96capricemgr

iTrader: (1)

If you took an engine added 8% displacement, 20% more head flow with larger valves, .2 more compression, and a larger TB (15% larger diameter).

How much more HP percentage wise do you think the new engine would make with the same cam and would it be everywhere or vary across the curve?

HCI2000SS

iTrader: (2)

I have no clue, but that's a interesting question for sure

redtan

iTrader: (5)

17.849% more HP.

A.R. Shale Targa

iTrader: (2)

Are we talking production GM....bone stock....A to B....?.....
I'll guess 7%

NAVYBLUE210

SWAG ~12% Hopefully!
Lots of variables and
Unknowns. Care to share
Any more Specifics?

DavidBoren

First and foremost, is the redline of both the same?

I think that the extra displacement and the added compression are going to "eat up" a bunch of that cam, making it seem tiny for the displacement it's trying to feed.

But it's hard to under-cam an engine, and the additional head flow/bigger throttle body would match the additional inhale of the larger displacement.

I wager a full 10+% increase in power, under the following conditions:
A) the cam was a decent size for the original displacement, and
B) the redline remains the same.

Your hypocritical inquiry almost exactly represents the difference between the ls6 and ls3... ~8% difference in displacement, .2 compression difference, ~15% difference in tb diameter... And all this equates to a ~8% increase in power but with entirely different head designs, so that particular comparison is fruitless and irrelevant.

A.R. Shale Targa

iTrader: (2)

Hardly irrelevant really if you're wondering why GM put such a large runner head on a 6.2 liter engine trying to make average torque throughout
The OP does own a 2015 SS and has very close ties to Phil @ AI so I'm a bit curious where he's going with this loaded question.....Dwayne ????

speedtigger

iTrader: (16)

Not specific enough. Spill all the details and lets do this right.

DavidBoren

I'm saying that this hypothetical situation shouldn't be comparing the ls6 to the ls3, due to their differing head designs. It's not a fair comparison between those two engines, because we will never know if the head design change, alone, would have netted the same power increase without all the other changes. Being as how, to my knowledge, GM never developed a rectangle port head for the ls6.

The only way this discussion of comparison is relevant is if the designs are similar enough to actually compare.

Any cathedral port to rectangle port comparison is apples to oranges.

But, yes, please spill the details. What, exactly, are we hypothetically comparing?

96capricemgr

iTrader: (1)

David, so the comparison isn't stacking up the way benchracing says it should so it is inherently invalid? Not even worth discussing?

What if we compare the L77 and LQ9 same displacement so one less variable?

Far as A.R. Shale Targa's comment about Phil at AI, I haven't so much as exchanged an email with him much less spoken to him in years and my SS is not getting warranty compromising mods for some time, so NOTHING going on there..

A.R. Shale Targa

iTrader: (2)

96capricemgr

iTrader: (1)

http://www.hotrod.com/how-to/engine/...re-port-heads/
On a 408 317 heads with less compression and a rectangle port cam were down 38hp peak from LS3s but were a lot better below 4000rpm.

Here is a quote from Brian Tooley pulled from yellow bullet, I have seen this here but haven't been able to find it again.

Magazine dyno tests are good because they spend money on testing many of us want to see BUT they also do it with an angle often trying to sell stuff for vendors so they rig the tests, like not balancing compression and picking a cam to favor one design over the other. Other times I have seen them test a MAF and change the airfilter from old and dirty to fresh, or optimize timing on one set of heads and not revisit it for the other sets.

Would love to see that test with 243s......

Tuskyz28

Well I went into my scrapbook and decided to do a test with a 243 head 408ci. Motor was given away but it was dyno tested by Richard Holderner before it left westech.
Here is the link..... I know you been waiting on Tusky to chime in anyway

http://onthedyno.com/GM-LS-motor/grand-prize-giveaway-600-hp-408-ls-stroker/

RixTrix

Changing more than one thing at a time is a violation! This will be noted in your permanent record! :^)

Tuskyz28

The cam tested with with the 317, AFR, and LS3 head was a 239/255 duration..
The test I linked to with the 243 heads the cam specs are 239/247 duration....
can't get much closer than that.
Even the first test where they tested 3 different heads those cam specs are really aimed towards a rectangular port headed motor... notice the wide duration split which rectangular port heads respond well to those type of grinds.

A.R. Shale Targa

iTrader: (2)

Milling a 317 head to 243 chamber size is kinda unfair as it hurts the flow.
Welding up the chamber the way Phil (A.I.) does will also add a variable as would a domed piston in order to keep the static compression similar.
The smaller CC combustion chambers ALWAYS reduce the BSFC numbers, however the trade off is shrouded flow depending on valve size and shape given the particular architecture.
NASCAR **** has been using 30-35 cc chambered stuff for years and will even run a dished piston in order to not exceed the compression ratio limit.
SBF stuff in heavy NOS applications sometimes run 0-6 degrees of total timing lead because the flame front is just so quick and fast/efficient

96capricemgr

iTrader: (1)

When the chambers are welded then run with the same CNC profile how is that a variable?

I will say flow is a factor in the milling difference but with 20tq across the board probably not the primary factor. Has someone published a solid figure on what they see for flow reduction milling 317s?

1989GTA

Regarding the displacement I think you would gain more HP with boring versus stroking. With stroking you might not gain anything. Adding .2 compression will add a little but not a whole lot. Now adding more air flow because of the heads should add power but that depends on other things like the exhaust and if anything else in the total air tract is close to being maxed out. I would not put the gain very high, maybe less than 5%. However as stated we need to know the total package for a better definition.

Tuskyz28

Caprice... I spoke with Brian Tooley the other day. He simply told me the chambers in the 243/799 head is a different shape from the 317 and this is why the 243/799 head makes more power even if the 317 head is milled down to the same cc as 243 head.

96capricemgr

iTrader: (1)

Thought everyone already figured out this is a LS6 vs. LS3, same stroke, more bore, the peak numbers for each are taken from Vettes with dual mode exhaust.