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Old 03-25-2008, 05:02 PM
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more cam on stock SBC 305

I have a bit of an odd project I'm thinking of. I have a bone-stock '80 Malibu with the 229 V6 (this was the 3/4 of the 305). It was rebuilt stock about 10 years ago, and runs fine... but between the low power, 3 speed, and 2.41 gear, was never considered powerful. Economy is marginal, low 20s highway.

I was looking at the stock 305 cam specs (same as the V6), especially the HO L69 305. I see that Comp and others offer a very mild cam for these engines. They're advertised to improve low end torque and power, and increased economy. Sounds too good to be true--anyone have experience with a cam swap on a stock 305?

The OE cam specs are: 176*/194* @ 0.05" with 0.234/0.257" lobe lift.
Mild upgrade cam has: 192/200* @ 0.05" with 0.26" lobe lift.
Compared with the L69 305: 201/206* @ 0.05" with 0.26/0.27" lobe lift.

My goal is not to make this a street rod, and want to make low end torque. Just more than 115 hp and 170 ft.lbs. of torque, and something in the mid range for passing gear or highway merging. Do plan to clean up the heads, lots of room to improve the intake runners. Comp's CamQuest program predicts 140hp and 200 ft.lbs. with just the cam change--that would be nice, but seems optimistic.

Any thoughts or opinions?
-Michael

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Old 03-25-2008, 05:40 PM
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The chevy v6's respond to the same thing as a V8 does.
If you are going to cam up your V6, you need to up the compression ratio and Improve the intake manifold, cylinder heads and exhaust system for more airflow.
The engines torque curve will move up in the rpm range. the car will want a higher rear gear ratio and a higher converter stall speed.
Its very easy to over cam a small CIDi motor.
It all has to work together. A camshaft is just one part of a system.


I'd start by accuratly measureing the engines actual compression ratio.
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Old 03-25-2008, 06:31 PM
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Right, that's exactly what I was afraid of happening. I don't want something that makes power at 4000 rpm when it never sees more than 3000. That's why I was wondering if anyone tried a similar cam on a stock 305--did it work well, or just kill the bottom end.

Was also talking with a guy who said the stock cam has very short duration with retarded timing, in order to meet emissions (even at the sacrafice of power and economy). He was saying the Comp cam with the 194/200 duration was what it "should have been" from the factory.

I don't know... the one cam is advertised as being "great for high gear ratios, low end torque and good economy." I would really like to see power/torque curves for this, but of course nobody has done that on an old 6 cyl... Would be fine if it moved the peak torque and hp up a bit, as long as it did not decrease the idle-2000 figures.
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Old 03-25-2008, 07:33 PM
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Quote:
Originally Posted by mhamilton
as long as it did not decrease the idle-2000 figures.
You can bet it will. I would look at a short, tork y 185-190 cam with more compression and a home port job on the stock heads.
Possible 1.6:1 rocker swap. Small tube exhaust headers.

You have to keep the cam small or the torque curve shifts up too much. especally critical on a small ci motor with stock gears.
Improve the stock head flow, compression ratio and exhaust system to get power. What is the stock valve size on those heads?

Last edited by F-BIRD'88; 03-25-2008 at 07:41 PM.
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Old 03-25-2008, 08:17 PM
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Valve size is the same as 305, 1.84 and 1.5 inches.

Definitely room to improve the heads. Has the extra 1/8" of casting (around the pushrod holes) blocking the intake ports, otherwise the port matching would be very good. The stock intake is a cast aluminum, single plane. So a little better than the iron 305 parts.

I appreciate the suggestions, but those other mods would be going further than I want with this engine. For real performance I would not be bothering with this 229, would go with a V8 or a 4.3L V6. I would like to keep the car mostly stock, and see if I can get more low end torque and power.

Compression would be a problem on this engine. Currently it's borderline for tolerating regular fuel (8.6:1 stock, but a bit more after being bored and decked slightly). I'm sure you know these 229 and 305s were notorious for pinging, and I just fixed a big problem with it detonating on the highway.

I know the stock exhaust is hugely restrictive. But, noise is an issue with me. I need to cruise comfortably down the interstate with the a/c on and not hear any exhaust or engine noise... so no headers on this car.

