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Old 05-19-2017, 01:35 AM
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What do you all think of my combo SBC

357 10.1:1 flat top pistons, rpm air gap manifold, dart pro 1 200cc heads, comp 1.52 roller rockers, pistons are .040 in the hole and I'm running .015 gaskets, lunati 268 flat tappet .505" will attach pic or card, hooker super comp 1.75" long tubes, msd 6al timing 21 at idle 36 all in at 2500.
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Old 05-19-2017, 01:36 AM
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Oh and a quick fuel 650 mechanical secondary. I think I might benefit from a 750 but would like to hear opinions. My first performance build. Wish I would have got the block decked. Can believe how far pistons are in the hole
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Old 05-19-2017, 08:47 AM
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Quote:
Originally Posted by 1969chevynova View Post
357 10.1:1 flat top pistons, rpm air gap manifold, dart pro 1 200cc heads, comp 1.52 roller rockers, pistons are .040 in the hole and I'm running .015 gaskets, lunati 268 flat tappet .505" will attach pic or card, hooker super comp 1.75" long tubes, msd 6al timing 21 at idle 36 all in at 2500.
If you encounter any cool or cold weather where you live and this is a street motor, you may experience drivability problems with the Air Gap intake manifold due to lack of heat in the manifold to help atomize the fuel droplets coming out of the carburetor. Other fellows have made us aware of this problem from their own experiences. A better choice (assuming conventional heads and not a Vortec design), you may have been better off with a standard Edelbrock 7101 or Weiand 8150. Personally, I feel that Edelbrock Corporation is doing a dis-service to the buyers of their products by not warning them of this drivability problem in cooler weather.

You may experience fretting (wearing away of the material) of the aluminum heads by using steel shim head gaskets. All aluminum head manufacturers recommend a thicker composite head gasket to prevent fretting. None of them recommend a steel shim gasket. I understand that you are aware that the piston is too far down in the bore and that may have been because of using a piston with a reduced compression height. 350 pistons are 1.560" or maybe a little taller, while "rebuilder" pistons can be 0.010", 0.015", 0.020" or maybe even 0.025" shorter. Obviously, the way to build a motor with a good, tight squish/quench is to use a piston with a taller compression height along with cutting the block decks a little. The decks need to be cut anyway, to square up the block so that the heads will fit squarely on the block and the intake manifold will sit squarely on the heads and seal up the manifold/head interface.

You may or may not have good luck with a flat tappet camshaft. Most fellows today realize that flat tappets are last century's technology and that they will have to jump through hoops to prevent fragging of the cam and lifters with today's commonly available motor oils. Here is a tutorial that I wrote several years ago, after we began having trouble fragging cams and lifters due to the lack of an extreme pressure lubricant in "off the shelf" motor oils.....
http://www.crankshaftcoalition.com/w...ips_and_tricks

Depending on the Dart chamber design, you may not need quite so much ignition lead. I would maybe begin at 32 and sneak up on it at 33 or 34. I you are planning on using a 2500 or higher stall converter, you could lock out the advance in the distributor and run 32, 33 or 34 at the crank, using a momentary off switch in the hot line to the coil to crank the motor.

I have seen those Comp roller rockers turn blue from friction. Hope your experience with them is better than that.

.

Last edited by techinspector1; 05-19-2017 at 09:11 AM.
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Old 05-19-2017, 08:53 AM
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Quote:
Originally Posted by 1969chevynova View Post
Oh and a quick fuel 650 mechanical secondary. I think I might benefit from a 750 but would like to hear opinions. My first performance build. Wish I would have got the block decked. Can believe how far pistons are in the hole
When using mechanical secondaries, you will definitely want to include a looser stall converter to prevent bogging the motor with a full shot at low r's. 750 is the proper size for max power on a 350, so I might expect a lesser MAX power figure with a smaller carburetor, maybe 15 to 25 horsepower. Drivability at less than max rpm power may be a little better with a smaller carburetor.

I have seen other youngsters use the English that you are using here, so I have to believe that you picked it up from others. What you should have said is.....
"Can't believe how far pistons are in the hole." Or...."Cannot believe how far pistons are in the hole." Using "Can" in this context makes no sense at all.

.

Last edited by techinspector1; 05-19-2017 at 09:09 AM.
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Old 05-19-2017, 10:07 AM
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Yes tech I meant cannot. motor is already in my car. I have a 2800_3000 converter. The thing runs really good now. I will try a little less timing if I get a chance to tinker on it. Thanks for your words of wisdom Tech.
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Old 05-19-2017, 10:11 AM
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Sorry for the bad English I'm not trying to, it's just when I post from my phone I can really see what I'm posting and I have big thumbs. Thanks for bearing with me and understanding what I was trying to say.

Darin
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Old 05-19-2017, 10:31 AM
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Quote:
Originally Posted by 1969chevynova View Post
357 10.1:1 flat top pistons, rpm air gap manifold, dart pro 1 200cc heads, comp 1.52 roller rockers, pistons are .040 in the hole and I'm running .015 gaskets, lunati 268 flat tappet .505" will attach pic or card, hooker super comp 1.75" long tubes, msd 6al timing 21 at idle 36 all in at 2500.

I'm in agreement with Tech.


