What the most duration I should run in a 85 IROC 305TPI? We are putting Vortec heads, headers, catback, and some misc. stuff to it. Thanks

 

well it realy depends on your compresion. i think your 305 would have like 9:1 with 58 cc cambers, by puttin vortec heads on 64 cc chambers u will drop the comp ration prolly half a point. i wouldnt run any think more than 214 @ .050 any thing more would give u "soggy" low rpm performance, however u can mask this with a high stall converter and step gears

 

We are trying to find set of smaller chamber Vortecs, If we cant then we will probably get the heads shaved a bit and use the smallest head gasket available.

I think we are going to go with 1.6 rockers and a 218 duration cam with .450 lift

 

You wanna stay reletivly small with a 305..especially a TPI one. I wouldn't go any larger than a 20x in/21x ex cam.

 

Man, that's a toughy. I agree with everyone else though, I wouldn't go too big if I were you.

 

By "smaller chamber Vortecs", I hope you mean shaved L31's, not 305 Vortecs. The 305 version don't flow anywhere near what the L31's do.

The '85 TPI was the "dumb" TPI - you don't want to throw too many curves at it. Perhaps this is a good time to upgade to a later system.

LB9 compression was 9.5:1 with 4-relief flat tops, 58cc chambers, steel shim gasket. Compression isn't much of a factor with regard to the cam and what the TPI will think of it. The cam is the much bigger player.

You sure you want to go Vortec? $425 for heads (okay, probably less if used), another $150 or so for self-aligning rockers and the shaving to get to 58cc, and a whooping $400 for the Vortec TPI base. Still have press-in rocker studs & really poor springs (that .450" lift is w/1.5 rockers, right?. That's .480" w/1.6 rockers - too much for the springs). Or, World S/R Torquer 305's for about $700, use your existing base, will have good springs & screw-in studs. Port 'em if you like (I liked). Will certainly run with the Vortecs if bowl-blended. If treated to the full SA method...

 

Very good points, I will have to reconsider my thinking. Thanks!

 

While the 85 TPI ecm may be 'dumb', I have seen quite a few quick 85's on the stock ecm. Dont forget CCC cars are stupid too.

The stock cam is already in the 20x/21x range. Dont waste your time with a replacement if you are going to put virtually the same thing in there. I'd suggest a comp cams XE256H-12, its a 212/218 with .449/.456 lift and 112LSA. I'd suggest new valve springs as well.