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Old 12-02-2004, 07:22 PM
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305 SBC buildup - opinions wanted

Hey everyone. Sorry I haven't been around in a while. My truck is in the process of getting the motor rebuilt, and I thought if I threw out my combo of parts that someone might be able to tell me how it looks.
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1979 Chevy 1/2 ton 2wd truck.
engine: 305 SBC bored .030 over
cam: Comp Cams Magnum 280H - 230 duration - .480 lift
pistons: flat top 9.5:1
intake: Weiand 8004 dual plane
carb: Edelbrock 600 cfm
headers: Hedman full length, 1 5/8 tubes
exhaust: 2.25" pipe, 2.25" X-pipe, dual original 40 series mufflers
transmission: TH400 automatic w/ shift kit
rearend: 3.73 (12 bolt)
tires: 275/60-15
ignition: MSD 6A box, HEI advance curve kit
--------------------------------------------------------------------------------
We haven't picked out a torque converter for it yet, my guess was to find something that fully locks up around 2000 rpm (roughly)...? The motor is going to be basically stock as far as everything else goes. I'm having my mechanic do the work for me, so forgive me for not knowing more "in depth" specs on everything. Before I had everything above, minus the new cam, pistons, and MSD ignition.
Not only is this going to be a "new" motor to me, but am I going to notice a drastic change in the sound and performance overall? This isn't going to be something I'll be competing with at the track, just a daily driver around town on the weekends. Thank you for your time, and any advice you might have.

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Old 12-02-2004, 07:49 PM
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that cam is a little big for a 305. maybe you should consider a Comp XE 268 or a Comp Magnum 270. maybe go even smaller with a XE262 or XE256 if your after low end torque.
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Old 12-02-2004, 07:55 PM
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what heads? Would be a great 350 build... you could be dealing with high 300 to low 400 horse if you have decent heads....

K
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Old 12-02-2004, 08:19 PM
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Heads are basically stock (rebuilt), I think the valve springs were replaced with a set of double-spring valve springs, and bronze valve guides. No porting or polishing has been done. I've got a buddy who has a set of 305, 75cc heads, that have been ported and polished for about $75. I didn't think much else about them at the time, because I thought they would be more than I needed...for no more than I was doing to the whole motor. Should I consider them later on?
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Old 12-03-2004, 08:07 AM
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3-5 build up

I agree with Mike on the cam being too big. I would recommend the XE 256 (best bet) or the XE 262. You could run either with your stock converter.

If those heads have been done right, I would jump on them now and not mess with a tear down later to put them on. Good ported heads are one of the best things you can do for your engine, regardless of what else has been done.

The only other thing I see would be to run 2 inch instead of 2 1/4 inch exhaust, unless you already have the exhaust system.

The reason I support the 2 inch vs 2 1/4 inch exhaust is from experience with a 302 Ford (same volumetrics as your 305, basically). I had 2 1/4 inch exhaust on a mild 302 in a Ranchero, and the 2 1/4 inch exhaust actually hurt my bottom end. What I did to cure the problem was to get a set of collector cones that necked down my collector from 3 inch to 2 inch and inserted them in between the header and origional collector cone. Worked great.

Having the smaller diameter exhaust will improve your lower end torque curve, more than large pipes will help you on top end. And being that you are dragging around a 4000 + lb truck, you definately need the bottom end torque.

On the ported out heads, If the intake ports have been polished, do they have a florentine finish or are they mirror smooth? You need the florentine finish to keep your fuel air mixture suspended. Polished intake ports have been found to allow the fuel to become unsuspended and return back to liquid state, negating the advantages of having them ported.

However, on the exhaust side, theres no such thing as polished too smooth.
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Old 12-03-2004, 08:30 AM
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I agree ...to much cam for that combo... Id stay in the 215-220@ .050
The 305 I had in my 76 1/2 ton short step had the Edelbrock Performer cam...it ran 14.20s.

The 305 I had in my 86 GMC Caballero, I had the comp cams XE256..it ran 13.70s with 3.08s. very easy to over cam, & over carb a 305.stay conservative, youll be much happier
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Old 12-03-2004, 08:45 AM
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305 buildup

I totally agree with Stepside. In fact, were it me, I would opt for a smaller carburetor, around 500 CFM.

