Not to start and argument about big cubes versus more boost but....

You can just add more boost to a smaller displacement motor and get more HP out of it. Well that may be true to some extent. However my guess is that with a larger set of Turbos and a large displacement engine you can run a relative low boost solution (10lbs or so) and still achieve say 800RWHP without breaking a sweat. What's nice is that the risk of lifting the head on our poor LS1 motors is mush less at that point.

My new setup will be a 406CI motor with some pretty good size Twin Turbos.

Who here plans on holding the heads on at high boost? Say 20PSI? Harlan what boost are you looking for? With the new notched PA K-members I can put some pretty good size Turbos in there with custom headers.

Thoughts on the subject?

 

I was running my stock 346 at 10 PSI and made 486 RWHP and ran 10.98 @ 126 MPH.

I am moving up to 422 CID, try to run about 6, 7 or 8 PSI and expect to make mid-600's or maybe even touch the 700's. <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> AND, the motor will be built more conservatively than what an NA motor might be built at.

Safer build, safer boost. Hoping for performance AND longevity.

I agree... there is STILL no replacement for displacement.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">What's nice is that the risk of lifting the head on our poor LS1 motors is mush less at that point. </font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Can you please explain why?

 

Just because a few guys had head lifting problems doesn't make it a weak spot for everybody.There are so many issues here you can't possibly say this could be an issue for everybody!
For instance Turbos run a hell of a lot of exhaust backpressure which makes lifting the head more of an issue than a supercharged combo.
You will need to run more cylinder pressure with a smaller cube motor to equal a larger cube motor.
No argument there.

But at 800hp there won't be a tremendous difference in cylinder pressure in a 406 or a 346.
60 cubes is not much.To take a 346 and make it "act" like a 406 takes only about 3psi boost. Once you begin to boost the larger motor it takes more and more boost for the smaller motor to be the equal.
A 7psi boosted 422 will "act" like it has 620 cubes of cylinder fill.
A 346 would need around 11.5psi to equal the 7psi 422 in cylinder fill.
This is just theory and parasitic loss, cylinder head flow and cam events, tuning, compression, could make or break either combo.

Since we have guys with well thought out N.A. cars running 9's with a hell of a lot less power, I hope some of you aren't just creating big heavy dyno queens <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

Steve

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by SJH:
<strong>For instance Turbos run a hell of a lot of exhaust backpressure which makes lifting the head more of an issue than a supercharged combo.
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Care to explain that one??

it's cylinder pressure that causes problems, if that's from power output, excess boost, detonation, it doesn't matter.

15 psig is the initial plan <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by JAS:
<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">What's nice is that the risk of lifting the head on our poor LS1 motors is mush less at that point. </font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Can you please explain why?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Well I agree that there's a very complex theory here about what is actually causing heads to lift. I've personally learned from a few GN guys as to the tricks of keeping the heads on. Now as to why heads lift is up for grabs. However it seems that the higher boosted cars tend to lift heads. Now why is that? Well there's a lot of explanations that I've seen from people on the subject. Higher boost means higher cylinder pressures AND potentially higher heat values. This combination of heat and forced air add to the potential for detonation. Detonation (even slight) can deform or break the seal between the head and the block. Now is it strictly detonation that can cause this? I don't know for sure. At some point there will be enough pressure in the cylinders to overcome the clamping potential of the bolts that surround the cylinder through the head. Or even deform the head itself. However GN guys have a similar head design and can clamp some 50PSI (don't know for how long).

So in short the reason I believe that lower boost and a larger bore is better is due to the lower potential heat and lower effective compression ratio when the cylinder is filled.

As far as heavy dyno queens is concerned I do believe that the Lingenfelter Corvette which runs low 9's (fastest forced induction LS1) is a rather large bore. Not sure how much boost the guy was running but some jamoke at Lingenfelter decided it would be a nice thing to have on the car for all out drag performance.

If you have your own theories then I'd like to hear them.

 

I think it depends on how much POWER you want.. You could safely run 10 to 12psi on a forged 346ci and dyno 600rwhp plus if you have the right setup.. It has already been proven that you do not need a whole lot of boost. MMS did a 346ci with a vortech with 8psi and dyno'd 597rwhp.. This was Golddiggers old setup.. As far as I know the stock shortblock is still running, but Golddigger got frustrated with breaking drivetrain and other things.. I personally would be happy with 550rwhp for street use.. My new forged 346ci shortblock will see no more than 12 psi.. I think I could run that safely with a compression of 9.5:1 or less..

 

What some of you people didn't mention was turbo/blower SIZE

yes with a similar turbo/blower a larger cubic inch motor *should* make more power due to the larger inches

But you can easily make more power with a larger blower/turbo on smaller inches and still get away with it....

me personally, i'm going to have a little 355 with iron junk heads, no intercooler and some boost. we'll see how fast my POS old school SBC goes in a mid weight thirdgen

Larger bores are nice in boosted applications, but it also gives you a lot more surface room on the piston to detonate. That is what people have told me

 

I agree a bigger blower/turbo would work best with smaller cubes.. Plus with the bigger blower/turbo you will be running less boost and produce more power.. I believe if you run 10psi with a bigger blower/turbo you would make a lot more power if you were running the same boost with a smaller blower/turbo...

