The F119 power modification thread

Road courses are not drag strips. But, like I said, you just keep thinking that way.

 

I will because it's a fact. I know a road course isn't a drag strip. If you are lugging the thing and pulling through low/mid rpm and peak torque you are in the wrong gear.

No matter what type of racing, max acceleration wins and that is achieved by keeping it as near to peak horsepower as possible.

 

It is no skin of my nose what anyone here believes to be fact, but for those of you reading this thread because you want to learn, consider this-- when you exit a turn on a road course in your 348, you do not get to choose what RPM the engine is turning (obviously assuming that you are in the appropriate gear for your speed) because we do not have the option of changing individual gear ratios in our cars (and even if we did, gearing most corners would still be somewhat compromised).

The narrower the powerband, the greater the chances that the car will not accelerate at its maximum potential exiting a corner... or passing someone on a backroad. IIRC, the 355 makes peak torque at 6k RPM and peak hp at 8250, so if you exit a corner with the revs below 6k the engine is not pulling as well as it should and if you exit a corner at 7k RPM you're going to have to waste time shifting sooner than you'd like. The powerband is effectively 2500 RPM, since the engine revs to 8500.

The 348 makes peak torque at 4200, peak horsepower at 7200 RPM, and revs to 7500 RPM. So the 348's powerband is effectively 3250 RPM wide, meaning that your chances of being in the sweet spot of the powerband exiting a corner is much better than it would be if we had F129 engines in our cars, which is even more important in a 348 since we have one less gear to choose from.

My point all along is that if you are interested in real world performance, either on a road course or in daily driving, you would be much better served to consider modifications that increase peak torque while either increasing or at least maintaining the width of the powerband.

If you modify a naturally aspirated engine with a focus only on peak horsepower you will almost certainly wind up with a peaky high revving engine that is frustrating to drive in traffic and not nearly as quick as you might think on a road course. In road racing you want an engine that is capable of pulling hard coming out of every corner on the track, so unless you have a 1200 lb formula car and the ability to choose individual gear ratios based on the track and its condition, that means a broad powerband.

Consider two hypothetical 348s, one modified to emulate the 355's powerband, and one modified to increase torque over a wide range. When exiting a corner there will be a much better chance that the car with the broader torque curve will be able to accelerate more quickly than the car with the narrow powerband. And even if the car with the narrow powerband makes more peak power, and is therefore able to reach the same terminal velocity at the end of the straight, the car with the wider powerband will have attained that speed sooner, and will therefore have covered the length of the straight in less time. Note that this scenario doesn't even take into consideration that corners are often tied together, imcreasing the chances that having the car in a particular gear will be a compromise, at which point a wide powerband is even more advantageous.

I have developed road course cars for many years and have driven literally hundreds (probably more) production based cars on road courses. There is a very good reason why experienced engine developers concentrate more on the depth and breadth of the powerband than they do on peak horsepower. Don't take my word for it-- ask someone with lots of years of experience in both car development and driving what they'd rather have-- impressive peak power, or a broad torque curve.

 

So shifting the 348 at 7500 puts you at

4900rpm on the 1-2 shift

5200rpm on the 2-3 shift

5600rpm on the 3-4 shift

5900rpm on the 4-5 shift.

Again, all well above the peak torque rpm.

Of course you have the option of changing individual gear ratios, it's called the shifter.

There's no "better chance" of anything. Drive the car in the correct gear and you will rarely be passing through peak torque rpm, if ever.

Set up for a corner at 60mph, you can either take it at 4200rpm in 3rd or 5900 in 2nd. Which gear will accelerate you out of the corner the fastest? 2nd, because horsepower wins races.

Having a peaky high rpm engine is basically exactly how these cars were designed and are geared accordingly. There isn't a steep enough drop between gears to pull it through mid rpm's so you can't compare this to other vehicles that do not have similar gearing and rpm potential.

If you're slogging this thing around at 4k rpm you aren't going to set any records and another 20ft/lbs at 4k rpm's will feel better on the street in normal driving but will do zero to reduce lap times.

