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Old 12-26-2011, 03:54:34 PM   #1
robmaxfli
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Smile GM Cam used in 330 HP 350 HO Eng.

Part # 24502476 (212/222)

I have been trying to figure out the missing piece of the puzzle as to why my 330HP clone is not as quick off the line as I thought it would be. I have verified my timing and that my Q-Jet secondaries are opening properly.

Here is some advice that I received a local shop here re: this issue:

"In order to get these GM cams to really pull you need to advance them to a 106 ICL. The 327/350 has an ICL of 110 degrees so I advance them 4 degrees. It makes all the difference in the world, either in a 327 or 350 they will pull like a freight train."

I was curious if 1) you guys agreed with this?... and 2) how do you go about advancing the cam?

thanks in advance
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Old 12-26-2011, 04:02:11 PM   #2
Damon
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You're not likely to feel much difference from 4* of cam advance. And if I recall correctly you aready have quite a bit more compression than a factory 350 HO so I'm not sure that raising the cylinder pressure any higher is a good course of action in this case (advancing the cam raises cranking compression).

Why don't you start with a basic cranking compression test as it is now. I bet you're cranking 180 PSI or higher with that little cam and 10+:1 compresion already. Plus the compression test might reveal something (like if it's low across the board maybe you got the cam installed one tooth retarded at the chain).

Wondering what secondary rods and hanger that QJet has in it as well. Where did you gat the carb and was it built for a street performance application?
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1990 454SS pickup. Original "tow truck motor" 454 upgraded to something a little more "aggressive." Seems pretty stout but the fuel bill is nuts.

78 Malibu. Inherited with only 35K on the odo! Mild 383 with Weiand 142 blower on top. Mid 12s appears to be the best it's gonna do on street rubber. Runs so good I may never drive it again.

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Old 12-26-2011, 04:20:31 PM   #3
robmaxfli
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I'll see what I can do for the compression specs:

Here are the specs on my Q-Jet:

# 17059205

Primary jets: 73
Primary rods: 41K
Secondary Rods: "AY"
Secondary Rod Height: 41/64"
Float Level: .420"
Idle mixture screws: 4 turns
Secondary windup: 3/4 turn
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Old 12-26-2011, 07:42:22 PM   #4
Damon
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AY secondary rods are awful lean at tip-in (they don't make a set any leaner, actually). I found most QJets like a nice, fat tip-in. See if you can get hold of a set of DR or CP secondary rods the drop them in (they are installed from outside the carb by removing the hanger screw and lifting the assembly out). That's likely to make a pretty nice difference in torque right there.

You can also try easing up on the air valve tension a bit- about half a turn from the zero tension point is usually more than sufficient.

None of this is likely the biggest reason for your lack of power, it's just a little tuning that almost always helps on street driven QJet.
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1990 454SS pickup. Original "tow truck motor" 454 upgraded to something a little more "aggressive." Seems pretty stout but the fuel bill is nuts.

78 Malibu. Inherited with only 35K on the odo! Mild 383 with Weiand 142 blower on top. Mid 12s appears to be the best it's gonna do on street rubber. Runs so good I may never drive it again.

"Last remaining QJet tuner on planet Earth!"
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Old 12-26-2011, 07:56:10 PM   #5
robmaxfli
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Ok - I'll report back later on...thanks Damon
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Old 12-27-2011, 10:29:39 PM   #6
robmaxfli
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Quote:
Originally Posted by Damon

Why don't you start with a basic cranking compression test as it is now. I bet you're cranking 180 PSI or higher with that little cam and 10+:1 compresion already. Plus the compression test might reveal something (like if it's low across the board maybe you got the cam installed one tooth retarded at the chain).


I just finished a compression check on these cylinder numbers. Here are the results:

1 - 120
3 - 130
5 - 130
7 - 135

I warmed up the car, pulled all the plugs, disconnected the ignition, and floored the throttle as I cranked away.
BTW- only 1K miles on this rebuilt motor.

What do you think of these numbers so far?
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Old 12-27-2011, 10:54:24 PM   #7
Damon
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FAIL!!!!

WAY WAY WAY too low for a 10:1 (or higher) motor with that small a cam in it. You should be up around 180, maybe 160 at the low end of the "sane" range. My gut says you got the cam installed 1 tooth retarded at the chain. But that's not the only thing it could be.

Take a deep breath and look through the disappoinment I have just dealt to you (served up ice cold, I know) and realize this is ultimately a GOOD thing you have discovered. You now know it's not the carb, ignition timing, or anything to do with the tune. It's a HARDWARE issue. You have ABSOLUTELY discovered the reason your engine is a gutless wonder. My 8.0:1 blower motor with a similar cam (214/224* on a 112* LSA) puffs up about 135 on the gague. You're 2 full compression points higher than me and not making any more cylinder pressure. You see why the red flag on those numbers, right?
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1990 454SS pickup. Original "tow truck motor" 454 upgraded to something a little more "aggressive." Seems pretty stout but the fuel bill is nuts.

78 Malibu. Inherited with only 35K on the odo! Mild 383 with Weiand 142 blower on top. Mid 12s appears to be the best it's gonna do on street rubber. Runs so good I may never drive it again.

"Last remaining QJet tuner on planet Earth!"

Last edited by Damon : 12-27-2011 at 10:58:50 PM.
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Old 12-27-2011, 11:04:02 PM   #8
cmonson
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What is the compression on the other bank? I fully agree with Damon though.

What is your compression ratio? Did you build the motor?
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Old 12-27-2011, 11:07:35 PM   #9
gregh
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My math says this engine is very low 9:1 compression(9.07:1) assuming a .039 4.100 bore head gasket & that those 4 relief pistons are actually -12cc's as some other websites claim.

But even with that, 120-135 seems awfully low, I'd be checking the timing chain as Damon suggested.
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Old 12-27-2011, 11:08:53 PM   #10
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maybe re lash your valves? they could all be too tight.
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Old 12-27-2011, 11:28:13 PM   #11
Todd80Z28
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For comparison with my 9:1 LM1 350 with 12cc dish pistons, 63cc Trick Flow heads, .039 4.19 gasket (Felpro 1010) and ZZ4-spec cam (207*, .478 on the intake)-

I got 180-185psi cranking compression on all cylinders. That was several years ago, haven't checked lately, but the power feels about the same as then.
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Old 12-27-2011, 11:47:04 PM   #12
robmaxfli
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Thanks for the replies and good (bad) news

I had my short block built by a "reputable" machine shop/builder. I installed the heads and set the lash. I called my builder to ask him what the compression ratio came out to be. I think that I just used the standard head gasket in the Fel-Pro kit so he thinks that I would be at a 9:7:1 compression ratio.

Do I need to pull the timing cover at this point? Not real sure how to remedy this from here.
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Old 12-27-2011, 11:51:17 PM   #13
gregh
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I'd re-do the compression test & then do it a third time squirting a little oil in each cylinder first. That should show if it's a ring issue. I'd guess you should be 170-185psi with this engine, 120 is screaming problems.

Even get a 2nd gauge to make sure before tearing things apart.
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Old 12-28-2011, 03:28:47 AM   #14
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Agree with others. 120-135 psi is WAY off. You should be at atleast 170 psi
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Old 12-28-2011, 12:57:03 PM   #15
robmaxfli
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I will do another compression test tonight. Couple of ?s:

1) Is it mandatory that I warm up the engine before doing the comp. test?
PIA to install, remove plugs - lots of burns

2) Even though I put the pedal to the metal while cranking do I still need have the choke plate and secondary air flaps propped open?
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