Best approach for more power: Better heads or More boost
Guys,
I have a procharger setup making 7lbs P1SC on a beefed up LT1 bottom, shorty headers, flowmaster exhaust. I have been doing a ton of research to try to approach getting 600HP at the crank, 500RWHP. I think I am near 400RWHP now (I may be delusional here). On the highway the car has taken down a newer Viper hard top and a crotch rocket from 70 to 130 MPH pulls. On paper it shouldn't have, but it did - both times.
It looks like for a given budget I could do a cam swap and upgrade to an 8 rib setup and push boost in the 11-12 pound range (maybe more if I am getting belt slip now - don't think I am tho.
OR, I can do a nice set of heads and a cam.
The one constant will be to put an ATI balancer on - should get a 1 pund boost increase from this.
Believe it or not both options will cost about the same. Can't afford to do both.
Here is how I see it: More Boost
Advantage: Don't have to pull motor, crack open all gaskets, and go through a lot of work. This is a big plus.
Disadvantage: More heat on intake charge, maybe more prone to detonation, more stress on gaskets, blow by. Can you run 12lbs on a daily driver? And I do mean a daily driver 20-25K miles a year - got to enjoy it, right?
Heads:
Advantage: Similar power level, maybe more. Will lower boost. Should run cooler. Valves and springs get upgraded. Less pront to detonation because boost should drop.
Disadvantage: A lot of work. Cracking open a non leaking motor. All C4's will leak at some point and its not now. This motor has 5K miles on it. Boost will drop-(Anyone know how much?). I will " disturb the system" - may get belt slip someday.
It comes down to how reliable and quirky will a 12 pound stock headed car be to really drive and enjoy daily?
Last edited by HighMileage; 07-23-2009 at 12:33 PM.
IMHO I would think that the additional 5 lbs boost will produce more power then new heads and cam. Assuming you have some sort of blower cam in there now. The LT1 heads are not all that bad out of the box.
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93 Automatic White Vert. 4.09 gears, Yank 3000 converter, Hot Cam, ported heads, Exotic Muscle LT headers, magnaflow mufflers Meziere water pump, and professionally tuned by Alvin and it passes emissions!!
My best run 11.82 ET at 116.52 mph. and 1.66 60ft.
My wifes best run 11.71 at 117.31 mph.
362 rwhp
379 torque
93 6 speed White Vert. 383 with a rear mount 85mm turbo. water to air intercooler, 6 pt. rollbar. Gen. 7 dfi. and many more extras. No numbers yet!!
Well, do you know what your compression ratio is for your engine? I think you said in a previous post that you have blower pistons.
If they are just forged and not dished pistons then you'll be better off doing the heads and cam, if they are lower compression then I would think that the pulley swap would be less hassle, easier, less messy.
I'm guessing that your piping/airfilter setup can handle the extra HP? What about your fuel system? Are you planning on getting this car dyno tuned after the work? Just some extra things to think about.
Oh, and just a matter of forum etiquette, you shouldn't post the same question in both the C4 and C5 forced induction forums. If you feel that your question has not been answered after several days that is one thing, but to post them both right away is another.
Well, do you know what your compression ratio is for your engine? I think you said in a previous post that you have blower pistons.
If they are just forged and not dished pistons then you'll be better off doing the heads and cam, if they are lower compression then I would think that the pulley swap would be less hassle, easier, less messy.
I'm guessing that your piping/airfilter setup can handle the extra HP? What about your fuel system? Are you planning on getting this car dyno tuned after the work? Just some extra things to think about.
Oh, and just a matter of forum etiquette, you shouldn't post the same question in both the C4 and C5 forced induction forums. If you feel that your question has not been answered after several days that is one thing, but to post them both right away is another.
MN,
I have blower pistons with 21cc dishes (Sealed Power). I computed about 9.25:1 Its between 9.0 and 9.5 depending on what the head gasket compressed height is and if the block were decked .020".