 

With the 348, we don't really have prodigious torque to call upon, so its the HP values that rule our performance. This is why we live in the higher rpm range. Yes, we have already improved our torque numbers as much as we can, but better aspiration is going to enhance this. Spinning the engine faster is going to hopefully get us more HP but probably not too much more torque.

Totally agree with you Mike on the forced induction. In fact when I started my power search for this mill, I wanted to do exactly what I have done as Step 1. Step 2 was to incorporate a light duty turbo installation - gothspeed has even done some prelims on this. There is enough space by the 348 to allow for a very small single or dual turbo installation. We figured we needed extra fuel, so we were considering an additional single or two injectors per side fitted into the upper plenum behind the TB. Then one needs an ECU to handle everything, not to mention a knock sensor to keep the predetonation down.

We had this all mapped out. In fact, in the search for torque this installation is optimal. But there goes the stock appearance and possible ever getting a smog approval in this state again. So,...

We are on the current path, which is to wring out as many ponies from this engine as we possibly can in as close to stock configuration as possible. Hence, in my case, large valves and a modern ECU to better tune what I got. Then I am sure to need a higher capacity intake plenum. My personal goal is to get close to 355 output at lower rpms, say 360 at 7500 with peak torque about 10% higher than Ernie's cited 234.

 

Yes, but +20 ft/lbs from 4k to 7.5k rpm will. If you are improving the breathing at 4k by 20 ft/lbs, you are likely to maintain that advantage all the way through redline, which will reduce lap times. Although HP is useless without sufficient traction coming out of the corner. Also increases in low end torque can reduce lap times by eliminating an unnecessary shifts at some speeds, particularly if you are near redline on corner exit and had to grab a gear when you would be better off accelerating out of the corner.


Sent from my SM-G920P using Tapatalk

 

Yes of course, 20 more ft/lbs at 7500 rpm equals about 29 more horsepower.

We are in agreement that any improvement anywhere in the power band is a plus (as long as it doesn't make the top end suffer).

I was simply responding in regards to your comment "Horsepower sells cars. Torque wins races"

Sure you may have picked the wrong gear here and there and somehow pulled the rpm's down too low but driven properly and for maximum acceleration you will absolutely be hovering around peak horsepower and well above peak torque 99% of the time. The reality of that is the opposite of your statement.

If you truly believe what you wrote than you would believe that shifting a 348 to keep it as close to 4000rpm as possible would out accelerate/outlap an identical car maintaining rpm's as close to 7200rpm as possible. Simply is not happening.

 

While the F355 has its TQ peak near 6K, the powerband starts at 5K where the intake resonances start working. It just so happens that there is a helmholtz resonance in the 6K range where the TQ comes up another 5 lb/ft, but realistically, from about 5.3K through 7K you are riding a nice flat TQ peak. If you shift at 8250 RPMs, 1st gear drops to 5,800, 2nd drops to 6,150, 3rd drops to 6500.

 

Oh boy, one of these discussions. Here's the truth.

***All of the following assumes that the power curve has a single local and thus global maximum point (not always true, but a useful assumption to understand the problem at hand). It also assumes that you can shift instantaneously (again not accurate but a useful assumption to avoid over-complicating the discussion)***

I have seen the "when to shift" argument so many times over the years. I've learned two things. Most people are wrong about when to shift and the real answer isn't actually that hard to find out. This simple thought experiment answers the shifting question-at any given vehicle speed the driver can choose what gear to be in. At any given instant in time you need to be in the gear that will accelerate the hardest. The easiest way to figure out when to shift your car is to put an accelerometer in the car and, in theory, run it through the full rev range possible in EACH gear separately. The moment you get to a vehicle speed where the next gear up provides more acceleration than the gear you're currently in, you need to shift at that moment. Because there is a multitude of factors determining how hard the car pulls at different vehicle speeds, and because the ratio split between gears is basically never equal from gear to gear, the optimal RPM to shift at will vary by gear. It works out mathematically that the optimal shift point will always be past the power peak of the powertrain, assuming that it has one single peak. How far past the power peak to shift depends on the shape of the power curve, and while you could solve it using pure math it's way easier to just hook up the accelerometer to the car and figure out how hard each gear pulls at each vehicle speed. That being said, if you are shifting at the torque peak you are leaving something on the table. If you are shifting at the power peak you are also mathematically leaving something on the table, although it may not be that much in the real world depending on the exact shape of the power curve.

