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Old 11-26-2012, 09:42 AM
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help plan my 350 build

I just got a 91 355 short block with roller provisions. I need to take it to the shop to have freeze and galley plugs put in along with cam bearings. Has new flat top pistons on it right now. I have a Cloyes double roller timing set too. Here's what i'm planning on so far:

-LT4 hot cam (Duration at .050 in. 218/228, Lift .492/.492)
-Vortec heads and lifters with porting if I can learn how to do it
-LS6 springs with Comp 787-16 retainers
-Edelbrock Vortec carbed manifold with a q-jet
-Summit HEI distributor
-Shorty headers

Would this get me to my 375-400hp goal? Any input is appreciated! Anyone have a link with how a 1 piece RMS oil pan gasket goes on with all those O rings? Also what do you guys prefer? Advanced or retarded cam? that timing set allows me to go either direction by 2 degrees.

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Old 11-26-2012, 11:50 AM
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Quote:
Originally Posted by gsoleski View Post
I just got a 91 355 short block with roller provisions. I need to take it to the shop to have freeze and galley plugs put in along with cam bearings. Has new flat top pistons on it right now. I have a Cloyes double roller timing set too. Here's what i'm planning on so far:

-LT4 hot cam (Duration at .050 in. 218/228, Lift .492/.492)
-Vortec heads and lifters with porting if I can learn how to do it
-LS6 springs with Comp 787-16 retainers
-Edelbrock Vortec carbed manifold with a q-jet
-Summit HEI distributor
-Shorty headers

Would this get me to my 375-400hp goal? Any input is appreciated! Anyone have a link with how a 1 piece RMS oil pan gasket goes on with all those O rings? Also what do you guys prefer? Advanced or retarded cam? that timing set allows me to go either direction by 2 degrees.
1. The only thing I can agree with on your list is the Quadrajet.
2. You cannot intelligently choose a camshaft for a motor until you know the static compression ratio of the motor and have calculated the dynamic compression ratio from the intake valve closing point of the cam.
3. Shorty headers are girly.
Let's start over with you showing us a photo of the pistons, along with a complete explanation of the specs on them. Are they cast, hypereutictic or forged? Is the piston to wall clearance correct for the pistons? Do you have piston rings? What type rings? What material? Are the bores honed for the type of rings you want to use?
Looking for factual data here, so we can answer you intelligently.
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Old 11-26-2012, 12:00 PM
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help plan my 350 build

You should be right at 400hp with your parts. Just be sure to use the compression calculator. With iron heads you want no more than 9.6:1. My understanding is the rear main seal just taps in after the crank is in. The one piece oil pan gasket is easy just use a bead of balck rtv where the oil pan rails and the front and rear bearing caps meet. You should find someone to help you to degree your cam in or just install it straight up dot to dot on the crank gear and cam gear. Most cam manufacturers grind 4* advance in the cam.
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Old 11-26-2012, 12:06 PM
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Well the lt4 hot cam if its an orginal gm its for a 350 hp engine right? i would assume you are not going to make more than 350-375 with that cam. Probably closer to 350. A little bigger cam may produce some better results.

I thought the only reason to run the lt4 hot cam was because you had EFI. Without efi you can run some bigger cams without much trouble.

Hope this helps.
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Old 11-26-2012, 12:21 PM
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very mild cam. get your heads done first,see if you can get some flow numbers,determine the max RPM you will need,work out your CR with Tech,fine tune from there.
when you talk cam specs lift and duration is where you start, Tech can help you dial in when the valves should close. His info will be accurate if you give him specs to work with.
Note: he is more conservative than me so if you see us argue,ignore the noise and listen for what applys to your situation
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Old 11-26-2012, 12:42 PM
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gsoleski,
You said you have flat top pistons. Any idea of the volume of the valve releifs? How far down in the cylinder are they at Top Dead Center? How many cc's are the head combustion chambers?
I used some average values for the previous values and plugged them into a CR calculator.
5cc piston valve reliefs
0.025" in the hole
0.039" thick gasket w/4.166" dia.
58cc combustion chamber volume
standard 4.0" bore
Comes to just over 10.3:1 static CR
Too high for iron heads on pump gas even with a pretty big cam for street use IMO.
If any of the values are lower than what I guesstimated, CR is going to be even higher.
Heads with 64cc chambers gets it down to 9.6:1 if everything else stays the same.
Need to figure out what cruise rpm you plan on running for a decent recomendation for a cam, and let horsepower fall where it may. IMO
ssmonty
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Old 11-26-2012, 03:11 PM
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woah this is a little more calculating than I thought! I was given the block so I'm not entirely sure what kind of pistons they are, rings, ect. Right now I'm just trying to get a parts list together, I don't even have my heads yet. Have to go to the local U-Pull next week. As for needing the shorty headers, my car is pretty low and long tubes would cause clearance issues. Here's what I have to work with

Last edited by gsoleski; 11-26-2012 at 03:23 PM.
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Old 11-26-2012, 08:05 PM
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Quote:
Originally Posted by gsoleski View Post
As for needing the shorty headers, my car is pretty low and long tubes would cause clearance issues.
That's what cutting torches and Sawzalls are made for. No room?...Make room.

