Question on Natural Aspiration

Ok, my cousin has a 91 protege GT with a 1.8L DOHC 16 valve inline 4. It's currently producing about 170HP stock but he wants to get it up higher, possibly to the 225 range. He could take the easy way out and just turbo it but he'd rather not use forced induction.

So I'm looking for information on tuning an engine through natural aspiration. Among other things I suggested possibly boreing and stroking the engine. I'm not sure on any of the specifics of this particular engine such as it's current bore and stroke(although just from the time period and type of car I thinking it's probably pretty square) But i was thinking possibly boreing it to a 2.2L(again, not sure if it's even possible, but hey, let's just pretend for now ;)). Then, strokeing it back down to a 2.0L to increase the redline because he wants more top end power then lowend torque.

Also, I'm looking for all the different ways to up the engines compression to whatever it can take(while still being able to run on pump gas, i think it's about 11.0 or 11.5 to 1?).

Now what would be needed to do this job? both in parts and procedures, and what possible problems might there be?

For example if we shorten the stroke to increase redline would we need a new cam/valve system? possibly a custom machined one?

And if this all worked out, pushing up the compression, increasing displacement, and increasing redline. Just how much of a gain in HP do you think we could manage?

Also, whats a good estimate for the new redline if the current one is about 8000RPM?

Thanks in advance for any advice you guys might have :D

yeah, you could do taht, replace the parts with lighter titanium wones, differently times cams, if you wanna stay n/a, then get the insides polished, port the heads. There's a lotta stuff you can do, but putting on a turbo wont kill it with all those other parts anyway, so i figure you might as well

Yeah, but with the added cost of all these parts plus the bore, stroke, and porting it would make turboing something for the fairly distant future(unless he wins the loteory or something.)

Plus, the car already has 100,000 miles on it and it's his daily driver. So if we can get about 225, possibly like say 250 or maybe more N/A then that would be all we want because the car only weighs 2000lbs as is, once it's finished it'll probably be closer to about 1700lbs, And 225-250HP is plenty for a daily driver that weighs so little.

Plus we just like the challenge of tuning the engine as opposed to just turboing it :)

Why spend a lot of work and money on NA when you can get twice the power at the same price with a turbocharger.

yeah get a turbocharger and spend the same amount of money in gas as n/a....do n/a

...Or buy a lumpier cam and stiffer valve springs.

See thats also a concern, since it's a daily driver he doesn't want it to eat gas like say a turbo would.

Originally posted by CAptynCrunch
See thats also a concern, since it's a daily driver he doesn't want it to eat gas like say a turbo would. You can't have your cake and eat it too. In the world of engineering, it is full of compromise.

Originally posted by CAptynCrunch
Ok, my cousin has a 91 protege GT with a 1.8L DOHC 16 valve inline 4. It's currently producing about 170HP stock but he wants to get it up higher, possibly to the 225 range. He could take the easy way out and just turbo it but he'd rather not use forced induction.



I don't know where your cousin is getting his info, but according to the information I can find on the net the naturally aspirated "BP-DE" 1.8L DOHC 4 cylinder only makes 125hp (and redline is at 7000 RPM, not 8000 RPM). Even the turbocharged version in the 323 GT-X car only made 163hp, the larger turboe'd version found in the 323 GT-R made 185hp. So unless your cousin's car has an engine I can't find any information on, could you make sure the specs you gave are correct and if so what is the engine code?

Turbocharging is the only smart way to go with this engine, if your cousin is more concerned about speed than anything else he'd definitely see that. If he just wants something to sink a bunch of money into without great results, then have at it in NA form and watch the costs spiral.

The JDM version of the 1800 GT-X made 180hp, and the GT-R made about 240hp. :)


I have seen them avliable from importers in the US, and swaping one in really is the most efficant method of getting a whole lot more go into your Cousin's car.

Turboengines can have a quit good milage, what about a 500 hp engine which only uses 8l/100km or 29 miles/gallon during normal driving?

To get cheap speed from that 1,8 engine I whould have equipped it with a MHI TD04HL-18T turbocharger, these costs around $300 if you buy it in second hand. Then, modify the stock manifold or build a own manifold with steeltubes. A bypass valve is needed, but these are cheap, just go with a bosch stock valve, price around $30. Intercooler is good to have, and doesn't have to cost so much. Then the compression ratio must be lovered, the easy way is to go with a thicker head gasket, why not a copper one with o-rings. Copper gaskets with o-rings are what they use in top fuel dragracing cars, the only downside is that the block (and the head if wanted) must be machined. Tubes from the turbo to ic to intake is a must, 2" is probably the right size for this application. Then it's just to figure out how to get the extra fuel, this depends of what fuelsystem the car has and how much money one would spend.

