question about boost compression ect....

[Twister]

Ive been pondering this today and dont know the awnswer so hopeing you guys can help me..


I know that if you have a stock gen3 at 450 rwhp and you add the basic paxton or basic Roe TT your power will go from 450 rwhp to 650 rwhp. Im thinkin g the stock boost on the paxton and TT is 8 psi? Someone please correct me.

So from my reading on here many have said that due to the compression of the engine on gen3's that 700 rwhp at I belieave 9-10 psi is the limit?

So a paxton with the extra trimmings and timing adjustments ect or the ROETT with boost a lil higher.

My question is this. My car is currently 500 rwhp with a few bolt ons and CC cam. Im planning on adding a throttle body and American racing headers as well as letting Greg good Heads port my stock heads and intake. Just shooting for 550 rwhp that is very safe and drivable.

So if I throw on a stock paxton or roeTT at the I belieave stock 8 psi, would I be able to safely drive around at 750 rwhp and a max of 800 rwhp since Im not adding more boost but just started with an extra 100 rwhp over a stocker from my modifications?

Ive been told that the clutch and drivetrain is safe up to 900 rwhp. So mostly just interested in the compression vs boost.

Thanks for any help.

 

[Roysviper]

 

[FLATOUT]

Twister I hate to remind you but you popped it already with stock power. If I were you I would start demodding that thing immediately.

J/K, I don't have any experience with boost on these things (yet) so I don't want to pass on any misinformation.

 

[plumcrazy]

is it a built motor ? forged pistons ? if so, you can up the boost and get 800+ safely with the right combo and tune on a paxton. more with TT

if stock pistons, keep it under 700

your problem is going to be tuning id think. more power = need for precise tuning and your island probably doesnt have much options for that

 

[mbccenter]

I would not run the stock pistons past 650rwhp.

 

[VIPER R]

If in doubt try adding water injection

 

[Red Snake]

I would not run the stock pistons past 650rwhp.

This.


Putting F/I on a Gen III without forged internals is running on borrowed time. Period.

Has it been done? Yes. Can you make it work? Yes. Are you taking a HUGE chance on keeping it safe? ABSOLUTELY.

If you want F/I, forge it.

 

[GONABITE]

Well if you are seriously considering the ROE TT do not buy headers as your stock manifolds is what you will need for the TT kit.
My car puts down 720 HP and 735 TQ with 7.5 lbs boost. I have had no issues in the past year with the car as far as detonation as I believe Sean has a good tune set. I will say that I have an adjustable boost controller that allows me to have 3 levels of boost at either 4.5, 6, or 7.5 lbs. I generally run around on 6 lbs and save the 7.5 for road kills or drag racing. I dont remember off the top of my head the HP for each of the setting I want to say the 6 lbs was around 680 and the 4.5 was around 630 give or take.

 

[Twister]

I feel like Im more confused now...

If your gen 3 power is 550 rwhp with ported stock heads and a mild cam with bolt ons...

Then why is 650 rwhp the max? I mean if your 550 rwhp with those mods then shouldnt just 4 ps1 of boost get you to 650 rwhp? 4 ps1 of boost is next to nothing.

So wouldnt the normal 8 ps1 of boost put you at 750 rwhp but still be putting the same amount of pressure on the internals at half a bar of boost?

At the 450 rwhp stock level my understanding is that 10 psi is whats needed for 700 rwhp and this level of boost is pushing it with the stock internals.

Im talking about a egine already makeing 550 rwhp and then running 7-8 psi for 750 rwhp.

How is 8 psi on a stock 450 rwhp engine for 650 rwhp any less strain on internals than a 550 rwhp ported heads CC cam engine at 8 ps1 and 750 rwhp.

Arent the internals still both seeing exactly the same amount of pressure?

 

[dipapa]

Well for any particular motor from a hp perspective increasing the volume of air going into a cylinder via efficient flow and increasing compression ratio slightly or solely increasing the air pressure into a cylinder via forced induction has the same effect of increasing hp.

If I can recall the appropriate equations, Boyles and Charles laws control the thermodynamics process in a basic sense.

Obviously on a stock viper piston 650hp @ 8psi is gonna be safer than 750hp @ 8psi.

Maintaining a fixed mechanical compression ratio, 650hp @ 8psi boost or 650 hp @ 4psi boost & great flow, if that's even possible, each individual piston is still gonna be exposed to the same force required to make that 650 hp.

So I think no matter how you cut it, at any specific hp your piston is exposed to the same loads. Adjust intake pressures & air flow mass & cylinder volumes are really only ways to get the same results. Viper stock piston is only good for the specified hp many have been quoting... give or take a bit assuming no detonation...which changes everything.