Now on to the powerband discussion. It's again a simple answer. It depends what RPMs you are comfortable cruising around at. If you like cruising at 3500RPM and want instant passing power when you mat it, then you need to help the motor make more power starting at 3500 RPM (although if this is the case you should have bought a vette). If you like to wind the car out a lot to 8500 RPM, then it's worth increasing the power produced in that region of the powerband. While there are some mods that will help you all the way through the rev range, at some efficiency level you will start to be faced with trade offs - make more power in one part of the rev-range while sacrificing a bit in the others. For me it's a no brainer. I already own a car with a 509 big block Chevy and over 600 lb*ft of torque, peaking at 4,200 RPM. The Ferrari is a complete wimp in the low end grunt department and it always will be and that's OK. I would optimize mine for the 7000-9000 RPM range because I feel like a peaky powerband adds to the unique sensation of driving these cars and is in line with the overall character of them.

To summarize:
-Buy an accelerometer. Test YOUR car's acceleration at various vehicle speeds in each gear to figure out what RPM is the best for each gear change.
-Power band "shaping" is very personal. What character do you want the car to have? If you just want to go fast in a straight line building a motor for a high RPM powerband usually allows for the most acceleration, but only when you wind it all the way up. If you want the car to "feel" fast from a cruising roll, then you need to get the motor to make more power starting from the RPM you cruise at.

 

I don't remember saying that.


Sent from my SM-G920P using Tapatalk

 

This is an example of an insightful and indebth anaylsis. I understand what you said and appreciate your presentation. Thank You

 

Yes, that's because you didn't! Sorry about that

 

Thanks awilson. I should've added something else to the summary:

-If you've only driven small displacement sports cars and you really want to scare the **** out of yourself, get a ride in something with a large displacement motor (think over 500 cubic inches) or something with a positive displacement blower and a lot of boost (i.e. Kenne Bell Terminator). You will leave that experience with a whole new concept of what fast is

 

Assuming I have one of these, in what way would I conduct this test? Is it just to simply put it in each gear and mash the accelerator to red line, or is it more involved? I guess I'd be looking at the acceleration curve for each gear from a specific rev range. From 1st, I'd start at a rolling start at some point where I could start thinking about using 2nd. That's because it makes no sense comparing a rev range where there is obviously a single gear choice - like at stop. Likewise, I would compare 1st and 2nd until it makes sense to use 2nd, say 3500 rpm or so. Same methodology for 2nd/3rd, etc. The real tell for a 348 (with 5 gears), it seems to me, is where the 2nd-3rd shift should occur especially when I'm canyon running at lower speeds. At the track, I'd be more concerned with the 3-4 shift since I seldom drop to 2nd, unless there's a low speed hairpin.

Anyway, what's the drill?

 

One reason for this is the runner does not need to be as big above the injector as it is flowing only the air and not the fuel. (but I agree that there appears to be room for improvement)

 

Have you considered putting a 8mm Phenolic spacer between the engine and runner. This have been proven to reduce air inlet temperatures.

 

Would you expound on what you are saying. Any links to which you speak. I am about to begin this little adventure and am looking for any information. I can't get my car on a dyno until next Wed for my " before" data.

 

By adding a Phenolic spacer you thermally insulate the intake manifold. Phenolic is a thermally stable phasic that is often used in these types of allocations. Several sites report the manifold to be 5°C to 10°C cooler after installing the Phenolic spacer. Consequently, the intake manifold is cooler and the incoming air is not pre-heated. Cooler air equates more power.