#1: got a question about what my compresion is. every calculator gives me a different value. its a 305, 64 cc pro topline vortecs, 0.015 cylinder gasket, 4.100 gasket bore, stock pistons.

#2: i'm probably going to change my cam to a bigger one this winter. right now its 208°/214°, 0.467"/0.482" 112 LSA. i choosed the cam cause i wanted to stay at tbi first. so what cam do you recommend you? max lift can be around 0.520" with these valve springs. a supercharger compatible cam would be nice.

other specs in sig.

thanks,
nebu

 

bump?

 

Would be nice to know some specs on the pistons. Dome/flat/dish, cc...

edit: try using this calc

 

piston, block, crank is all stock from a 91 lo3.
this calculator says i should be around 8.5:1.

i looked around and came across this cam.
87+ up hyd. roller, 227°/234°, 0.478"/0.480", 112LSA.
what do you think?

nebu.

 

Pro Top's Vortecs are machined for more valve lift, right?

 

yes. i've read somewhere that theyre capable of ~.540" lift. but the vortecs seem to flow best around .500". so i think it would be better to stay in this area. with this cam im at ~ .510".

 

Who do you trust, the caculator or the compression tester?

 

errrr, how should i measure my compression ratio with a compression tester? i thought you could only measure the pressure....

 

You are correct, Nebu, on both accounts (valve lift and the compression tester versus calculator). I looked into the Pro Top's heads and they are machined for more lift. However, the flow really doesn't look that altered. Cam selection depends a lot on what kind of induction you plan on putting on the engine.... Sure you can drop a large cam on it, however, if it is TBI, keep in mind, the more aggressive you get, the more PROM tuning you will be needing to do.

As far as compression testing, yea that works, if getting the cylinder pressures is what you are after. All the compression ratio is, is the ratio of total space above the pistons (at BDC) to the total area at TDC. Nothing more than a ratio. Compression testing takes cylinder pressures, which takes into acount the valve timing, any leaks, this that and other. I have not yet seen a way, or even heard of one being possible, to derive an accurate compression ratio from cylinder pressures, other than speculation.

 

tbi was thrown away long ago its got a 650DP atm.
i'm planning on switching to a bigger cam this winter and next year a centrifugal blower. drive this until the block comes apart and throw the stuff onto a 383. (with ported heads, intake etc) want to have some fun first with the 305
but i think with the 8.5 compression and if i keep the psi low, it will hold some time. only thing im worried about is the headgasket. 0.015 copper....

nebu.

 

ttt