So i think you just have to keep the load on your stock piston maneagable based on the rated strength & fracture toughness of those pistons.

 

[RECOIL]

Could someone PM me the name of a good installer near/around VA? I'd like to get a quote to go forged.

 

[Twister]

Well for any particular motor from a hp perspective increasing the volume of air going into a cylinder via efficient flow and increasing compression ratio slightly or solely increasing the air pressure into a cylinder via forced induction has the same effect of increasing hp.

If I can recall the appropriate equations, Boyles and Charles laws control the thermodynamics process in a basic sense.

Obviously on a stock viper piston 650hp @ 8psi is gonna be safer than 750hp @ 8psi.

Maintaining a fixed mechanical compression ratio, 650hp @ 8psi boost or 650 hp @ 4psi boost & great flow, if that's even possible, each individual piston is still gonna be exposed to the same force required to make that 650 hp.

So I think no matter how you cut it, at any specific hp your piston is exposed to the same loads. Adjust intake pressures & air flow mass & cylinder volumes are really only ways to get the same results. Viper stock piston is only good for the specified hp many have been quoting... give or take a bit assuming no detonation...which changes everything.

So i think you just have to keep the load on your stock piston maneagable based on the rated strength & fracture toughness of those pistons.

Well said. Anyone else with knowledge confirm this?

 

[WillH2010]

The issue with cast pistons is not simply detonation from the tuning aspect, but also cylinder pressure. Depending on the efficiency of the turbo system and the flow characteristics of the turbos, you could run 10psi or 2psi and blow your motor. The fact that your car is running ported heads and a cam, simply means that you can force the cylinder pressure higher with less boost. So where a stock SRT may handle 7PSI without breaking, yours might only take 5 to pop a piston. I recently witnessed a Gen IV car make 900+WHP on 6PSI.

 

[dipapa]

Well said. Anyone else with knowledge confirm this?

I'll keep it real simple for you.

with a 700hp crank motor and 10 cylinders thats 70hp/cylinder.

Hp can be written in terms of force as

Hp = Work/time
Hp = Force*distance/time
Hp = Pressure*Area*distance/time

Area of piston, distance & time (rpm) remain constant.

Therefore

Hp is a function of Pressure at constant rpm

So any way you cut it more hp requires more pressure.

If you want to make power reliably its gonna take stronger parts and allot of labor. No way around it.

 

[Black Moon]

Because IT WILL BREAK! Ask any of the builders and anything over 650 won't work with stock pistons, peroid. Ask Sean, Dan at VSP, Doug Levin what they say don't rely on answers here.

I feel like Im more confused now...

If your gen 3 power is 550 rwhp with ported stock heads and a mild cam with bolt ons...

Then why is 650 rwhp the max? I mean if your 550 rwhp with those mods then shouldnt just 4 ps1 of boost get you to 650 rwhp? 4 ps1 of boost is next to nothing.

So wouldnt the normal 8 ps1 of boost put you at 750 rwhp but still be putting the same amount of pressure on the internals at half a bar of boost?

At the 450 rwhp stock level my understanding is that 10 psi is whats needed for 700 rwhp and this level of boost is pushing it with the stock internals.

Im talking about a egine already makeing 550 rwhp and then running 7-8 psi for 750 rwhp.

How is 8 psi on a stock 450 rwhp engine for 650 rwhp any less strain on internals than a 550 rwhp ported heads CC cam engine at 8 ps1 and 750 rwhp.

Arent the internals still both seeing exactly the same amount of pressure?

 

[FastMatt]

I will let you know soon, I am installing a Paxton on my 2001 Cream puff as we speak. And my motor is a Striker heads/cam car that put 612 hp to the wheels N/A. and it's 11.1 to 1 comp.

Power does not brake pistons detonation does.

Most people want to error on the safe side and pull out these numbers like "cast pistons to only 650rwhp". And thats OK. There is more then one way to skin a cat.



Well my stock bottom end cream puff has put 612 rwhp for about 4 yrs all motor, and for the past yr I have been spraying it with allot of NOS, as high as a 250hp shot. You should of seen the thread on the "other" board when I said I was putting NOS on my heads/cam cream puff, they started posting pics of Nukes going off and telling me how the motor was not going to last a week. Well here it is a yr and at least 30 15# BOTTLES of nos later and it's still going strong. In fact I just did a leak down test on it and it had 2% or LESS leak down on all 10 on my gauge.

