RIXSEVEN

What is the easiest way to get more horsepower and torque in my 1985 RX-7 GS (12A engine)? Any ideas would be great. I am adding a Racing Beat exhaust system, but what else could I put on it for extra power? Thanks for your time.

V8kilr

thats a good start,

i have a bunch of bolt-ons im selling for a 12a if your interested,

i have a complete msd direct fire setup for sale,

and just about any other thing you can get for a 12a

eddierotary

iTrader: (7)

custom cold air sistem and a k&n filter

RIXSEVEN

The idea of having a cold air intake is a exellent, but I cannot find anyone who sells a kit for my 1985 RX-7 GS (12A engine). Can someone tell me what company makes a cold air intake or how they make their own? Thanks for your time. Also, how much power is gained from that msd direct fire system?

RIXSEVEN

V8killer, what other bolt on idems do you have for my 12A engine? Thanks for your time.

Directfreak

iTrader: (2)

Pittdp's 1st Gen Page

rx7passion

well what plans do you have for the car performance wise? you going to race it? autocross, drag? first make sure everything is working great good fuel system with decent fuel pump. add exhaust, msd, maybe make up some ghetto cold air intake then save up for a carb upgrade or buy used one. that will make your car decently fast

SilverRocket

If you want more power, get an aftermarket carburator, ie. Weber, Dellorto, Holley. The stock ports on the engine limit power to about 150hp, which can be achieved with this type of setup. Once you have exhaust, this is the only mod that will make significant power other than bigger stuff like porting, turbo/supercharger, or nitrous.

But do your research first; if bought used these carbs *must* be rebuilt and jetted properly. It isn't a small job. Don't listen to anybody that tells you they have a carb which is "ready to bolt on", "pre-adjusted", etc. No carb comes pre-adjusted for your specific car, altitude, driving style, etc. Not to mention, lots of people have some very interesting ideas about what constitutes a "nice running" carb. Count on spending a bunch of money getting the carb running properly on *your* car.

You'll also need a better fuel pump and a fuel pressure regulator. Don't worry about ignition right now, it won't get you much power and it's not worth the money, although people will tell you otherwise. Bottom line - spend your money where it will make the most power, and after that worry about the little things (electric fan, ignition, whatever.)

You can squeeze a few more hp out of the stock Nikki with a trick or two, but it's never gonna touch a good aftermarket carb.

mar3

iTrader: (8)

Do you have to pass emissions? If you do, does it include a visual inspection? Can't help without knowing that stuff...aftermarket carb setups are tricky when you have to pass emissions, as well...oh, and the electric fan is an easy 65 HP gain!! hahahaha...maybe not...

V8kilr

check out this thread


p.m. me if you have any questions

PaulFitzwarryne

It is dobtful whether a 'cold air intake' has any impact on performance. Once the vehicle is moving the difference between outside air and that being swept into the engine compartment is really minimal. With luck you may get 1/4 hp advantage. Sitting in urban traffic is a bit different depending on the power of your fan and the difference could net say a theoritical 1/2 hp extra.

ghetto-rx7

How much horsepower increase would you get if you had a strait pipe going from the headers to the back. Im talking like if you made this yourself. Oh, and also would it be unbareably loud?

82streetracer

iTrader: (1)

i put a edelbrock proflow triangle foam filter on myh 82. It seamed to make a difference and it sounds cool.

Manntis

Paul, I must disagree. Radiant heat around the engine is absorbed by the air in the engine compartment. People running exposed cone filters under their hood are sucking in heated atmosphere with significantly fewer oxygen parts per million than those with a cold air system; this is the reason for air boxes around filters. By pulling air from outside the car as in the configuration shown by DirectFreak in the above post you get more oxygen per volume, which results in better combustion inside the engine.

Directfreak

iTrader: (2)

By the way, that's Pittdp's car on the forum. I wholeheartedly agree with Manntis.
Which is hotter?

Would you like cool air to blow on your radiator or HOT Air?
Turbo applications show the benefits tenfold, Why do Intercoolers improve performance so significantly?
They cool off the charge air, and are more dense, which means more oxygen per unit of volume than non-intercooled air.

mar3

iTrader: (8)

It would be horrendously loud to the point you couldn't even hear the bass line from a 140 dB sound system...

PaulFitzwarryne

I have real doubts on the use of a cold air box on a NA. The figure often quoted is a drop of 12 degrees gives a 1% increase in horse power. At say 60mph you will be unable to measure any significant change in temperature or Oxygen from adding an external duct to the standard air filter box.

V8kilr

im gonna disagree if you do the job right,

look at the pic of my car for the key element to make it work



if you guessed hood scoop you guessed right
10 points for you

but this also inturn creates a positive air pressure in your engine bay

PaulFitzwarryne

The basic fact is an eleven degree Fahrenheit decrease in temperature creates an increase in power of about 1 per cent.

