However I’ve read that vvt goes from as advanced as Much as 8.5 at idle and as high as 22.5 retard somewhere higher rpm. I didn’t bother with vvt and just used with 0 advance with earlier calculation. I think it’s definitely an estimation for sure. I plan to see if the thicker deck on these heads allow for anymore leeway for valve clearance. However so far GPI has said I’d have to fly cut. 028 for higher dcr with same cam or even more overlap on more aggressive came while still having good pressure. Like you mentioned factory allows using 87 without damage and I could probably go with. Being that is 99% of factor spec it should probably be a decent mid range performer. 040 gaskets and the GPI ss3 cam it shows dcr of around 9.8:1. įactory LT1 including cam shows dcr of right around 10:1 I also found a formula online to estimate dcr utilizing your scr and cam specs. 040 thick and 4.1” bore raise it up to about 11.8 Anyhow best I can tell that change in chamber brings it down to about 11.3:1 scr. I’ve had some trouble making static compression calculators work with stock lt1 specs but worked backwards to get the numbers right. These heads with 59.8 cc chambers will be down on static CR which basically limits your starting point as far as dynamic or effective CR goes. I’m trying to find a chance to call their tech department. GM builds the engines to work down to 87 octane but no one should ever run that in a 11.5 CR engine. It can be done.Did you talk about this with the company your getting the heads from? I wouldn't exceed the 11.5 ratio that the stock Lt1 comes with. #Flycut raise comp driversOne of my daily drivers is a 3600lb 57 chevy 4 door with 350" and ported 601 heads with 10.87 compression and ran it for 6+ years with a 268H with an intake lobe that closed 2 degrees earlier than the 260H.Ĭustom grind.225 PSI cranking pressure.It pulls my 20 foot 3500 lb pontoon to the lake also. Keep coolant temps in check, I like to stay under 190 f and start conservative on timing. but willy nilly slap stuff together without some massaging and you are on your own. but i put together a 396 with open chamber heads and compression is 11:1 on that one with comp 280H again and 210 PSI on the gauge it likes 38 total and 921 octane.Īgain all sharp edges removed and roughed up ported intake runners. Small chamber heads are less detonation prone I hear. The heads were ported 305 heads with 1.84-1.50 valves.ģ5 total timing 91 octane it was a happy camper. 015" gasket something like 11.9 compression. Overbalance I have heard is a good thing for higher RPM.Īnother engine I built with 57cc chambers was a short rod 385" and the 280H comp magnum flat tappet cam. Say it was zero balanced and you took off 30 grams you would have an over balance situation and i have went with lighter pistons and got the same and Never an issue. If you took some off the tops of those pistons you would not be removing much weight and a rebalance would not be needed in my mind. Roughed up intake runners to promote atomization of the fuel. To make it work all sharp edges on piston top and valve reliefs and on chamber edges were smoothed. Was very happy for 70,000+ miles right up until the pick up screen fell off the tube.ĩ1 octane liked 38-39 total timing depending on weather. It had the comp 270H magnum hydraulic flat tappet. 028" and I ran 186 castings milled to 54cc after porting etc. I ran 11.9 compression in a 350" with cast flat tops but with gasket in place my piston to head was. As a non-stock cam, many Corvette guys run cranes F-278-2 and says it works ALOT better and apparently more friendly to higher compression with non-race gas.Īny compression wizards here give me some advice? Since this is a period motor going into a near NCRS resto - I'm looking one of the old factory GM cams - either the venerable -346 30-30 cam or the more than likely, the -178 LT1 camshaft - both of which are long duration, lower lift, wide LSA camshafts which I know bleed off a ton of compression - but i'm guessing not enough to be safe with 93 octane. This would yield me 12.5:1 but with an aluminum head and probably a much better chamber that might tolerate higher compression - but i don't wanna guess here. If i shelf the Z28/LT1 heads, i'd consider running the new Trickflow DHC175 heads which look like the old Z28/LT1 heads but are cast aluminum, but are as cast with 60cc chambers. Yields me 11.81 which i think is too high under almost all circumstances to run 91 or 93 octane pump fuel (which is what is regularly available to me) Running the stock 64cc heads - factoring in. TRW 7009p pistons which have an 11cc dome Trying to determine if i can make this combo work.īuilding a period appearing 1970 LT1 engine for my 70 Corvette.īlock is an undecked 350 that will be.
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