i agree with that...The air will be forced regardless...no since in wasting the doe on P&P head work when you really won't notice the benefit under boost. Invest the money into water meth injection and dyno tuning with a VERY qualified tuner...In our area, i know of 2 i would trust. One is a GM guy and the other is a Ford guy, but tuning is tuning when you have lap top capabilites and piggy back split second electronics that you will have with the S/C from GSM.

 

Porting will help with s/c applications, especially on the exhaust side. Headers and a good cat-back should be on the list as well, if you don't already have them. If you're forcing that much more mixture into the engine, you need the exhaust side to be up to par or you will not realize all the possible gains from your (very expensive) s/c. You will get impressive gains from the s/c alone, but why just go halfway? Think of it like this: S/C = "X" amount of HP. Head porting = "Y" amount of HP. X+Y="XY" amount of HP, AND "Z" amount of HP. The "Z" is the HP you realize from the two working together, and is in addition to the HP you would get from the s/c alone, or the head porting alone. Hope that makes sense.

 

I agree.

 

I see the headers, high flows and cat back being benificial, especialy for lower EGT's and under hood temps...but the increase in hp from P&P heads on a S/C application would be small, especially for the money...and once you reach the hp numbers S/C will attain, adding another 20 (maybe) from P&P heads wouldn't even be realized.... if you want more power, spend the money towards a forged bottom end increase the boost with a smaller pulley and tune for it...this topic is like many others, it's subject to opinions. It's your money, do w/e you want with it...I don't think by not P&P you're doing it half ass by any means.

 

I would have to see airflow #s from stock heads to be sure, then compare to P+P heads. Most of the factory heads I've seen are not real great on their airflow, so the gains from porting with a s/c app/P+P would probably be greater than 20 HP. If the heads are good from the factory (ala Chevy LS6), then the gains from P+P will be less. It's a case of diminishing returns, you've gotta spend the $ on bad heads, but is it really worth it on good heads? The initial gains I'm seeing with a P+P on the hemi heads makes me believe they may not be that great from the factory, so I would think a P+P with the s/c would make sense. The forged bottom end would be mandatory with a high boost app, I would also assume the stock pistons are cast/hyperutectic, not forged, so I would not excede 6psi in any case with the stock internals. What is the compression ratio on the 5.7? You might get into trouble there too, if the ratio is too high. As Dookie says, it's gotta be tuned right, or expect a lot of fun (for a very short time) then.....KABOOM!!! Time for a rebuild. Trust me, been there, done that.

 

Hello LAsrt8,

I think with any forced induction or nitrous application, you will want to strengthen up the weak points. In those casses the weak points are going to be stock components. Since the Heads are the easiest upgrade to do they are the logical first step. If the springs become weakened over time from repeated, and frequent WOT's, then there is a chance of valve walking which can cause the valve to be in the wrong place when the piston compresses the chamber. If this happens enough there is a good chance the valve will break and drop into the piston chamber then when the piston compresses again, bye, bye. There are a lot of things that can happen with forced induction. But essentially it is a good idea to look into the upgrade options. I would be happy to provide you with any additional information that may help with your evaluation process.

Please contact me at (859) 816-1824.

Best Regards,

Jeremy Steinman

 

ok what about the intake should i upgrade that. guess i will wait for a head and cam package to come out before i install them thanks for all the help

 

I assume with your screen name you have the SRT8. Since it has an aluminum intake you could extrude hone the intake and also port match it to the heads. I base that advice on past experience with other engines. You should check with pros for specifics, I have no experience with the 6.1 motor. There are at least two vendors here on the board that can P+P the heads and intake, and guide you down the right path with cam choices.

 

On GM LS1 or LS6 motors, FI guys usually say that the intake itself is NOT that helpful... plenty of big power guys using the good ol' stock LS6 intake.

