should i use 1.5 rockers or 1.6 rockers

the heads are torquer s/r's (max 0.560 lift)
and the cam's a comp cam XE274H (.487 intake .490 exhaust)

the engine's a 400 sbc (no overbore)

 

whats the cam manufacturer say gross lift is obtained using?

 

1.5 ratio.

is going to a 1.6 rr that much better then a 1.5?

0.487 -> 0.520 intake
0.490 -> 0.523 exhaust

 

It depends on the rpm the engine is going to run. It would make more sense on a 400 than a 350 since the 400 will spend less time in the upper rpms. There's a very good reason they don't make a 274' .520 lift cam (1.5) in a flat tappet. Lots of people swear by 1.6s . Lots of people don't give a rat's behind about durability either...

 

Typically the difference between a 1.5 RR and a 1.6 RR is 5hp.

Adding the increased lift means checking the entire valve train to make sure it's capable of the extra lift. Will the valve hit the piston? Will the valve spring bind? Will the bottom of the spring retainer hit the top of the valve guide? The increased ratio moves the pushrod closer to the rocker stud. Will the pushrod rub on the guide hole through the head?

 

The XE cams already accelerate the valve pretty damned fast for a flat tappet cam with stock diameter lifters. I use 1.6 rockers all the time but on the XEs you might be pushing it. Might work fine, but it might cause problems. I've used 1.6s twice with XE cams and all it did was increase valvetrain noise (which was already pretty bad) without making any noticable increase in power. Those were combos that I had already made sure could take the extra lift and had the proper springs on it. On an older design cam with less aggressive ramps 1.6s usually give you the (modest) improvement you would expect.

Given that the S/R Torquers are fairly pooped out flow-wise around .500" lift I tend to think that 1.6s won't buy you much, even if they work just fine. But as with many hot rod parts, it's a try-it-and-see kinda thing.

 

Since you are picking and installing the cam of your choice, use a cam that matches the engine and its intended use, and use the 1.5 rockers. 1.5 is the standard ratio that all SBC cams are measured at, and its got the dimentions of the stock rockers (pushrod bump, stud hole, valve tip roller) that all the factory and aftermarket heads were designed for. If you use 1.5 rockers, you'll avoid alot of potential problems, like pushrods rubbing in the slots in the heads/guideplates, valve spring bind, interference with pistons, etc.

IMO 1.6 rockers are more trouble than they are worth IF you are changing the cam anyway. They add more math and measurements into building an engine properly, and they add more 'chance' into whether or not all your new parts will jive with each other. If you are replacing the cam anyway, pick a cam that matches the rest of the combination and put it in with the 1.5 rockers that will cause less problems than the 1.6 rockers.

1.6 rockers are fine if you just want "more cam" without changing the cam, but if you are replacing the cam anyway, using 1.6 rockers just causes more problems than the very little bit of extra valve lift is worth.

Just my 2 cents though.

 

thanks for the input!

think i'll go the 1.5rr route.