Expected power gains from mods.

[Stav]

Well the time has come to share some figures on rough percentages on power gains with different mods.
If you believe otherwise,put your case forward and if you are right well go with corrected results.

Extractors and exhaust-15-25% increase
Cam 5-7% increase.
Stall converter. 1-10 % loss top end but more power down low.
Headwork 10-40 % increase (not sure on this one)
Manual box 10% increase in power
Diff artificially increases lower power by ratio percentage.

[Casper]

Originally Posted by useless

Headwork 10-40 % increase (not sure on this one)

I'll agree with most.. just not the headwork. While the head can be mode to flow up to 40% better it will NEVER EVER translate into a 40% gain in power at the rear wheels. It would be lucky to see 5% on a good day. The cam/head combination can see good gains too.. but still wont see 40% increases in rwkw's. alone.

[EFFalcon]

i think it all depends on whats already done to the engine.
if you've already got everything but cam and headwork done, then a 40% gain could be pretty close, it depends how restrictive you're talking compared to the other mods.
if it was a stock car and u slapped on a ported head and cam then the gains wouldn't be near as much as its not the limiting factor.

thats why threads like these never quite work, because we do mods in a different order, it influences the figures.
for instance, you may gain 30rwkw with a dev 5 head and cam package, and only 4rwkw from an ECU, simply due to the combination not needing the ECU so bad.
how ever you may get a ported head from elsewhere, with a 1521a for instance, slap it on and only gain 20rwkw, but then ECU goes in and you pickup 15rwkw.
some cars gain a lot from exhaust, yet gain nothing from extractors.
especially when we're talking peak power.

[pks54]

Originally Posted by useless

Well the time has come to share some figures on rough percentages on power gains with different mods.
If you believe otherwise,put your case forward and if you are right well go with corrected results.

Extractors and exhaust-15-25% increase
Cam 5-7% increase.
Stall converter. 1-10 % loss top end but more power down low.
Headwork 10-40 % increase (not sure on this one)
Manual box 10% increase in power
Diff artificially increases lower power by ratio percentage.

This is a very hypothetical qustion, as depends on what type and specs of mods.
For instance, some exhuast combos can decrease power. However if its maximum best combo available the 15-25% seams to be very very good.
Cams and head work is where you get power and this can be anything as it all depends on the specs and the combination of how its all put together is critical. you cannot just put a figure on this at all.! eg. i used to have a 351 clevo, probably come out of factory with 200HP (flywheel). after mods of extractors, exhuast, cams, heads, big carb it had an estimated power output to close to 350HP, let me tell you it aint the carb or exhuast that gave it the 150HP increase. Note! this head/cam combo wasnt what you would call radical either.
The stall dont give you power at all, just like you have realised with the diff ratio. the stall converter just makes your engine slip to a higher rpm faster where you have better power before the converter locking up, if this is the correct terminology dont quote me.
manual or auto means nothing. sure typically manuals perform better, buts its not because its given you extra power, its due to a better spread of ratios.

[Stav]

Ok Casper. Lets change that figure to 5%. I do this cautiously because I still have a feeling that there is more than 5% in a head. I do know that head work in a V8 is worth 10-40% increase.

[pks54]

Originally Posted by useless

Ok Casper. Lets change that figure to 5%. I do this cautiously because I still have a feeling that there is more than 5% in a head. I do know that head work in a V8 is worth 10-40% increase.

mate it can even be more!

[EFFalcon]

yeah, 40% if you're using E7 heads on your worked windsor.
as i said, it all comes down to what the restriction is.

[jonbays]

This is a hard one to truly pin down as there are lots of variables but I would as a general guide expect the following sort of gains on a TYPICAL AU I6 which I will say should run around 105rwkw on a FAIR dyno.

Extractors and exhaust UP TO 115rwkw 10rwkw gain or about 10%.
Well worth while on any AU.

Mild Cam (no good without extractors) UP TO 140rwkw 20rwkw or about 20% gain. well worthwhile on any AU for the response and rev range improvement.

Street Strip Cam (no good without extractors head work heavy duty valve springs and ECU Change) AROUND 160rwkw 45rwkw or about 40% Worthwhile on any Manual AU where driveability was not a priority.

Headwork and flow gains really work on any cammed car but the bigger the cam the higher the revs the bigger the gains.
Say from a mild to wild cam you will gain 5-10rwkw but mostly at high revs.

Stall converter. A good mod an any cammed performance auto. Will show maybe 5% less power on the dyno but will pick up 2 tenths on the 60' at the drags strip and win you all the traffic light races you have been losing with an AU Auto. Average rpm on any city suburban trip will increase and with that so will fuel consumption.

Manual box will show 5% more power on the dyno and drop the full qtr mile time by almost half a second. If you want a manual you should BUY ONE in the first place really though.

Diff artificially increases lower power by ratio percentage. No power gains here but it does put the power you have into a speed range you can use.
So in an AU Auto it will make third gear much more responsive and slightly improve the performance in first and second but not a lot. As you lower the peak power in third speed from 180k stock down to 145k say with a 3.9 diff the qtr mile improves out of sight. Average rpm on any freeway trip will increase and with that so will fuel consumption. City and suburban could be marginally better as you may be able to use a higher gear more often and acceleration requires less power.

[Stav]

My mate from autoech mentioned that the manual box on my Au should be worth around 10 rwkws.10% for a 100 rwkws au.

Despite the ratios being much better the extra power has to be a bonus over the power killing auto. I have seen a standard AU with exhaust and extractors put out 127 rwkws.Thats why I am basing my range between 15-25%.

[JC]

Well, I expected 100rwkw inmprovement when I fitted extractors, but I only got about8, so i was very disappointed. I also thought the XR badge on the back would be worth 10 or 15, but it turns out it's worth 0.

What's the point of saying a cam is worth 10-40%? You might as well say that starting the engine is worth 0-100%!

[Stav]

Hmm...based on my observations of the i6 these are rough estimates of what I think they are worth and are not written in stone as I am open to real examples. If you notice I wrote extractors and xorst figures.If people are getting 15% + from extractors and exhaust then you have to ask yourself about the product installed on your car.If you dont like it,like I did not like the results of some of my stuff then it is a rude awakenning for both of us.So..we have to just get over it and face the truth.

i reckon the gains you get from headwork ,depend on how bad the head was cast in the first place.if it was pretty good from the factory to start with than the gains will be minamal .
doing the cai upgrade and extracters ,high flo cat and exhaust give you excellent gains .at least 20% + more rwk and cam and chip should give you that much again . ]
i tend to agree with ef falcon ,it depends on what is the biggest restriction .cam chip headwork will give you minimal gains with a crap exhaust .good exhaust cam + headwork will give you minimal gains without a decent chip.
the trick is getting it all to work together nicely