Perhaps the best bet is, as you say, not to try and re-cam this engine, just clean up the heads and keep the stock cam. I know GM designed it for low end torque. I guess the cam advertising sounded too appealing. Hard to say when there's no data to really back those claims up. Then again, I suppose the worse I could do is try a new cam and have to change it back to stock if it didn't work.
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Old 03-25-2008, 08:27 PM
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Also, I've been collecting some cam specs in a little spreadsheet:
http://mikesradios.googlepages.com/camdata.xls

I was looking at the Crower cam because it had not such an agressive intake duration, but I coudln't figure out why they trimmed the exhaust duration more than stock? Unless it was because they moved the centerlines around.

Though not the same, the old Cad HT4100 had stock specs the same as the Comp Cam I was looking at. Although similar in displacement, that engine was undersquare, so I know it's apples and oranges.
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Old 03-25-2008, 08:46 PM
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if that is what you use your car for ( efficient quiet hyway cruising ) then you are barking up the wrong tree and wasting your time.

A complete 4.3L vortec V6 motor and transmission from a 96-2000 GM truck is what you want.

A back yard home brews remote turbo system would be a lot of fun too.
www.ststurbo.com

You'd be grinning from ear to ear.
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Old 03-26-2008, 04:31 AM
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Correct me if im wrong. But I believe you can install a set of headers and still keep your car quiet.
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Old 03-26-2008, 04:47 AM
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Quote:
Originally Posted by mhamilton
Though not the same, the old Cad HT4100 had stock specs the same as the Comp Cam I was looking at. Although similar in displacement, that engine was undersquare, so I know it's apples and oranges.
That's more like "apples and hedge balls".

FWIW I put a very similar cam in a stock '81 305 and it really woke it up with no degradation in idle quality or mileage. A friend put a slightly hotter Summit 1102 cam in a boneyard '78 305 in a '63 Bel Air with a Q-Jet, duals, a 200-4R and 3.08's. It was no neck snapper with those gears but got around well in traffic and could pull 20-21 MPG on the highway. At idle it had just a faint "burble" to the exhaust, not lopey at all.

Leave the 229 alone and replace your 3 speed AT and 2.41's with a 200-4R and a set of 3.55 or 3.73 gears. You won't believe the difference in performance! Mileage should be better too, at the very least it won't be any worse unless you keep trying out the new gearing.
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Old 03-26-2008, 11:06 AM
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I do realize I have many things working against making good power, and that the 2.41 is killing acceleration. However, with this car, I want to keep everything as original as possible. Aside from that, with a drivetrain swap, I'd be better off starting with a later model Monte that was set up for computer control, 4.3L, 2004r, and a 3.x gear already.

That said, moving the power curve in the 229 up a touch wouldn't be a bad thing. As-is, I have the th200c trans, which has slightly lower gearing than the th350 (200 has 2.7 and 1.6 1st & 2nd IIRC). Even with that, 1st gear is pretty useless. The engine makes noise that sounds like power, it revs, but the car doesn't accelerate. The engine runs out of power long before gears. Once it drops into 2nd, then you can feel the torque and it accelerates better. Chevy did offer the 2004r on '81+ models with the 229, but I'm not sure how it really performed (doubt many were optioned with it anyway).

The stock engine feels like power drops to 0 after 2500 rpm. Forget about passing gear, over 45mph it accels slower in 2nd than it does in 3rd. More mid range power would be pretty useful.

I don't know... maybe I should leave it all stock. But then, I know 3.8L is capable of more power without sacrificing any daily-driver qualities.
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Old 03-26-2008, 11:25 AM
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Ok, i'll bite, what are "hedge balls"????
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Old 03-26-2008, 05:06 PM
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The L69 305 Camshaft was a 1981 350 Corvette camshaft.

Shane
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Old 03-26-2008, 06:21 PM
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Right--I have the specs on that in my Excel file. The cam I was looking at was not as agressive as the L69 (it's more in line with the B-body LT1 cam). I know the HO305 had the cam, Crossfire heads, and higher compression. Did it have a true dual exhaust? Still had stock manifolds. My thinking is, if it will work on the 305, it should work on the 305 with 2 cylinders gone... just 25% less power.
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Old 03-26-2008, 08:28 PM
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Ok, i'll bite, what are "hedge balls"????

The fruit, if you can call it that, of the hedge tree. AKA "hedge apples". They are bright green and vary in size from the size of a hardball to a small cantelope with a surface texture similar to a brain. They come on in the Fall and are not edible but they are supposed to help keep away insects if you place them in your basement or crawl space. Great for throwing too. Probably not a real common sight in your neck of the desert.
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