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Old 02-14-2015, 12:06 PM
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New 383 stroker with little vacuum

Hey guys hope I didn't post this more than once it's like my third try to post as a new member ha.. So my problem is I installed a new 383 stroker I bought from a builder online and out of state... Not a good idea so I'm having trouble keeping a reliable idle and my brake booster won't work because I have only 6 iches of vacuum at idle and about 15 max.. My question is that normal . I don't know what cam is in there but I do have a cam analysis sheet if that helps..

Some basic engine info I do have

383 stroker 465hp
10.5:1 comp on premium pump gas
Total timing 34 degrees not using vacuum advance
Aluminum heads
Roller rockers
2300 stall
Holley carb 750.


So any info would help I'm defiantly a beginner here and would love some insight. So too little vaccum?
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Old 02-14-2015, 12:09 PM
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camshaft specs? The brake issue is easy to fix. Is this a Corvette or other car that might have a vacuum leak in a headlight system,,,etc?
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Old 02-14-2015, 12:16 PM
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I wish I did have the camshaft specs but I do t.. Did you see the photo of the camshaft anylisis? Does that even help? Yea I'm pretty sure I know what I need to do to fix the brake booster bc it just doesn't have enough vacuum .. What I'm wondering is 6 inches at idle and 16 max inches seem right for my setup?
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Old 02-14-2015, 12:18 PM
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It's. 1972 c-10 truck. Don't believe I have a vacuum leak bc they are all new line all I have is one to the brake booster one to the Pcv valve and one to the th350 tranny..
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Old 02-14-2015, 12:30 PM
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from what I can read and isnt obscured,I would toss that cam in a trash can. Im not saying its a bad choice in profile. Im saying a cam that big needs a wheel on the follower. It will have a rough idle and poor vacuum at idle and wont impress me with its performance. With out more information its all going to be a guessing game. If you gave me that engine for free I would not use it. I would take it apart and measure everything and make changes as I saw fit,,,
what is the brand name of the heads,intake,distributor,pistons,rockers? what are the exact specs of everything.You own the engine,they should supply exact info right down to the balance specs, piston to wall and piston to valve. They should say exactly where the ICL is and why

How is the power? does it melt the tires etc?
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Old 02-14-2015, 12:44 PM
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It's not the cam. Matter of fact, if I were building the motor, I might have used more cam than they did for 10.5:1 static compression ratio. Only difference is, I wouldn't use one of those fosdick XE cams and I sure as hell wouldn't have used a flat tappet cam.
Here's the cam card....
21-227-4(Single Bolt) - Xtreme Energy™ Hi-lift Hydraulic Flat Tappet Camshafts

Here's what I would do:
Find zero on your damper by following the wiki article I linked for you here, then dial in 12-14 degrees or more initial timing at the crank and dial in total timing (initial at the crank plus centrifugal) based on the heads you're using. Without knowing EXACTLY where top dead center is on the damper, you will be shootin' in the dark. Maybe some of the Mopar guys will jump in here and suggest the total ignition timing you should shoot for, because I'm not a Mopar guy, but that's my best guess as to the lack of manifold vacuum, that the motor is seeing too little ignition timing, assuming that the valve lash is correct.
http://www.crankshaftcoalition.com/w...op_dead_center

EDIT: I just went back and read that this is a Chevy truck. The cam card you linked is for a Mopar 383, not a Chevy 383. What's goin' on ???????? Did the builder give you the wrong cam card or have I slipped a cog ?????

.

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Old 02-14-2015, 12:53 PM
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What is the timing at idle? Sounds more like a tuning setup issue. Camshaft is not a bad selection at all. Your basic comp cams style XE 275. 230 231 @.050 .521 .522 110lsa. Not a bad grind for a hot street 383. It has some moderate overlap at 13 degrees. It is going to idle a bit rough. Should be a responsive nice little engine. How does it run off idle?
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Old 02-14-2015, 12:56 PM
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Thanks I will look into it. Mopar? Isn't that dodge.. I'm running a 383 chevy
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Old 02-14-2015, 12:57 PM
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Quote:
Originally Posted by Weikel View Post
I wish I did have the camshaft specs but I do t.. Did you see the photo of the camshaft anylisis? Does that even help? Yea I'm pretty sure I know what I need to do to fix the brake booster bc it just doesn't have enough vacuum .. What I'm wondering is 6 inches at idle and 16 max inches seem right for my setup?
Yes that sheet you posted gives you all the info you need about that cam.
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Old 02-14-2015, 01:14 PM
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Quote:
Originally Posted by LSs10 View Post
Yes that sheet you posted gives you all the info you need about that cam.
Yeah, except the cam card is for a XE-275-HL10 (21-227-4) which is a Mopar cam. You can make a 383 stroker Mopar from a 318 and you can make a 383 stroker Chevy from a 350, so I didn't question what make the motor was when I first answered. I just went by the cam card.
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Old 02-14-2015, 01:22 PM
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Yes I assumed it was a chevy cam card as well. Not sure why they would give you the wrong card. Im betting that the specs are almost exactly the same. But I would call the builder and verify to be 100 percent certain.
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Old 02-14-2015, 01:28 PM
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Quote:
Originally Posted by LSs10 View Post
Yes I assumed it was a chevy cam card as well. Not sure why they would give you the wrong card. Im betting that the specs are almost exactly the same. But I would call the builder and verify to be 100 percent certain.
Problem is, if they sent the wrong cam card, what cam did they put in the motor? Jeez, I think I'll go back to bed and start over later.
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Old 02-14-2015, 01:30 PM
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Quote:
Originally Posted by LSs10 View Post
What is the timing at idle? Sounds more like a tuning setup issue. Camshaft is not a bad selection at all. Your basic comp cams style XE 275. 230 231 @.050 .521 .522 110lsa. Not a bad grind for a hot street 383. It has some moderate overlap at 13 degrees. It is going to idle a bit rough. Should be a responsive nice little engine. How does it run off idle?


So at around 780 rpms it's running pretty rough and it doesn't feel to reliable the initial timing is about 10 degrees if I bump it up to say 1000 rpms it's around 18 .. It's defiantly has the power at WOT can't keep the tires from spinning . Wondering if I should mess with the centrifugal advance and take some of it out . I'm really green to all of this so I'm pretty hesitant to try it for now. Haha also it's pretty hard to adjust this holley carbs idle circuit seems like it doesn't do to much to the idle or the vaccum ( although it's pretty bounce vaccum reading with this cam). Wondering if I should open the secondary blades a little too
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Old 02-14-2015, 01:31 PM
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Quote:
Originally Posted by vinniekq2 View Post
I would take it apart and measure everything and make changes as I saw fit.
Vinnie, I should have paid more attention to you in the first place.
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Old 02-14-2015, 01:33 PM
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Originally Posted by techinspector1 View Post
Problem is, if they sent the wrong cam card, what cam did they put in the motor? Jeez, I think I'll go back to bed and start over later.
Well that is pretty messed up that it's the wrong cam card".. It's denintly a Chevy 383 wonder what's the deal with the wrong card.. I will have to find out... Thanks for the info!
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