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Old 03-21-2011, 12:13 AM
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350 budget build - need help

Hi all,
I just finished building a 350 on a lean budget for my 72 Chevy 4x4. The engine is in and runs really nice and smooth, but seems to be lacking some power. I have a 350 shortblock with 30,000 miles on it, the bottom end is tight and clean, heads looked good. I did not do a valve job, but the valves did have a little pitting on them. My compression on the cylinders averages 130psi ( 125 lowest, 140 highest ). The motor has:

Flat top pistons
new RV cam and lifters
new double roller timing chain set
Edelbrock dual plane intake
Edelbrock 650 carb- rebuilt
MSD ignition, distributor, coil from previous motor.

I am running about 18 deg BTDC, checked the plugs after a couple hundred miles and they are a very light tan and clean. I'm pretty sure my compression is too low, but it still seems too sluggish going uphill or pulling a load. I'm also thinking about rejetting the carb, maybe its too lean? Any other ideas?
Thanks!
Colby.

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Old 03-21-2011, 12:49 AM
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Put some vortec heads on the engine it will wake it up.
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Old 03-21-2011, 05:39 AM
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Quote:
Originally Posted by Farmstore34
Hi all,
I just finished building a 350 on a lean budget for my 72 Chevy 4x4. The engine is in and runs really nice and smooth, but seems to be lacking some power. I have a 350 shortblock with 30,000 miles on it, the bottom end is tight and clean, heads looked good. I did not do a valve job, but the valves did have a little pitting on them. My compression on the cylinders averages 130psi ( 125 lowest, 140 highest ). The motor has:

Flat top pistons
new RV cam and lifters
new double roller timing chain set
Edelbrock dual plane intake
Edelbrock 650 carb- rebuilt
MSD ignition, distributor, coil from previous motor.

I am running about 18 deg BTDC, checked the plugs after a couple hundred miles and they are a very light tan and clean. I'm pretty sure my compression is too low, but it still seems too sluggish going uphill or pulling a load. I'm also thinking about rejetting the carb, maybe its too lean? Any other ideas?
Thanks!
Colby.
There are some issues w/the >10% variation between cylinders, you'd like it to be less... but it's not terrible. Maybe a little low, but there are variations between gauges and techniques to be considered, too.

You mentioned 18 initial ignition timing, what does the rest of the timing curve look like- i.e. how much total timing and when is it all in by? Are you using a vacuum advance?

Also, what is the cylinder head casting number, and the block casting number and/or the suffix from the passenger front of the engine where the head meets the block?

Do you know the cam specs or have a p/n for it? Because like GMC said, a set of Vortec heads could wake this combo up nicely- as long as the CR isn't too high w/them for the RV cam, and you'd be willing to spring for another intake to fit them. If the cam lift isn't more than about 0.450", you could get by w/just a set of springs to make them work just fine.
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Old 03-21-2011, 12:26 PM
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Thanks for the replies!
The cam specs are lift: 0.420 int./0.442 exh, duration @ 050 inch: 204 int./214 exh. I'll have to check on the casting numbers, but I know the heads are the pretty typical ones from the late '70s.
When I can afford it, I want to rebuild the original 327 that came out of the truck. It was an absolute BEAST! It was balanced to 10,000rpms, with a real lopey cam. Not much low end but it would rev like crazy. Better suited for a car than a work truck though!
Colby.
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Old 03-21-2011, 12:47 PM
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engine

hey how doing.Does your truck have headders and good mufflers im leaning towards back preasure.
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Old 03-21-2011, 09:25 PM
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I am running the original ramhorn manifolds, with dual 2 1/4" flowmaster 44s. I was wanting to upgrade to headers and maybe bigger exhaust. Would that make a noticeable difference?
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Old 03-22-2011, 02:20 AM
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Quote:
Originally Posted by Farmstore34
I am running the original ramhorn manifolds, with dual 2 1/4" flowmaster 44s. I was wanting to upgrade to headers and maybe bigger exhaust. Would that make a noticeable difference?
definitly on the headers, that was the first mod I made to my little 305 it made a world of difference
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Old 03-22-2011, 06:36 AM
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with flat tops and heads from the 70s you should be near 10.1.

i would check the timing chain and make sure its "straight up" a cam that is not installed correctly will bleed compression off.

also try a leak down test to see if your valves are sealing well.
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Old 03-22-2011, 06:57 AM
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It will take the early closed chamber heads (pre smog era) to get around 10:1 CR w/FT pistons, unless the heads were originally on a smaller displacement engine than the 350, having smaller chambers.

Open chamber 76cc heads typically found on the late '60's/early '70's-up 350 SBC engines will net about 1 to 1.2 points less CR than the early 64cc heads.
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Old 03-22-2011, 08:55 AM
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a 1972 4x4 is a load for any engine.

gears and tires will have a huge effect. what are you using?

Yes, headers will help a lot in the mid range torque. Get some long tube, 1-5/8 tube with 3/8" flanges.

your heads are most likely 76cc smoggers. And the pistons are most likely 4 valve relief with a sort of shallow dish, but they look like flat tops. So, assume a 8 to 12cc piston volume. With these pistons, you will get about 9.3:1cr with 64cc heads and 8.3:1 with 76's. CR also depends a lot on deck height and gasket thickness.

need to know the ignition timing at idle and at 4000 rpms (without the vacuum advance connected).

vortec heads will also help a lot. But they require another intake, center bolt valve covers, self aligning rockers, and machine work to handle more lift.

building a 327 for your truck is going in the wrong direction. Look for a 400 block. you need torque, and lots of it.
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Old 03-22-2011, 09:51 AM
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Wow, thanks again! You all are great!

Gears are 411:1, tires are about 32" tall (265/75/16). I know my big mistake was not doing the valve job. The motor came out of a 78 suburban and always ran great even bone stock. The 72 that it's in now is my DD and work truck, and I use it.
I need to get a timing tape for the balancer, I'm running 18 BTDC at 700 RPM.

I have to say, that 327 was an incredible little motor in that truck. I hauled 2000+ lbs in the truck over the mountains here with no problem, as well as pulling a stock trailer like it wasn't even there. Eventually I want to build another motor for it, with the horsepower of that 327 but alot more lowend torque.
Thanks!
Colby.
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Old 03-22-2011, 10:32 AM
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With just a little effort, a 350 can be built to have both more torque and hp than the old 327, and even more so with a 400, as has been suggested .
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Old 03-22-2011, 11:46 AM
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As has been suggested already,,,you need to find out what your total timing is. 18 deg BTDC is the base timing. Two other aspects of timing are the mechanical advance and the vacuum advance. Adding all of them up will give the total advance.

If you have not already done so get a calibrated timing tape on there after you have found TDC:

http://www.crankshaftcoalition.com/w...op_dead_center

http://www.crankshaftcoalition.com/w..._a_timing_tape

These are a must do for any new setup IMO, then you can setup your timing limits and curve with some confidence. You can usually find some more performance and mileage out of a good tune, also then the carb:

If you have a 650 eddy What is the number stamped on the bottom of left side the carb base when viewing from the front of the carb? 18xx?, have you checked your fuel pressure? do you know what the rod and jet sizes are?
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