The plan: Maximum power on minimum parts. What's REALLY necessary? (1994 RX7)
 

https://cimg3.ibsrv.net/gimg/www.rx7...15078038b5.jpg
Hey all,

I've got a 1994 RX7 I bought last year, it's all stock except for all the maintenance mods and a full 3" exhaust.

My plan is to leave as much of the car OEM as possible but I do want to increase the power as far as I can, I'd love to hit 350-400hp with a VERY stock appearing engine bay.

From what I've seen it looks like a lot of people put on a lot of parts that really just aren't very necessary for their HP level. I'm all for a pimped out engine bay on some projects, just not this one.

From my research here it seems the the OEM fuel system can handle 15psi and 400hp.

It also seems the the stock twins can go pretty far as well although I'm not sure of the actual HP limit of them.

I'd like to run an Apexi Power FC for tuning and I will be running water injection with a 50/50 mix of water/methanol.

It seems to me that the stock IC will be fine as long as I have the water injection installed.

I don't really think the stock IC pipes are a true and actual flow restriction at or below 400hp on this car.

The WI should extend the stock turbos efficiency as well which should help things.

I plan to run the water injection into the stock air box feeding both turbo inlets from right there.

So my real question is - how far can I go with just exhaust, water injection, PowerFC tuning and more boost?



Thanks!
Fred


https://cimg7.ibsrv.net/gimg/www.rx7...d58dfaee7d.jpg

I'd say 320-350 whp max, the restriction being the stock injectors, even at this level they may run near 100% duty cycle (depending on the tune as well) which is a very risky game as maxing out the injectors means running lean.
I'm not sure about the stock turbos though, pretty sure BNR twins (which will keep your stockish look and feel) can make that much of power.
Water injection with stock intercooler sounds like OK to me.

The car looks very clean, btw

I would agree on the turbo and injector upgrades which would only look other than stock to a trained eye.

Where in Missouri are you located? I'm in the south KC area.

I'm in Carthage, just south of you a little ways down 71.

Oh cool, I've ridden down that way a few times on the bike. There are some great backroads around there.

You can easily hit your goals if you spend the money and focus on "stock appearing"

Do a few simple things:
1) BNR (BNR-Supercars) Stage 3 twin turbos (will look stockish still)
2) Upgrade the fuel system. Keep the 550 primaries and send your secondary 850cc injectors to RC engineering to have them ported to 1300cc and put in a Supra Denso Fuel Pump.
You can also go with newer secondary injectors like like ID2000s or FIC 1650s with a CJM secondary fuel rail that will keep the FPD and stock FPR. The rail and injectors would be changed and would appear relatively stock.
3) Definitely need AI if you are keeping the stock IC, just go with a bigger nozzle or two if you are running BNRs and I would run it under the stock compression tube.
4) Clutch will probably need some love due to slippage. Excedy or ACT Clutch
5) Power FC will allow you to run up to 17psi without changing out to a 3 BAR map setup

That will get you in the 350+ whp range or more.

*The stock fuel system is NOT adequate for increased boost. I'm not certain where you were searching, but more is required.
*The stock IC is small, inefficient and as much a flow restrictor as anything. AI/WI at the intake won't help that. Additionally the stock intake scavenges air from the IC duct, further reducing the IC efficiency. That can be fixed easily though. Search in the 3rd Gen. Section under "Cheap Bastard Intake" mod.
*Running AI into the stock air box will require a relatively large fluid reservoir with a management system. Packaging for such a reservoir and system will be difficult and aggravated by your wish to keep a stock appearing engine bay.
*The stock twins quickly run out of efficiency past about 12 psi (20% above stock level) and start producing as much heat as boost. AI will help, but is not a silver bullet for that. Now while you're sending ALOT more boost to the IC inlet, it's being reduced significantly by the stock IC. The PSI going in isn't being realized at the throttlebody. The stock twins life-span is also reduced. How much is a variable.

IMO hitting your hp goals will be difficult/not practical with your requirements. I think compromise is needed. Either lower those power goals (the car will still be a lot of fun) or be prepared to put some aftermarket bits under the hood.

WHAT HE SAID^^^^^

BNR twins
99 Y pipe (factory piece from a different year and aids reliability in my opinion)
There are fuel systems that can use factory banjos or use fittings to appear as stock as possible.

Pretty sure

Thanks for the reply,

I read this thread about using the stock fuel system to hit 15psi and 400hp -
https://www.rx7club.com/time-slips-d...-boost-833955/


Running WI into the stock air box will not require a larger reservoir than any other nozzle location. Also running it pre-turbo actually allows you to run a MORE simple WI system, one that doesn't even use a pump or controller but uses boost pressure to feed the water (mechanical water injection).

I also don't buy the common lore that running higher boost noticeably shortens the lifespan of the stock turbos, it may take them from 150,000 miles down to 100,000 or something but it's not going to kill them inside of a year or anything, there's just no reason it ever would.

Also I should clarify that my goal here is not just a stock LOOKING engine bay but it's to actually make the most power I can using as many stock parts and as few aftermarket components as possible. So upsized injectors and rails and BNR turbos are out of the picture for now.

Thanks

Suit yourself. And best of luck.