I have stock pump in tank and ATI supplied boost pump external. Plan is to upgrade both to Walbro and I will get it tuned properly.
The intake filter, intercooler, and pipe work is all LT1 procharger, stock mass airflow sensor.
Sorry about the etiquette, I just noticed that there are a lot of ex C4 guys on the C5 forum and there seems to be more activity over there. I am hoping to do my part to contribute here on C4 (I have my 5th C4, 1st supercharged, and don't ever see that I'll have a C5 now - will go to C6 when prices come down in 5-6years) Never really cared for C5 body design and the fat ass. The C6's are really well styled cars.
I have logged more than a half million miles in C4's!!!!
I definitely not in a mad rush to tear the motor down, it has 5K miles on the rebuild, it runs exceptionally stronger than I expect it should but I will if a good set of AFR195's makes same power with less headache and reliability. I will "try" to put over 100K miles on the car and there is no glory in blowing things up and constantly wrenching out other "demons".
Really looking for real world experience on a 11-12+ pound boosted car. Boost with brackets could actually be higher if I am getting a little slip now and don't know it it. I also may be losing some boost through the stock throttle body which I will uprgrade to at least a 52mm. ATI said the throttle body will not help, but it doe not make sense in that stock TB is good for about 675-700CFM and a 52mm should be good to 900CFM.
Last edited by HighMileage; 07-23-2009 at 12:36 PM.
Given the additional info I would suggest upgrading the intercooler first, before you do anything else(except maybe the fuel pump). The stock ATI intercooler will max out around 500hp. This number I got directly from an ATI tech guy when I was looking at getting one of their systems. There's no point in doing anything else to the car if there is going to be a big bottle neck in the intake tract.
Given that you have a lower compression I would definately go with more boost if you are increasing horsepower. If something doesn't work quite right with it then the car is still great as a daily driver, but you just won't get as much HP on the top end. If you upgrade the heads and cam you are going to loose some driveability and if something is done incorrectly the car is stuck. Reprogramming WOT only is also much easier.
I'm sure that there are a bunch of people here that have tips and tricks for keeping belt slip to a minimum. There was even a person working on a sprag cogged setup, but I'm not sure what happened to that.
As far as the TB goes, you can upgrade, but I'm not sure it will make a difference. You have to remember the VOLUME of air that passes through the throttle body is roughly the same as a stock naturally asperated engine. When an intake valve opens up and the cylinder goes down you can only get 0.7125L(5.7/8) of air regardless of how much boost you are running. There are more air molecules because the air is denser, but the cubic feet per minute of air is the same. Now if you look at the CFM of air going into the supercharger, that is different, but the TB sees about the same. Does that make sense?
What you are saying makes sense, but here was my train of thought on the throttle body:
When you change cam and heads, you improve flow and I think peopley typically see the boost go down because flow was improved and the air does not back up as much in the manifold. Boost is measured at the manifold.
Taking that one step further, if the throttle body presents a restriction to the flow, you will see a pressure drop across the throttle body due the resistance of air flow. Now if you remove that resistance and improve the flow through the throttle body, you could see more boost at the manifold, which is where we reference the boost.
This is also akin to the flow through the air to air intercooler. The ATI tech guy told me that there is a 3-4 pound drop across the intercooler, relative to the pressure coming out of the head.
Kind of starts to make you think of ditching the intercooler and going meth/alky injection.
You are very correct on all accounts, however, the question remains "Does the throttle body cause a restriction?". The CFM for the engine has not changed by adding boost, so will changing out the throttle body gain you anything? It depends on if you think the stock throttle body causes a restriction on a slightly modified motor or not.
Oh, and if you are going to upgrade to a 52mm, the 58mm is just about the same price. All you have to do is to grind out the opening on the intake manifold a bit.
But back to the matter at hand. I suggest changing out the intercooler for a larger one. Meth is nice, but if you run out or get some kind of slosh in the tank, or the relay doesn't engage for some reason, the motor is toast. For reliability I would stay with a IC.
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Best approach for more power: Better heads or More boost
