Roe s/c: 5psi w/ported heads vs 7 psi w/unported heads

[FE 065]

The thought just struck me, concerning creampuffs (CPs) more than non..


If CPs can run 5psi with ported heads safely, couldn't you run a 7psi pulley with un-ported heads on a CP and be okay?


What's the horsepower difference between 5psi/ported and 7psi/not ported, if any? - The horsepower reflecting the pressures in the cylinders, all other mods being equal.


Ported heads yield up to 60hp, and I don't think a 7psi pulley alone adds more than that does it?


Sean, or Larry Macedo.. any data for comparison?

 

[Joseph Dell]

Actually, I think (and I'm not the expert, but I think) that you have it 100% backwards. the SC generates pressure in the manifold... and if you have ported heads, the 5lb pulley won't actually yield 5 lb of pressure b/c the heads are flowing better. In this case, you could take ported heads and use a 7lb pulley... what would you see on your gauge? probably 5 lbs...

Which has more power... a 5lb pulley showing only 3 lbs on ported heads OR a 5lb pulley on stock heads showing 5lbs? That would be the ported heads with less boost! This is why more boost doesn't always = more power.

Now 7lb on an unported head vs 5 on a ported head might be close...

JD

 

[FE 065]

..Now 7lb on an unported head vs 5 on a ported head might be close...

JD

I think they are close, and if so, aren't the CP pistons/ring lands under a similar load in both situations?


If a 5psi/ported engine and a 7psi unported engine are both at let's say... 650hp?

A pulley's cheaper than ported heads... but the real question is: Are the CP pistons (more) at risk with a 5psi pulley and ported heads?

 

[Joseph Dell]

Actually, the load on the pistons and rings is based on the pressure in the cyl and _not_ on the rated pulley. So the pressure in the cyl in the ported heads situation where you have a 7lb pulley but only see 5lb of pressure in the manifold is EXACTLY the same as the situation with stock heads and a 5lb pulley where you see 5lb of pressure in the manifold.

Risk - same. I'd run a 7psi pulley on ported heads on a CP... if I had one.

JD

 

[FE 065]

Actually, the load on the pistons and rings is based on the pressure in the cyl and _not_ on the rated pulley. So the pressure in the cyl in the ported heads situation where you have a 7lb pulley but only see 5lb of pressure in the manifold is EXACTLY the same as the situation with stock heads and a 5lb pulley where you see 5lb of pressure in the manifold.Risk - same. I'd run a 7psi pulley on ported heads on a CP... if I had one. JD

Actually, I think I've been pointing to cylinder pressures all along.


How about a 7psi pulley and no ported heads? Saving about $4000?

 

[2002_Viper_GTS_ACR]

I wouldnt give up on the ported heads so quickly. I have a feeling, you will make more power with ported heads and lower boost pressure, then stock heads and higher boost pressure. Also, since you have a creme puff motor, why not get the heads ported and dont shave the heads when its done, so you can have lower compression heads (say 8.9 to 1, vs stock 9.6 to 1). This will actually allow you to run more boost, and less likely to detonate. Remember, cp are only bad when you detonate. If you control detonation, then CP will work just fine. Forged pistons just give you a "safety" marging if you do have temporary detotation. But even forged pistons cant/wont last long under continued detonation.

Jon

 

[RedGTS]

Actually, the load on the pistons and rings is based on the pressure in the cyl and _not_ on the rated pulley. So the pressure in the cyl in the ported heads situation where you have a 7lb pulley but only see 5lb of pressure in the manifold is EXACTLY the same as the situation with stock heads and a 5lb pulley where you see 5lb of pressure in the manifold.

Risk - same. I'd run a 7psi pulley on ported heads on a CP... if I had one.

JD

You're confusing the pressure of the intake air with the pressure in the cylinder at combustion, which are two very different things. The intake air charge may be 5-7 psi, but cylinder pressure is measured in hundreds of psi. I think many cars these days have cylinder pressures of around 1,000 psi in stock form. Lots of things besides the pressure of the air charge (really the heat resulting from the pressure) affect cylinder pressures, such as compression ratio, timing advance, etc. Otherwise a radical 600 rwhp n/a engine would have the same cylinder pressures as a stock engine. Lots of us creampuff guys wish that were true!

