Important Info

Keep in mind that I did considerable research before I undertook this project and invested many hours to see it through. If you have built your own engines before and have a firm foundation of mechanical knowledge, then have at it and save some cash. First check your local emissions laws if you plan to drive your turbo car on the street and check your local drag strip's safety regulations if you plan to race it. However, if you are not well versed in working on your own car and fabricating parts when needed, then this may not be the project for you. By making changes to your vehicle, you must realize that you are taking on the responsibility of any possible consequences of these modifications. If done correctly, these methods have proven safe, but you need a general knowledge about how engines work and a degree of moderation. Every vehicle is different and the results can't be predicted absolutely. Some modifications are "hands off" because they take care of themselves, while others need frequent or even constant attention. I will make mention of the risk of each modification listed here. The best advice you can get is to work your way up slowly and think through every step. No one else is responsible for any consequences of your actions, whether you use any of this information or not. (Obviously the greatest risk is a blown engine)

Make sure you uprate the suspension and brakes before beginning engine modifications. Also change all suspension bushings

One major problem I've noticed over all of my years as a car nut is that the average person has no clue how to properly interpret data. If anybody shows a dyno and proclaims, "Look, our special brand X makes Y more horsepower compared to brand Z!", that people will generally believe it to be true. Now, maybe it's the trained scientist in me, but it really offends me that people would post such nonsense. This is perpetuated by the bozos at car magazines who do a SINGLE baseline run and a SINGLE post-mod run and claim that the 2 hp difference seen is a significant difference. These charlatan-like assertions are just plain laughable... any number of things could cause these miniscule differences (car cooled off while installing part, original part being replaced was dirty/malfunctioning, etc.) If you want to truly make claims that are at least somewhat reasonable, you need to have MULTIPLE runs with the same condition to find averages and trends. This problem rears its ugly head again when people make speculations here and there about how these turbos compare to those turbos. As usual i always make multiple runs before posting my dyno sheets and hp numbers. As an example I have two dyno sheets that show the 999cc fire turbo producing over 200hp, but this was a mistake on my part caused by the wastegate being disconnected that forced the turbo to push 14psi of boost into the little engine. I was lucky the engine did not fly apart, the calculated maximum stress this engine can take is 290hp (this was according to my calculations using F1 data from books i have around). This number only means a stock block will not break before that, I should also say it'll cost a lot of time/MONEY to get past the sweet spot on this engines, not to mention reliability issues to get around.

The problem is companies of low character who go for the "bigger is better" angle in their advertising.

The key to making this work, is not how much boost, but how Efficient you can make the engine to get the most out of the power you feed it. Boost does not make power. Efficiency makes power. The more efficient you make your heads, and exhaust on a blown application the more power you will make.

I believe that it is possible to have an efficient enough head that you would actually see boost drop off, and power go up. These numbers are pitiful compared to the numbers that my friends cars are running on pump gas. So this is nothing new.

In addition, someone made a comment about a stock bottom end not surviving on 16psi. I am going to have to disagree. There is a limit, however, that limit changes when using a boosted application. The rods will deal with a lot more power when power is made with compression. With a boosted application the rods are under a constant load, so instead of the stress being put on the rod by stretching of the rod, the compressed air puts pressure on the piston and loads the rod, so in a boosted application the rod will take more than in a N/A application.

I'm going to talk about common mistakes here; bear in mind that optimizing your engine/chassis combination will require dyno work or at least serious experimentation. When I say serious, I mean taking good notes and compare before/after data. A dyno is by far the best method to compare modifications but if one isn't available a good accelerometer is the next best option. A stopwatch is not an effective way of measuring performance and neither is the so called "Butt Dyno"!!!.

Throttle Body Too Large

Actually, the problem here isn't with the throttle body, and it isn't really too much breathing with an overlarge throttle body either, it's problems you run into when installing the biggest TB you can get your hands on. The reason behind using midsize throttle body bores is that installing an overlarge throttle body makes a step in the transition from t/b to intake manifold, forcing incoming air to "step up" as it goes through the intake tract. Most of the air traveling along the walls of the throttle body will "bounce" back out of the throttle body (reversion) when it encounters this step. The bigger the step, the more air reverts. A too large TB will also cause the engine to bog at low rpm while a too small TB will restrict at high rpm. There is also the matter of worse fuel injector atomization performance as the pressure drop in the intake manifold is reduced, but the primary factor is throttle body bore to intake manifold fit.

Ignition Timing Advance

This is a great one, but it only applies to cars that have adjustable timing. You'll hear some guy at the races rattling off his mod list. "Intake, exhaust, header, advanced ignition timing..." I don't know about you, but when someone says they advanced their ignition timing that pretty much means they turned the distributor all the way to the stop. The reasoning behind this is that advancing ignition timing means that the sparkplug fires earlier before the piston hits TDC. When you advance the timing as the engine idles it actually revs higher. So it seems like more torque is being produced. Well this is true... but only within a certain RPM range, so you might get a little more umph down low where you can feel it, but doing this usually sacrifices major power everywhere past 1,500 RPM or so. Over-advancing timing also causes spark knock, and that'll kill an engine in a short amount of time. I've personally seen power gains on the order of two to three horsepower during dyno tuning sessions with those gains coming from changes to ignition timing less than two degrees from stock. And that's even on engines with pretty decent mods such as intake/exhaust/header and wild street cams.

