How much compression is everyone running?
Thread Starter
Joined: Apr 2007
Posts: 9,711
Likes: 999
From: Evansville,IN
How much compression is everyone running? I am helping my friend build the engine for his 95 Z. It's 355 w/ balanced bottom end. He is using speed pro replacement pistons. The machine shop checked the heads and they are 52cc.
I talked to them before they had a chance to check the deck height on the block be he said the compression ratio should be around 11.5 I know LT4's came with higher compression than the LT1's.
The cam is 236/242 on a 110 I think.
It's a Lloyd Elliot spec'd cam and his LE2 heads.
My friend is going to call him tomorrow and get his input.
One thing I am wondering about is quench. I don't know how far stock LT1 pistons are down in the block. Which head gasket we are using hasn't been decided yet.
I will know tomorrow. Any input would be appreciated. Mike Norris is going to tune the car. I am going to talk to him tomorrow and get his input too.
I talked to them before they had a chance to check the deck height on the block be he said the compression ratio should be around 11.5 I know LT4's came with higher compression than the LT1's.
The cam is 236/242 on a 110 I think.
It's a Lloyd Elliot spec'd cam and his LE2 heads.
My friend is going to call him tomorrow and get his input.
One thing I am wondering about is quench. I don't know how far stock LT1 pistons are down in the block. Which head gasket we are using hasn't been decided yet.
I will know tomorrow. Any input would be appreciated. Mike Norris is going to tune the car. I am going to talk to him tomorrow and get his input too.
If you have a set of calipers, quench is actually a very simple thing to measure. And since the heads are not on yet, I would suggest getting a set and measuring it before you buy head gaskets.
As far as stock quench goes, it varies from engine to engine. I have been told (yes im regurgitating information here) that with factory tolerances on the block it could be anywhere from. 065 to. 030 in the hole. On the 3 LT1s I have here at the house, one is .047 and the one is. 039. The other one has the heads on it still.
As far as stock quench goes, it varies from engine to engine. I have been told (yes im regurgitating information here) that with factory tolerances on the block it could be anywhere from. 065 to. 030 in the hole. On the 3 LT1s I have here at the house, one is .047 and the one is. 039. The other one has the heads on it still.
To calculate compression you need to know gasket thickness and piston valve relief volume in addition to the chamber size and piston to deck height you mentioned.
That said 11.5 is NOT particularly high for an NA LT1, people go over 12:1 all the time, some folks even go over 12.5:1 on pump gas street/strip motors.
The LT4 was 10.8:1 stock.
I think you will find that once someone knows how to deal with piston rock they will measure .020-.035 on most LT1s with most falling more like .025. If you measure towards the lifter valley or the outside of the engine the piston can be rocked in the bore and give a very high or low reading.
That said 11.5 is NOT particularly high for an NA LT1, people go over 12:1 all the time, some folks even go over 12.5:1 on pump gas street/strip motors.
The LT4 was 10.8:1 stock.
I think you will find that once someone knows how to deal with piston rock they will measure .020-.035 on most LT1s with most falling more like .025. If you measure towards the lifter valley or the outside of the engine the piston can be rocked in the bore and give a very high or low reading.
Thread Starter
Joined: Apr 2007
Posts: 9,711
Likes: 999
From: Evansville,IN
I just talked to my friend who owns the engine. He remembers the machine shop saying the piston is down .025 or real close to it. To get a better quench we would have to deck to zero and run a .041 gasket or use the thinner .029(or whatever it is)gasket.
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as for the quench i wouldn't go any tighter than .030 with a steel stock rod.....just to be safe........even with an aftermarket rod its risky......im at .027 on mine with a billet steel rod and for a motor that sees some street usage to me its not worth going closer........as for gaskets I'm running cometics down at .026" .....
my old 355 was at 11.2:1 CR and it ran just fine on 93 octane....
my 385 was at 13.92 last year and this year it will be at 14.24:1.......not really pump gas friendly lol
my old 355 was at 11.2:1 CR and it ran just fine on 93 octane....
my 385 was at 13.92 last year and this year it will be at 14.24:1.......not really pump gas friendly lol
that sounds about right.....the standard deck on these things ususally runs around .020ish down the hole.........plus depending on the compression height of the piston u used..........your gonna have pretty big quench with that.......you could chop the gasket way down but the problem with that is you compression is going to come up dramatically......which may take you off pump gas with that small of a head.....
I think I'm running ~11.5:1 but I could never find a definite answer on stock piston volume. Whatever 53cc heads and a .029" gasket work out to with the pistons .015" in the hole.