FWIW, Sean thinks you could run 5-6 psi on a creampuff with ported heads safely. That setup with a cam should produce in the upper 600's at the wheels. Once the intercooler comes out, I think we'll start to see some Roe blown 700+ rwhp creampuffs running around.

 

[txlen]

actually the compression on most motors is in the hundreds....a stock viper motor is spec'd at 150-165 psi..in each cylinder....Len

 

[robntguy]

Curious to see what the stock psi @ each piston actually measures .... 01 for example ?

 

[FE 065]

Two concerns, cream puff piston life, and overall cost. I know guys with over 600hp, 5psi, and stock heads on their CP. If the want more power they can add: ported heads $3000+ new head gaskets $500labor and misc $1000(?) or a new pulley $200? More psi to shove the mixture past through the OEM ports.Unless you're actively campaigning the car at the strip, or money's no object, why not go with the smaller pulley and skip the $5000 for new heads? 675hp is still 675hp..

 

[2002_Viper_GTS_ACR]

I bet 675hp on a higher PSI blower car, has LESS power under the curve then a motor (heads) and SC car making the same 675hp power.

Jon

 

[Joseph Dell]

I agree with Jon. Less PSI on a built motor will have more power under the curve.

If I wanted maximum power out of a creampuff going the ROE route, I'd port the heads and slap on a 7lb pulley... definitely do headers and exhaust as well, as you don't want _that_ restriction in place either.

JD

 

[GR8_ASP]

actually the compression on most motors is in the hundreds....a stock viper motor is spec'd at 150-165 psi..in each cylinder....Len

I think what was referred to earlier is peak cylinder pressure. That for most performance engines is in excess of 1000 psi. Compression is the near static pressure created during cranking speed (obviously with no cylinder firing).

You cannot compare cylinder pressure by measuring intake pressure (or depression). There are too many variables that must be taken into account.
Two engines making the same RWHP with one by porting and lower ratio supercharger pulley versus another with a higher ratio supercharger pulley will not have similar characteristics. First, the porting will change the flow characteristics of the cylinder head, and may impact swirl and tumble (movement of the charge prior to, during and after ignition). The different supercharger ratios will require differing amounts of crankshaft power to turn them. In effect the higher boost pulley will have higher cylinder pressures to offset the higher friction loss. In addition, the higher boost will also have higher inlet air temperature, making the charge more prone to detonation.

The bottom line is that in general an engine that produces its power without or with minimal boost, will be easier on the engine due to a lower IMEP (indicated power of the engine prior to friction) to produce the same BMEP (brake mean effective pressure - the average cylinder pressure required to produce the measured work). This is only a generalism as other combustion variables (f/a ratio, ignition timing, etc. all have a major impacton the combustion).

 

[RedGTS]

Ron is correct--I was referring to peak cylinder pressure at TDC, and Len is talking about cylinder compression without the engine running--two very different measures. Excellent points too; about as far as you can go without defining a lot of unknown variables.

 

[vegasviper]

Red GTS, Dont do it. I lowered my compression 8:9 to 1 (84cc chambers) ported heads 7PSI pulley


End result, Blown engine


Do you want to buy my Heads?

 

[RedGTS]

Red GTS, Dont do it. I lowered my compression 8:9 to 1 (84cc chambers) ported heads 7PSI pulley


End result, Blown engine


Do you want to buy my Heads?

I don't know about that, but I'd be very interested in some more info on what happened. Did you have cast pistons? Were you running 7 psi with the ported heads or running the 7lb pulley (which should have resulted in around 5 psi with ported heads)? What kind of fuel system upgrades did you use, and what were you using to tune the car (I assume VEC2)? Please PM me if you don't want to post the details.

