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1984 corvette
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33 Posts
Discussion Starter · #1 ·
good morning guys and gals. I have been along time reader here and have learn a lot of things. today I am stumped. me and my son are back on our (farther-son project) here is what we have so far
sbc 400 .040 over
dish pistons
291 heads (complete work over .was at the shop for ever)
MSD ready to run dizzy with a 6al
E3 plugs
quick fuel 750 carb vac seconds (slayer)
hooker headers
comp cam valve springs
roller rockers 1.6
summit cam 0.458 / 0.458 lift (part# sum-k00052)
comp cam hydrolic flat tappet lifters
double roller timing chain
wiend single plane intake

here is what is going on. its slow to turn up and when its in drive it wants to be sluggish when you hit it.. Im having a hard time getting it tune.
I set the timing at 12 and try to get the best vac then it loses power
I guess what is the best way to do a good tune for dummies
also how to correctly adjust the roller rockers and valves? thanks for help
 

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1984 corvette
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33 Posts
Discussion Starter · #8 ·
I home made a toolder that slides down a drilled out spark plug and when it slides to the top the piston is at the top.it figure it's off a couple of degrees due to the swing of the crank shaft as it passes TDC
 

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Registered SBC Addict
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897 Posts
some more initial/total timing would probly be better, 36-38* is usually safe..
see what the motor wants, listen for any pinging and rattling..
add some more initial and see if the starter kicks back when the motor is hot??

have you checked for vacuum leaks? re-torqued the intake manifold??
what kind of vacuum do you see at idle??

is the vacuum advance on full or ported vacuum??
full vacuum will help with the idle, cooling, and bigger carb tuning..

was the cam degreed in when installed??
 

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1984 corvette
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33 Posts
Discussion Starter · #10 ·
Yes. I have checked for vac. Leaks
At idle it showed 12 -14 (it's very erratic though) no the cam was not degree when installed.. I have the vac advance connected to the metering block?? Thanks guys for all the help.I don't mean to be a bother.. I wanted to give this car to my son for a graduation present
 

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Registered SBC Addict
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897 Posts
its no bother Pat, we have all been there, we all learn and share..
is this in the 84 Vett??

if your not sure about setting the valves , and the vacuum gauge is erratic?
I think I would check it..
the exhaust opening and intake closing method is purty much bullet proof..
except for the "feel" it takes to find zero lash,
as he says the up and down works better than the spin method..
http://www.hotrodders.com/forum/best-way-adjusting-valves-sbc-132599.html#post923692

as for degree-ing the cam, I found 1or2 cams that were off quite a bit over the years,
i think? one was a Summit and one was a PAW cam..
 

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Registered SBC Addict
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897 Posts
the metering block may not be full manifold vacuum??
try it on a vacuum port below the throttle blades or on the manifold..

you should get a good idle speed/rpm increase when its plugged in at idle..
 

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1984 corvette
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33 Posts
Discussion Starter · #13 ·
Thanks. Yes it's the old vette..it's not much, but my son loves it. What grade of motor oil would you recommend?
 

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1984 corvette
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33 Posts
Discussion Starter · #14 ·
We removed the tired 350 (smog engine) and installed this 400. We had clearance issues with the balancerest a few mods and that was done. No I trash the cross fire. I can't tell what my compression is all I know is what's in the engine. I would guess 9-9.5
I just started it a few minutes ago and noticed that I have a small clapping sound in the valve cover. I would think this is why my vacuum is so crazy. Maybe first I will adjust all valves and recheck my TDC with my timing tab. Then set timing to 12-15°
 

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Cars, Trucks, Boats, Motorcycl
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7,481 Posts
I home made a tool holder that slides down a drilled out spark plug and when it slides to the top the piston is at the top.it figure it's off a couple of degrees due to the swing of the crank shaft as it passes TDC
OK, you must use the two TDC marks divided in half method using a locking piston stop tool to find real -0- TDC...

If those are 'general rebuilder' dished pistons, they may be sitting a ridiculous .080" down in the bores! Giving horrible engine quench effects and low compression ratio... This would also require base ignition timing of 18 - 20 degrees and total mechanical timing of 40 degrees to get any kind of snappy engine...

http://www.crankshaftcoalition.com/wiki/Quench
.
 

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Race it, Don't rice it!
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8,108 Posts
The timing is set to 15 degrees. Can you please elaborate on parts? Thanks for your help
Single plane intakes don't general work as well as a dual plane intake on the street.
291 heads and dished pistons are generally best together. Not enough CR.

Doesn't really matter right now cause your trying to the do the best you can with what you have. I think you need to get the timing right. Verify the timing marks are good, set timing at 16-18 initial and 36 total at 3k. Set the valve properly. Degree the cam if possible, and then work on the carb.

On the comments about moving the push rods up and down instead of spinning it is sound advice. You mentioned 1.6 rockers and is that with roller rockers? If so you must be using poly locks and with poly locks, you can turn the lock with you fingers real gently until it stops. It's be a pretty solid feel when you get to no lash when gently holding the lock with oily fingers. I like turn it another flat on the hex and lock it down.

You gonna find about 100 different ways of setting the lash. I advise to find someone trust worthy and listen to and only them to avoid confusion.
 

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Cars, Trucks, Boats, Motorcycl
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7,481 Posts
If the rebuilder pistons sit .080" down, 22cc dish pistons, and .041" rebuilder compostion head gasket, 64cc combustion chambers then I get about 8.4:1 as a (hopefully worst case) compression ratio... rather low for a 218/218 cam...
 

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1984 corvette
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33 Posts
Discussion Starter · #18 ·
Thanks guys for all of your help. It's funny that most of the shops around my place don't even want to take the time to answer a few questions I have, and yet complete strangers will go above and beyond to help.. from the bottom of mine and my sonson heart we THANK Yall so much. We both have been under the weather a few days I hope to be back on it this evening. Yes the rockers are roller with Polly locks
 

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1984 corvette
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33 Posts
Discussion Starter · #20 ·
Ok..so I'm out side working on the 400.. I just adjusted all my valves.. and now it runs worse. I pulled the plug wires while the engine was running and noticed that numbers 6,7,8 are all dead. Could I have my valves to tight? I adjusted them by the number 1 and adjusted a few intakes and then got number 6 up and done the others..any ideas
 
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