Heads stall at 0.550 lift
07-24-2008, 08:48 PM
#1
Heads stall at 0.550 lift I have a set of 5.3 heads that have 2.0int and 1.60 exh valves. THe heads are milled to achieve a 54 cc combustion chamber and ported from a local shop over in New Orleans.
I got an incredible buy on these heads for $400 used as the guy needed the money to fix his transmission.
I had them flowed and they flowed 283@.550 lift on the intake with good midlift numbers(cant remember exactly what but they are very comparable to other ported heads from venders) . At .600 lift the shop just shows stalled but did not show what they went down to at that lift.
ANy way , my cam that I am going to run is a 239/243 .612/.612 112 lsa 110 cl cam. This is going in my project Nova with a 11.73/1 compression, 347 . How much will the stall in head flow hurt me?
PLEASE NOTE: If you have no Idea and are not experienced in this area, dont just guess and spit out a number.
I could change cams but this car is a bracket car and I am looking for low 10's. It is very light at 2400 lbs when it had the big block with Iron heads before so I am looking at 2250 range or so with the almuminum Ls1 plus me at 250 lbs.
Its a big tire car with a 12 pt cage th350 trans with a 8" stall in the 5300 range.
31 inch tires with 4.30 gears in the rear.
I dont think it will be an issue but how much will I really leave on the table from the heads stalling before peak lift?
I got an incredible buy on these heads for $400 used as the guy needed the money to fix his transmission.
I had them flowed and they flowed 283@.550 lift on the intake with good midlift numbers(cant remember exactly what but they are very comparable to other ported heads from venders) . At .600 lift the shop just shows stalled but did not show what they went down to at that lift.
ANy way , my cam that I am going to run is a 239/243 .612/.612 112 lsa 110 cl cam. This is going in my project Nova with a 11.73/1 compression, 347 . How much will the stall in head flow hurt me?
PLEASE NOTE: If you have no Idea and are not experienced in this area, dont just guess and spit out a number.
I could change cams but this car is a bracket car and I am looking for low 10's. It is very light at 2400 lbs when it had the big block with Iron heads before so I am looking at 2250 range or so with the almuminum Ls1 plus me at 250 lbs.
Its a big tire car with a 12 pt cage th350 trans with a 8" stall in the 5300 range.
31 inch tires with 4.30 gears in the rear.
I dont think it will be an issue but how much will I really leave on the table from the heads stalling before peak lift?
07-24-2008, 09:14 PM
#2
Here is the deal and it is called "dwell time". With the higher lift cam that means that the valve will be open longer for maximum flow for the heads. As long as the heads are not doing something funny such as going into turbulance at .600 lift than you will be fine and make more power.
07-26-2008, 03:47 PM
#6
ok, either the heads have the tightest short turn radius on earth, or those heads are SCREAMING for a valve job. A good VJ can net you more CFM and help straighten out the flow provided the port isn't garbage.
PM me if you're interested I can recommend you to a great valvetrain guy to get your straightened out.
PM me if you're interested I can recommend you to a great valvetrain guy to get your straightened out.
07-26-2008, 03:49 PM
#7
Here is the deal and it is called "dwell time". With the higher lift cam that means that the valve will be open longer for maximum flow for the heads. As long as the heads are not doing something funny such as going into turbulance at .600 lift than you will be fine and make more power.
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07-26-2008, 06:13 PM
#9
The 5.3 heads aren't that great as far as resisting short turn seperation. There is a difference between stalling and going turbulent (or sonic). Stalling is simply reaching the airflow limit of a certain CSA. Flow doesn't die, it just...stalls. When a port goes turbulent, flow numbers drop big time.
07-26-2008, 06:17 PM
#10
well, if he knows what he's doing, it can probably be saved by smoothing out the radius. It's going to increase the runner volume a bit. Maybe it could still be solved with a valve job. But I am just guessing on the internet, the heads need to be seen and heard on the bench to solve the problem.
good luck on it
good luck on it
07-26-2008, 06:24 PM
#11
I may just try them and see what the car does. if it runs the numbers , leave it along. If it dont then i can either try a cam with lower lift, or get new heads.
Thanks guy's, It should be running in about 2 months or less and I will figure out if I should leave them alone. WIth stock truck valves before going 2.0 1.60's the heads were on a 4000 lb trans am with an f14 cam and fast intake and went 11.42 at 120 mph with a 3800 stall converter.
Thanks guy's, It should be running in about 2 months or less and I will figure out if I should leave them alone. WIth stock truck valves before going 2.0 1.60's the heads were on a 4000 lb trans am with an f14 cam and fast intake and went 11.42 at 120 mph with a 3800 stall converter.
07-26-2008, 07:00 PM
#14
I have 4 cc pistons and the valve clearence will be checked before the motor is spun over.
This is not a stock bottom end.
stock crank, 6.125 Scat I beams and 4 cc mahle pistons. Stock mls gm head gaskets, heads are milled a lot . I am waiting for pushrods to check clearence. I checked with a pushrod tool and I need 7.35 length pushrods so i will get some before checking ptv clearence.
If the cam is to big then I will most likely get a asa cam and be happy with what it runs.
This is not a stock bottom end.
stock crank, 6.125 Scat I beams and 4 cc mahle pistons. Stock mls gm head gaskets, heads are milled a lot . I am waiting for pushrods to check clearence. I checked with a pushrod tool and I need 7.35 length pushrods so i will get some before checking ptv clearence.
If the cam is to big then I will most likely get a asa cam and be happy with what it runs.
