Mike, The original Ferrari cat for 308/328 has a flow rate of about 490 CFM. An Hyperflow cat has a flow rate of about 500 CFM. A 60 CFM difference or 12%. A 12% difference in back pressure can easily generate a 4% gain in HP even if your original cat was in perfect working condition. This is basic physics! Best,
Flyingti, In tis case, the CFM tests are real world. Basic mechanical engineering has proven for a long time that back pressure eats up horsepower. Hence the advantage of Hyperflow of 100 cell racing cats. You can have all of the upsides of running your Ferrari with racing pipes without the downsides. That's the most important point as you will not see a great difference in a 4% HP gain. The fun will be in the exhaust sound! Best,
I would be interested is seeing where those flow figures come from... However, there are several things to be aware of regarding this sort of stuff: First, if the flow info comes from the folks who are trying to sell you something, disregard it. It is really easy to make the figures say what you want them to say. As an example, let's say we apply a "flow" at x inches of mercury and we determine that an oem CAT can flow 400 CFM. Then we take our aftermarket cat and apply x+5 inches of mercury and see that it flows 500 CFM. NOW, we can advertise (and believe me, that's exactly what they do - I've been involved in it) that OUR aftermarket cat flows more; we just leave out the part that the flow was calculated differently. Along the same lines, even if it does flow better than the oem under the same parameters, if the engine can't flow more than what the oem can provide, the "increased' flow cat will not provide the slightest improvement. Same is true of air filters. If the oem can provide 400CFM and the engine only needs 350 CFM, than putting in a filter than can flow 10,000CFM does nothing. Ignition systems are another classic example...if, for example , it takes 30kvolts to fire the plug at full throttle/max load, that's all that is needed. If the oem system can provide that 30kvolts, then installing an MSD with a coil that can generate 50Kvolts will not do a darned thing. You can make incredible claims without lying. All you need to do is leave out some information. The bolt-on performance parts market works exactly the same way as illusionists do. Misdirection is the most important part of it.
My point is that you can't simply connect the dots in the real world between: OEM->hyperflow->12% backpressure decrease->4% HP increase It may sound great on paper but the proof's in the puddin'
In designing an engine exhaust system , the basic rule of thumb is that 2.2 cfm per open-pipe hp means zero loss from backpressure. Now, let's look at my 308 QV an an example: 237 HP at the crank. 237 X2,2 = 521 CFM for zero HP loss due to back pressure. The original cat had is rated 490 CFM. This was the best techology available at the time. This means that the flow from the original cat had a restriction of 31 CFM (521-490) or 5% loss. This results in about 11HP loss compared to an Hyperflow cat that has a 550 CFM rating. This also doesn't mean you will get all of the 11 ponies if your exhaust system can't let 521 CFM through... Also, remember that these ponies are measured at the crank. So we have to deduct the parasitic losses (16 to 20%) to get rear wheel HP. The bottom line is: there are gains to be made in better desingned exhaust system. Does the cost justify the expense? When I did the math, added a cooler running engine and the sound... I decided to go for it! I don't regret it one bit!!!
Again...WHERE are you getting the Cat flow figures? I agree with you that IF the oem cat actually restricts the exhaust output of the engine and the HF cat does not, then the HF cat can increase power, assuming that the engine management system can adjust for the change. Early cats were known as power robbers but that was over by the mid 80s and I have never seen a dyno test that showed a noticeable power change by exchanging one cat for another or removing a cat UNLESS the cat was clogged/rotted internally.
Mike, Before purchasing an Hyperflow cat, I got all the data I needed from them (and I did compute!) and also from Sterbro for the 100 cell racing cat. The Hyperflow had better CFM. I purchased the exhaust from them but not the cat. You are right as to the fact that some manufacturers play with numbers. That works if the end user can't read between the lines! The 490 CFM for the original cat is from factory. It also computes with cats from that era used in other german high performance cars. It is not surprising to see a 31 CFM gain in a 25 year period... In any event, only by looking at the design/functionality of the original cat (pellets covered in precious metals) versus an hi-performance cat (bricks of various size covered in precious metal) , the conclusion is quite easy! The newer designed cats perform better!
OK, I think perhaps we don't really disagree - Perhaps the difference betwen 328/308 cats is part of the issue. I am not familiar with what came on 308's or the published flow figures for the cats that were used. If you look at an oem 1989 328 cat and a new HF cat, they are identical internally construction-wise except for the fact that the oem 328 cat has a much larger internal/external diameter in the section containing the catalyist than the HF cat. Looking through the cats, the oem APPEARS to actually have more capacity (area) for flow than the HF though that is just based on eyeballing, not on flow tests of either one. The older 308 cats may be of the pellitized design of the first generation of cats which were quite restrictive. One semi-scientific way of viewing this is by examining the euro/us 328. Based on the fact that the euro 328 managed only 10 more HP than the US version even with more compression, dual exhaust, and more advanced timing pretty much verifies that the cat alone (as of the late 80's) had no adverse effect on power on a stock 328. If removing a cat (on a 328) could add 11% HP, then none of those other changes would have been necessary to gain the 10HP for the euro model- they could have made the euro/US engines/exhaust/ign timing identical and the euro car could have gained 10 HP just by NOT having a cat.
Mike, It is entirely possible that the 1989 328 cat is substantially different. Ferrari hasn't published much info on these. I know thhat the 308 1985 QV cat is what we call a 3 way cat: designed to tone down hydrocarbs, CO2 and nitrogen oxyde. With better A/R ratio management, manufacturers moved to 2 way cat around 1990. These are much les restrictive. Cheers!
