[pwpanas]

Originally Posted by mrnickleye

FAQ on Modifying the Toyota Supra

Thank you for the post - I agree it's very informative.

Here are a few comments/corrections to that article. The points are listed in the same order as the article:

• BPU is not a TM of Suprastore. They've been trying to claim it is for years, but at least one MKIV Supra owner actually did go to the trouble of tracking it down with a trademark search...and there isn't one. All that said, I've got nothing at all against Suprastore. Imo/ime, it's a reputable site to purchase aftermarket parts.
• A catback exhaust is not required for BPU, since there are no horsepower gains at BPU level from swapping out the stock exhaust. In other words, the oem MKIV TT exhaust flows just fine for BPU. As many who read my posts know, I make it clear when I post opinions, but this isn't an opinion. I have personally done back-to-back dyno runs with my own MKIV Supra using the oem exhaust and an aftermarket one to prove this fact.
• Although a boost gauge is not technically part of the formal BPU definition, it's rather irresponsible to install modifications that raise your boost without having any idea how much boost you're running after the mods. Note this isn't an article correction, it's a suppliment to that article, and my recommendation to ammend the definition of BPU.
• APU actually refers to any modification that goes beyond a simple bolt-on. Therefore, an Mkiv Supra, still with the stock turbos, but (for example) with nos and 264 cams and a complete aftermarket fuel system would be considered APU and not BPU+++, according to the original definition. Oh, and yes, I was personally part of the MKIV Supra community way back then.
• You should NOT run 18psi with the oem twins UNLESS you also run either race fuel or methanol injection. Anyone that says you can, for example, run 18psi with 91 octane cali 'premium' is someone that will be impossible to track down when you post how your engine got damaged when you followed that (lousy) advice. Again, this isn't an opinion, it's another fact.
• Bleeder-T is a boost leak. The clamp mod is a much better way to raise your boost. Yet another fact.
• TTC mode does NOT "allow for better midrange power". How could it? It increases lag by preventing the first stage of sequential operation. In other words, midrange power suffers, and you get almost no boost at all until about 3200rpms or so...
• TTC does NOT "allow for a smoother power band". How could it, when you get no boost till 3200, and then both turbos hit hard right at that rpm point lol
• The EGR mod does NOT "prevent super-heating of the number 5 and 6 cylinders". I agree this was the intent of the mod, but it just doesn't accomplish that goal. EGR gasses are INERT, and therefore REDUCE the heat & cylinder pressures in #5 & #6 by reducing the % of combustible air+fuel in those cylinders.
• Fwiw, I've never seen a "BPU-only" Supra Twin Turbo dyno 410rwhp on pump gas (and I've seen a LOT of "bpu-only" MKIVs dyno'd). In theory it might be possible, with a brand-new engine and brand new turbos with race fuel on a very cold day, but trust me when I say this result is near impossible (especially with an auto-tranny Mkiv!!!!). A more common expectation for BPU-only Mkiv Supra Turbo with 50K+ on the odo, on pump gas is about 340rwhp (auto) - 375rwhp (6spd). The vast majority of MKIV TTs that exceed 400rwhp are bpu++++ and they're running race fuel.
• You don't need to reset the ecu to get a good dyno result...in fact, this is a bad idea because your air:fuel ratio will likely be adversely affected. The oem ecu VERY quickly readjusts both air:fuel and timing after you add race fuel.
• On the street, you'll make more power (not less) because of the additonal load on the engine. More load=more exhaust gas=more boost=more power.
• You won't get a BPU 6spd into the 11s, with drag radials, no matter how well you drag race. I do agree than an auto BPU++++ with drag radials or slicks can hit 11s.
• This is the worst (i.e. the most dangerous) error in the article: BPU mods absolutely can adversely affect your engine life IF you choose to run too much boost on pump gas.
• The 2JZ-GTE's internals are reliable to over 800rwhp (6spd) with proper tuning (NOT 700rwhp). The record for the oem 2jz-gte shortblock internals (Pistons, Rods, Crank, Head Gasket etc) is over 1000rwhp. 800rwhp is a 'walk in the park'.
• The oem 6spd V160 Getrag (as well as the oem 6spd diff) has proven itself to 1450rwhp+. The article states 800rwhp is the limit, which is a rediculously low figure.