 

[vegasviper]

As mentioned above, CP engine, Ported Heads w/ lower compression, 7PSI and 50# injectors.

Vec 2


Its just to much cylinder pressure for the new pistons

 

[FE 065]

I agree with Jon. Less PSI on a built motor will have more power under the curve.

If I wanted maximum power out of a creampuff going the ROE route, I'd port the heads and slap on a 7lb pulley... definitely do headers and exhaust as well, as you don't want _that_ restriction in place either.

JD

I'd really be interested in maximum power per dollar out of a cream puff! Blower-wise.

There's not that much space under the curve anyway in a drag race. Shifting at 6000rpm for example, finds you above 4000rpm in each new gear anyway. Which leaves you with 2000rpm thru each gear.

If a reliable 700hp engine was the goal, or if a guy was faced with, Which last mod am I going to do? Just a little more.. Not trying for the dyno champ, but looking at two engine combinations that yielded virtually the same horsepower, except one cost $4000+ more.
Going back to the piston/ring land question on the cream puff cars, what supports spending $4000-$5000 for the ported heads, for 675-700hp on a budget compared to just going to a smaller pulley for the same horsepower gain.


- Other than the thought that ported exhaust ports in the ported head are contributing in a way the 7psi non-ported set up cannot....

 

[RedGTS]

Vegas, I've got to assume there was a problem with the tune somewhere, as the increased risk from that setup as compared to the basic 5 psi kit seems relatively minor to me if you have enough fuel and its tuned right. We know there are several CP cars running around making mid-700 rwhp with centrifugal setups and STOCK heads & compression, and I believe Sean knows of a few people running a setup similar to yours with cast pistons that haven't melted anything. Did you talk to Sean about it, and if so, what was his opinion? There's certainly risk involved in adding a blower to any car; it's just hard to quantify without knowing how many similar cars are out there and knowing every minute detail about any failures.

 

[vegasviper]

Red, w/ the 5psi the car ran with out any problems even with our Vegas heat. When adding more cylinder pressure its a gamble.

Keep in mind that i do not baby my car, but drive it extremly hard.

 

[2002_Viper_GTS_ACR]

I agree with Jon. Less PSI on a built motor will have more power under the curve.

If I wanted maximum power out of a creampuff going the ROE route, I'd port the heads and slap on a 7lb pulley... definitely do headers and exhaust as well, as you don't want _that_ restriction in place either.

JD

I'd really be interested in maximum power per dollar out of a cream puff! Blower-wise.

There's not that much space under the curve anyway in a drag race. Shifting at 6000rpm for example, finds you above 4000rpm in each new gear anyway. Which leaves you with 2000rpm thru each gear.

If a reliable 700hp engine was the goal, or if a guy was faced with, Which last mod am I going to do? Just a little more.. Not trying for the dyno champ, but looking at two engine combinations that yielded virtually the same horsepower, except one cost $4000+ more.
Going back to the piston/ring land question on the cream puff cars, what supports spending $4000-$5000 for the ported heads, for 675-700hp on a budget compared to just going to a smaller pulley for the same horsepower gain.


- Other than the thought that ported exhaust ports in the ported head are contributing in a way the 7psi non-ported set up cannot....

I guess your missing the point, Area under the curve is EVERYTHING BELOW your peak number, so while you might PEAK at 675 with just boost, a heads and cam motor will keep you CLOSER to that peak even in the UPPER rpms. I'll try to simulate what I am saying below

7 psi w/no head work: 675 hp
3000 500 hp
3500 525 hp
4000 550 hp
4500 600 hp
5000 625 hp
6000 675 hp


5 psi w/ ported heads: 675 hp
3000 520 hp
3500 545 hp
4000 575 hp
4500 630 hp
5000 650 hp
6000 675 hp

Get the point ? PEAK power is the same, however, power below the peak number is GREATER on the heads and cam motor.

BTW, I got news for ya, if you have identical kits on identical cars, but one has heads ... heads is gonna make MORE power.. period. Want proof ??