Those piston crowns have no flat area to generate squish. If you want to build a low compression motor, use 'em. If you want to build any kind of performance motor, chuck 'em over the fence.
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Old 11-26-2012, 10:25 PM
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That's what I was afraid of. Then what about these?
Summit Racing® Hypereutectic Pistons SUM-17350-30 - SummitRacing.com
This is not a very high dollar build, nothing forged for me.
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Old 11-27-2012, 12:15 AM
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Quote:
Originally Posted by techinspector1 View Post
1. The only thing I can agree with on your list is the Quadrajet.
2. You cannot intelligently choose a camshaft for a motor until you know the static compression ratio of the motor and have calculated the dynamic compression ratio from the intake valve closing point of the cam.
3. Shorty headers are girly.
Let's start over with you showing us a photo of the pistons, along with a complete explanation of the specs on them. Are they cast, hypereutictic or forged? Is the piston to wall clearance correct for the pistons? Do you have piston rings? What type rings? What material? Are the bores honed for the type of rings you want to use?
Looking for factual data here, so we can answer you intelligently.
techinspectors got it dead on. ill be interogating you whenever i get my short block 406 built, whenever that might happen
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Old 11-27-2012, 12:17 AM
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Quote:
Originally Posted by gsoleski View Post
That's what I was afraid of. Then what about these?
Summit Racing® Hypereutectic Pistons SUM-17350-30 - SummitRacing.com
This is not a very high dollar build, nothing forged for me.
those are the same as what you have...
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Old 11-27-2012, 12:26 AM
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http://www.summitracing.com/parts/ue...make/chevroletthis might be what your looking for. much more expensive, but has the area for your flame front or "quench" to be a lil more agressive with vortec heads
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Old 11-27-2012, 07:07 AM
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Quote:
Originally Posted by gsoleski View Post
That's what I was afraid of. Then what about these?
Summit Racing® Hypereutectic Pistons SUM-17350-30 - SummitRacing.com
This is not a very high dollar build, nothing forged for me.
The dished pistons you have in the engine now should put the CR at about 9.6:1, give or take depending on the exact measurements. That CR assumes the dish is 11cc w/a quench distance of 0.040" and a chamber volume of 64cc. The design of those pistons- round dish w/a chamfer around the OD- leaves a LOT to be desired, though.

That CR will be a good match for the Hot cam. And there is nothing wrong w/that cam, per se- it just depends on whether the power band it has is a match to the rest of the vehicle combo (gears, stall speed, vacuum requirements, etc.) and if it matches what you want. Remember- it is YOUR dime, your time and you're the one who has to live w/the results once the engine is built. A page that techinspector1 put together some time ago is Cam vs. CR compatibility. It will help you to see the relationship between CR and cam duration at 0.050" lift.

Whether or not you can reuse the pistons depends on the bore wear and overall condition of the pistons. Either way you'll need at least a light hone and fresh rings. If that doesn't exceed the piston to wall clearance, then fine. But chances are very good there will be too much wear to reuse them in a honed bore.

The Summit pistons you linked to are FT w/4 valve reliefs and they have the correct 1.56" compression height. Those things will help the quench effect (more on this below). The thing is, using them your CR will be around 10.2:1- too high IMO. If you want to try to run them w/an iron head w/64cc chambers, you will need at least a different cam. But even then you're going to be pushing the limits of pump gas- if not exceeding the limits.

If you want to play around w/the numbers, there are static and dynamic compression calculators you can use.

You have to be careful when entering the dome or dish volume into the online calculators- some will want you to use a negative number for a dish or valve reliefs, others will want a positive number. The static compression calculator I linked to below is clearly marked to use a "-" for dished pistons. Other calculators may or may not be so clear on this, so pay attention.

Other numbers that you'll need to figure CR:

Most head gaskets for a 4" bore SBC will have a gasket bore diameter of 4.09 to 4.1"

You will also need to know how far "in the hole" the piston is. A stock Chevy 350 block will be close to 0.025" in the hole. But when a block is prepped for a rebuilt engine, often metal is removed from the deck to clean and square up the surfaces. This decreases the piston deck clearance.

The cylinder head will also need to be measured to see exactly what the volume is. For the same reasons as the block is milled, the heads are often milled and also milled to gain compression in some cases. So you need to know the actual volume to be accurate. But for now, use 64cc for the Vortecs.

To see what the dynamic compression ratio is you need to know the rod length (stock is 5.7") and the intake closing point of the camshaft. This lets you estimate whether a combination of parts will be able to use pump gas w/o detonation, for example.

A couple calculators for dynamic compression ratio:
Kelly Dynamic CR
KB Dynamic CR

One last thing- do yourself a favor and read up on quench. It's an important part of the engine build and can make the difference in having an octane hungry pinging engine or an engine w/o detonation.

Good luck.

Last edited by cobalt327; 11-27-2012 at 07:22 AM. Reason: Add link.
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Old 11-27-2012, 09:46 AM
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Great info thank you. So to keep the compression ratio down wouldn't I need to have a dished piston? Not saying i'll use those but get a piston with around -11cc like you said. I'll read up on quench and compreesion
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Old 11-27-2012, 01:56 PM
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Quote:
Originally Posted by gsoleski View Post
Great info thank you. So to keep the compression ratio down wouldn't I need to have a dished piston? Not saying i'll use those but get a piston with around -11cc like you said. I'll read up on quench and compreesion
In the case of a 64cc head and the HOT cam, a dished piston would be needed. The best dished piston will have a D-shaped dish instead of the round dish.
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