Is anyone running Vortec heads on their older 350??

[Poohbair]

Is anyone running Vortec heads on their older 350, and are you running flat top pistons? If so, what cam are you running and how does it work for you?
My buddy has this setup in his 72 and it is absolutly pathetic. We are going to try and fix the problem by changing cams, and the Extreme 4x4 Grind number X4270H has been recommended, but I am trying to find someone else running a similiar setup.

 

[branrat]

Your compression ratio is 10-10.5:1 You will need a cam with at least 280-290 degrees duration to run pump gas. This is going to kill your low end unless you run a stall converter.

I run a Comp XE274 in my 10:1 383 But have problems due to poor gasoline.

Crane makes a grind that would work for you as long as your heads are set up for a higher lift:

H-278-2 #114801 2500-5500rpm 3000-3400 cruise
278/290 222/234 .467/494 114 LSA 72 ICA
7.65 DCR straight up.

 

[dyeager535]

Running them in my truck.

Vortec, TPI, Crane Roller Cam.

I've got the cam card somewhere in my garage (been awhile since I bought it) but some "general" specs on it are 112* LSA, .454" lift on exhaust side @.050, intake somewhere around .430".

Compression as calculated (not CC'd though) by the piston manufacturer with the 64CC heads and the Speed Pro flattops, is 9.2:1.

No problems whatsoever, and feels quite a bit stronger than it was carbed. If this tells you anything about head design, the ECM running it is from 1987, and I knew right off the bat that the Vortecs would like less timing...set to factory "base timing" (4*) it would ping under heavy load and increased throttle...backing it off to 0* cured that problem.

Obviously a carbed setup isn't going to react exactly the same, but as you can tell, they don't want as much timing as older heads.

 

[Blazer1970]

[ QUOTE ]
Obviously a carbed setup isn't going to react exactly the same, but as you can tell, they don't want as much timing as older heads.

[/ QUOTE ]

Actually, for a given compression ratio, the Vortecs will tolerate a lot more timing advance without detonation. By using flat tops with the 64cc combustion chambers, you may have raised your compression ratio enough that you needed to back out some advance. I have Vortecs on my carbed 350 with stock type dished pistons, and I can run a lot more advance than I could with the stock heads (and also make a lot more power).

 

[ntaj*ep]

I have the Vortecs on my K5 with the comp cam grind #cs xe256h-10
Its a 212-218 duration .454 lift stick also used their roller tip 1.5 rockers. The motor has dished pistons, and an auto. PM me if you want more info. /forums/images/graemlins/peace.gif

 

[dyeager535]

It's just well documented that the Vortecs require less advance to make max power than older heads...you can run more advance, but that isn't where they make the power.

 

[Poohbair]

I think it is the flattops that is messing everything up... making the comp ratio too high. We ordered a diff cam recommended by the guys at Summitt, so in a week or 10 it should be back together and we will see how she works!!

 

[ZooMad75]

[ QUOTE ]
Is anyone running Vortec heads on their older 350, and are you running flat top pistons? If so, what cam are you running and how does it work for you?


[/ QUOTE ]

Branrat's right. Your compression ratio with flat tops is going to be over 10:1. Keep in mind with the cams that have been suggested Vortec's really can't take much more than .490" lift stock. Any more and you will run into issues with the spring retainers slamming into the valve guide bosses and negating the extra lift. There are a couple of things you can do to avoid this. Without taking the heads off you can switch to a comp cam's beehive shaped spring orginally intended for LS1/LS6 gen III small blocks. They are big enough to fit over the bosses, but the beehive shape allow for a smaller retainer and the spring itself can handle the higher lift. you can swap them out without removing the head. Otherwise you need to pull the heads and have the bosses machined down and spring pockets enlarged to fit a regular small block spring like some Z28 units.

If you do end up yanking the heads consider running a slightly thicker head gasket to reduce some of the static compression ratio you got. Fel Pro has them in a few different thicknesses so you might be able to drop it down by .3 to .4. Every little bit helps.

 

[dyeager535]

From what I saw with my pistons, flat tops do not equal high compression. All they need to do is move the connection rod portion or shorten the "head" on the piston to reduce compression, no?

And FWIW, at my .454" lift, I was ALMOST at min. clearance for retainers to guide. Anything more than about .460" lift on mine would have resulted in less than "minimum" retainer to guide clearance. As it is now I am VERY close, but with the RPM range of the engine, it won't be an issue.

 

[branrat]

In general a stock piston is -12 to -13cc & sits .045 'in the hole' in an undecked block. Many of your flattop pistons are -6 to 0cc [depending on valve reliefs] & sit .025 'in the hole'. A standard Felpro head gasket is .039 to .041 thick

My calculations were based on 2 valve relief [-3cc] , '0' deck & standard gasket.

As a rule of thumb for a truck motor I like to use flatop pistons with 76cc heads or a stock piston with a 64cc head, this gives me around a 76cc chamber to size a pump-gas torque cam that is friendly.

My 383 has flatops w/74cc chamber so I have to run a bigger cam than I would have liked to. I would have been better of running a stock piston with those heads or a -22cc piston with a vortec head. I could have ran more of a torque cam than this racing cam[ It is fun though!!!]