Increasing boost on stock turbos will cause them to fail earlier. It's well known and I suggest you search more threads. Increasing boost increases the speed at which they spin, increasing wear. It increases heat in the underhood compartment, shortening life. Also, there is a pressure ratio that is on the exhaust side as well, so by increasing intake charge, you raise the backpressure as well, increasing heat, pressure, and velocity. Over-doing it on stock parts will cause premature failure, even as short as a year or less. Again, do some more searching.

What you have heard about the twins going far probably refers to BNR upgrades, or non-sequential and heavily ported 99+ twins.

This damn car is like Ying and Yang.,
If you put a YING On it you better have a Yang to make sure you have the YING operates cirrectly.

In other words,Putting on ONE part is not advisable without knowing the circumstances of what that part will do in reference to the car's operating ability.

Case and point.
I wanted to upgrade fuel...ok..
New Injectors..Check..New rails..new lines..new regulator..new pump....(holy cow..we done yet?...nope!)
How will the car run now?..crappy..need new ECU..
Neeed new Turbo..Intercooler..couplings,pipes..OH..exhaust downpipe..Manifold,wastegate.,blow off valve.

I'm broke now..and all I got left is this internet....

Stock appearing is do-able. VERY stock appearing not so much because you'll be replacing a lot of stock items.

If you are referring to the fuel lines themselves, that is correct. However in order to provide enough fuel for 400HP you will need to upgrade the pump and injectors. You can stick with the stock rails and lines. Keep the stock primary rail with the silly side feed injectors, then use proper top feed injectors on an aftermarket secondary rail because it will give you better options. 1000 - 1200 CC secondaries would be fine. There are side feed options if you REALLY want to keep the stock fuel rail.

About 300 - 320HP is the practical, reliable limit of the stock twins. But that comes with boost control issues as well as decreased turbo life. Just not drastically reduced.

OK. I'm not knowledgeable in the Power FC but it seems to be popular with the FD crowd.

I wouldn't recommend it. The stock intercooler is undersized for the stock twins. There are upgraded units available which fit into the stock location, and will be adequate with water injection.

No, but they are plastic and they suck. You will want to replace them. Paint the new ones flat black.

Post turbo is much more efficient.

Note that you didn't mention any cooling. The stock rad is insufficient in a stock configuration. Plan on upgrading to an aftermarket rad.

Ok so I think the plan is I'm going to add nothing more than the water injection system and the Power FC and get it on a dyno and simply raise the boost until it either runs out of fuel, runs out of turbo (won't hold boost until redline) or stops making more power even with more boost.

This is really the only way to know for sure how far the stock parts will go.

I'm 100% certain somebody else has done this before in the 23 years this car's been produced but for some reason this knowledge just doesn't seem to be out there or I'm not looking in the right places.

Nobody does it on purpose because it results in a blown engine. Leaning out and detonation has been happening on individual cars for decades and those failures have led to the suggestions being offered here.
With any upgrade, compare the risk involved with not doing it: Would you rather spend $500 on injectors or spend $3K on an engine rebuild plus $500 for the injectors?

Lastly, finding the limits of stock parts is like finding out how fast a 80 year old person can sprint. You get a particular data point on old technology and worn out parts, but you'll probably kill it.
Whatever you end up doing, good luck.

You're quoting one line from a thread 7 years ago about a race car company with no supporting details. That's the equivalent of starting a story with "My buddy's cousin's gilfriend's uncle's car..."
Ironically, the suggestions in that thread are identical to the ones here and you are choosing to dismiss those too.

What's your plans for the car?

Just drive it around on nice wknd?

I drive it on nice days and the wife and I take it to Coffee and Cars.

Dude come on. If you are going to mod the car do it properly. Don't try to save 200 here and 200 there. Be a responsible grownup. Keep the stock twins. Get fuel. Clutch. Intercooler. Hks twin power. Power fc. Run 15 psi. Make 350 Rwhp. It's not rocket science.
Throw in meth inj for added reliability.

What's the deal here. What are you trying to prove.

I don't think the stock map sensor supports 17 psi. I am rusty but I thought it was more like 15.7 psi

This is false. It's fine to run 15psi everyday for years. You will make good power too, around 350 on a healthy car.

I guess this is the "new" forum belief. Back five yrs ago when I was around more just about everyone ran 15psi on the stockers with tremendous success.

I ran 15psi for 8 years and the car was amazing. I had a low setting of 12psi. But absolutely never ran 12psi unless I was on a road coarse.

350 on a stock motor stock twins car is absolutely reliable. I'd check with guys like fritz Flynn if you don't believe me. Many would argue that this is the best setup in terms of reliability and street ability on these cars.

But then again everyone is into drifting now. :(

I'm not trying to save money :) I'm just trying to avoid buying any parts that aren't truly needed for 350-400 hp (my target) and also keep as stock looking of an engine bay as possible. With water/meth injection it may be possible on the stock IC and piping, I'm honestly not sure, I'll have to try it. If it isn't then I'll get a M2 medium size IC and all the other parts required to run that, but I'd like to avoid all that if possible. I'm ok with the twin power if the stock ign system can't do at least 350hp. Clutch is no problem if needed.

Now that sounds like the voice of actual experience. Thank you.