Talking streeters;
Having experienced a tight-Q 367 engine since 1999, I would never build any other kind,now.
With open chamber heads this becomes rather expensive. It can be done in a couple of different ways, but no matter how you do it, you are stuck with the crevice volume, and a lot of exposed metal in that chamber, none of which contribute to the making of power or fuel economy; and all of which are probably gonna make it detonation prone, at the compression ratios required to optimize any performance cam.
This doesn't mean that you can not build a 340 with pop-ups and open chamber heads. It just means careful planning and a lot of machining. If you can find a machine-shop that can do the job right .... the first time...... then it becomes doable.
In my case tho,not one out of three shops could get it right, and all three were big-name shops out here. So I am done with multiple machinings. I would sooner pay triple for the proper pistons to make the tight-Q happen, than take a chance again on machining.
To that end also,I would not use an open chamber head .
The thing is, this can get expensive, what with new closed chamber heads and custom pistons. These costs are offset somewhat by not having the machining costs, but it's still gonna cost more.
One of the payoffs is more flexibility in camshaft selection. If you engineer it right, you can have the compression ratio adjustable by the headgasket thickness, and still be operating within the tight-Q effective range. So if you don't pick the right cam the first time, you can go up or down one cam size..... and not have to tear the whole engine down again to optimize it. That gives you about a 3 cam range which is just doable.
If you built with open chamber heads,
firstly; it's gonna be pricey to get into the Tight-Q zone, and you're not gonna want to destroy that with a thicker gasket.
and secondly;You can still install a bigger cam,but you will lose some bottom end. And perhaps that will cost you a new TC or more rear gear, neither of which are particularly street-friendly
Do you have to have tight-Q? NO! But if you are already spending $3500 or $4000 on a performance build,another $1000 will make it a real ripper ........ without putting bandaids on it, that make it less street friendly.
If the bottom end is already bought and paid for, and open chamber heads are now more or less mandatory, Then the trick is to stay away from the Q's detonation prone zone of .050 to .080.... Which with factory big-port heads is pretty easy,lol. You end up with a little less compression than you mightta hoped for; so then you just have to work around that with the ICA, or the bandaids of stall and gear.... and then an overdrive becomes a big attraction.
So then;having Tight-Q is not a deal-breaker. I'm just never going back there.
Having an SBM WITH tight-Q, that spins 295s to 60 plus mph with 3.23s and a 223 cam.......trapped easy at 106, and made mileage in the high 20s USg with an overdrive,
kinda spoiled me.