• If you want your BPU Mkiv to pass emissions, not only do you need a high-flow catalytic converter, but that high-flow catalytic converter needs to be installed in the downpipe immediately after the turbos (as it is with the Random downpipe). If you weld a high-flow converter (for example) into the downpipe near the middle of the car, it won't get hot enough to do it's job. Yep (you guessed it) I know this from first-hand experience too. Btw, there's almost no space to weld the high-flow cat right after the turbos, so Random's setup really is an excellent, very-difficult-to-duplicate design. Lastly (on this topic), note that you'll loose at least 20rwhp (NOT 5-15hp) by using a high-flow catalytic converter instead of a straight-through downpipe on a BPU MKIV Supra.
• The stock air filter assembly is not a flow restriction at BPU, AND the stock filter assembly acts as a cold-air intake. Replacing/upgrading it at BPU level is a waste of $$$.
• The stock fuel system is actually safe to 525rwhp+ (6spd) (NOT 450rwhp). Of course, this assumes your injectors are clean, and your fuel pump does not have 200,000 miles on it.
• Unfortunately, an EBC will generally not completely prevent spiking or over-boosting. In fact, if you spend enough time & tuning on the install, a manual boost controller can actually regulate boost more precisely/responsively than an EBC!
• The article again states "I don't recommend going regularly over 18psi". This is VERY BAD ADVICE, especially on 91 octane Cali 'premium'. Each and every time you hit 18psi on 91 octane fuel, you will damage your engine a bit more. If you don't boost to 18psi "regularly", that just means you damage your engine a bit more gradually (but it's still getting damaged!!!). 14psi max is a much better max for cali 91(r+m/2) octane and 16psi max for 93 (r+m/2) octane in the rest of the US.
• There actually is only one wastegate with the MKIV's oem twins setup. The article implies that there is a wastegate for the secondary turbo that should not be hooked up to the EBC. In fact, there is no wastegate at all for the secondary turbo.
• A reprogrammed oem ecu actually can measurably increase performance in specific scenarios, by increasing the rev limit. One clear-cut example is when drag racing a 6spd. With the oem rev limit, you'll need to shift from 4th to 5th before you cross the 1/4 mile line. With a raised rev limiter, you can get through the entire 1/4 mile run in 1st through 4th.
• The AEM is overkill waaay beyond overkill for a BPU Mkiv Supra. If someone recommends an AEM for a BPU MKIV, they either have no idea what they're talking about, or they're only recommending it because they're going to make $ on the deal (or both). Just mho.
• You can safely run 22psi or more at bpu, as long as you have a sufficient octane of fuel to match that boost level. Of course this will be a bit harder on the turbos, but it's perfectly safe for the engine (again, with enough octane).
• The GReddy SP exhaust has also been discontinued.
• An underdrive crank pulley is not only dangerous (as the article states), it does NOT provide a 10rwhp-15rwhp gain. It does allow for a slightly quicker spool-up of rpms, but this benefit is offset by the damage that will be caused by the lack of axial twist dampening.
• I can't agree that the oem mass-airflow sensor should generally be considered to be "highly restrictive". In fact, at least one maf-equipped MKIV made over 700rwhp.
• An aftermarket bov vented to the atmosphere can cause more than stumbling in between shifts. It can cause stalling.
• An SP61 is too big to run with the oem fuel system.
• Ime, a stock clutch will NOT hold the power levels of a BPU Mkiv Supra...not for very long anyway. As soon as it starts to slip in 5th gear, you've got maybe a week or two at most to get a new clutch in there...
• Removing the trac fuse only disables the 155mph speed limiter on US-spec MKIV Supras...

Again, I'd like to thank mrnickleye for posting the link. Although the info at the link isn't completely accurate, I'll even give Stuart B 'props', since I believe he did his best to provide as much accuracy as he could. There really is some accurate info in the article, and I (obviously) didn't post any corrections to those accurate points. In other words, to me, the data in that article actually does represent a good start. I hope no one minds me posting improvements to that article over here on our board. I'd also welcome feedback or questions on any of the corrections I've posted.

Oh, note that I tried to post this all as a feedback/comment on that website, but here's what is displayed when you try to post a comment:
"No Comments for this article."

Peace.