Turbocharging my F355 - Or how to remove any market value from your F355 remaining.

While this is not my first rodeo with turbocharging, I am not really a "car guy" either. My day job is being a clinical psychologist. That said, I know a few things:

1. I don't plan or desire to sell my F355.
2. I like to tinker with things.
3. I like cars that are unique and reflect the creativity of their owners.
4. I got a car that essentially had a motor that was toast.

So what to do? Naturally rebuild the whole damn thing. It has a number of things that I have found bad along the way and I had some decisions to make... return to stock, or blaze a different path that reflected my creativity. It was actually a hard decision to make, as I do believe that I have a responsibility not to lose the aspects of the car that make it "special" in the first place. Believe me, several people have suggested slamming an LS motor in it... which to me would be completely wrong. What makes the F355 is it's high RPM fast revving nature, so I wanted something that would accentuate that, not destroy it.

So I have decided to turbocharge it.

Objectives:

300-350 ft/lbs torque and 400-500 HP at wheel (at 8250 RPM: 300 ft/lbs = 470 HP; 318 ft/lbs = 500 HP; 350ft/lbs = 550 HP).
Spool-up: 3,500-4,500 RPM, 10 PSI by 4k would be perfect.

Most people would suggest a pair of small/medium turbine, large waste gate, moderately large compressor, ball bearing turbochargers with twin water to air intercoolers, and a high end programmable engine management system. I agree, they have arrived at an answer that is complex and expensive, but generally correct.

No doubt, the twin turbo answer will work, but is there another answer?

I would argue that there is another answer, and although it is not as "elegant" a solution, it has it's own advantages. The best analogy I can make is the difference between using a ratchet wrench and a speed handle. Sometimes is important to have a specific tool, and other times, not and may even slow you down.

So unlike most people following the conventional wisdom. I will be running a single journal bearing oil cooled rather large turbocharger with single intercooler 11x11" core with a 2.5" inlet and 2.5" outlet. I will be managing the engine with Megasquirt MS3-Pro as my engine management unit with 650cc/min injectors.

Turbocharger details:

Compressor wheel 68.7mm/97.8mm A/R=0.66
Turbine Wheel 87.4mm/77mm A/R=1.05
Inletivided T-4 Outlet: 3.5" V Band

Wastegate:
Dual 38mm wastegates set for 6-10 PSI
boost control solenoid will be used to manage wastegates above base pressure

Intercooler
11x11x2.5" core
17x11.5x2.75" overall
11" SPAL 800 CFM 11" Low Profile Fan

Header to turbine inlet:
(2) 2.5" V-band to divided T-4 flange

Things that I have not decided yet.

1. How much to lower static compression ratio vs changing intake valve timing to reduce dynamic compression ratio.

2. Am I crazy...

 

You would not turbocharge at all? Or do you just disagree with specific choices?

I am always open to hearing a different opinion. It will be interesting. The great thing is that I don't really have a ton of money invested in the turbo and intercooler, so if I decide that twins are a better idea, I can easily adjust fire and not feel bad about it later.

I suspect that I may have gone too big on the turbine side and it may hit (as you stated earlier) like an F40.... which would not entirely offend me. My Miata which had a T3/T04E compressor was essentially half the size and made about 320 RWHP... spooled late (4500 RPM) and pulled like a beast all the way to 8500 RPM. Strangely enough the BP4W mazda 1.8 liter motor is surprisingly similar in regards to cam timing with regard to the intake valve closure and overlap (although I am quite sure the Ferrari head flows better).

 

I decided on the single for a number of reasons:

When I realized there are benefits of running a long tube header on a flat plane motor provided I could avoid reversion in the system, that sort of sealed it for me.

These were the other reasons:
1. A single turbo versus a dual system has nearly 50% of the stuff to break. Having less stuff that can break will increase reliability. On a twin turbo system, you lose one turbo and essentially the car is down.
2. There is a very inexpensive set of turbos that are all T4 twin scroll units that will prevent reversion between the two banks of 4 cylinders. The location of the old bypass valve is a perfect spot for a single large turbocharger.
3. This high central location also places the turbo high enough to make returning the oil to the sump trivial with regard to the oil outlet on the turbo. I will concede that mounting it lower near the heads would provide several distinct advantages (faster spool for starters).
4. I will not have to build turbo headers, I can use my existing headers without modification. I simply need to make a set of 2.5" pipes from the collector to the turbo inlet on each side.
5. It won't melt anything where I am planning on putting the turbo... having turbo's down near the CV joints and engine mounts already causes enough problems with heat management.... two glowing turbo's much WORSE!!!
6. The 97 Ferrari relies on a single MAF, so rather having to route two intake streams into one central location, I can use a single outlet to feed a single inlet. Once again, less stuff to break. Fewer sensors and probably minimal gain in performance for the work.

