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Old 01-16-2008, 12:58 PM
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383 cam question...

hey guys, i did some research on the stroker i picked up for cheap, and apparently the guy really did need a new cam!

i read that keeping a dynamic compression below 8.25 or so is the goal to have a well running motor. i used wallace racing's calculator for the cam i'm using.

ELGIN 290/290 .480 lift. 110lsa

Static compression ratio of 10.44:1.
Effective stroke is 3.28 inches.
Your dynamic compression ratio is 9.24:1 .
Your dynamic cranking pressure is 191.39 PSI.
Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 0 PSI is 9.24 :1.
V/P (Volume to Pressure Index) is 193

the DCR was through the roof. no wonder he had tuning issues.

any ideas on a good cam choice? btw desktop dyno gave me the IVC(ABDC):49.

i'm aiming for a ****** sound, and a lot of go. neither the heads or the block have been decked excessively, i want lift, but i'm also worried about piston to valve clearance. please help, an suggestions would be great. thanks guys.

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Old 01-16-2008, 01:14 PM
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Unless you have shaved heads or alot more duration and lift than the cam you listed, then piston to valve clearance should not be a problem. But ALWAYS check to be sure.

The bigger question here is "How are you going to use this 383", daily driver? drag racing? Street/Strip? Towing?

What vehicle is it going in?

manual or automatic?
Stall? (if auto)
Rear end gear ratio?

Do you want flat tappet, or roller?

These all affect what you are going to need for a cam. I like the XE268H for all around power, and the XE274H with a bigger stall and gears, or the XE284H for balls to the wall with big stall, gears, headers and compression. If you are going to tow with it, it is a whole other ball game.
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Old 01-16-2008, 01:30 PM
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the motor is going into a 1990 240sx, fully dressed it'll weigh around 2600lbs MAX. the car is going to be a weekend pleasure driver, but knowing me i'm going to fall in love with it and drive it everyday anyways, umm, it might make a few 1/4 mile passes/drift like crazy.

manual trans, either a 4 speed muncie or saginaw, or the t-5 WC, idk yet.

the read end is a 4.08 stock gearing on the 240.

and i'm not sure, what would you recommend? flat or roller? i tried to research them, but only got the fact that tappet is cheaper?

as you can tell i'm not a pro, but i'm very eager to learn.
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Old 01-16-2008, 02:16 PM
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also on Desktop dyno, i have a few questions pertaining to cams, do i select seat to seat? or @.50? and what would i put for either of them with this cam? and how do i find the Intake center line?


http://cgi.ebay.com/ebaymotors/ws/eB...TODAY.m238.lVI
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Old 01-16-2008, 02:39 PM
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It's all good man, you gotta start somewhere. For that setup, I would suggest a smaller, XE268h, cam otherwise you are just going to fry the tires off of it at every stoplight.

There are lots of differences between flat tappet and rollers but what I like about rollers is that it lets you run a lot more duration and lift without sacrificing low end driveability. If you notice most Flat tappets top out at .500 lift (there are exceptions as always) but that is where roller cams are just getting warmed up. The reason is because they can open up valves quicker hold the valve open longer and close quickly to maintain vacuum and compression.

They don't cost anything more to produce, so why do you think they are so much more expensive? Because they work.


Anyways enough about that...use dur @ .050 which is how manufacturers classify their cams.
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Old 01-16-2008, 02:48 PM
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Increase your duration so the intake valve closes later and get that DCR down to around 8.0-1 if you want to run 93 octane. There's plenty of big cams to pick from just plug some into the calculator till you find what you need. You can run higher DCR if the heads are aluminum. Or you could use heads with a larger chamber to lower the static and resulting dcr.
Don't run the 268 like previously suggested or your DCR will go even higher.
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Old 01-16-2008, 03:16 PM
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I've seen many engines with over 200psi cranking compression run on 87 octane, it just takes a half decen chamber design and the right spark tuning. 8:1 used to be the rule for 87 octane, but that line is crossed most of the time nowadays, even in factory tuned engines. I would go with the 268, its a great all around part- kinda like the RPM AirGap manifold or vortec heads.

Oh, and FYI roller cams do cost more to make, much more.
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Old 01-16-2008, 03:18 PM
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well i am using aluminum heads, and i keep trying different cams, but i keep getting IVC degrees around 45ish. and that wont work. i don't get this. but if i put in the seat to seat and put in the full duration (advertised) i get a better degree readout.
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Old 01-16-2008, 03:28 PM
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Quote:
Originally Posted by ap72

Oh, and FYI roller cams do cost more to make, much more.

Why? Special Materials? Tighter tolerances? All things being equal it would be the same.
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Old 01-16-2008, 03:58 PM
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double v can you find out the stuff on that 268 cam for me? like the actual IVC degree?
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