another sbc question
I have asked this question a while back, but now I have some more info on my motor. I currently have a 355 sbc with SR torquer heads (76cc, 2.02/1.6, 171cc intake runners) street port/polish, an Edelbrock Victor Jr, Holley 750 vacuum sec., Lunati cam with .480 lift int/exh 292 adv dur, 230@.050., and Sealed Power L2256F30 pistons. The motor came assembled with the Fel-pro blue gaskets (.040) and the motor is claimed to be a 10:1 400hp. With the heads, I'm thinking its about 370 and 8.5:1. I swapped out the gaskets for
.015 steel shim gaskets, but I figure I'm running around 9:1. I've been looking at the Patriot pn2168 aluminum head to get that 400hp or slightly more. Would these heads be a good choice or is there better for around the same price?
you need to have flow numbers and your cam specs.bigger heads can make more horse power,too big of heads and the engine will not run well. whats wrong with the engine you have as it is?
vinniekq2, the motor is fine but it was advertised as 400hp. With the heads that are on it, I'm guessing around 370 hp, which makes me feel kind of ripped off. What other cam specs do you need? I listed everything except LSA and centerline. LSA is 109 and centerline is 107. This is going into a 76 Datsun truck that I hope tips the scales at less than 2500lbs. and will run somewhere in the 12s because this is actually a mild motor.
Im not sure about that combination. The heads you have could support 400 hp.I dont like the cam.That intake is what I use on a 434 solid roller motor. carb is fine.
If you want to rum high 12s,you need a car that hooks well with proper gear set/transmission. weighing only 2500 pounds makes the task a lot easier. Is the car set up now? is the 355 in it now? weigh it,make a pass,get the mph and actual weight and decide if you need more power or just want bigger numbers?
Engine 362 horse 355
Crankshaft GM cast
Con Rod 5.7 GM Pink
Piston Old TRW Pwr Forged F/T, 4 reliefs
Rings 2 x 5/64 Moly, 1x3/16
Head 340292, 64 cc, ported, angle plug
SCR 10.0:1 (.025 deck, .019 gasket)
Intake valve 2.02” Back Cut 30/Polished
Exhaust Valve 1.6” Back Cut 30
Rocker 1.6:1 Comp Stainless Roller
Cam Comp Magnum 280, 230/.480 I&E 110LSA
Carb 750 Holley
Exhaust 1-5/8 Long Tube
Torque 370@ 4500
Horsepower 362 @ 5800
The 292 head uses a smaller 64 cc but old fashion chamber so your Torquer's larger chamber while you probably need a few more degrees of advance the end result between them should be close.
The old Comp 280 cam in terms of duration and lift at the valve from .050 is close to the Lunati 292; I'd expect similar performance between them.
Your Victor Jr will out breathe our Performer, but given the limits of head flow and combustion efficiency downstream of the intake I rather doubt the bottom end can work the Victor Jr anywhere close to its capabilities to deliver mixtures to the cylinders so its presence is a moot point in my mind.
Your piston selection is identical to the old TRW Power Forged with the same old wide rings just with a coating on the skirts. My experience shows that skirt coatings are not where most piston friction is; that's in the ring pack, the skirts hold a pretty good oil wedge between themselves and the cylinder wall. A narrower ring pack and lighter tension rings nets measurably less friction but drive other tricks to seal over the long haul on street motors and really push the limits on windage control technology. A high volume/pressure oil pump, stock oil pan with narrow low tension rings will build you an oil burner.
So all-in-all I think your guess at 370 is in the ball park. The Patriot 2168 head will bring a much better configured (Vortecish) combustion chamber which will pick up the power with no other changes. The aluminum will let you push the compression up which the rampy cam you have needs as for its duration it takes it forever to close the intake valve. Back cutting the valves, especially the intake greatly, improves low lift flow for a rampy cam working a 1.6 rocker can have good advantage to improve flow as the valve is opening and closing on these long ramps.
Hopefully you measured deck to crown clearance while the heads were off, this distance from .025 OEM to maybe zero as remachined plays a heavy part in the compression ratio as well as the squish/quench effectiviness.
the pistons measured around .028 in the hole and add the .015 head gasket gives .043. Other specs are that it has a Milodon stock looking pan with Dzus fastened windage tray, MSD ignition (mechanical advance), stock crank, stock shot-peened rods, Fluidamper balancer, double roller chain, 1 3/4 primary into 3" collectors custom headers and long slot rocker arms. The two engines seem pretty comparable. The Patriot heads are 185cc with 64cc chambers and 62cc exhaust.
Heads are too big in the chamber you really need to pump up the compression. I don't know what the deck clearance is but assuming it's OEM at .025 inch even with your .015 shim head gasket you're at 8.8 static. With these pistons it would take 64 cc head to get to 10 which any decent cam is going to need.
You really need to change the cam to something like a Comp XE268 which gets on with lifting the valve quickly and holds it open late to pump up the ponies. You gotta get the compression up whether that's milling the crap out of the Torquer's or replacing them take you're pick. You need to know what the deck clearance is going because if this block is already zero decked that will control how much you mill on the heads. You've got to run the Dynamic Compression Ratio (DCR) for your compression ratio adjusted for the intake closing point. Later closing needs more Static Compression Ratio (SCR) to drive out a high enough dynamic. Aluminum heads need about one more point of compression than cast iron as they suck heat out of the combustion chamber way faster than does cast iron just in case you go that route.
Even with the Comp cam and decent 64 cc chamber heads it'll take 1.6 rockers perhaps with competent pocket porting, depends on whose heads many of these new heads are easier to screw up by grinding on them than you're likely to get more power from them, to get 400 horses from a 355 with the pistons you have, the Comp XE268, 1.6 rockers with the the Partiot 2168 heads , the intake set up you have, a pair of long tube 1-5/8ths tube headers should prove to be a no-brainer 400 horses on an engine dyno.
Sorry it took so long for my last reply, but thanks for the info. I had already figured that the 76cc heads were killing the CR, but my original plans were to make it driver on pump gas. Nowadays with technology that is possible with higher CR. The Lunati cam is supposed to be a good mid rpm cam with a range of 2000 rpm (?) to 6,000 which would put it as a good match for the intake and Lunati recommends higher CR. What you say sounds good, though.
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