from 157 to 149 psi, making your low rpm soft all the way to a breakeven point somewhere around 3000 or a lil higher. in your combo, 3000 is around 25mph at WOT.
You said;

So is losing bottom-end torque a good thing?
How much difference will it really make?
Well the Wallace predicts a P/V index of 131 with the factory cam, compared to 119 with the XE252. That is a loss of 6.3*, which will feel like a loss of 8.1% cubic inches. Making your 318 feel like a 289. read about P/V here; V/P Index Calculation
The only way around the pressure loss is to increase the Scr(Compression Ratio); but you didn't mention that.
Well there is a second way, which is to advance that XE252 cam 6 degrees to math the Ica of the stock Chrysler cam ; but this trades away power extraction to get compression, not really a good idea in a cruiser. To get the extraction back you would need a split pattern cam of about 6 more degrees duration on the power stroke. But I don't think anyone would grind you a funky cam like that.

The point is that the 2800TC will give your stock-cammed 318 a huge increase in bottom-end that no 252 cam can match.
Now, if you did both, lol, I would install that XE252H in a heartbeat or even any good used 360 2bbl cam...... which is also a 252, lol.
Happy hotRodding
Click to expand...
P/V index mean?
 
I put a stock 360-2bbl cam in a 318 I had in a 83 D250. made a huge difference. I am looking to do the same in my 78 Fury to its 318.
On the truck I also added Magnum heads (those from a 92-newer 318/360) the Fury is getting a set of '302s instead. along with a Performer intake and one of a couple 4 bbl carbs that I already have here. None of which is a Holley.
 
I wouldn't put a stock 318 cam in a friggin' thing. I don't care what AJ's math says.
 
RustyRatRod said:
What do YOU want? Do you want a noticeable lumpy idle? Do you want to melt tires? A little of both? Regardless of what anybody ELSE tells you, only you know what YOU want. Tell us what that is and we can help you make a better choice.
Click to expand...

RRR

What I really want is a reliable, trouble free engine that runs on 87 pump gas. A lumpy idle would be great, but not at the expense of having to run headers, a high stall torque convertor. etc... I'm at a point in my life (health wise) where driving the Golden Oldie to a few weekly events is the main objective. If I can squeeze in a few longer trips, this summer, that would be awesome too. Since I'm "cam dumb" I'm leaning toward telling my engine builder to just use a stock 318 replacement cam.
 
OldmanRick said:
I might be a broken record sometimes, and while that Mancini cam is decent, i can't pass up on the mild Summit grinds for that price. Just get the best lifters you can afford and let it eat.

PLYMOUTH Summit Racing SUM-6900 Summit Racing™ Classic Camshafts | Summit Racing
Click to expand...
I agree 100%. I think that would fit the bill perfectly for what he's lookin for. That's the same grind as the old Edelbrock Performer camshaft. It's just a good all around grind. Won't make the forum gurus happy, but I think @DartGTDan will like it.
 
The bonafide Comp 901-16 springs are very reasonably priced and perfect for it. I wouldn't run it without good springs like that, though.
 
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