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Author Topic:   Vortec compression. Steve?
UFnARacing
Member
posted October 19, 2003 11:21 PM
The class I'll be racing next year will have me racing with vortec heads. I'm going to run a 383 with 6" or maybe 6.125" rods. The vortec's I have are flat milled .040". I believe that puts the cc's at 60. I'm trying to get the compression as high as possible. What's a realistic number? Valve lift will be around .550" or so. I do think that I'll have to pony up for some custom pistons. I don't really want to, but feel like I'll be stuck around 12:1 without them.

Steve, what are you getting for compression numbers using the vortecs? Any suggestions would be very appreciated.

Thanks,
Randy


sdhnc29
Member
posted October 20, 2003 09:01 AM
Randy ,

Will you be allowed to use a dome piston ? If not , then you will be limited on compression ratio . With a Vortec head that is flat milled .045" , you get a 56.8cc chamber using a 2.020/1.6 stainless valve . If you stick the piston .005" out of the hole , use a Ferrea .035" thick x 4.060" head gasket , and a piston with a -.005 cc valve pocket , you'll end up at 12.5:1 on a 383 engine . You can angle mill the Vortecs .085" + .015" flat mill and get them to 51.6 cc's . Doing this with the same numbers from above will put you at 13.3:1 on a 383 .

There are plenty of way's to squeeze the compression ratio tighter on a flat top . Such as getting your custom pistons without valve pockets and making your own , and starting with an oversized valve , like 2.100" , and cutting it back down to a 2.020" . This will give you a thick valve that displaces more cc's in the chamber . Taking everything into account , it is possible to get a flat top Vortec head engine into the high 13's and possible 14:1 range .

If your allowed to use a small dome , then this would help the situation and eliminate some added machining cost's .

hope this helps ,
Steve

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Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


BrianW
Member
posted October 20, 2003 10:52 AM
I'm thinking of building a similar setup - shooting for 14:1 or so, and I can run domed pistons....

So my question is if there is a "shelf stock" piston that I can use to get to ~14:1 and still have good flow on the Vortec heads... Or will I be better off running the Pro-Topline 50cc heads??

sdhnc29
Member
posted October 20, 2003 02:51 PM
If you can run the Pro head or the Iron Eagle , then that's what I'd use over the Vortec . The Vortec is a great head for classes limited to OEM castings , but if you can use aftermarket heads then it's the only way to go .

There are shelf stock domed pistons that will work with the Vortec , but the dome must be modified to clear the spark plug area inside the chamber .

Steve

------------------
Hendren Racing Engines
Rutherfordton , NC
(828)286-0780


rocket36
Member
posted October 20, 2003 03:26 PM
good point you made steve.
alot of guys here are switching to the pro action heads (spec head for 360 sprintcars).
I saw one the other day that was built by a "big name" engine builder and he had ground the centre of the dome away (on the pistons) to clear the spark plug (pro action heads) and it was really ordinary. I think even a blind man would have seen that these would have a major flame travel problem in the combustion chambers. I'm pretty sure that i have seen advertised somewhere that ross make "off the shelf" type pistons for the pro action heads, they've got to be a better way to go.
sorry, i've gone a bit away from the vortec subject.


UFnARacing
Member
posted October 20, 2003 09:52 PM
Thanks for the help. And, yes I can run any piston. I called JE today and they told me that they don't sell an "off the shelf" dome piston that will work on a vortec headed motor. He said that you would have to cut the dome down so much that it will severely hurt the flame travel. I do like the idea of using the flat top with oversized valves. Maybe I should spend the $300 on that, instead of custom pistons with bad flame travel. JE does sell some flat tops with -.005" valve pockets, so I could get to 12:1 pretty easily.

Are there "off the shelf" pistons with a small dome that would bump compression, while still retain a pretty good flame travel? I know the JE's are $500 for flat tops and $800 or so for customs. I like the idea of good flame travel, after all the vortecs are good for that reason along with the swirl characteristics and flow, right?

Thanks again,
Randy


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