I was wondering what we think are the max HP gains with bolt on parts (ie not changing internals or forced inductions)? I would assume there would be some overlap and it would not be cumulative. But it is fun to think about it. The GT3 gets 475 without forced induction.

Power kit – 30 hp = $11k (not including install)
IPD Plemun – 14 hp = $1k (not including install)
Exhaust – 14hp to 45 hp = +$2k (not including install) From Suncoasts website.

Oh to dream about 475 of naturally aspirated HP

Marc

 

Yeah, unfortunately it doesn't quite work that simplistically.

First of all gain in HP or torque are RPM dependent So any of the quoted mfg "gains" would be maximum at some specific RPM and not necessarily cumulative. In theory you could overlay the HP and torque curves of the bolt ons and at given RPMs they might be additive.

And these kind of individual "gains" are often well overstated by the mfg... But the Power kit is going to give you some solid gains. The extra torque bump is in the 4500 rpm range and the HP at high RPMs past 6500 RPM where without the X51 kit it starts to roll off. Not really how much you are going to see at lower RPMs other than the bump in torque at 4500.

The Exhaust isn't going to give you 45 hp, that is a fantasy. Think about it, if it was that simple most likely Porsche would provide a better exhaust and for virtually no cost and advertise 45 more hp as part of the base car.

I'd also call the power kit a bit more than a bolt on, since you are essentially going to tear the engine down. Personally, it is something I'd only order with the car..

I'm not saying the bolt on's don't help, but you have to be realistic and about what you are really getting and it's benefits.

The whole goal of intake and exhaust mods is to help increase the volumetric efficiency of the engine. In simplistic allow it to breath in and out with less restriction. This allows you to balance out the cylinder power, and not waste energy getting air in and exhaust out. And the gains from these are dependent how good or bad the stock design was. If the stock design was pretty good, then your potential gains are reduced.

On any engine, depending on how good the stock intake and exhaust is, the gains can be from almost nothing to a measurable gain. But most of the HP increase is going to be at high RPMs (i.e redline). I always think about intake and exhaust mods not as gains, but what you get back because of the inefficient stock design... You aren't bolting on additional HP like you would a NO2 or forced induction which physically allows you to burn or pack more fuel in the cylinder.

So if you are racing the car, yeah it might help you out. if you DD and never approach redline normally you are going to get the benefits at lower RPMs that you might be expecting.

 

That's solid advice except....

A tune, provided the engine is capable of more fuel delivery and not already close to maxed out, can provide documented gains that can be felt anytime you go WOT.

My 6.1 SRT-8 went from 365rwhp to 398rwhp with i/e/tune. torque jumped from 355rwtq to 420.

On the same dyno, same day, a canned tune was 388rwhp, dyno tuned went to 398 and with race gas to about (its been a while) to 413rwhp / 432tq

 

Fair point about the fuel delivery. Yeah I oversimplified. You can indeed get more fuel into the cylinder with a tuned induction and exhaust.

A good illustration of that is that with old carburated V8's, when we simply added tuned exhaust headers, we were immediately running too lean, which indicated that more air was flowing with the same amount of metered fuel. So we had to richen the carb a bit to account for that.

But yeah, I think the gains you get are dependent on how good/bad the OEM design is originally. With an un-optimized design greater gains are possible.

I however don't have enough experience with the 991 boxer yet to get a feel for how optimized it is, other than the general comments on the forums. My feeling is that Porsche probably did a fairly good job on the overall design so the gains are probably thin (for exhaust and induction).. But of course with the X51, which I consider much more than a bolt on.. the gains are more significant.

To your point about the race fuel.. I also suspect that a lot of the aftermarket products use different fuel when they do their dyno runs which can explain a lot given that the porsche engines compensate for lower octane fuel. So run it stock at 91 oct as a baseline then test with bolt on with higher octane.. That alone can be fairly significant.

 

Agreed, the push rod, 2-spark plug per cylinder 372? ci 6.1 V-8 had room for tuning. A smaller, higher output per liter motor may not.

True about the fuel. The manufacturer must adhere to, sadly, the lowest common denominator of 91 octane and few factory engines "tune up" to higher octane. As you suggest, the jump to 93 octane can make a difference.

 

I love the debate. Especially when it gets technical.

My post a just a little tongue in cheek. Not so much serious.

I was listening to a GT3 video and just drooling over the sounds it makes. Apparently the person that posted the video came to their senses and removed it. It was a video of him/her driving WELL above the speeds limit in Texas. But Oh what a glorious sound.