Valvetrain upgrading is a very good idea, but that doesn't mean you've got to pony up all the $$ for shiny new heads. Will better flowing heads help? Sure. Are they worth the cost? Maybe. IMO, you'd be better off using that cash to install forged internals (especially dished pistons/rings). One important factor to consider for FI is what compression you plan on running; you may need different heads to attain that number.

I had to do that for my turbo LS6, and I went with AFR 225's 72 cc. If you can afford it, I don't think there's a downside to high-flowing heads... especially those that flow better PRIOR to peak lift, etc.

 

Going P&P heads and intake with the cat back. The SRT comes with shorties.

Heads and Intake = @ 50rwhp
SC = @ 120 rwhp
Lookin @ 525rwhp w/ combo

 

Money better spent would be on quality rods and pistons then you can up the boost. never trust oem pistons, rods, or valve springs for any real performance

 

If I had read about a bunch of guys grenading motors I would be all about adding to the bottom end of the motor. Running low boost (under 6-8lbs) and changing pistons and rods to compensate for the increase strain may be going overboard, IMO. A motor is an air pump, so the faster and more efficient you get air in and out, the more HP you make. I am sure you know this. Head work will only add to your HP since it makes the motor flow better. Heads are where you make power. PERIOD. If your forking over 5k for a blower whats another 2k for a solid vavletrain and good flow?

 

So, Heads before SC?

 

I would get the heads/ valvetrain in order first if it were my car. You are more likely to float a valve than tear up the internals, and if you float a valve, you are tearing up internals. How much boost is another big question. Mustangs can handle 10-12 lbs before you have any issues other than fuel and with an intercooler I have seen cars running 15-16 lbs on stock bottom ends. I am pretty sure the motor in a charger is that strong. I haven't heard of anyone slinging rods or blowing head gaskets on chargers, but that could be due to the limited number of people who have built cars.(meaning more than exhuast and a CAI:grin: ) I am basing all of this on genral motor knowledge, not charger specific so if I am wrong about anything, please let me know.

 

With out going deep into this and spending hrs typing trying to explain I'll give the short and sweet of it.

I have ALOT of experience with F/I, in short the gains from ported heads on a F/I motor can be much larger then on a N/A motor here is why.

Lets say you have a 340hp motor that you are going to run 14.7 psi of boost (2 bar absolute pressure) into. There is more to it, but in a perfect world this would turn that 340 HP (at 1 bar absolute pressure) into a 680hp at 14.7 psi of boost (2 bar absolute pressure) motor.

So now lets say you take that same motor and put ported heads on it and now it's lets say a 380 hp 1 bar motor (0psi) and you run 14.7psi into it now you have a 760hp 2 bar (14.7psi motor).

So by gaining 40hp with the ported heads when not on the boost you now gained 80hp on 14.7psi of boost boost. (or 60hp at 7.35psi of boost and so on)

Now there are other things that fall into that, like compressor efficiency, intercooler efficiency, exhaust restrictions ect but in a nut shell that’s how it works.

Now with a turbo VS a blower there are more things that fall into that.

Adding ported heads to a turbo car that has waist gates that control boost the turbos will simply spin faster to maintain boost and you will see the gains as long as the turbos are not already maxed out.

On a blower car adding ported heads that flow better and not changing the blower pulley to add back the boost will mean you will have a lower boost pressure so the gains will not be so pronounced. So you add a smaller blower pulley and now you are making much more power at the same boost.

But I always say I would like to make as much power as I can at as low of a boost # as I can. Boost is nothing but back pressure, moving the air threw the motor is what makes power not boost #'s.



That is truly as simple and strait forward as I can make it

 

But I always say I would like to make as much power as I can at as low of a boost # as I can. Boost is nothing but back pressure, moving the air threw the motor is what makes power not boost #'s.

I'm a turbo/SC newb, so let me see if I understand how this works...