So you wants the horsepower. First Overhaul the engine, give it a bore and stroke. Give it a good cam but not to hot of a cam. Easy way to increase compression is to get good pistons. Increasing compression is really a good thing to do because that is where alot of power is loss from todays engines. With your cam you need lifters and then if you gots money left go get a good intake W/ HEADERS. And dont worry were you redline at. Make it a daily driver w/ balls not a ricer w/ a turbo. Most people think all they can do is strap on a turbo which is not the case. Lot more work goes into supercharging cars than most ppl think

Originally posted by The Dude
Make it a daily driver w/ balls not a ricer w/ a turbo. Most people think all they can do is strap on a turbo which is not the case. Lot more work goes into supercharging cars than most ppl think

To have any kind of balls that engine needs forced induction, it's not a good candidate for an NA buildup. And while its true that ignorant people don't know what it takes to build a solid, reliable turbo engine, fortunately in this case the factory efforts already have two different examples for him to follow based upon his specific engine.

Ps- Most ricers do stay NA, all they have is a set of plug wires and a farty exhaust.

Originally posted by texan




Ps- Most ricers do stay NA, all they have is a set of plug wires and a farty exhaust.
:D OMG!! I was working in a shop a year or so ago and a customer came in w/ a Neon. He was bragging about how fast his car was. I was rotating his tires and replacing a valve cover gasket and notices he only put bright yellow tubing over all his stock wiring under the hood and spray painted the valve cover silver. Typical ricer...:bloated:

Thanks a lot guys, you've been really helpful. I've shown my cousin your replys and he's starting to agree with your opinions and is currently looking at turbo's. Or possibly importing a gt-r engine. Not quite The 13b he orionally wanted to put in it, but i don't think transplanting a rotary engine into a protege would be the easiest or cheapest thing to do.

On a side note, does anyone have any input on the difficulties/practicality of converting the FWD GT to 4WD like the GT-X? Could it be done simply by installing the necesary parts(differentials, etc..) form a 4WD model?

Sadly the floor pans of the 4WD and FWD models are TOTALY differnt.

Iv seen it done on a Lancer in Ausie, but the guy was a panel beater and had to buy a GSR Lancer, and weld the floor from it into his FWD Lancer coupe.
Far to much work for any normal person to even think about.


I dont know what models were avlaible in the US but in Japan there were non-Turbo 4WD models, which will easily take a Turbo swap.
However you dont get the bigger brakes and stiffer suspension of the GT-X or GT-R models.




A Rotary engine could be possibly. Theres a 13b powered Mini running in many local races here at the moment and doing quite well.

You would need totaly custom engine mounts. A suitable FWD G/box capable of handling the power (for the mini its a Toyota Corona 5sp), with custom axles to suit. And a custom adaptor plate between the engine and Box.

Then you have to worry about making the engine work. This means basicly a custom engine bay wiring loom. as well as a suitable fuel supply.

Its not really a back yard swap.

Originally posted by Moppie
A Rotary engine could be possibly. Theres a 13b powered Mini running in many local races here at the moment and doing quite well.



Not to mention a green 323 with a 20B I beleave?

Anywho, about the thread. Some mentioned the concern about gas consumption with a turbo. Just because you have a turbo doesn't mean you have to drive around on boost all the time. I think that considering the base engine forced induction would be the best way to go. I'm sure given the time and money one could hit your target HP figures leaving it N/A, but it would be less costly to turbo it. And once you add a hairdrier, there is a whole new field of tuning to get into... Hybrid turbos, remapping boost, all that good stuff :licker:

Originally posted by Gonthrax


Not to mention a green 323 with a 20B I beleave?



that's a good example of what can be done if you really want to. this car started out as a FWD 323. it now has a non turbo 20B driving the rear wheels, sounds cool and goes hard. as i understand it this guy's brother started making a FWD rotary 323 but it didn't get finished.

from what i understand the BP is pretty similar to a miata/mx5 motor, surely some of these have been worked as atmo's?

Originally posted by cadet



from what i understand the BP is pretty similar to a miata/mx5 motor, surely some of these have been worked as atmo's?


I dont know, they will be similar since both are Mazda engines, but visualy they look very differnt.

However that said, there are plenty of Turbo kits avliable for the MX5 (miata for the yanks) and Im sure it wouldnt be hard to make one fit a 323.

Us and Canada got some awd protegés. with the sohc 1.8 engine. a pretty rare car. as they are mated with the fm15-r tranny, a bpt swap isnt a good idea.