I really look at it from the standpoint of whether the incremental gains are worth the effort. I suspect that if I were making a cost no object system, yes, I might go with a twin setup, a sequential turbo setup, or even a twin charged (supercharger/turbo hybrid). Hell, I would even consider a KERS system, if it were feasible. Unfortunately, I do have a number of constraints. To me the above reasons were compelling enough to risk going down a different road. Yes, I am in San Clemente (SoCal).

 

Thankfully, I do not have to smog the car. It's registered in a state that does not require emissions testing and being that I am currently on active duty, I do not need to smog the car in an unfriendly state. That said, I would like to (at some point) see if I can make it comply at the tailpipe with regard to what the factory emissions were, provided I do not have to sacrifice reliability or safety to achieve the goal.

Nitrous is always an easy solution, the only problem with nitrous is that the bottle is always empty when you need it most. Just ask the chump who had to race my turbo Miata 3 separate times with his nitrous fed Trans Am, before I caught him with a full bottle and he was finally able to beat me.

Would the F355 handle a 100 HP shot? To answer the question about the F355 and nitrous:

Yes, above 4000 RPM, I have little doubt the F355 can handle a 100 HP N2O shot. It is low RPM nitrous use tends to kill motors, hitting a 100 shot at 2,000 RPM would be much more likely to hurt the motor. A 100 HP shot of nitrous at 2000 RPM is a 262 ft/lb of torque increase over stock, but at 4000 rpm it is only an increase of 131.3 ft/lbs (and only 65 ft/lbs at 8000 rpm). Horsepower is a measurement of work over time, but torque is the amount of force per turn of the motor. Keep the HP the same between two motors, but halve the RPM of one of the motors and that slower motor must generate twice as much force to make the same HP as the one spinning faster.

 

You need one or two tools to really tune an engine for power and general drivability...

1. Individual cylinder EGT's
2. Wide band Air Fuel meter

That's it.

To tune like the OEM's do it, you need to have a dyno cell, chassis dyno, or other method to replicate the widest range of driving conditions. This is where you can really dial in drivability at the edges of the engines maps, but one can do this with datalogging and autotuning as well.

I am not saying that OEM's don't spend a lot of time on ECU mapping and development, but it's not for the reasons that most people think, and it's certainly not to get the car to run decently in southern California. It really isn't that hard to tune a car until you have the constraints placed on the OEM's. First, OEM's spend a lot of time is in optimizing the actual engine design in the first place to manage heat and airflow throughout the wide range of actual conditions while having to meet multiple conflicting objectives simultaneously (Fuel Economy, Emissions, Longentivity, Power, Smoothness, cold start, etc, etc). To be honest, thankfully, I don't have the same constraints, but a limited subset of them. I can choose to sacrifice fuel economy for longentivity or power. I can choose to ignore emissions in favor of power and smoothness. I am not worried about the catalytic light off time. Cold start performance is where many OEM's spend countless hours to meet EPA emission goals. I have had to help design and engine aftermarket turbo systems to meet CARB rules with regard to emissions (it's not easy). Second, I don't have to worry about performance in the Artic circle, variations in fuel quality, and all the other environmental variables like high altitude performance and other strange environments that OEM's are forced to deal with.

 

Thankfully, I am never selling my F355. (Seriously, Never.) I briefly considered a twin screw supercharger, but honestly, it will sound more like an F355 with the turbo.

 

The artfulness of a twin and the beauty of symmetry is not lost on me. I am hoping to preserve that in a slightly different way. I doubt that anyone would argue that the dual air boxes on the 97 feeding into the single MAF sensor doesn't not address the beauty and need for symmetry that is so important in building a car that looks "right". I agree with that.

The question then becomes, how does one keep symmetry and balance in a single turbo system. This is partially why I opted for two wastegates. I have not decided on one or two BOV's, utilizing two does achieve symmetry, however using one prior to the MAF may be more appropriate.

Although I am opting for 2 wastegates, I have not entirely decided how I am going to handle the exhaust fully yet. Half of me wants a similar to the 458 Italia or F40 3 pipe system (Except with two wastegate outlets and a single main exhaust), the other half of me wants to put four exhaust tips in the factory location with one waste gate and one exhaust on each side. Retaining the good looks of the car and the engine bay is extremely important to me, as the reason I was drawn to the car was the engineering beauty. I don't want to lose that in the least.