3.4 Egas modifications

Today I took my car to the rolling road to see how it was going, only had it a few weeks but was curious. Anyway on arrival there was a C4 on the rollers, I got speaking to the owner and told him I had a C4 converted to rwd etc, this 996 had the IPD inlet with large throttle body, 200 cell cats sports exhaust etc now I was very curious as to how this would perform. The car made 314 bhp & 280lb/ft torque so a slight increase over my C4 but not sure the mods are worth the expense

So, what power did yours have on the dyno? Most mods really don't give you good "bang for the buck" on naturally aspirated cars.

Was that 314bhp at the wheels? If so (and it was an accurate reading) then that would be impressive as, I understand, Porsche say their 3.4 makes 297bhp at the engine . I would imagine that the dyno adds an ~10-15% fudge to allow for drivetrain losses and atmospherics on the day will also affect dyno output. A dyno is a good comparison tool so it would be interesting to compare it to your cars reading if it was run at a similar time. What did your car make?

did he have the car remapped as that is another thing to do once you have more air coming in and out? you can get all the parts you need for this from Dean at Eporsche under the spyder performance brand. well the bigger inlet plenum to support the larger 82mm TB and the connecting pipes from TB to air box plus blanking plate. all the bits you need for the price less than just the IPD plenum ;-) see here: https://www.ebay.co.uk/itm/Porsche-...217585?hash=item4d775f52b1:g:dJEAAOSwIDZbQ-y6 200 CELL cats from Top gear and you are away. maybe a remap too and BMC air filter to help with breathing.

The figures are flywheel I believe, I didn't have my 911 on the rollers it's was my recently purchased MK1 Focus RS and it made 358bhp and I was told when I bought the car it was mapped to run 360 low boost & 440 high boost so its right on the money.

Put another way, sounds like you got 17bhp from making your exhaust sound nicer.

I agree if it were just the exhaust but I was led to believe the bigger TB and plenum would have added also. As others have said there might not be much to had bolting bits on to these cars. NLW, I didn't ask about the remap, the owner waited around until my car had been run up as he thought the power reading was low but for me on my car it was where it was needing to be. I think he was quite disappointed, my 911 is a great car to drive but so is the focus and the focus is in a different league power wise to the 911 but if I were covering lots of miles there is only 1 car I'd consider and I think we all know what one it would be but for a quick blast round the B roads the RS is hilarious and such an event to drive.

It doesn't matter how much air you put into the engine if you don't increase the fuelling to match. You can 'gain" horse power by losing less through reduced pumping losses with a better flowing inlet/exhaust, but you're still filling the same size cylinders at the same rate. Unless you burn more fuel, or burn the same amount more effectively, you won't see significant hp gains. Imagine fitting a larger TB. Unless the ecu 'knows" it is larger, it will measure the mass air flow but assume the standard cross section. It doesn't 'know" more air is going in! Happy to be corrected, but on efi cars, gains without remapping to account for physical mods will be limited.

Grifter, if the Air Flow Meter hasn't been modified in any way, it will still measure any air flow increase that changing the throttle body size gives (up to a point, at least) - it does know more air is going in. The only time that an ECU re-map is critical is if your mods put the operating range beyond the boundary conditions that the ECU can cope with (i.e. going too extreme with the mods). There can be further gains by fine tuning the fueling and/or timing, but the ECU can cope with a few mods without requiring a tune.

I expect a lot of these mods don't yield much extra power. When you read about the car 'revving more freely' instead you have to wonder.

So for a 5% bhp gain you're looking at ~£1700+ for the parts, dyno & remap if you fit yourself and your car is standard. I imagine that you won't really feel much difference on the road, better to sort the suspension, lose some weight and get the set up dialled in for your driving.

Good point. Also, with lambda feedback the ecu can of course cope with a certain amount of change to physical components.

there are a lot of mixed views in doing the change to larger TB and the different plenum. some of it can be placebo effect but the only way to know is do a back to back dyno run after changing the bits. or in similar conditions once the parts have been changed I remember seeing a comparison of dyno plots on a 996 between stock to adding the plenum and tb then to full remap with 200 cell cats....and it was quite surprising as changing to a bigger TB and plenum without a remap and 200 cell cats can actually make the car worse to drive on the road and lower power down low. it will change the power band and you can lose low to mid range torque which is not what you want for a road car. adding 200 cell cats and then doing a remap to compensate for more air and then add more fuel was the way to go. and with the higher flow air filter and the resonator delete for more cold air in. speaking to wayne Schofield on chip wizards who is a master of the NA engine and mapping he feels that by doing all the bits and the cats for better air flow AND the ecu remap is the way to go. and you will get gains BUT not huge gains like on a turbo if you were to do this. his view was that its a bit pointless really as Porsche have spent millions on managing exhaust flow and gas scavenging in the system to give the right mix of torque and power and delivery. its not just about all out numbers gains ...its got to be tractable and work on the road. you have to weigh up whether the $$ is worth the minor gains you will make as its like 10-15 bhp on a 3.4 car and maybe 20-25 bhp tops on a 3.6 maybe some new suspension, bush refresh and some michelenin PS4S tyres is going to make you go quicker and put some smiles on the zee face.

Porsche's own X50 kit only makes an extra ~25bhp and that requires many extra components including different heads and isn't cheap. Good point on low/mid range torque, that's what's needed on a road car.

X50 kit is a pair of Turbos.