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  #16 (permalink)  
Old 07-12-2005, 06:17 PM
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Do you know what the heads are off? Approximate year? Any guess on the chamber size? The early (60's) performance heads typically had chambers around 64cc. Later smog heads had chambers around 76cc. If you're running dished pistons they'd better be 64cc heads if you want a decent compression ratio for performance. With dished pistons and 76cc heads the compression can get pretty low (like 8:1) depending on the dish volume.

Does your machinist know that you're looking for performance? If I were you, I wouldn't spend anything on the heads until you know if they'll suit your application. Maybe ask him to measure the chamber before he cuts all the seats. The reason I say this is because you may be disappointed if you put it all together but it's got restrictive smog heads that won't flow enough to make decent power.
dh

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  #17 (permalink)  
Old 07-12-2005, 08:33 PM
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No, the heads we are still using from the previous build, they are not new.

I think they were the stock heads from the original engine build. If they were, the engine is from a 1973 Chevelle Malibu 4 door Sedan with the factor 350. Which is the actual car that we have right now that this engine is for. Which is where the heads probably came from, '73.


But I am not certain, they may be aftermarket, but my dad said they were GM heads....
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  #18 (permalink)  
Old 07-13-2005, 06:03 AM
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I'm guessing you've got 882 heads if they're off of a low performance 73 350, get the casting numbers off of them and reply back. Sounds like you're going to end up with about 8.3 or 8.5-1 static compression depending one what gasket will be used. Not enough compression to use any real performance cam. Why didn't the rebuilder/machinist use true flat top pistons?-they cost the same. Bob
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  #19 (permalink)  
Old 07-18-2005, 11:58 PM
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He didn't know really. He thought we were going with the same parts again for this second rebuild.


Could you please give me a very rough HP/TQ estimation Please!!

Thanks a lot.
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Old 07-19-2005, 05:00 AM
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If you're running dished pistons and those 76cc 1973 heads it'll be a dog with a 270 cam. Generally 270ish cams like 10-1 compression, your motor is going to be about 8-1. The engine will run but will be a real mutt down low. You either need to pick a smaller cam with 250-260 duration or bump your compression ratio up with flattop pistons and a steel shim head gasket-even then the compression ratio will only be about 9-1. Also if you've got stock springs the .470 lift 270 magnum cam will be too much cam and you'll have high rpm valve float from not enough spring pressure. Basic $40 Z-28 springs would work.
Get your combination right or this thing will be a dog. Pick a smaller cam or get the compression ratio up. JMO
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  #21 (permalink)  
Old 07-19-2005, 12:09 PM
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Well, I'm going to be going today to find out if the heads are the low performance stock #882's or a better high perf. #993
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  #22 (permalink)  
Old 07-19-2005, 02:48 PM
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Well i just found out some wonderful news!!!

I've got the high performance GM #993 heads!!!! They're also ported

I've got COMP valve springs with 2.02/1.60 valves, 1.6 Roller Rockers, COMP roller Timing Chain.


How's that?!
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  #23 (permalink)  
Old 07-19-2005, 03:09 PM
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Hey guys, I just found an engine that's very close to what we have, see what you think:

Displacement: 355 cu. in.
Carburetor: 750 Holley vacuum secondary
Heads: GM #993 castings, ported, with 2.02/1.60 in. valves and a 3-angle valve job
Intake: Edelbrock Victor Jr. and a 2 in. open-plenum spacer
Camshaft: Cam Dynamics 290, with 290 of duration, 234 of duration @ 0.050 in. lift, and 0.494 in. of lift
Headers: 1 7/8 in.
Pistons: Speed-Pro forged flat tops
Rods: stock
Crank: cast
Comp. Ratio: 9.0:1 to 10.0:1

MAX HP: 421 @ 5300
MAX Torque: 438 @ 4700

Combo 53 uses rebuilt #993 GM heads with 2.02/1.60 in. valves. The camshaft is a healthy grind, with 234 of duration @ 0.050 in. of lift. This 355 cu. in. engine produces 421 HP and 438 ft-lbs of torque.


MY ENGINE

Displacement: 355 cu. in.
Carburetor: Quadrajet
Heads: GM #993 castings, ported with 2.02/1.60 in. valves w/ COMP springs
Intake: Edelbrock Performer
Camshaft: COMP MAGNUM 270H 270/270 duration 224 @ 0.050 in. lift. 0.47 Gross valve lift, 0.313 lobe lift
Headers: Triwise custom fit to '73 Malibu sedan, at the head measured a little less than 1 3/4, at the pipe it measured about 2 3/4.
Pistons: Sterling Dished
Rods: stock
Crank: cast and balanced
Ignition: GM HEI
HV oil pump

MAX HP: ???
MAX TORQUE: ???


Would it be safe to hope for 400HP 425lb-ft??