 

y2khawk,
Exhaust back pressure not only keeps the heads in a longer pressure situation it also and probably more importantly retains heat and a lot of it in the heads which can lead to detonation.
I am not knocking a turbos induction method as I will admit is more effective in making HP than a belt driven supercharger, even with the exhaust backpressure. The losses from exhaust backpressure with a turbo are not as great as the power required to drive a blower. But they do have some consequences that may or may not complicate matters and I think the tuner can run into trouble faster.
With a head that may have marginal clamping force, this may be an issue when really pushing things or it may not. But it certainly won't help.
Heavily sprayed nitrous motors which do not have adequate exhaust removal have even been known to BREAK the rocker arms on the exhaust side and lifting of the heads is a side effect.

Heck, more boost actually can HELP parasitic loss in the motor on the intake stroke by pushing down on the piston with boost pressure.
We can argue over theorys but the guy who really knows his shiznit and can actually read a sparkplug will come out on top regardless of a few cubic inches in the forced induction arena.
Of course all IMO <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />
Steve

<small>[ June 11, 2002, 09:36 PM: Message edited by: SJH ]</small>

 

Well now on all race applications I've seen bores with 4.5" bores I believe. They found that to be the point of diminishing returns. I believe this was due to flame propogation issues. What I'm talking about is a 4.02 inch bore not a huge bore.

What size bore is optimal then? If 4.02 is too big or too much for FI then what size makes the math work?

 

4.02" bore is certainly not to big.
Sometimes what we think will happen and what actually happens are two different things.
But sometimes there is a pattern also to be found <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

There are a lot of other things to consider for a reliable forced inducted engine besides all this.
Ring gap,valve seat width,plug heat range, coolant temps, charge temps, octane etc etc etc.

<small>[ June 11, 2002, 10:43 PM: Message edited by: SJH ]</small>

 

The biggest thing I was driving at here was detonation issues. It seems that most that post about lifting heads seem to underestimate their fueling needs and have some sort of detonation problems that make short order of pistons, head gaskets, etc.

A few things to consider that don't help the situation when you go larger CI

- smaller cylinders reach their detonation limit at a higher compression ratio than larger ones (who are all those 422 guys trying to run 12:1 on pump gas? <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> )

- RPM, larger cylinders reach their piston speed and acceleration limits sooner ( I know none of you FI guys would run 12:1 and buzz that big cube motor to 8,000RPM. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> )

- other things to consider are the thermo charaterists of the large bore motors and coolant velocities to disapate heat, especially under FI

- guys have problems with resleeved blocks running N/A, what effects will FI have?

- emmisions... ( I know, I know, haha had to mention it. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> )

I'm sure there are a million other things I forgot.

I'm eagerly awaiting all your guys awesome torque monster results! I'll admit, it would cool to have a 4xx blown motor, but the $$$ involved... I'll pass. For now, I'll stick to a stock sized forged piston, stock compression, stock timing, a little more fuel <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" /> , and a lowely P-1SC-H with a few anti detonation measures and see how she does. By that time, you guys will all have your results in and we can all drool over cubes. <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

 

Opps... forgot one

- gobs of torque that are going to break parts all the time. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by chasgiv3:
<strong>My new setup will be a 406CI motor with some pretty good size Twin Turbos.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Do you have the GTBB35's or GTBB37's right now?

 

I am personally saving my money and running the forged 346ci.. By the time one of the big motor guys catch up to me on the street the race will be over.. Can you so less traction than me.. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

 

I think some simple points are being missed here.

346 CID at 10 PSI at 6400 RPMs ~ 490 RWHP

422 CID at 4 PSI at 5500 RPMs ~ 550 RWHP

This was one of the initial tests. Does anybody see a difference here that's obvious to me. <img border="0" title="" alt="[Roll Eyes]" src="images/icons/rolleyes.gif" />

Convince yourself that less cubes is more powerful if you must try to justify staying with less cubes. But, don't try to sell it to guys that are taking that step up.

Oh... and the 422 revving only to 5500 was because of then unresolved belt slippage issues and inadequate injectors.

It's not like the old days when 4xx Big Blocks would only rev to 4800 RPMs without special fixes. Today's lightweight rotating assemblies will rack up nearly as many RPMs as any small block solution. Some of these pistons and cranks are lighter than your stock assemblies and will not break a sweat revving way above 6 grand.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by VINCE:
<strong>I am personally saving my money and running the forged 346ci.. By the time one of the big motor guys catch up to me on the street the race will be over.. Can you so less traction than me.. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif"><img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> Vince, I know how to baby it off the line and lean my foot into it to let motor do the rest. <img border="0" title="" alt="[Razz]" src="gr_tounge.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by chasgiv3:
Not to start and argument about big cubes versus more boost but....
</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Happy now? <img border="0" alt="[fight]" title="" src="graemlins/gr_punch.gif" /> <img border="0" title="" alt="[Razz]" src="gr_tounge.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by JAS:
<strong>Opps... forgot one

- gobs of torque that are going to break parts all the time. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Now, THAT could be a problem! <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />