John Holmbergs Corvette C4
In mars 2003 I went to Germany to buy a black C4. After a few months I got bored with the 250 stock hp. I decided to upgrade it. first I bought a par off headman hedders, I knew the headers wood create a enormous mount of heat so I wrapped them in because there is a lot of plastics and the space in the C4 is limited. I also cut away the catalytic converter a welded together a 3" stainless steel exhaust, it made the vette sound great. The next step was to make the engine breathe more, to make it easy we start at the front of the car. First I cut off most of the air filter lid fig 1.3. Then I did some modifications on the MAF sensor. I removed the screen on both sides of the sensor and removed the heat sink fins with a hacksaw,(the screen is only good for keeping birds and rats oute of the engine) the MAF sensor works perfect whiteout them. (During hot weather testing in Death Valley I'm told that consists of wide open throttle for hours and then shutting down without any cool-down time, a couple of MAF´s failed). The next step was to increase the diameter of the barrels in the throttle body. Stock diameter is 48 mm witch flows the same ass a 600 cui carburetor. I machined it up to 52 mm which is the same a 750 carburetor, I also made an air foil fig 1.4 and 1.5. Then I had to do something about the intake manifold. The long tube runners on the stock TPI motor will make it peak at 4200 to 4500 RPM. This is wonderful for grandma around town, but it will not get the job at the track. So I bought a LT1 intake in eBay fig 1.6. The LT1 intake have much shorter runners which allows the motor to peak its power at higher RPM. But there was a lot of issues to take care of. First the cooling was a problem. The LT1 doesn't have the same water system. I had to make a thermostat box witch includes the thermostat and the water neck bolt on top of it. Now it's time to fix the bolt pattern. The four corner holes are correct, all the rest are wrong. I first filled all the wrong holes with Weld. Then I bought stock standard V-8 gaskets to locate my new holes. I also had to drill a hole for the distributor. Then it is time for the fuel system. If the engine needs more air it also need more fuel. I hand to make my own fuel rails and adjustable fuel pressure regulator Fig 1.7. After al upgrades the car can mustard a 0-100 in 5.9 sek.
Stock MAF sensor with screen and heat sink, remove it and
it will increase the flow. |
Machining of the throtle body from dia 48mm to 52mm,
which is max what it can take |
Before machining |
After machining and airfoil added |
Drilling of the LT1 bolt pattern to match it to the L98 |
 |
The new LT1 intake with the fuel rails and adjustable
fuel pressure regulator powdercoted looking good! |
The old intake whith runners but without the plenum |
The stoc TPI intake |
The vette and the cobra together, looks cool !! |
The nice wood interior and ortopedic seates |
Cornering at Kinnikulle raceway |