Formula:

CID X RPM divided by 3456 = CFM needed.

Example:

305 X 6000 = 183000 divided by 3456 = 529 CFM.

From experience. In the early 70's I had a 302 Mustang, with a mild Erson cam, Weiand hi rise with a 650 cfm carb. I was doing good to run 15.50 in the 1/4.
I went to a 500 cfm Holley and picked up nearly a second, getting down to 14.60 in the 1/4. The larger carb was killing my bottom end.
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Old 12-03-2004, 09:04 AM
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yep...the 600 would work...but smaller likely to work better over all...I ran 570 Holleys on both of mine.
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Old 12-03-2004, 09:13 AM
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305 buildup

The only reason I brought up the carb thing, the 600 Edelbrock has mechanical secondaries. If it had vacuum secondaries, then to my notion, the carburetor thing would be somewhat moot, as vacuum secondaries only open up to what the engine needs, rather than throwing the barn door open on mechanicals, and its down in the basement to about 3000 rpm, where that will hurt you most.

The 600 is not seriously over carbureting like dropping a 750 on it would be.
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Old 12-03-2004, 09:18 AM
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actually the Edelbrock/ AFB carbs are air valve secondary carbs, the butterflies do open mechanically, however , the gate inside does not.
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Old 12-03-2004, 09:29 AM
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305 buildup

Stepside, thank you for that bit of info. I was under the impression they were a totally mechanical secondary setup. Having the vacuum air valve setup kills my questioning the carburetor.

I thought it operated just like the Holley mechanical secondaries.

Last edited by Max Keith; 12-03-2004 at 09:29 AM.
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Old 12-06-2004, 06:04 AM
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Thanks for all of the information guys. I'll be sure to let you know how things turn out, and as I get them... I'll keep adding photos to my gallery.
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Old 12-06-2004, 06:35 AM
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I agree with the cam thing.....BUT

You DO NOT want those 76cc heads on a 305. With typical flat top pistons that will put your CR around 8:1 or a little less. That is TOO LOW. You want a set of 58cc combustion chamber heads so that you can get compression ratio up to about 9.5:1. You will have a complete dog of an engine with that low CR. The only chance with those heads is dome pistons to make up the difference. You would be better off with a set of HO 305 heads. They are floating around on ebay.

We did a 305 build for my Dad's surburban years ago and started it off with a 262 comp cam, flat tops, a set of 76cc heads, edlebrock intake, 600 edelbrock carb. It was a complete dog. We changed to a set of the HO 58cc 305 heads and it was different engine. It just made the combo come together.

As for the the exhaust, I think the 2.25 is plenty good. I personally would never run 2 inch, but that is just me. You are thinking about getting a set of ported heads, which adds power in the top end of the power range. To put a set of small pipes to try to increase bottom end power is just shooting yourself in the foot.

You have to understand that it is all about the total package. You want to build a vehicle so that the whole package comes together. This means engine, weight, trans, gearing....everything. For what you are doing a mild cam, small port heads and small carb will make you the happiest. Most people get all caught up in having the biggest baddest cam, carb and whatever else. All they end up with is a vehicle that has no power and is a dog to drive. This is especially true for small cubic inch engines. Unless you are planning on racing with tall gears and high RPM, then smaller is better.

I just finished a 350 build with the smaller is better frame of mind. Even with 2.73 gears in a 4000lb truck it will roast the tires. And it is a junk engine by most peoples standards.

Chris

Last edited by TurboS10; 12-06-2004 at 06:42 AM.
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Old 04-09-2005, 08:13 PM
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Hello everyone, just a quick msg to let you know the motor turned out great. Since spring is here, I decided to make an audio clip for anyone who wants to listen to it. It can be found HERE
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Old 04-09-2005, 08:26 PM
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Sounds really healthy! Revs pretty smooth it seems. Everything worked out for you? Got any numbers for us? Great work hope to see ya around here.

Chris
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