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  #16 (permalink)  
Old 03-02-2012, 03:35 PM
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Quote:
Originally Posted by ccase2727
What would b an ideal compression ratio for a pump gas engine? Mileage I'm not too concerened about cause its gonna b a Sunday driver
I'd build it 9.00:1 for a Sunday driver and use a short cam with long ramps, like those ground by Melling and others.

Very strongly suggest reading the book that crussell85 linked for you. Once you begin to understand how everything works together, we can begin your online education. You don't know enough right now to understand what I might begin throwing at you, but if you get some basic knowledge under your belt, I and others will be glad to help you learn how to build a motor that will do what you want it to do. It's all about the combination.

CAUTION: DO NOT BUY ANY PARTS YET. YOU WILL NEED A RECIPE TO GO BY AND YOU HAVE NO IDEA YET WHAT THE RECIPE WILL CALL FOR.
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Old 03-02-2012, 04:31 PM
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Quote:
Originally Posted by ap72
Too low of compression is just as hard to deal with as too high. Its less damaging but makes for lower power and worse mileage.
72cc heads with flat tops and 4 valve reliefs isn't going to be low compression. Stock 350 heads usually are 76cc, and most of those are dished pistons.

Mm
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Old 03-05-2012, 04:48 AM
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Yep thanks guys! Gonna get a book and do a little reading! I've already bought the cam I hope it will work with my application! I guess I will find out! My friend has some deeper gauges so I'm gonna get the quench this week! So at tdc get a straight edge and when this piston will not go up any further that would b the quench? Is there a basic quench?
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Old 03-05-2012, 10:08 AM
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Quote:
Originally Posted by ccase2727
Yep thanks guys! Gonna get a book and do a little reading! I've already bought the cam I hope it will work with my application! I guess I will find out! My friend has some deeper gauges so I'm gonna get the quench this week! So at tdc get a straight edge and when this piston will not go up any further that would b the quench? Is there a basic quench?
The quench is the area between the top of the piston, when its all the way up top, to the flat part on the head next to the combustion chamber. The flat area on the head that is over the cylinder but not where the valves are.

I hope I explained that well enough. So, the distance between the top of the piston and the top of the block, say for example around ".040, now you need to add the thickness of the compressed head gasket, lets say around ".013. In this case you would have a quench of ".053.

For this engine you are building its not one of the things you really need to worry about. Worry more about having your heads, cam, manifolds, all working together at the same RPM's. Also make sure your valve springs are matched to whatever cam you are using.

Buy a Smallblock motor building book and read it! You will have lots of questions after that, and will be able to use our answers better.

Mm
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Old 03-05-2012, 10:15 AM
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You do need to worry about the quench in any engine you build!
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Old 03-05-2012, 11:45 AM
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Quote:
Originally Posted by crussell85
You do need to worry about the quench in any engine you build!



X2, although many seem not to care, and wonder why thier motor is harder to tune.

the 64cc heads will put you around 10.3:1 with a proper .040" quench, and the 72cc heads will put you at around 9.5:1 with a proper .040" quench. the 72cc heads would be what you are looking for. but read up some first, that will help you out the most in the long run.

and by the way since you decided to go with a hydraulic flat tappet cam i would strongly recomend the 1.5 rockers and not 1.6 rockers, you dont want to mess with the ramp rates too much on a flat tappet cam.
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Old 03-06-2012, 10:38 AM
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Let me help you out a little....

Block Deck Height- the measurement from the centerline of the main bearing bore to the flat block deck where the heads bolt on. Factory spec is ~9.025". With a 12" dial caliper, measure the diameter of the main bearing bore without bearings. Divide by 2 and write it down. Now, measure from the lip of the main bearing bore to the block deck. Write it down and add half the bearing bore. Change the block deck height by cutting material off the block decks where the heads bolt on or by changing the "stack" measurement.

Stack height- the sum of measurements of the piston compression height, the connecting rod center to center and the radius of the stroke of the crank.
Radius of a 350 crank (3.480" stroke) is 1.74", so if you had a 350 with 5.700" rods and a piston with 1.560" compression height, the stack would add up to 9.000". If the block deck height measured 9.025", then putting a stack of 9.000" into the block would result in a piston deck height of 0.025".

Piston Deck Height- the measurement from the piston crown to the flat block deck where the heads bolt on with the piston at TDC, NOT INCLUDING THE HEAD GASKET. Factory spec is ~0.025"-~0.045". Down and dirty is bring the piston to TDC. Stand a straightedge on edge about a half inch from the edge of the bore, at 3:00 or 9:00 as you are standing at the side of the motor. Checking at 12:00 or 6:00 will allow the piston to rock on its pin and give you an erroneous reading. Put feeler gauge blades together until you get a set that will slide under the edge of the straightedge with just a little effort. DO NOT ALLOW THE PISTON TO BE PUSHED DOWN IN THE BORE BY THE INSERTION OF THE GAUGE BLADES.

Squish- the measurement from the piston crown to the underside of the cylinder head, INCLUDING THE THICKNESS OF THE HEAD GASKET. Add the piston deck height and the gasket thickness together to find the squish. On a small block Chevy, 0.035" - 0.045" works well to limit detonation and also to allow engine operation on a lesser grade of fuel. As the mixture is "squished" out from between the bottom of the cylinder head and the piston crown, the mixture is "jetted" across the chamber just as the plug fires. This jetting action homogenizes the mixture and eliminates rich or lean pockets of mixture in the chamber so that all of it gets burned.