Anorted basic fact is that a turbo comprises the air causing an increase in temperature, the amount depending on boost, thus an intercooler is a good component. an effective IC gets rid of about 80 per cent of this increase.

The question is to what extent a 'cold air' box decreases the temperature of incoming air.
A good fan will pull a vast quantity of outside air through the radiator so the increase in temperature is small. Heat from the engine will heat the components but will have no real impact on the air going into the air filter. Thus, at the most you are looking at a 1 per cent increase from a 'cold box' as the increase in temperature in air going through the radiator is rarely more than 10 degrees.

In summer I drive in 105 degrees so know the impact of heat. At times I have to put the heater full on to keep
the engine temperature below red. In theory I loose 10 per cent ofpower

A final point, in a 12a I think the outside cold air is cut off so the carb always receives air at a relatively constant temperature to keep the air/fuel ratio right. If this is corect the impact of putting in a cold air box or ducting is being overcome.

WackyRotary

If someone didn't already include this, the stock blue air cleaner has ducting that diverts air from the exhuast manifold when its too cold, hence, the cold air box is a phycological effect for the people who put it on. Those who argue that they can remove the flapper are going to run lean when its cold out since the carb is designed for that flapper to open up as it gets cool out. If they believe it actually helps, let them race a 1/4 run in a non-cold air box car with all the same mods and see who wins in 3 passes.

Pittdp

I think that the gains would range from 3 - 5 % hp, but who can really tell 3 - 5 % anyway. The way I look at it is that wehn you add cool air intake, exaust, upgrade the carb, or even port your engine, you start to see the combined benifits. I think I do feel a little boost with my high flow exaust and cool air box , but it could all be in my head. I would have to have a dino before and after to prove anything. The biggest problem our cars have (12A's) is that if it is hot out side we do not have a computer to adjust the air to fuel mixure and vis versa.

PaulFitzwarryne

I agree with Pittdp that it is the combination of many small improvements that give you the chance to reach say 150ho , the max for a stock ported NA 12a. The problem of measuring each improvement is that it is too small compared with the accuracy of the dyno and variations in temp/pressure.

My changes to date are:-
RB style header, presilencer. exhaust, muffler;
Upgraded Nikki, thanks to REVHED, including mechanical
linkage and K&N airfilter.
Removal of airpump and AC, plus turbo rad fan.

Changes I have thought about but can not justify; fuel pump and ignition-- they seem to work adequately up to the max of a stock port. I nearly upgraded the fuel pump but just changing the filter worked.

Not quite at the magic 150 target but very close!

To solve the problem, as givem by Pittdp, of ouside temperature changes on the air/fuel mix requires some radical thought. My range of temperature is minus8C to 45 degrees, in theory a 5% drop in power output.

Other than changing tune with the seasons, what is the opinion of changing the octane rating of the fuel. High oct when there are problems of too lean and standard when its too rich?

Defprun

I still want that damned hood!

diabolical1

iTrader: (3)

i couldn't have said it any better!

the only issues that you would face with a performance carbie is the emissions ... i don't know where you live and how many loophole options you have for emissions, but if you want to keep the car legal, then it's going to becaome a game of carefully planned mods and the cash to make them happen.

PaulFitzwarryne

I must disagree with Silverrocket and Diabolical. Tuning a RX-7 is solving a series of interger problems. In simple terms, critical components have different limitations.

The first real point is the the limitation caused by the size of the stock ports at about 150hp. This can be reached with a header/exhaust and modified Nikki plua few minor mods. An aftermarket carb does not overcome this limitation therefore is unnecessary.

The second point is the potential limit of a street port, which brings a limitation at about 180-190. A well modified Nikki will just get you there, but a Holley or Webber will get there easier and perhaps be justified. An upgraded fuel pump is necessary.

The third point is the limit of the ignition which is about 230-240hp. the ouput can be reached with a bigger port say a bridgeport, or a stock TII turbo. Clutch and brakes are becoming design envelope concerns.

After that the limitation is the size of your credit card. In practice you need to upgrade everything even the 12a! Bigger turbo is the main option, better ignition, stronger components including dowelling, as the power heads for 400hp +. Keep on spending money and you are going fae a 7 second quarter and frequant rebuilds.

The RX-7 is poorly cost-engineered as the components have different potentials. Fortunately its not like the old Ford T where if someting broke thr research was to redoce the strength{cost] of other parts so there was no redundent strengths. The design of the RX-7 is such that you can progressively upgrade it towards your performance target. Thank your god that it was designed by engineers not accountants!