Last edited by Malibu73; 07-19-2005 at 03:33 PM.
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  #24 (permalink)  
Old 07-19-2005, 06:36 PM
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*bump*

It's on the downhill side
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  #25 (permalink)  
Old 07-19-2005, 09:35 PM
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Quote:
Originally Posted by Malibu73
Hey guys, I just found an engine that's very close to what we have, see what you think:

Displacement: 355 cu. in.
Carburetor: 750 Holley vacuum secondary
Heads: GM #993 castings, ported, with 2.02/1.60 in. valves and a 3-angle valve job
Intake: Edelbrock Victor Jr. and a 2 in. open-plenum spacer
Camshaft: Cam Dynamics 290, with 290 of duration, 234 of duration @ 0.050 in. lift, and 0.494 in. of lift
Headers: 1 7/8 in.
Pistons: Speed-Pro forged flat tops
Rods: stock
Crank: cast
Comp. Ratio: 9.0:1 to 10.0:1

MAX HP: 421 @ 5300
MAX Torque: 438 @ 4700

Combo 53 uses rebuilt #993 GM heads with 2.02/1.60 in. valves. The camshaft is a healthy grind, with 234 of duration @ 0.050 in. of lift. This 355 cu. in. engine produces 421 HP and 438 ft-lbs of torque.


MY ENGINE

Displacement: 355 cu. in.
Carburetor: Quadrajet
Heads: GM #993 castings, ported with 2.02/1.60 in. valves w/ COMP springs
Intake: Edelbrock Performer
Camshaft: COMP MAGNUM 270H 270/270 duration 224 @ 0.050 in. lift. 0.47 Gross valve lift, 0.313 lobe lift
Headers: Triwise custom fit to '73 Malibu sedan, at the head measured a little less than 1 3/4, at the pipe it measured about 2 3/4.
Pistons: Sterling Dished
Rods: stock
Crank: cast and balanced
Ignition: GM HEI
HV oil pump

MAX HP: ???
MAX TORQUE: ???


Would it be safe to hope for 400HP 425lb-ft??
The 993 casting head is not a performance design according to Mortech, The chamber size is 75cc's which will give you about 8-1 compression. Your cam needs quite a bit more static compression if you're looking for any performance off idle. The engine will run ok when you get it spun up but it'll be a dog down low. You'll be able to run 87 octane for sure. You might be happy with the performance but IMO you're leaving a lot of power on the table by not getting the compression where it should be for this cam.

Get your shop to trade them dished pistons with some flattops. Use steel shim head gaskets if the block hasn't been milled. Bob
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  #26 (permalink)  
Old 07-19-2005, 09:55 PM
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I don't think the block has been 'milled', it's been bored .030 over if that's 'milling' then it's been 'milled'.

Are you just assuming this is what the CR is going to be? Because we've had the same engine in there earlier when it was first built and it had the COMP 268H in there, which is 218 duration @ 0.050" instead of 224 duration @ 0.050" and the car ran fine and was powerful...

I'm listening to your advice but I don't think we can swap the pistons... I'll see though.

Any other opinions please?
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  #27 (permalink)  
Old 07-19-2005, 10:43 PM
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I agree with baddbob, those pistons are really going to hurt your performance. Also, I don't think 993 heads are anything special. They are open chamber smog heads. Porting may help, depending on how much they are ported. They are stock around 160 cc intake runners with chambers in the mid to high 70's. Even ported they will never flow as much as vortecs or anything aftermarket. Who is telling you that 993's are good for performance? Is it the same mechanic that bought dished pistons? Unless he just doesn't understand what kind of power you're hoping for, I would start to guess that he doesn't know much about high hp small blocks.
Do a search online for compression calculators. I guess you'll have to figure out the volume of the dish. Count a deck height of 0.025 (at least), with 75cc chambers I bet you'll be 8:1 or less.
Sorry to be the bearer of bad news, but my guess for hp is about 300-325. In my opinion you are a long way from 400 hp. Maybe you'll be happy with this engine, but if you really want 400 hp, you're going to have to change those heads and pistons.
dh
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  #28 (permalink)  
Old 07-20-2005, 12:21 AM
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Well changing the heads is out of the question. Changing the pistons is do-able, but changing the cam is probably the thing.

Could I change out to a smaller Cam and make more power?

What's really going on here is, the machinist knows what he's doing, he's been in the business for like 30years, but my dad wanted to make the engine for gas mileage (pointless for a V8 I know) but we've got the engine and I do a 36 mile round trip to school during the school year and he wanted it to be a MPG car rather than a powerhouse....

I on the other hand want power, I still want MPG but I realize that it's not going to be great with a 350 V8. When the engine was built before with the Comp 268H cam, same pistons/heads/rockers/lifters/crank/HEI/Turbo350 tranny/4 barrel Carb etc... It got between 15-18MPG and when he had the tuning dialed in it got 20MPG on the highway.

So I guess i'll have to have a talk to him about what's going on. What are my options?

1. Swap pistons for flattop
2. Get smaller cam

Is that about all I could do?
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  #29 (permalink)  
Old 07-20-2005, 12:41 AM
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Here's the specs of the cams which is the only thing we're changing

Old cam: Comp High Energy 268H: 268/268 218 @ 0.050" 0.454 gross valve lift, 1500-5500 rpm range

New cam: Comp Magnum 270H: 270/270 224 @ 0.050" 0.470 gross valve lift, 1800-5800 rpm range.

It's not even that big of a difference. This cam is just a little bigger than what we had in there. What we had before ran great, was fast, got good mileage. That was without a Qjet carb on it.

I think this build will be even better - I have to go back to the machine shop tomorrow so I'll talk with the guy again.
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  #30 (permalink)  
Old 07-20-2005, 03:44 PM
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Hey I just thought of something, couldn't I just put in a stall coverter to offset the low CR and off idle power?

somthing like a 2000-2400 stall?
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