Stock = 421 hp
heads = 502 hp

And I have the dyno graphs to prove it. So you see even in drag racing, you will benefit from the extra power under the curve ABOVE 4,000

Jon

 

[GR8_ASP]

All the arguments with "heads" assume an across the board increase in power. Depending on how the ports are modified and how it is matched with combustion chamber, intake, exhaust and camshaft changes it may make peakier power (higher power at a specific speed with significant power drop-off at other speeds) or a broader torque/power curve, or anywhere in between.

 

[RedGTS]

Going back to the piston/ring land question on the cream puff cars, what supports spending $4000-$5000 for the ported heads, for 675-700hp on a budget compared to just going to a smaller pulley for the same horsepower gain.

The other thing you're missing is you can't make the same power with a smaller pulley and stock heads that you can with a heads/cam/blower combo at lower boost pressure. Virtually all of the cars with the Roe blower and stock heads & cam come in around 630 rwhp with the 7 or 8 lb pulley (excluding those that have added NOS too of course). For whatever reason, boost creep becomes an issue shortly after 600 rwhp and the power gains from spinning the blower faster fall way off. Perhaps the upcoming intercooler will help this situation, but right now, if you want to get to 675-700 rwhp with the Roe blower you have two choices: add ported heads and probably a cam, or add NOS. You're comparing apples and oranges as the stock car with a 7 lb pulley will be substantially lower in power and higher in potential detonation issues than a heads/cam car with 5 psi.

 

[1TONY1]

Red GTS, Dont do it. I lowered my compression 8:9 to 1 (84cc chambers) ported heads 7PSI pulley


End result, Blown engine

Guys, You can not pay me enough to go more than a 5 psi pulley on cast pistons. If you do this, even with lower compression....you better know that you may be installing more pistons in the future. If you want cast pistons and more boost, send it to DLM.

 

[1TONY1]

A pulley's cheaper than ported heads... but the real question is: Are the CP pistons (more) at risk with a 5psi pulley and ported heads?

To answer your real question: I think a 5psi pulley and ported heads would be creampuff friendly. More so than 7 psi and stock heads.

 

[FE 065]

I agree with Jon. Less PSI on a built motor will have more power under the curve. If I wanted maximum power out of a creampuff going the ROE route, I'd port the heads and slap on a 7lb pulley... definitely do headers and exhaust as well, as you don't want _that_ restriction in place either.JD

I'd really be interested in maximum power per dollar out of a cream puff! Blower-wise. There's not that much space under the curve anyway in a drag race. Shifting at 6000rpm for example, finds you above 4000rpm in each new gear anyway. Which leaves you with 2000rpm thru each gear. If a reliable 700hp engine was the goal, or if a guy was faced with, Which last mod am I going to do? Just a little more.. Not trying for the dyno champ, but looking at two engine combinations that yielded virtually the same horsepower, except one cost $4000+ more. Going back to the piston/ring land question on the cream puff cars, what supports spending $4000-$5000 for the ported heads, for 675-700hp on a budget compared to just going to a smaller pulley for the same horsepower gain. - Other than the thought that ported exhaust ports in the ported head are contributing in a way the 7psi non-ported set up cannot....

I guess your missing the point, Area under the curve is EVERYTHING BELOW your peak number, so while you might PEAK at 675 with just boost, a heads and cam motor will keep you CLOSER to that peak even in the UPPER rpms. I'll try to simulate what I am saying below7 psi w/no head work: 675 hp3000 500 hp3500 525 hp4000 550 hp4500 600 hp5000 625 hp6000 675 hp5 psi w/ ported heads: 675 hp3000 520 hp3500 545 hp4000 575 hp4500 630 hp5000 650 hp6000 675 hpGet the point ? PEAK power is the same, however, power below the peak number is GREATER on the heads and cam motor.BTW, I got news for ya, if you have identical kits on identical cars, but one has heads ... heads is gonna make MORE power.. period. Want proof ??Stock = 421 hpheads = 502 hpAnd I have the dyno graphs to prove it. So you see even in drag racing, you will benefit from the extra power under the curve ABOVE 4,000 Jon

Gee thanks for the simulation..

