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  #16 (permalink)  
Old 11-12-2017, 03:22 PM
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The 1971 245hp 350 is 8.5:1 compression with dished pistons and 76cc heads. My mother had a 1971 Chevelle I talked her into buying new in 1972 that had one of these motors. Beautiful car. Copper brown with white stripes and white buckets/console but not an SS. I was 16 years old and it was a great car to borrow to tool around in.

If your bottom end is solid and you want to make some decent power without killing driveability, the best thing you can do for it is to get the compression up some with some modern 65 cc aluminum heads like Pro-filer 185cc, get rid of the single plane intake and go to something like Edelbrock Performer RPM (not air gap), and get some decent small tube headers. Find out what cam is in it as you need one that will not kill your dynamic compression.

Typical novice builds have large chamber heads, dished pistons, and too big of cams for the compression ratio - and this sound like what you have. Does it idle smooth or does it lope?



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Old 11-12-2017, 03:47 PM
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Quote:
Originally Posted by 2001Blazer4x4 View Post
The 1971 245hp 350 is 8.5:1 compression with dished pistons and 76cc heads. My mother had a 1971 Chevelle I talked her into buying new in 1972 that had one of these motors. Beautiful car. Copper brown with white stripes and white buckets/console but not an SS. I was 16 years old and it was a great car to borrow to tool around in.

If your bottom end is solid and you want to make some decent power without killing driveability, the best thing you can do for it is to get the compression up some with some modern 65 cc aluminum heads like Pro-filer 185cc, get rid of the single plane intake and go to something like Edelbrock Performer RPM (not air gap), and get some decent small tube headers. Find out what cam is in it as you need one that will not kill your dynamic compression.

Typical novice builds have large chamber heads, dished pistons, and too big of cams for the compression ratio - and this sound like what you have. Does it idle smooth or does it lope?



.
I'm new to this, but lopey idle is where the RPM bounces a but during idle correct? It idles smooth at a constant RPM as far as I can tell. What am I looking for exactly?
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Old 11-12-2017, 10:16 PM
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Guess I was a year off then. So with the aftermarket Edelbrock 4 BBL it would more than likely be making 300hp or whereabouts? I'll post when I have the head casting codes as well to figure out compression ratios a bit better. Also looking to test compression anyways. Thanks!
Engine assembly can be as much as a year ahead of meeting its chassis back then. The mantra of "just in time production" was not possible with the tooling and manufacturing management systems of those times.

Yes with the top end that you have this is easily on an engine dyno a 300 horse engine. The intake on it is really costing mid rpm torque, a good dual plane such as the Edelbrock Performer RPM would really fatten up the off idle through the mid RPMs with very little if any sacrifice of top end.

Long tube headers of at least 1-5/8ths primary tubes with 2.5 to 3 inch collectors into 2.5 inch duals for the street or 3 inch duals if you're dreaming way over 400 hp. That level of power with modern heads starting with the L31 Vortec and including a bewildering number of aftermarket heads is easily possible with a very streetable cam.

Bogie
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Old 11-13-2017, 11:53 AM
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3986339 stock heads. 1.72 intake/ 1.5 exhaust
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Old 11-13-2017, 12:03 PM
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Also looks as if the rocker arms and springs are extremely clean, possibly redone at some point, or just fantastic condition for a '71
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Old 11-13-2017, 01:30 PM
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Id definitely decide what youre doing about the heads before you buy an intake-unless you get a good deal and can resell it later. Some heads like the l31s use a different bolt pattern


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Old 11-13-2017, 03:06 PM
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Originally Posted by Jojo'sdaddy View Post
I?d definitely decide what you?re doing about the heads before you buy an intake-unless you get a good deal and can resell it later. Some heads like the l31s use a different bolt pattern


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I think I'll stick with stock heads for now, get a dual plane Edelbrock intake more fitting to my RPM range, and then add headers and a dual exhaust and maybe do more down the line.
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Old 11-13-2017, 03:07 PM
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Quote:
Originally Posted by Baldr333 View Post
3986339 stock heads. 1.72 intake/ 1.5 exhaust
Junk, as far as any performance goals are concerned. Very small valves, poor combustion chambers.

Best plan on a head swap.
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Old 11-13-2017, 03:12 PM
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Quote:
Originally Posted by Baldr333 View Post
3986339 stock heads. 1.72 intake/ 1.5 exhaust
Junk, as far as any performance goals are concerned. Very small valves, poor combustion chambers..

