Che70velle

iTrader: (6)

They will fit a 4” bore with offset dowels. I’ve got it mocked up in my shop right now. Is it a good idea? No. Will it fit? Yes. But just because you can doesn’t mean you should.

G Atsma

Wouldn't that tight a fit cause MASSIVE valve shrouding issues?

Corona

from to many Professional Porters exhaust works itself out..you move the dowels when your just wanting to cut cost/quicker, as the Exhaust valve needs moving or being shrunk..Elimination of Shrounding? As moving the heads with moving the dowels moves the Intake towards what?. Aka look at TSP small bore ls7 heads using a 1.59 exhaust valve for a minimum bore of .065

If going this route you either have a free set of heads to move the dowels or buy a as cast head to replace the exhaust seats without the Bowls or Throat being did.

Che70velle

iTrader: (6)

The LS7 intake valve is massively offset in the chamber to begin with. There’s a lot of room on he intake side. It’s the exhaust valve that’s the problem. It’s pushed waaaay over in the LS7 design to make room for that big intake valve. Offset dowels in this situation will move the exhaust valve away from the wall .030 to .050…depending on which offset dowel you buy. The .030 dowel gives you about .018” between the exhaust valve and the cylinder. It’s tight but it fits. The .050 dowel will net you about .038” clearance. Again, we are talking exhaust side here, and as Andre mentioned, the exhaust side really doesn’t matter that much in the big picture. Cam it correctly and the exhaust side works itself out.
Sure a bigger cylinder helps everything always. I’ll never say that anyone should put a set of LS7 heads on a 4” bore, but if someone wanted to “just because” it can be made to work with minimal effort. I’d venture to guess that a set of LS3 heads with offset dowels again to unshroud the INTAKE valve, as I’ve done in the past with terrific results, would yield more useable power across the board on a 4” bore than the cobbled up LS7 head setup. It’s just too tight.

G Atsma

Thank you, Andre and Scott for very thorough explanations.
I keep learning...

01CamaroSSTx

iTrader: (3)

Yes it's nice having some more insight on the subject. Are we saying the higher runner LS7 heads will not make more power and torque than LS3's on a 4.03 or smaller bore? I was curios if there was anything to gain by switching to LS7 heads and intake. The intakes are reasonable to come by for now and if I were to make the switch I'd probably go with aftermarket small bore LS7's anyway before ponying up $1000 for a set of stock LS7's.

Che70velle

iTrader: (6)

I’m speculating only. I’m my opinion, you’d end up having to cam it in a very unusual fashion to optimize the heads on a 4” bore, and I still don’t think they would outperform a set of LS3’s, for average power. I could be wrong, wouldn’t be the first time. The LS7’s are designed to work on a 4.125” or larger bore, and we both know cubic inches helps every aspect of performance. I should get to working on the build in the shop more diligently. It would be a cool experiment to gather data from, and I love data.

Corona

The most Basic illustration was the Ls3 head test, the Mast 12 degree valve angle vs the factory 15 degree showed more than a 40hp difference.

Stop. Ls7 vs Ls7 was way closer like Brodix 275,TSP 285 and 265 were 10 to 15 hp off from MAST. Scroggins with a Factory ported head showed a 8hp difference from MAST with 810 fwhp.


Valve angle with a higher runner FTW. If you've got a 12 degree ls3 head No reason to Switch.👍

Corona

Factory style Ls3 vs Factory style Ls7 on a smaller Bore?

Ls7 all Day Everyday twice on Sunday.
Smaller runner 1st off and better Valve angle. No Brainer. Having done Both.
Shrinking the exhaust valve isn't major with a unported as cast head. If a guy has a real porter it's nothing Major.

Corona

You'll see this trend if using ls3 heads with smaller CID. Everytime I see a decent build the runner is being filled