Rotorque

I will be getting a boost gauge soon (RB sound better than Autometer to me from what I have read on this forum) as a precursor to tickling a bit more power from my '86 turbo conversion. At the moment the stock boost gauge indicates that it only ever boost to about half way between 0 and +40, so obviously way under what is possible without further mods (if the gauge is to be believed). My question is, if when I get and accurate reading from my new boost gauge it still shows 4.5ish psi (rough guess), couldn't I simply get a boost controller and raise the boost up to 7 or so for a bit of added fun without having to do much else (FCD etc...)? Would there be a decent enough gain in power or would I really need to do something to the exhaust or intake to reap the rewards of this (and risk getting too much boost and having to port wastegate blah blah blah...)? My mate was going to do a full 3" exhaust for me but it sound like I would get too much boost for the stock turbo and have to spend more than I would like replacing or porting etc. Any help would be appreciated because I don't know anywhere near enough about cars and if this idea works it will keep me happy for a bit longer before I have to scrape real money up for a decent string of mods. Ta.

NZConvertible

You not need a boost controller to raise boost, just a freer flowing exhaust and intake. Then you'll probably have too much boost! You'll need an FCD for over 8.6psi, and you will need to port the wastegate or upgrade to a S5 turbo and manifold if you want more than a very mild increase in performance. Sad but true...

NZConvertible

Rotorque

yeh, I know that. I am just interested in why a boost controller would not work for getting maximum boost out of the set up I have now ie. as I said in my original post above, without spending heaps of money. As in just to optimise what I already have (basically stock). Thanks for your post though. I guess I should do it properly.
On another point, I was talking about all this to a friend of mine who has been hotting up RX7s for years and he has never heard of porting the wastegate! That pissed me off a bit. Is it only done on the '86 turbo? What is different about the S5 turbo to make you (NZconvetible) say 'OR upgrade to a S5 turbo'? Wouldn't I have so much boost for the S5 turbo with the proper way you described anyway?

NZConvertible

Ah, you (and many others) have made the mistake of assuming boost = airflow = performance. This is not necessarily so. A boost controller will simply force the turbo to work harder against the restrictions of the standard exhaust and intake. You will get the boost you want, but that doesn’t necessarily mean the power you’re expecting. If you free up the exhaust and intake, you remove these restrictions, lowering the pumping losses associated with them and increasing flow, and the turbo will be not have to work as hard as it would with them there. Too many people just aim for more boost; you should aim for more airflow first, then look at increasing boost. Your friend can’t have done many 2nd Gen RX-7s then. The wastegate on the Series 4 turbo is simply too small. Increase the flow through the turbine by putting on a full 3” exhaust and the wastegate can’t bypass enough exhaust gas to hold boost levels constant. The result is boost creep, and your stock fuel system won’t be able to keep up with the sudden boost increase, fatally leaning the engine out. The solution is to enlarge and shape the wastegate port for more flow. The Series 5 turbo has a bigger, better wastegate, so the problem isn’t nearly as bad, although I hear these can benefit from some work too.

Rotorque

Thanks NZ, that was EXACTLY what I wanted to hear. I suspected as much I just needed to hear someone in the know say it. Well, my mate is going to do make me a full 3" exhaust from scratch so that is a start. The other mate (the one who had never heard of porting the wastgate) said that this will not necessarily give me more power or boost (which is strange because REted said I would easily get 12psi from that) and that I need to do open up the intake in order to get more boost. I guess I should do that too. Is that what is referred to here as the TID (Turbo Intake Duct) mod? If so, its apparently easy to do. Best I find out where to get all the stuff I need (FCD, boost gauge, boost controller etc) being in Australia. Thanks again NZ. I need all the help I can get.

Felix Wankel

You will gain more power and boost fom the 3'' exhaust. You will get about 5-6 more psi, as opposed to about 1-2 psi for the TID mod.

If you port the wastegate, you will probably only get about 6-7 psi to start, as opposed to 10-12. This is good because you can then raise it back up to where you want with a boost controller, and it won't spike like it would with a stock wastegate. This way you have much more predictable and solid boost.

All you really need to do, is get the exhaust, intake, a good fuel pump, a boost controller, and port your wastegate. You will be very surprised at how much this wakes your car up.

Rotorque

Thanks fellas, you've been a great help. Felix, I'd obviously need an FCD for going over 8.6psi to wouldn't I? After doing all those mods I would ideally like to max out the setup whilst still being safe, so I would like the boost at about 9 to 10psi (just below stock turbo safe limit). I guess a A/F gauge wouldn't hurt too at that stage. Thanks again.

Felix Wankel

Yeah, you'd need an FCD. I had been awake since 2 pm the previous day when I wrote my last reply.

Anyway, while you are replacing the exhaust is the perfect time to yank your turbo off and port the wastegate. I say its easy, but I've done it a couple of times. That will keep you from hitting the fuel cut while you are enjoying your new exhaust.

Once you have all that done, since you are only wanting 9-10 psi, you could just rewire your fuel pump to get rid of any voltage drop (provided it is a TII pump, you did say your car was a conversion, didn't you?).

Next I would put the FCD on. Then you can either do the TID mod or put the boost controller on. I would do the TID first, so you are getting all the boost you are going to get. Then if it isn't enough, you can buy a boost controller to raise it up. If it is making enough for you without one, hey, you just saved some money

My car with the stock turbo (ported wastegate), twin scroll actuator and door removed, a 3'' TID, 3'' downpipe/midpipe to an HKS 60mm catback (plus the FCD, open BOV and a fuel pump) was getting 7-8 psi. Once I put the hybrid turbo on that has a clipped turbine wheel, it was only getting about 6-7 psi, so I put a vacuum T fitting in the wastegate line. That bumped it up to around 11 psi.

Welcome to a time and money consuming hobby

Ryde _Or_Die

Ever hear "its better to be safe than sorry"? Well this is especially true with rotaries and even more so with turbo rotaries. Get the safety mods first(FCD, ported wastegate, gauges, fuel pump/injectors, fuel controller), then have all the fun you want with power mods.

NZConvertible

That's good advice; everyone listen to this man!

Rotorque

Thanks again Felix and NZ.

Ryde, are you saying I need bigger injectors too now, or were you just being thorough?

And Felix, yeah, its a money and time consuming hobby, but its harder for me as I don't have the time or ability to actually do any of the work myself (I'm a graphic designer). Luckily I have lots of generous mechanic mates who occasionally volunteer their time and garages. Sounds like a lot of work though - don't want to strain the friendship too much. What does everyone else do if they don't do it all themselves? Must cost a fortune to have all that done profesionally. What a predicament .

Wankel7

I would not call a FCD a safety mod. Maybe the last mod before you open things up after adding the needed fuel. Such as exhaust and intake.

James