Pistons that are .040 in the hole as measured from where the actual deck or from the top of the gasket setting on the deck. Point 040 is too deep and indicates that these pistons are for a mass rebuilder or for a stock type compression ratio with a decked block. Standard Chevy SB piston crown to bare deck is .020 to .025, having .040 says these are rebuilder pistons and that with an undecked block is not going to give any 10 to 1. I can see using a .015 shim to try and keep the compression clearance under control but the heads are not going to be long term happy with that reference what Tech is saying about that.


Bogie
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Old 05-19-2017, 11:08 AM
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yes she is 10:1 i've done the math. i realized that i need different pistons for optimum quench but i just threw it together to get me by for the summer
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Old 05-19-2017, 11:12 AM
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Picture of compression calculator figures give or take a little but close to 10.1.
I know when I slap another block together I'll zero deck and get it up to closer 10.5
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Old 05-19-2017, 11:11 PM
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she runs alright needs more tuning but here's a little VIDEO

https://youtu.be/Gac6iF1149g
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Old 05-20-2017, 05:02 AM
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Quote:
Originally Posted by 1969chevynova View Post
Picture of compression calculator figures give or take a little but close to 10.1.
I know when I slap another block together I'll zero deck and get it up to closer 10.5
Quote:
Originally Posted by 1969chevynova View Post
she runs alright needs more tuning but here's a little VIDEO

https://youtu.be/Gac6iF1149g
It seems to run pretty darn good to me. We talk a lot on this forum about quench distance, and it is truly important for a street driven car and for maximizing performance. Performance meaning WOT driving and fuel economy, but it's not a deal breaker to be at .050-.060" IMHO. It's just a matter of if you're putting the motor together, then why not build it the best spec possible. The difference in your quench and optimum quench might be worth another degree or two of timing - that could equate into another 10-30 HP. If your motor is 400hp, then you might have been able to get 425 out of it. On the street the difference between 400 and 425 is negligible to me. At the strip is another story. As always, it comes down to what you end goals are.

Depending on the application you ought to be somewhat careful about engineering more compression than 10:1 in any motor that is going to be a pump gas only build. 10:1 with aluminum heads is more than safe. You can definitely go higher and still have success (many have), but it takes the correct cam and tune for that to work - don't mess it up or it turns into either a poor running pig or a do over. If you had the opportunity to change anything about your present build, then dropping the quench distance via decking the block and then softening up your chambers to keep the compression at 10:1 would be a much better and more effective choice. Again IMO.

A good example of a higher compression street engine is member here Greg's 388 build. He has spent plenty of effort getting the correct components to run with that compression - the results are quite good - over 500HP IIRC. I think if you search 388 stroker you'll find some of his threads about it.
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Old 05-20-2017, 09:41 AM
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The main problem created by too much quench distance is engine overheating which can lead to preignition.

If you have more than .020" deck clearance, install a good temperature gauge and keep a close watch in it, especially in warm weather. Combustion temperature is why the deck clearance is called "Quench" . The deck clearance will quench the excessive combustion temperature or reduce the fuel heat release.

Did you ever wonder why Pistons are dished in order to lower the compression ratio rather than increaseing the deck clearance......overheating.

My associate had a 1966 Pontiac 2+2 with 421 engine. When he rebuilt the engine to 428 CI, he wanted to lower the compression ratio. He had the tops of Pistons machined .030", increasing the quench distance, in order to increase the combustion chamber volume and lower the compression ratio. The engine overheated so bad he could hardly drive it.
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Old 05-20-2017, 09:51 AM
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Nice looking car and sound good. I agree with above members, flat tappet cams are yesterday. A roller cam would likely have given you a slightly milder idle but at a cost for a little "more" power
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Old 05-20-2017, 10:26 AM
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Originally Posted by vinniekq2 View Post
Nice looking car and sound good. I agree with above members, flat tappet cams are yesterday. A roller cam would likely have given


you a slightly milder idle but at a cost for a little "more" power

Yes I have a 1988 roller block for my next build.
This block I put together To summers ago with camel humps that let so much oil through the guides it wasn't funny.
Just threw on the dart heads to get her up and running for the summer before I tear it down for rust repair and what not. Thanks guys for the comments and suggestions
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Old 05-20-2017, 10:43 AM
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Be certain you get the valve spring pressure correct or you will end up with a piece of junk.

"More's Law" should not be used with a flat tappet camshaft. Today's motor oil will flatten a camshaft if you have bone crushing valve spring pressure. Unlike the good old days when you could have over 200 lb seat pressure and over 350 lb open pressure with high lift flat tappet camshafts. The "catch 22" is that higher valve lift requires higher valve spring pressure.

Maximum daily driver valve lift and open pressure with a flat tappet camshaft is .525" and 325 lb . The Maximum seat pressure with a flat tappet camshaft is 125 lb. If your heads have hardened seat inserts, you can have more seat pressure only if you can remain within limits of the open pressure. R

That is why automakers were conservative in the 60s and 70s when it came to valve spring pressure. They had automobile warranty issues to deal with.

That is why GM installed the same valve springs on the hydraulic lifter grocery getter engines, the engines in the solid lifter fuel injected Corvettes and the solid lifter engines in the Z-28 Camaros. 90 lb seat pressure/300 lb open pressure.
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