Marc

 

Eh, it's nice to actually talk a little technical.. Kinda bored with fluffy discussions about wheels and $400 oil changes

To your comment about the GT3 video... There is NOTHING better than the sound of a porsche engine wound out... If you ever get the chance to go to the Porsche museum in Stuttgart, they even have a listening cone for different porsche engines..

Sound of a Porsche is so distinctive, sort of like how you can hear your kids voice in a crowd of 500 people and immediately recognize.

 

Agreed. I used to have a number of modified RX-7s. They were so complicated for their time. Opening up the intake and exhaust then trying to get the fuel/air ratio right. Fiddling with boost on sequential turbos. Then flattening a vacuum hose. Starting all over again. Great car. 350-400 hp from a 1.8 L rotary. At full tilt it sounded like a chain saw cutting through a steel table.

I love sport exhaust open and standing on it through a tunnel. Never enough tunnels.

I would be interesting to see what HP gains there are with reasonable “bolt-ons”. Great point that Power kit is not really bolt on. I think anything that would be interesting is to see what type of HP variation there is from one car to the next. Is it 5 hp or 15hp?

I think you all should give me some money to buy 5 or 6 911s from around the country and dyno them.

Everyone in?

Marc

 

With bolt ons you may get power up high and lose down low or vice versa, you have to be careful what the mnfr claims. Also in my experience you would typically need a tune to dial it in. At the end of the day you may see some modest gains but it won't be cheap and you could have warranty issues depending on the mod and problem. I would love to see some real numbers vs. mnfr claims.

 

Yeah, and lower the windows so you can hear better. This tunnel thing is a guilty pleasure of mine. I've got a route to work where I have a short tunnel..

I've also found that a good way to get some pops and gurgles is to drive with the revs up to about 4K RPM, then let off the throttle... Sounds really cool in a tunnel..

 

All very true. For a normally aspirated engine even the ECU tunes tend to be suspect..

When you get a turbo, the ECU story is a bit different since you can drive up the boost (if you are brave enough to risk the engine and warranty ). That seems to be very popular with the turbocharged Audi's and the power gains are real.

 

The tune (GIAC) is certainly going to produce noticeable gains, and many users have voiced their positive experiences regarding this. While the factory exhaust does leave something to be desired in the flow department, it isn't going to leave anywhere near 45 horsepower on the table. In my experience, you'll typically gain 10-15 horsepower when changing the OEM (non-PPK) exhaust for an aftermarket unit. You can couple these mods with a plenum and filter and you're looking at realistic gains of 30-50 wheel horsepower with much better response at the low RPM's.

 

Has anyone done a serious before and after dyno using the IPD plenum? Looking at the design and openings it looks to be the same as the stock one. How does the aftermarket one increase performance. I will admit Im a newb with this one.

 

I'm not sure 10 HP for a tune is exactly what I'd get a woodie over. My experience with NA tunes is that the throttle remap probably contributes to most of the perceived increase in performance especially in the lower RPMs of a 991 (and when I say lower I'm talking 2K not 4.5K).

Not saying it isn't worth it, just calling it what it really is. Below about 3500 there isn't really much in terms of HP gain, there is some torque kicking in by about 3K which does help. But certainly not a nirvana.

Most of the folks who get a significant increase in performance on a tune are turbo-charged. Had a 1.8 Audi once that was turbocharged and the gains were truly amazing, but that is what you get when you up the boost on a turbo (hoping not destroy the engine) but getting much out of a NA seems to be more about a small incremental gain with the tune and attempting to move some torque down to the lower RPMs..

I think if you couple them all together (tune + exhaust + plenum) it starts to be significant. . 10 for the tune, 15 for exhaust and 10 for the intake then you are getting to that 40 HP increase.. now you are in the 10% increase range although I'm not sure it is always additive at the same RPMs..

Not saying all of those aren't a bad deal.. Probably still less than the price of the X51 with a bit more gain.. But I'm not sure I'd be blown away with the before and after anymore than I have been with an X51.. it is about incremental gain.

 

I haven't and one of my frustrations with all of these bolt on's and tunes is the lack of dyno run data that back up the claims. Seem that all of these enhancement guys are never willing to be all that forthcoming.. Seems like everything is always shrouded in PM's.. The more critical might interpret it as snake oil, although my personal interpretation is that the gains are there, just somewhat overstated in the larger context..

But with any type of intake enhancement it is about smooth airflow (i.e reducing turbulence) and minimizing pressure drop. It is essentially a fluid dynamics enhancement. And in general the less optimized the original OEM design, the better the enhancement tends to look.