A few yrs ago on the Corvette board they were saying the same thing about the LS motor’s cast pistons, now there are so many stock bottom end LS motors making 700+ rwhp at 10+psi of boost you could not count them all if you wanted to. Hell a yr ago they were still saying that about the LS7 “no more then 4psi on the 11.0 to 1 Stock LS-7” But have they been proved wrong on that one, there are tuns of guys now running 8+psi into them now. 10 yrs ago the 3000gt/stealth guys were convinced that the stock cast piston V6 bottom ends would not live at anything more then 450 whp, till I started building car after car that made 600, 700, and even 800 awhp on stock bottom ends. Hell I even ran 9.7@151 mph on a stock cast piston bottom end Dodge stealth. Ever see a piston from a gen 2 stealth? talk about week the top ring is as thick as the top ring land, and 35psi of boost into a 8-1 motor is a effective Compression Ratio is 27 to 1! In 2005 the Lotus guys were convinced that the 3.5L V8 lotus’s cast pistons would never live past 400whp, then I made 511 rwhp with one and 6 yrs later the car is still running. That's with 20psi of NON INTERCOOLED boost going into that Lotus motor.


Would it be safer for me to put some forged pistons in it? YES. But frankly so many people saying it will not work makes me just want to do it on stock pistons more.



“Those who say it can't be done are usually interrupted by others doing it.”


I plan on running about 6-7psi into my 11.1 to 1, stock bottom end Cream Puff, and I expect that will put me over 800 HP to the tires all the time and that’s were I want to be. I am installing a Snow water/**** kit. 7psi of boost into a 11.1 to 1 motor is a effective Comp. Ratio of only 16 to 1.

 

[dipapa]

Some good advice from Roe Racing.

Roe Racing: FAQ

Many good recommendations here to calm down the occasional Yahoo!

Scroll down and pay particular attention to info on using a supercharger on a higher compression engine with factory pistons and the one about having modified heads.

Hey nothing wrong with being a risk taker..its usually a good test.

Let us know how it goes.

 

[Red Snake]

Twister, there are 2 different components to the common failures in the Gen III "cream puff" pistons. First of all, the 650-700 rwhp limit that you see is in reference to the stock piston rods' capabilities. The rods in a 2003 motor were forged (just the rods, not the pistons) and can handle 700 with no problem. The 2004-2006 rods were not forged and that is where the limitations come from. Some have gone well beyond 700 without failure. Some have had failures WELL below 700. I even know of several "stock" or relatively stock Gen III motors that have broken piston rods.

The second failure results from the pistons. All OEM Gen III pistons are cast and by design have a very thin upper ring land area. This makes them prone to detonation failure, not only in FI applications but in N/A applications as well. This is a result of both the "cast" make up AND the thin upper ringland. You could easily pop a Gen III piston (OEM) in a N/A motor with detonation. Look at side profile pics of stock Gen III piston and aftermarket forged pistons and you'll see the differences.

Bottom line for me is that it just wouldn't be worth the risk to add F/I to a Gen III motor without going with forged piston and rods.

 

[Toma]

I didn't read all the posts, so forgive if this has been covered....

Boost does not equal power.... boost that you see in your intake manifold is just an indication of your engines restriction to airflow from the blower.

Say you have a Paxton that normally peaks at 8 psi at 6000 rpm on a stock motors. Start freeing up flow with exhaust, headers, cam, heads etc, and it will not make the same boost. That same pulley combo may only now net you 6 psi.

Now, power WILL go up even though boost will fall, but not necessarily cause the Paxton is flowing more air. It goes for several reason, some of which are: less boost = less heat = denser air charge.
Less restriction = lower losses to "pumping" work (ie, pistons moving air and exhaust, Ie, pumping it in and out.
Blower may end up in a more efficient 'range', so again, less heat, and less power lost to turning the blower.

Now, what fails fragile engines is not Peak HP, forget that notion. It's peak cylinder pressures. Things that increase peak cylinder pressure are increases in VE, increases in boost, increases in compression ratio, increased timing, and increases in heat.

So, in the end, it's not boost that will fail your motor. Its that increase in cylinder pressure, and the motor doesn't KNOW or care if you got that increased cylinder pressure through boost, or better flowing heads/cam, or both.

All things being "close enough", no matter how you reach the cylinder pressure limit of the viper engine, it will fail at around the same point.

Now, things to consider are that any crank driven supercharger will "waste" some of your precious cylinder pressure in order to turn the supercharger. A blower to pump 1000cfm of air, will consume somewhere around 80hp right off the front of your crank.

Not that turbos are "free power". The restriction they pose in the exhaust system results in the pistons doing more "work" to actually "pump" out the increased volume of residual exhaust gases (after the blow down period). BUT, even a system designed by an amateur will generally put more power to the ground than a supercharger moving the same air.

Anyway.... sorry about the novel and direction less blabbering lol.