• More power comes from moving greater air mass through the engine.
• Air mass is proportional to volume x pressure.
• Assuming we don't bore or stroke the cylinders, volume isn't changing.
• So power comes from getting higher pressure air in the cylinder (pre-compression stroke)
• Ported and polished heads reduce pressure drop between the intake and cylinder, leading to higher pressure in the cylinder (pre-compression of course)
• Same story with higher flow intake and filter.
• Turbo/SC forces higher pressure air down the intake. Boost PSI is measured at the turbo side, rather than in the cylinder, so there's still a pressure drop across the heads.
• And of course air temp plays in too, since PV=NRT if I remember my physics right. Cooler air means heavier air, all else equal.

That makes sense to me I guess. So a normally aspirated engine works to suck air at roughly atmospheric pressure through the filter/intake/heads into the cylinder. What kind of pressure drop do we normally see through that path? At the bottom of the intake stroke, what kind of pressure is the air in the cylinder normally at?

And does the pressure drop across the heads change when we put the turbo on? In other words, if normally aspirated we lose say 4 psi across them, when we switch to the 14.7psi boost in your exmple is that still a 4psi drop, or does it go to 8psi? Your HP example suggests it goes to 8, I think. I suppose that makes sense, since it's probably a percentage pressure drop we see across the heads, rather than a specific magnitude, and the percentage stays about the same regardless of the pressure differential across it.

I'm sure it's all a lot more complicated than that, with wave effects and other fun stuff happening at different RPMs too.

 

Boost over 6psi will degrade the piston on the upper ring land in a short period of time the pistons are not designed for boost. That’s why most shops selling superchargers or turbos limit them to 6 psi. If you install good pistons you can run much higher boost pressure 8-10psi.Thats why they offer their kits to be upgradeable. Upgrading is much cheaper than a good set of heads. Heads will make more power! But do you trust a stock production connecting rod a 500hp? I don’t!! If you’re willing to tear down your motor install good pistons & rods. If a budget is not an issue do both. But remember 8 psi will put you over 500rwhp with stock heads. I would hate to put on a 6000 dollar supercharger on then add 2500 heads just to blow a rod out the side of the block or blow a hole in the piston. Just my opinion

 

8psi on a STOCK 5.7L Hemi will put you over 500 RWHP? I have talked to quite a few guys here lately out in the real world running 6psi SC kits from a company we all know, that are not even getting 350 rwhp. (most of it having to do with Extremely rich A/F, and I totally understand why thy send the programming out that way in a "canned" tune, rich is safe, and the end user and lean it out.)


Edit

I just clipped this off of GS motorsports web page, and thy have a very nice SC kit for these cars... "6lb kit on a stock Hemi motor produces:389rwhp" 2 more PSI of boost is not going to give another 111hp.

 

he is talking about the 6.1 not the 5.7

 

Quote from GSM for the 6.1 SC

6lb kit on a stock 6.1L Hemi motor produces:
500 rear wheel hospower & 507 rear wheel torque

Quote from GSM for the 5.7 SC

6lb kit on a stock Hemi motor produces:
389rwhp = 123rwhp added (47% increase)
387rwtq = 97rwtq added (35% increase)

These dyno charts are for a stock motor. Just keep in mind about valve trains floating under pressure. That's why a good head job is in order before adding any boast....JMO

 

NOPE...porting and polishing allows better pressurised flow which produces more flow with less pressure which means cooler air.

 

And yet again I am impressed by the knowledge of our members!

 

Vindes, you confused the hell out of me and I understand how it all works!

 

Thanks guys for the information as I am considering the forged 6.1L motor from GSM. I will also run the P&P kit and the S/C. The only question that I have is what cam should I run? Now only if I can get a really good tune!!!!

 

get a custom ground cam.

 

So then I should call Comp when the motor is at the machine shop so that I can get the exact numbers for them. This shold be a combo that Comp has seen before right?

 

Im not sure if they have seen that combo before but cam selection is pretty much the same on any motor. All the variables i pointed out above is what determines your cam specs.

 

Thanks for the info. Really need the project to go smooth. I am really hopen to get close to 600rwhp. Its probibly all in the tune?...Kevin

 

With FI its always in the tune. A bad tune will kill even the toughest parts.