Dj1981tpi

Hey everyone. New to the forum this is my first thread. Ive got a 1981 corvette that i dropped a 1990 corvette engine into (map). A few questions here. Its got just a k&n air filter on the throttle body and its making a LOUUDD hissing noise. I doubt its just induction i think its a vacuum leak. But it runs fine? Also. Im looking to do the throttle body coolant bypass. Remember this engine is in an 81 corvette so the engine bay isnt the same. Where does this coolant line go? How do i bypass it?

Dj1981tpi

Im not sure how to post photos. And i also tried building a cold air intake for the car but the hissing noise is still there. I want to do the bypass because after the car reaches operating temp, it really loses seat of the pants power. Im blaming it on the hot coolant running through the throttle body. Regardless i want to bypass it.

Ps. Emissions checks dont exist where i am. Im in alberta

caddyboy84

The coolant line on the passenger side goes to the heater core, the other goes to the manifold coolant nipple right under the throttle body. Bypass it by taking the heater hose right to the manifold. The other heater hose goes to the waterpump.

Dj1981tpi

Do u have a photo of what this looks like exactly?

caddyboy84

I have pics of my car on my page here, I don't know if you'll be able to see anything usefull though. Click on 1988 Corvette under my name on the left. After that click on "see more pictures" on the left.

94z07fx3

OP you could take a cardboard box and cut it to fit snug around your K&N and only leave a tiny bit open. As a test device at idle your car won't need much air. This might dampen the sound enough for you to hear if any other source is contributing to the noise. How many vacuum ports are there on the L98? Disconnect them one at a time and put your finger over them to see if there is a difference finger vs connected hose.

Cliff Harris

If you think you've got a vacuum leak, the "smoke test" is the way to find it.

From a previous post in another thread: Pull off a vacuum line and blow smoke into the manifold. Here's funny guy Scotty Kilmer showing you how:

http://www.youtube.com/watch?v=zMok2...5&feature=plcp

caddyboy84

I was wondering, you didn't say exactly what was on the engine you swapped. Did you keep any of the pollution stuff on it that may be hissing. Try the old trick of spraying the manifold with a carb spray or W-D and see if it stops the hiss. Usually a vacuum leak will effect the idle, there really isn't too much goin on in that area that would be hard to find. Try putting your hand partially over the throttle body and see what happens, if there is a leak, I'm thinkin it would be harder to stall the car by covering the throttle body.

Dj1981tpi

Yeah total polutions delete. Here in alberta we dont need any pol. Control. No pump, longtube hdrs. Egr dlte. A lot of the unnecesary sensors are out to. the computer on it basically just runs the injection for optimim. These engines really come alive if u strip all the s**t off oft them. An ill post a pic of my engine bay here soon.

caddyboy84

Are you sure it's a problem and not just the normal air-intake sound, it does have a sucking sound and probably more so with a total delete. You said you had an open air-cleaner, all the air-cleaner ducts on the L98 quiet it down a bit, I would imagine it being a little louder without all that.

Aqualoo

Does it have an idle air control valve? Mine makes a "hissing" noise till it warms up a little. (After about 30-90sec) Also I did my coolant bypass in Florida during the summer when it was in the upper 90's everyday. Didn't see any difference at all. However the throttle body does stay cooler but of course then you have the hot intake plenum after it.

C4in mesa

I was wondering what if any benefit there is to me bypassing the TB ? It is over 105 here during the day brutal hot ! You said none with your car. I have a 1988 C4. I am having issues with sitting at a light and it getting over 240 degree's.