Theres a guy running around where I live with a 323 with a Probe/Mx6 V6 swap. Thats a pretty damn quick little car...the guy has no interior save for two racing seats and mabye some speakers, im not sure. But regardless, its an amazing car.

Here's the real deal
It takes X amount of gas to move X amount of wieght at X speed.
no ifs, ands or buts about it
when hopping HP you must plan on
1- the engine will not run as smooth
2- you will use more gas
3- maintance quadruples
HP is no fun if you don't use it
A super or turbo charger is the quickest and cheapest major HP gain.
Either on a stock engine gives the biggest boost for the buck.

For anyone out that that has ever thought about using a turbo no matter how big it is may be it is not a fix to make your car fast and you cannot just avoid doing other work. There have been tests from two of the same cars on was stock and the other had a huge turbo on it. The car that ran the fastest believe it or not was the one with no turbo. Without doing other mods to an engine and just putting a turbo on will cost the same amount of money in the end if not even more because of things breaking and you could have to get rid of the whole engine by braking a rod. So in the sum of things you are better off to have other things done to your engine first and the last thing you should think of is forced induction.

Why spend a lot of work and money on NA when you can get twice the power at the same price with a turbocharger.


Show me.

I can't get twice the power with turbo without twice the cost in fuel -- race fuel. Otherwise, it's whopping intercooler, water injector, and pump crap 91 octane, and maybe 20% power improvement at low RPM or mid-rpm high load, and finally 40 to 60% improvement at high rpm. I'm presently at 80hp/liter NA at 6200rpm, no gadgets, leisure maintenance intervals, and I get to hear my 5 valves per cylinder chop the intake air. A turbo obscures that beautiful sound. Anyway, I've a turbo on the other _broken_ car. <<< get it?

Show me.

I can't get twice the power with turbo without twice the cost in fuel -- race fuel. Otherwise, it's whopping intercooler, water injector, and pump crap 91 octane, and maybe 20% power improvement at low RPM or mid-rpm high load, and finally 40 to 60% improvement at high rpm. I'm presently at 80hp/liter NA at 6200rpm, no gadgets, leisure maintenance intervals, and I get to hear my 5 valves per cylinder chop the intake air. A turbo obscures that beautiful sound. Anyway, I've a turbo on the other _broken_ car. <<< get it?
Add a turbocharger, lower the compression ratio a bit and modify the fuelsystem. With 1 bar of boost you should now have twice the power compared to the stock engine. How much would it cost to make the same power increase when keeping the engine NA? It wouldn't be cheap.

Most stock NA engines can handle boost pressures up to around .5 bar with stock compression ratio when an efficienct intercooler is used (the fuel system must of course be modified). A small drop in compression ratio would easily increase it up to 1 bar without the need for any racingfuel.

Spending the same money on a NA and a turbo engine the turbocharged one will easily have more than twice the power.

"There have been tests from two of the same cars on was stock and the other had a huge turbo on it. The car that ran the fastest believe it or not was the one with no turbo. Without doing other mods to an engine and just putting a turbo on will cost the same amount of money in the end if not even more because of things breaking and you could have to get rid of the whole engine by braking a rod."

Those guys that did that test have probably not made anything right, if there is any test at all. I know of engines which are turbocharged and the only thing that is modified is the engine management, fueling, compression ratio is decreased and a better head gasket is used, then a turbocharger and intercooler is added, with this the power output is more than doubled - on pump gas. Among others I can mention a BMW M5 engine (the old 3.8 inline 6) developing more than 700 hp with those modifications. What that will do for a cars performance needs no explaining.

Show me.

I can't get twice the power with turbo without twice the cost in fuel -- race fuel. Otherwise, it's whopping intercooler, water injector, and pump crap 91 octane, and maybe 20% power improvement at low RPM or mid-rpm high load, and finally 40 to 60% improvement at high rpm. I'm presently at 80hp/liter NA at 6200rpm, no gadgets, leisure maintenance intervals, and I get to hear my 5 valves per cylinder chop the intake air. A turbo obscures that beautiful sound. Anyway, I've a turbo on the other _broken_ car. <<< get it?

Don't forget that that the power of the engine is directly proportional to the amount of fuel (air/fuel if you want to be technical) you're stuffing into it. Sure on an N/A you can port and polish the cylinder heads, stroke it, get in lumpier cams and all that. All you're really doing is getting more gas into those cylinders. A turbo does the same thing: stuffs more air in there so you can mix more gas with it and have a bigger boom.

And the reason that turbo's produce more power (generally) is becasue quite simply, it can stuff more air into the engine than the engine would be able to suck in itself. An N/A engine would be hard pressed to get positive pressure in the cylinders at BDC.