I think most of the fellows on this board would recommend validating the main bearing bore in the block first. If the bore measures parallel and round within specs, great. If not, either align-hone or align-bore the main bearing saddles to get round, parallel holes for the main bearings. The block can then be registered on the main bearing bore and the decks can be cut to the desired block deck height according to the stack of parts you will use. This will set the piston deck height and will also help to equalize the volume in all cylinders, which will tend to help equalize the static compression ratio in all cylinders. You need to know the compressed thickness of the head gasket before you begin cutting the block decks. Equalizing the block deck height on all four corners of the block will insure that the heads sit level on the block, front to rear. The heads sitting square and level on the block will unsure that the intake manifold will sit square and level on the heads.

Let's say that you have a stack of parts that measures 9.003" and you want to arrive at a 0.040" squish using a 0.028" compressed gasket. If you cut the block deck height to "9.015", the piston deck height would be 0.012" (block deck height of 9.015", less stack height of 9.003" = 0.012"). Now, if we add the piston deck height of 0.012" and the gasket thickness of 0.028", we find a squish of 0.040".

See, simple stuff. It just takes a little time to get your head wrapped around it.
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Old 03-08-2012, 10:17 AM
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Quote:
Originally Posted by crussell85
You do need to worry about the quench in any engine you build!
True, but for the most part this is built in to the pistons. The average street engine builder, especially those like the OP, don't really need to be too concerned about the quench.

Unless you are going to pull out that shortblock and plan on decking the block, I didn't think this was that kind of build?
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Old 03-08-2012, 10:32 AM
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Quote:
Originally Posted by Mmfh
True, but for the most part this is built in to the pistons. The average street engine builder, especially those like the OP, don't really need to be too concerned about the quench.

Unless you are going to pull out that shortblock and plan on decking the block, I didn't think this was that kind of build?
Please don't listen to this guy. If your not gonna build it right then why build it at all?
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  #25 (permalink)  
Old 03-08-2012, 01:21 PM
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Quote:
Originally Posted by techinspector1
I'd build it 9.00:1 for a Sunday driver and use a short cam with long ramps, like those ground by Melling and others.

Very strongly suggest reading the book that crussell85 linked for you. Once you begin to understand how everything works together, we can begin your online education. You don't know enough right now to understand what I might begin throwing at you, but if you get some basic knowledge under your belt, I and others will be glad to help you learn how to build a motor that will do what you want it to do. It's all about the combination.

CAUTION: DO NOT BUY ANY PARTS YET. YOU WILL NEED A RECIPE TO GO BY AND YOU HAVE NO IDEA YET WHAT THE RECIPE WILL CALL FOR.
Very good advice. For a Sunday driver going with an old cheap RV cam and 9-9.5:1 compression will be a VERY reliable and easy to tune combination. It won't win any races but it can still be a healthy combination and very nice for a Sunday driver.

A basic cheap recipie would be

factory heads with a good valve job
hypereutic pistons to get you your needed compression
a gasket picked to maximize your quench
a used RPM intake
a remanufactured edelbrock carb, a 1406 will be fine
a ebay HEI distributor with an ACDELCO module
1 5/8" long tube headers
basic rering kit with gaskets, moly rings, and good bearings (i like King for aluminum bearings, or clevite for tri-metals)
high volume standard pressure oil pump for low rpm cruising

reuse stock accessories, rocker arms, tin, and bolts

With decent heads and cam you can get an honest 350hp engine.
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Old 03-08-2012, 01:23 PM
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I'm glad you're building your first engine. It's always satisfying to fire up a new motor which runs just like you designed. You will want to use different parts for a heavy daily driver than you will for a hot street engine in a Nova.

Read up on engine building. Everyone here agrees with that. Don't just read the book. Search manufacturer sites for tech articles. Melling, Keith Black/Silvolite and many others have great information and calculators for this or that. Eventually you'll get an idea of how to choose parts that will make your engine perform the way you want it to.

After that, you can start a new post, get more specific answers, and spend agonizing hours trying to figure out what cam to use. Don't get in a rush. This should be a fun, learning experience.

Good luck.
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Old 03-08-2012, 02:25 PM
How fast is fast enough?
 
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There's also the crate option, which takes out the hassle, is dyno tested, is warrantied, and can sometimes be cheaper than building it yourself.

I've never bought a crate, but it is a valid option used by many.
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Old 03-18-2012, 07:27 AM
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Quote:
Originally Posted by crussell85
Please don't listen to this guy. If your not gonna build it right then why build it at all?
Your kidding right? Are you made of money? Didn't sound like the OP was going to build a engine the way you do I guess.

I have a machine shop and I'm ASE Certified Master engine machinist. Been doing this with new engine builders for about 35 years now.

What do you do?
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  #29 (permalink)  
Old 03-19-2012, 07:03 AM
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not to be mean Mmfh, but there is a few things aggrivate me so much about people who tend to just put motors together without the propper knowlege (i'm not saying this is you, i'm saying this is the OP). they almost always buy a set of rebuilder pistons, dont have block decked afterwards, and they just buy a rebuild gasket kit which will almost always come with a .040" head gasket. this puts their quench in the .080" range, which is just plain bad. i wouldn't care if the OP was building a 500hp sbc or a simple rebuild to a 250hp sbc, i would always advise them to pay attention to the quench and try to get it in the .040" range.
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Old 03-20-2012, 06:40 AM
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I guess I just had a picture in my head of what the OP was like and what he was doing, as I've seen this thousands of times before.

Sounded like he is playing around with his first engine and wants a little more power than stock, probably doesn't have a lot of money to spend.

How many of you guys who built your first engine actually even heard of quench when you were putting it together? I probably didn't.

Quench is something that does greatly affect how efficient the engine will run, but in this situation buying off the shelf parts will get him going so he can have some fun while learning some basics of engines.

That's the way I took it.

Mm
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