headers and Boost, What is the relationship?

[JanShelbyGT500]

So i have a Saleen supercharger with a 3.4 pulley but am only pushing 6.5 psi instead of the 9.5 it should. Somebody asked my if i had cams or headers. I have kooks headers and stock cams. He claims that headers led to a drop of back pressure and boost. I have never heard this theory. Any truth? Should i put a smaller pulley or look for boost leaks? When i took the car to the dyno, it showed a great curve, no belt slippage or drops of boost.

 

[JeremyH]

100% true. Boost pressure is just a measure of restriction of the engine it really has nothing to do with the power you make although we often associate a boost level with a power level. The better the flow of the motor the less boost pressure you will see and vice versa. So when you make it easier for the air to flow in and out of the motor you will see a drop in boost level. But the engine will still be moving the same cfm of air and make the same power if not more at the lower "boost" level.

 

[Brezick]

I have the kooks LT and hover around 1lb less boost that advertised, but still maintain a better power level.

 

[benjytps]

The Saleen S/C seems to be very sensitive to long tubes. We have seen it on every one of them we did long tubes on.Re-calculate blower speed , swap the pulley and let it eat!

 

[Fastbreak]

100% true. Boost pressure is just a measure of restriction of the engine it really has nothing to do with the power you make although we often associate a boost level with a power level. The better the flow of the motor the less boost pressure you will see and vice versa. So when you make it easier for the air to flow in and out of the motor you will see a drop in boost level. But the engine will still be moving the same cfm of air and make the same power if not more at the lower "boost" level.

So if I understand correctly you can basically run a smaller pulley, compensate for new found lack of restriction and probably see boost levels around the level they were supposed to be with the larger pulley- but have the hp levels of the smaller pulley?

I don't even know if that made sense in my own head- but hopefully you get it?

 

[JeremyH]

Boost is relative to your setup, yes the smaller pulley will bring boost back up and make more power.

 

[b00stedgt]

Headers and cams will lower your boost

 

[JanShelbyGT500]

So basically, we should raise the boost? Again, what is the limit on a stock engine? 450whp? 500whp? Get as close as possible w/o breaking a rod

 

[JeremyH]

Every car is different rpm and the tune also play a role. Most get away with 450-475rwhp for awhile.

 

[Sactown]

So basically, we should raise the boost? Again, what is the limit on a stock engine? 450whp? 500whp? Get as close as possible w/o breaking a rod

I was at 480rwhp for a long time, the motor finally let loose at 517rwhp. Every car is different, just make sure you get a really good tune.

 

[b00stedgt]

im at 452 for two years. stock motor/stock clutch. hot rod cams, long tubes, and 8 psi

 

[weather man]

im at 452 for two years. stock motor/stock clutch. hot rod cams, long tubes, and 8 psi

Perfect! Sounds good, Goes good!

 

[05stroker]

At 450 my car was fun at 500 it had a window in the stock block.

 

[VTXFrank]

As mentioned, the blower pressure drops when you allow the engine to push exhaust gases out faster via the headers.

It's all fine and good that the boost pressure dropped and you're making the same, or a little better, power level. But don't let this fool you into thinking you can just swap a pulley and get higher HP.

That smaller pulley will up the boost pressure and the headers really help get rid of the exhaust gases. But in doing so, you also, obviously, increase HP and TQ. In your situation, it isn't the boost pressure that will harm the engine, but the amount of power it's putting out.

I would do a dyno pull to see where you're at power wise and AFR wise.....due to the header install..... before doing anything further to the setup you have. It may not be in the best interest of your engines life span to go with a smaller pulley at this time.

 

[JanShelbyGT500]

I did put the car on the dyno. It pushed [email protected] psi with AFRs locked at 12.1-12.2 all around. This is with 89 octane gas, so i imagine that ignition is way back in the stone age. I have another JDM tune with race gas, i am going to try it on the dyno to see what numbers i get.

I am aware, that the problem of breaking the engine is not going to be boost but hp. Thats why i asked if the "safe" limit would be 450whp or 500whp. Of course, you can break a completely stock NA engine on a lousy tune, so its assuming 450whp or 500whp on a good tune with a solid afr.

I am gonna put the car back on the dyno with race gas and the other tune. A think that i may have a small exhaust leak trhu the headers gasket. Fix that also. If the car gets to 450whp or close i will probably leave at there. No need to break a stock engine looking for 30-40whp. Been there, done that. It ain't pretty

 

[JeremyH]

On 89 octane tune I would leave it alone where it is for sure.

 

[JanShelbyGT500]

Hey 89 octane it is staying there. I just want to see with race gas, my current pulley and JDM tune i can push close to 450whp

 

[Fastbreak]

So, what's considered the 'safe' (understanding that there are always exceptions) limit for a 93 octane tune?

 

[AbdullaGT500]

I got to see my rod on the side of the road with only 9 lbs. 450 whp is more than enough to destroy a stock motor. Like Jeremy said, RPM and tune are important. If you're going to rev it to the moon, it won't last long at all.

 

[weather man]

Octane doesn't matter. The trend has been that random rod failure starts occuring roughly around 450HP. Some guys run a lot more with no problems. Some guys less and popped the motor. Tune is key preventer no matter how modded and how slight the mods. Maximum repeated efforts seem to accentuate the problem which, not to shocking.