Best plan on a head swap.
Any suggestion on better heads I could get off of another engine, or maybe aftermarket on the cheaper side that aren't junk?
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Old 11-13-2017, 03:24 PM
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Originally Posted by Baldr333 View Post
3986339 stock heads. 1.72 intake/ 1.5 exhaust
In stock form those are 74/76 cc open chamber heads for 307 and 350 truck motors using a 1.7 inch intake and 1.5 inch exhaust.

These certainly aren't anything close to a performance head. Problem you're facing is if not original to the engine which the assembly code would say not, then what if anything has been done to build them into a performance head.

Things you'd be looking for:

- Ported runners

- Valve sizes increased from 1.7 to 1.94 or 2.02 on the intake with 1.50 pushed to 1.56 or 1.6 on the exhaust side.

- Then comes milling to reduce chamber size to increase compression.

- With that maybe decking the block to reduce compression distance which increases compression as well as squish/quench.

- Piston selection, the use of a flat top except for 2 or 4 valve reliefs would also increase much needed compression. Stock pistons would have a circular dish which reduces compression ratio.

About the only way to ascertain these things is to pull a head. But if this has stock components or even a modified head these still leave a lot of power on the table compared to modern Vortecish designs. But you really need to know what this has for pistons and deck clearance before delving into changing heads.

Bogie
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Old 11-13-2017, 03:30 PM
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Is a decent imported aluminum head bought bare then fitted with parts from a good source, at about the $550 price point cheap enough??

198-200cc intake port volume, 64cc chamber that will raise your stock low compression about 1.2 points, 2.02"/1.6" valves. Heads will easily make 440 hp with the right parts under them with a cam change and headers on your existing engine I'd expect 375 HP easily in a nice driver.

If so, just ask and I'll PM you a link to the heads and the valvetrain parts kit..
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Old 11-13-2017, 03:56 PM
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Originally Posted by ericnova72 View Post
Is a decent imported aluminum head bought bare then fitted with parts from a good source, at about the $550 price point cheap enough??

198-200cc intake port volume, 64cc chamber that will raise your stock low compression about 1.2 points, 2.02"/1.6" valves. Heads will easily make 440 hp with the right parts under them with a cam change and headers on your existing engine I'd expect 375 HP easily in a nice driver.

If so, just ask and I'll PM you a link to the heads and the valvetrain parts kit..
Yeah, that sounds good to me. If you could send me that link it'd be much appreciated.
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  #28 (permalink)  
Old 11-13-2017, 05:32 PM
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I'm new to this, but lopey idle is where the RPM bounces a but during idle correct? It idles smooth at a constant RPM as far as I can tell. What am I looking for exactly?
Just put a vacuum gauge on it and tell us how much vacuum at idle, and what RPM. Most any cam that idles with more than 14" vacuum should be OK for a 9.x compression motor (read OK, not necessarily optimum). Modern small chamber aluminum heads with a small cam will do more for air flow and power than a big cam with old smogger iron heads would - and guess which one gets better mileage and has better manners!! Eric will steer your right.
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Old 11-14-2017, 01:18 AM
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About a year ago I built an engine for a customer that wanted a mild streetable build with more of a focus on the show truck he was building and less on the engine/drive line.

The original vehicle he was restoring was sold to him as having a good 350 in it, but when checked it was a 305 that was well worn out. Below I put a list of what we picked up to do the build.

I found a used 350, had the machine shop bore it over .030, and traded out the iron heads #624 for a set of #113 Aluminum Corvette heads I had sitting in the shop.

Intake / carb was a Edelbrock Performer intake and Edelbrock 650 electric choke carb. Ignition was basic HEI, fuel was stock mechanical pump.

Exhaust was done locally, which consisted of shorty headers, cat back 2.5 inch pipe and Flow Master Mufflers.

Along with the engine we rebuilt the 700R4 adding the Z-Pack Clutches and the Corvette Servo.

Parts for the engine are below, prices are approximate. The machine work was about $250, and the heads I already had. If we had to source the heads that probably might been another $600 to $800.


Small Block Chevy 305/350 Mild (Budget) Build

Sealed Power SLP-KC-1014R (1400-4000 RPM)
Adv Lift, 1.5 Rocker 0.420 int./0.443 exh.
Adv Total Dur. 278 int./288 exh. $112.00
Cloyes Dbl Roller Timing Set $32.00
Main Bearings $28.00 Rod Bearings $31.00
Gasket Set Includes Head Gaskets and valve seals $36.00
Sealed Power +30 Flat Top Hypereutectic Piston Set $108.00
HV (High Volume) M55HV Oil Pump $36.00
Steel Oil Pump Shaft $10.00
Taylor Cut to Fit Wires $60.00
Wire loom Set $40.00


$493.00
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