Anyone use or hear of 1.85 valves?

OneLethal87GN

R.I.P. Lethal GN
Joined
May 26, 2001
The guy who is going to rebuild my engine told me a supplier of his is working on a new type valve. He says it is a 1.85 intake valve. He thinks it's just a cut down 1.90 valve. Anyone ever hear of these, or run these? I see most use the 1.77 valves. I told him to install bigger valves in my self-ported heads and this is the info he gave me on the ones he's going to install. Another guy told me he had very little clearance with his 1.77 and 1.60 valve combo. When I told my engine builder this he told me he had to modify them and he'd show me what he meant when the time came. He builds race engines for a living and has a very good reputation around here.
 
...forgot to add...... which is better... 1.77 intake, 1.60 exhaust...or... 1.85 intake, 1.50 exhaust?
 
i dont know how they would fit any bigger than 1.77/1.60 valves into the combustion chamber. I have them in my champions, and it looks like those are the BIGGEST that will fit. no more room!
 
I am by far no expert!!
But in my opinion, the 1.77 intake, 1.60 exhaust
combination would be better.

The air is going to get in(turbo makes sure of that)
Need to make it as easy as possible for exh. to get out.

Just my opinion, don't shoot me:D
 
I just read in an old issue ( May '97 ) of GM High-Tech that a guy had the 1.85 intake and 1.50 exhaust valve combo. He had the ESP heads though. It would seem to me that the 1.77/1.60 combo would be better too. There are just too many people running that combo. I guess the 1.85/1.50 combo is just old technology.
 
The most you can put in a normal set of iron heads without relocated guides is 1.77/1.50. Even then, often you need to cut down the intake valve to get a minimum of .025" or so between the valves. Anybody who thinks they're going to put 1.85s in hasn't looked at the space between them. If the guides/seats have been relocated, larger combos are possible.
 
OK, the direction of this thread seems appropriate for some questions I have about the best thing to do to a stock GN head relative to larger valves.

My understanding is that the diameter of the stock GN intake valve is 1.71, and that the stock GN exhaust valve is 1.50. And when people begin talking about bigger valves for the stock head, the most usual approach is to step up to a 1.77 intake valve. Why?

It would seem much more logical to me to leave the intake valve at 1.71 and enlarge the exhaust valve to 1.55 or 1.60. That way it would be much easier to get the burned gasses out of the cylinders, and the intake flow, backed by the boost of the turbo, would still be able to provide all of the air the engine needs through the 1.71 valve. Is there anything wrong with my logic?

Thanks.
 
On pretty much any streetable TR motor the exhaust manifold back pressure is going to be way higher than the intake manifold boost pressure. Way back when in the gnttype archives someone measured 40 psi in the exhaust vs. 20 psi boost on a stock motor (turbo, ic, heads). A few years ago turbotr measured about 30 psi exhaust manifold back pressure with 25 psi boost with ported GN1 heads, frontmount, and T72 (or maybe T76) turbo. To do much better the exhaust AR has to get a lot bigger, well over 1, the heads have to flow even more, and the turbo has to get a lot bigger/more efficient, and all that will just maybe get the exhaust back pressure down to equal to the intake manifold boost pressure (and be unspoolable on the street with less than a 4000 stall converter and 274 cu. in. motor). So, all that said, each particular combo will want a slightly different intake/exhaust flow ratio but staying with about the same ratio as for n/a motors works pretty well for us.
 
Good reply, Carl. On a turbo engine, the exhause IS at a higher pressure, and density, than the intake. So it is misleading to say the "turbo will force it in", because that ignores the fact that the "pistons will force it out", too. So, on an unblown engine, the inlet density and the exhaust density are close to the same, while the exhause is denser (takes up less room) on a turbo engine. Based on that, I would say go with bigger intake, a turbo engine should have bigger intake relative to the exhaust valve than an unblown engine. Make sense??? (Remember, Stage II heads go to 2.02 intakes)
 
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