Too Much Fuel Pressure

Ideally, we'd be shooting for a stoicheometric air/fuel reaction, which means there is exactly enough molecules of oxygen to react with every molecule of fuel. That works out to approximately 14.7 pounds of air to one pound of fuel (14.7:1). But engines are more of an assembly of compromises rather than ideal mechanisms so we have a bit of a fudge factor to deal with, and therefore we consider the ideal air/fuel ratio to be a bit on the rich side. Namely, anywhere from 13.5:1 to 12:1 (this is for power and not economy, most likely a stock car will fail emissions with this ratio).

Oversized Fuel Injectors

Same rules as the fuel pressure regulator. Normally you won't be swapping injectors to something larger unless you're dramatically increasing the engine's airflow capacity (10% and more). Running a basic wet nitrous system won't change the injector requirement, since the nitrous system is providing a good deal of the fuel. Swapping injectors also presents a variety of other technical difficulties because not all injectors open and close at the same rate. So you might swap out the stock injectors for another brand of injector with the same flow rating, yet the engine will run horribly.

Setting Adjustable Cam Gears

Shifting an engine's power curve fore and aft in the RPM range by adjusting cam timing is easy to understand: Advancing the cams advances peak torque; retarding the cams retards peak torque. So if you want to enhance low-RPM power for street use, advance the cams slightly. If you're going to be drag racing—which pretty much means shifting at red line and generally running only in the upper RPM range—retard the cam timing. The first impulse of many home tuners is to pull cam timing to get at that high-RPM power, and they'll almost certainly get a few more ponies by doing this, but there's a point of diminishing returns. Namely, over-retarding the cams to get one more high-end HP but losing 10 more down low. Same goes for advancing the cams; add some timing, get a great feel off the line but you'll be strangling the engine when trying to rev it out. A real dyno is the best way to tune, but cam gears can also be adjusted until peak manifold vacuum is obtained. This isn't an ideal emissions situation but will generally improve overall performance on most cars, especially those using speed-density systems such as Honda. Messing with the timing can lead to damaged engines.

One last thing about tuning cam gears on DOHC engines. Going too far forward or backward with both cams can cause problems with piston-to-valve interference. Narrowing the lobe separation angle (advancing intake/retarding exhaust) can cause problems where the intake and exhaust valve heads scrape against each other. While the adjustable cam gear can flatten up torque curves, it can also cause major headaches if not used properly.

Falling for the Gimmick

Funky little devices that increase intake air swirl, magic oil additives and little stick-on devices that supposedly improve fuel economy. When shopping for parts, remember if it sounds to good to be true, it is.

Removing the Air Filter

The removal of the air filter is some cars will actually produce a power loss because of a reduced intake length. Since it creates intake "growl" people seem to think it increases power.

Reduced Air Pressure in Radial Tires

The reasoning here is that a flat tire has a bigger contact patch than a full tire. As with most things automotive, what you can observe by eyeball alone with no backup data is almost always invalid. When a radial tire is flat, what you see are the sidewalls lying on pavement. What you don't see is the tread area of the tire folded up into a U-shaped cross section. So what you have on pavement are the tread shoulders and a little bit of the sidewall while the primary traction surface is on vacation. Some tires will run ok with reduced pressures in a drag race situation, but all the radials I've run on the strip preferred pressures anywhere from 60% to 90% of maximum pressure. Actually, the pressure didn't seem to influence 60-foot times as much as it affected trap speed, but traps were always better with more air pressure.

Parts of this text and ideas were taken from http://www.overboost.com , I'm not sure if the story is still available so I've taken the important parts and posted them here. I'm still awaiting the author's reply regarding copyrights even though I've reworded some parts. Originally written by: Scott Croughwell

The reason I'm trying to acquire outside information is so people don't think I want to influence them to do things one way or another. I believe that if something works good for someone it may not work the same way for someone else. One great example is the trannies I've been using, they all broke at some point yet this last one had the highest mileage and with an oil cooler has lasted 4kkm of track abuse and is still going.

What type of dizzy is this???

The type you get from standing up too fast when your blood pressure is low?

10: It's not Dizzy, it's a Distributor.
9: It's not Carby, it's a Carburetor.
8: It's not cammy, it's a camshaft.
7: It's not engy, it's an engine.
6: It's not an "O" pumpy, it's an oil pump.
5: It's not an "F" pumpy, it's a fuel pump.
4: They are not sparkys, they are spark plugs.
3: It's not a cranky, it's a crank shaft.
2: It's not a tranny, well,,,, OK, tranny is short for transmission.
1: And the big one, it's not a single 3 letter word "NOS", it's N, O, S, they are just the initials on a sticker that stands for Nitrous Oxide System, a company that sells Nitrous Oxide System's.

... and I suppose it's not a bonnet, it's a hood; not a boot, but a trunk and not a wing, but a fender. Yikes!