1.94 size?

[broncr]

I've got my spare head apart and am contemplating sbc 1.94/1.60's. I've read that they must be cut down. Does anyone have the measurements of the stock 1.94? My spare (ford) head 1.78 intake valves appear to be 5/16 X approximately 4-11/16". It just so happens that I have a dozen or so sbc 1.94's, :roll: but they're a bit snowbound right now, so I can't get my mitts on them.

My old FI Chebby heads also have performance springs that were designed for much more cam than my 300 will ever see. Are they also interchangeable?

The reason I ask is that I have a small (1 ex. valve) problem that has launched me into the possibility of rebuilding my spare head, at a time when I just sunk $$$ into a beautification project. Having tha valves and springs lying around :roll: , I thought I might as well look into using them for a budget valve job.

Back in November, there was a post on offset valve guides that led to a discussion of optimal port sizing. With my spare head stripped, I find that the rectagular intake port appears to be 1.625 x 1.1875 or 1.93 sq. inches. The optimal flow for the stock 1.78 intake requires a port area of 2.02 sq. inches. If I did my math correctly (BIG if), that (2.02) translates to 1.657 x 1.2195, or (-).016 - per side of the intake rectangle. Does that sound right?

For the 1.94's, I come up with a 1.8 x 1.3625 (-.0875 per side) to get the optimal flow port size of 2.45.

The stock flow bowl diameter (1.64) is actually at optimum in one direction, but slightly restricted in the other. It doesn't appear that much porting is needed to optimize the 300 head for flow with the stock intake valve...? I realize that there is a good deal to be gained from smoothing out some of the casting marks & such - especially on the short side radius near the valve.

I'm undecided on going to 1.94's - it sounds like the benefit might be marginal for my usage. My personal redline is ABSOLUTELY 4500 rpm, and I usually shift at 2500. I RARELY exceed 3500 rpm. With a 4x4 truck cam designed for improved torque in the idle - 4500 rpm, would the 1.94's be beneficial? This is a 5,000 lb 4x4 mule!

Sorry to unleash so many questions at once, but I've been doing my homework and it just happened... Comments, corrections or suggestions would be welcomed!

broncr

 

[StrangeRanger]

With your self-imposed rev limits, the 1.94s won't give you much. A mildly ported stock head with stock valves and a 3 angle valve job has its optimum flow velocity around 3000 and remains in the acceptable range to almost 5000. The 1.94s will raise the optimum RPM by about 500 and the peak RPM for decent flow velocities to almost 6000 IF you open up the ports thd the intake manifold to match. Bigger valves give you nothing if you don't open up the rest of the passages to match.

 

[broncr]

StrangeRanger,

Forgive me for failing to give you proper recognition. Those port calc's were based on info you provided in the Nov. thread - thank you.

Am I on track with the numbers this time?

Naturally, I'd go for optimum port size & flow bowl diameter for 1.94's IF I went bigger. I know my rev-limits are restrictive, but I've probably toasted my last fire breather and am now searching for a happy medium.

I'm no stranger to porting, & have a spare head & some time, just not a lot of surplus $$$ right now - thus my line of questioning.

thanks for responding,

broncr

 

[StrangeRanger]

Sounds like you've answered your own question. It's a whole lot of work to do something from which you're not likely to ever derive much benefit. Once you've opened up the bowl diameters and gotten rid of the ridge just above the valve seat, there's not a whole lot that needs to be done to clean the EFI heads up for the stock valves. The water jacket hump in the exhaust port is an insurmountable problem. The air injector bungs do need a lot of work if your head suffers from them.

 

[broncr]

SR

It's an '82 carby head... and yeah, it's really a no brainer. I just wanted to bounce some Q's off the "sounding board" here.

broncr