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Ralph Savarese
01-24-2002, 08:03 PM
Delema,
I have Two sets of heads
Can anyone tell me what is better to use
Center bolt valve cover heads with the swirl intake ports 1.94/1.50 68cc to give me 10.1 compression with my pistons
OR
Outside bolt valve cover heads non swirl intake port heads with the same size valves 3/8 exhaust stems 76cc to give me 9.2 compression with my pistons I am investing in stainless intakes and exhausts and I don't which heads I should put the valves in to use
I had a problem last year with tuliping intake valves but I think I narrowed it down to running hot from restricted risers
Any advice would be greatly appreciated
thanks
Ralph

GEOO
01-24-2002, 09:07 PM
Ralph,
The 10:1 heads will need 92-94 octane and you will have to be carefull with the timing. The 76cc heads would be better for you. I've seen you drive and the throttle is to the pins often. The 9:1 is less likely to heat up and cause a piston failure. You don't need the extra headache for the 10hp. GEOO

Ralph Savarese
01-24-2002, 09:14 PM
Thanks Geoo,
I was also tring to determine which heads actually flow better though would you know if the swirl heads help or hinder flow ?

turbo2256
01-24-2002, 09:36 PM
The swirl is to help with combustion a quicker burn rate for the way gas is formulated today. If you need to reduce compression use thicker head gaskets or machine a bit off the piston tops. First find out what your deck clearance realy is and calculate your actual compression. I know my shop is flowing 250 @ 6000 RPM with the Vortec heads with minimal increase in CCs with factory size valves he was still working on them last I spoke to him.

Ralph Savarese
01-24-2002, 09:45 PM
I still have to make a decision on which heads to use the the pistons have not been removed.
I was wondering what is better for a marine application Swirl or non swirl I am almost leaning toward going with my 76cc heads will bring my compression to 9.2:1 as Geoo suggested.
Ralph

GEOO
01-24-2002, 09:50 PM
Ralph,
Check out this Article maybe it will help. It' on Chevy heads.
http://www.chevyhiperformance.com/ GEOO

BigGrizzly
01-24-2002, 10:01 PM
If the compression is really what you said it is, and you drive like Geoo says I would do as Geoo says. The extra power usable power you might get isn't worth the hassle. I f you plan to change a bunch of other stuff than go with the other heads. With your application you wouldn't gain any speed and would probably actually loose some. I do have a 10:1+ compression motor in my Corsican and I have to watch it all the time. Babe Erson designed the cam for my applications years ago.It is really nice to have a cam maker an old friend. I have the same engine in both my boat and my 71 MACH I. When you say Tulip the valve do you mean the stem or the valve head? Remember over 5200 rpms your outdrive will suffer.
Its not just the flow, but the way it flows. In your case The 9.2: is the ticket.

Randy

turbo2256
01-24-2002, 10:02 PM
You need to know what your deck height is. If the deck height is on the high side and the piston height is low your compression might be less than you think. Also if your combuston camber is actually measured to be more than you think and/or a thicker gasket can also be used to lower the compression. If you dont know exactly what I am talking about most peterson books on rebuilding engines will tell you how to do these things. Fast burn is a good thing these days gas has changed and burns in a different way than it did in the old days. Also there is revised water jackts in the newer heads to help cool tings down better between the siamesed exhaust ports an there are some cheep things that can be done to help a bit more with cooling he head temps.

Jay Robertson
01-24-2002, 10:03 PM
Use the center bolts with a 110 lobe ceterline cam.The extra overlap will releave the combustion
pressure. Must have a very low restriction exhaust. If you don't; it wouldn't matter which head you used, it still wouldn't run. Also the swril chambers are to direct the exhaust out of the combustion chamber more efficently. The intake and exhaust valve are open together for a breif period. The name of the game is to suck the
intake air in and exhaust gas out by means of scavging. The only way this works is to create a vacume in the exhaust manifolds.If anyone would like to know how to create this vacumelet me know.
you could run pump gas on this combo.only if the exhaust will flow. You must get rid of the heat.

Ralph Savarese
01-25-2002, 07:25 AM
Jay The swirl port is only on the intake so how does it make the exhaust flow better?
Randy The intake heads will tulip.
Ralph

Forrest
01-25-2002, 09:15 AM
The problem with using a thick head gasket to reduce compression, or machining the tops of pistons, is that when your do this, your quench volume is increased. Quench is the distance between the flat part of the piston and the flat part of the head at TDC, and is necessary to create turbulence in the combustion chamber. The turbulence created by quench actually slows the burn rate and helps to prevent detonation (pinging). Assuming near zero to +0.005" deck height, a standard marine Fel-Pro SBC head gasket is about 0.040" thick (installed) which gives a 0.040" to 0.045" quench, which is about ideal.

Go with the 72cc chamber heads or replace your pistons to use the other heads.

Ralph Savarese
01-25-2002, 09:52 AM
The heads I have are 76cc chamber heads non swirl intake ports with my pistons which are hyperutectic with a .125dome will give me 9.2 compression. The original heads are 68cc swirl port heads give me 10.1 compression. Which is better for breathing with dome pistons ?
Besides compression!
If I figured correctly I would think that swirl port heads would not be effective with dome pistons redircting the swirl Hence defeting the purpose true or not?

turbo2256
01-25-2002, 10:01 AM
Dont go with the swirl ports all the auto companies got away from them. Seems the swirl causes the cylinder walls to become washed down with gas and excessive ring and cylinder wear occurs. So go with the older heads or a set of 906 vortec's

Ralph Savarese
01-25-2002, 06:16 PM
Scott,
I will have to let you know on Monday. I have the heads at work . They are nothing special 87 and up 350 heads 68 cc center bolt VC.
The other outer bolt VC non swirl port intakes and 76cc with 3/8 stem exhausts both heads have 1.94/1.5 valves
Ralph

BigGrizzly
01-25-2002, 07:21 PM
The swirl does not like the dome. flat or dished pistons with the same compression would make more usable power. The proper squish does deter detonation with higher compression ratios.
Its your choice Ralph. there are lots of ways to do it, just cubick dollars. What Geoo, Forrest and Iare doing is giving you the cheepest way out.

Randy

Ralph Savarese
01-26-2002, 08:27 AM
Randy,
I think I have made a decision I am going to go with the 76cc heads to give me 9.2 compression through you guys and some research I think working with to high a compression and swirl port intakes with dome pistons was a no no to begin with! Thats probably why I had valve tuliping problems due to detionation.
Ralph

Donzified
01-26-2002, 11:56 AM
Lower compression =longer life