355 Performance mods -- chip, chip + tubi, or rear differential change

As I consider ways to increase power of my stock 355 F1, I draw on lessons from my 93’ BMW M5 as well as a wide variety of previous posts. I offer some of these lessons, with hopes they may be useful to others – with requests for your experience + feedback.

First, the issue of chips. For my M5, there are several aftermarket chips, all considered highly cost-effective because they supposedly deliver around 20-30hp (and torque gain) to a 311 engine for only $300 US. But, I can tell you, the debate is endless about whether there’s a real seat-of-the-pants effect. Everyone who spends the $$ wants to believe it’s there, but it’s almost impossible to discern, based on my experience. HOWEVER, I did notice, and document a REAL effect , when I COMBINED the chip with another mod, an exhaust cam sprocket – as recommended by the the leader in BMW performance mods, DINAN. The sprocket opens the exhaust vales wider, and results in a real jump in torque -- and it's torque that matters. To illustrate, for my 1988 BMW M6, the chip + cam sprocket resulted in a 20% increase in rear wheel HP and torque as measured ON THEYDYNO, and you could really feel it. And, when I did time trials, for example on my 1988 BMW M6, I was able to lower the 0-60 time from 6.9 secs. to 5.9 secs.

Turning to my 355, a company called Powerchip in California, promises a gain of 20-30 HP (and somewhat lower 20 ft/lbs of Torque). To get this, you have to have a shop take off your ECU panel (it’s soldered on), ship it to Powerchip (while your car sits idle), then have them reprogram it, for the HP and TQ gains – which are specific to high levels of octane, such as 94+. Then, the ECU is re-installed. Cost for the Powerchip magic, about US$2,500. Cost to have your ECU removed and re-installed, well, you figure. From an engine that delivers 375HP in a banshee wail of up to 8500 rpms, I truly doubt I (or you) would be able to feel ‘seat-of-the-pants’ effects in acceleration. I mean, an additional 20ft/lbs of torque is almost negligible in a high rpm car that mingles HP, TQ and gearing to do its magic. Regarding the possible addition of an exhaust cam sprocket – as with my BMW M6 – that doesn’t figure for the 355 with it’s innovative 3 intake and 2 exhaust valves. It’s already there.

Ok, so how about Powerchip + Tubi. I’ve heard Tubi MIGHT give you an additional 15 HP (highly debated), resulting in a total increase of 40HP (and 30 ft/lbs of Torque??). Well, that’s getting more attractive but now we’re at ($2,500 for Powerchip) + ($500 to remove and reinstall ECU) + ($4000 for Tubi) = $7,000. And please forgive me folks, but are you absolutely sure you want the banshee wail that now exists from stock to become a double banshee wail with TUBI. I thought I did. But now, even with stock, I sometimes sink down a bit in my fly yellow spider when the engine is howling in stock melody – the idea of adding a Tubi so EVERYONE notices me coming is a bit much – at least to this modest soul. Furthermore, I just drove my stock 355 spider 600 miles with melodious and appreciated wailing so loud from the stock exhaust that I could hardly hear the CD/stereo. The outrageous rasp of a Tubi on such a trip could equate to a Tubi headache. Your choice.

How about bypassing the Powerchip, or Powerchip + Tubi, for a change in the rear differential, from 4.35 to 4.55?? or thereabouts. Anyone who knows street action knows the fastest way to increase acceleration is to change the rear differential. And with the 355’s high revs, and virtual impossibility of fully exercising that rev potential on North American highways, the small loss (5-10%) on the high end, accompanying numerically higher rear differential, is surely easy to live with.

Again, another insight from my M5. I supercharged my 3900 lb M5 to the point we realized 465HP at crank (vs. 311 stock), with no engine modification. Yet, low end acceleration didn’t improve much, even with all the HP gains that increased, relentlessly up to redline of 6800 rpms. The car is just too heavy to snap off the line. Yes, the M5 did hurtle along like an intergalactic frigate at higher speeds and rpms – almost alarmingly so – BUT w/o a changed rear differential, the Supercharger didn’t pull the car to much faster 0-60 times. And so, that’s where we’re concentrating our energies now, changing the rear drive from 3.73 to 4.10. We reckon the cost will be about $2500 for the ring and pinion gears, making use of the existing differential casing.

Where I come out on this is: POINT 1: if you want real seat-of-the-pants changes in acceleration (not autobahn cruising) spurn the chips, and spurn the chips + tubi, and go for a changed rear differential. And do so w/o doing any damage to you’re engine, or need to up the octane rating beyond what you use now (eg., 91+). How much will it cost. Using your current differential casing, probably about $3000 for the ring and pinion gears. And if there were enough of us to demand this performance mod, maybe there would be some economies of scale.

POINT 2: Demand real measures of all the hyped performance mods -- in terms of changes in dynoed rear wheel horsepower and 0-60 or quarter mile times. There's so much talk and so little evidence, as I found out when I started to post querries relating to my M5/M6, followed by dyno results no one else seemed to have.

Now, please be aware I don’t presume to have all this right. Yes, I have strong opinions that are experientially based, but so do you. So I welcome feedback, corrections, and construction opinions.

Cheers, Paul