I didn't miss any points, in fact I'd made them already.


Of course, on Vipers 4000rpm and above is where you want to concentrate power and make any power improvements for fastest ET.


So you spent almost $5000 for your Jeff Morys heads, head gaskets etc, and dropped back to a 5psi pulley to net 25hp under the curve.


There's a point of diminishing returns.


You could've picked up another 25hp for $250, but to each his own. I'm glad you've have the budget (really)



With unlimted funds I'd have a 542ci LPE engine with a blower and nitrous in the trunk.

 

[FE 065]

A pulley's cheaper than ported heads... but the real question is: Are the CP pistons (more) at risk with a 5psi pulley and ported heads?

To answer your real question: I think a 5psi pulley and ported heads would be creampuff friendly. More so than 7 psi and stock heads.

It'd be interesting to see some data. - Just a theoretical question Tony, same question to you... A few weeks ago you posted about ported heads. When I mentioned 60hp heads were $4000 from MI's Jeff Morys, you said you could just dial up the boost (smaller pulley I guess) to get 60hp. At the time I thought, "Why is he posting for ported head info then, if he's countering that he can get it from more boost?" Were you expecting more of a hp gain from ported heads?Cheers

 

[2002_Viper_GTS_ACR]

Gee thanks for the simulation..

I didn't miss any points, in fact I'd made them already.


Of course, on Vipers 4000rpm and above is where you want to concentrate power and make any power improvements for fastest ET.


So you spent almost $5000 for your Jeff Morys heads, head gaskets etc, and dropped back to a 5psi pulley to net 25hp under the curve.


There's a point of diminishing returns.


You could've picked up another 25hp for $250, but to each his own. I'm glad you've have the budget (really)



With unlimted funds I'd have a 542ci LPE engine with a blower and nitrous in the trunk.

Actually, I wont mention my price, but your a good chunk of change off in the bad direction. ;-)

Now, as far as power per dollar ? well, sure if thats your ultimate goal. But I believe in a concept called "base building." The heads are one of the limitations, given that the spring pressure wasnt made for positive pressure on the back side of the valve, so you need more spring pressure when you play with boost. Also, your forcing more air in, why not help lighten the load on the SC, by making the path less resistfull (intake) ? Then when your done cramming it in there, why not let it out a lot easier (exhaust) ?

My next answer, is for the simulation, I padded the numbers to help show you the difference, the reality of it, is simple , 5lbs with heads WILL make more power then 7lbs with stock heads. But since I was trying to show you area under the curve I kept the peak numbers lower then reality to keep them in line with your stock head and 7 lbs pulley, and you took it literallly as 25hp gain, then I guess it was a wasted effort.

Good Luck, whatever your budget. I hope you get to the number you want.


Jon

 

[Viper23]

Red GTS, Dont do it. I lowered my compression 8:9 to 1 (84cc chambers) ported heads 7PSI pulley


End result, Blown engine

Guys, You can not pay me enough to go more than a 5 psi pulley on cast pistons. If you do this, even with lower compression....you better know that you may be installing more pistons in the future. If you want cast pistons and more boost, send it to DLM.

That is a good thing I got a 96...lol

 

[1TONY1]

[ Tony, same question to you... A few weeks ago you posted about ported heads. When I mentioned 60hp heads were $4000 from MI's Jeff Morys, you said you could just dial up the boost (smaller pulley I guess) to get 60hp. At the time I thought, "Why is he posting for ported head info then, if he's countering that he can get it from more boost?" Were you expecting more of a hp gain from ported heads?Cheers

Haha, I was poking fun a the $4000 price.......BUT, what I said on that thread was Quote: "I can get 60hp by changing jets that I already have."
Meaning nitrous jets. Nothing was said about changing pulleys. However, I am soon to bump the boost up with stock heads. Any Viper should have it's heads worked at some point in the normal course of hp upgrades.

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