There are a few ways to answer this…
1) Drive your car in 5th gear at 50mph. Cruise along so that the rpms are half way to redline. Double this and this is as fast as the engine can run.
2) The biggest problem is wind resistance. As you go faster the force of moving forward through air goes up big time. Every time you double your speed air resistance quadruples. So you may never make it to top speed in 5th because of air resistance
3) The car could have a built in limiter. Normally around 110-120mph.
4) Tires with a small flaw (nail, low pressure, cracked sidewalls, old) will fall apart at about 100mph and you will die.
To answer your turbo question….WOW….there are a lot of factors here. IF your engine is healthy you can add about 100hp to it. If you want to build the engine the the skys the limit. Do it right the first time. If you buy a no name ebay turbo for $200 and just slap it on you will blow your engine in about a week. Please research more. It is all about TUNING. Get a good tune please.
the b16 engine (1.6 dohc vtec) in the high end civics from this period have anything from 158 to 185 hp as standard
(vti = 158, sir = 170, type r = 185)
Top speed is 137mph to 145 mph depending on modell. (japs limited to 115mph)
As for a turbo, there have been many, many turbos fitted to various civics in the past and in the future. the amount of extra power produced will depend on many, many factors. Most people will tell you to STAY AWAY from fitting one as a cheap boched job will fry your engine.
The whole car will have to be rebuilt to accomidate the extra power.
engine and transmition will have to be completly overhauled with upgraded internals, as well as new ecu mapping and extra cooling.
Usually will cost AT LEAST 5000euro for a deacent job and seeing as you will probly get a mint 98civic for 7000euro its gona cost a lot of money.
would be cheaper to buy a scooby or simillar.
You will get at least 50hp extra from the turbo on low boost but anything up to a 150hp gain is not uncommon.
One other Major factor for not fitting a turbo is that if you crash and the insurance company comes to assess your car and sees the turbo your in big, big trouble!
No Insurance company will insure it and you cant hide a turbo!!!!!!
Anyway hope this helps!!!
Austin hit it right on the head.
The amount of HP gain is dependent on amount of boost. Normal atmospheric pressure is about 14.7 lbs. If you run about 7 PSI boost this means in reality you will have 21.7 PSI absolute (or about a 45% gain). This will increase your HP (in theory) by 45%. This does not increase the possible top speed. It just helps you get there faster!
lets put it this way… my 2000 civic si barely hit 120mph… i know it would have went a little more…. and possibly.. but highly doubt 130mph… you having a 1998.. if its stock top end motor you could have is a SOHC VTEC,.. but still could probably do 115-125mph… itll take a long time though….. if you have a stock motor in you 1998 civic, i DO NOT recommend turboing it. Save your money and get a more powerful motor (such as the si motor) and then turbo it… it will be well worth it… you can get a b18b motor from japan (integra motor) for 700 bucks shipped… those are way better for turboing.
hope this helped!