: 70 caddy exhaust leak

03-30-11, 08:13 PM
hello, i have exhaust leaks at the rear of both manifolds where they meet the block. Can this effect how the car runs (as far as tuning it) or does it just effect performance and horsepower? my car is a 70 coupe deville

03-31-11, 02:44 AM
I don't think it really has any effect on anything, other than being really annoying.

04-01-11, 04:24 PM
There was no computer to mis-read any sensor reading, etc, so other thanthe loudness not too much.

04-01-11, 04:45 PM
Depending on how bad the leak is, you may experience and increase in torque and fuel economy (but it would have to be pretty bad).

cadillac kevin
04-01-11, 04:57 PM
sven, doesnt less back pressure (after a certain point) decrease your mileage and performance?

04-01-11, 06:12 PM
Here in the UK a blowing manifold would fail the MOT test, so it would need to be fixed.
If your worried about loss of back pressure, it would have to be a serious leak, if its only slight, on a 472, as others had said, you wont even notice it, dont worry about it.
unless you dont like the noise.

04-01-11, 11:02 PM
thanks for advice

04-02-11, 12:20 AM
sven, doesnt less back pressure (after a certain point) decrease your mileage and performance?


Backpressure can work with and against an engine. Some (stock) headers are designed in a manner that backpressure can increase the engine's performance at low RPM's. This is not necessarily the backpressure creating torque, but actually it backfeeding into the carburettor and altering the fuel air mixture, which simulates more power. As many of us know, stock headers suck at anything above idle. Ultimately, removing the restrictions will allow the engine to move more air. The more air the engine can move, the more efficient it will preform.

But there are cautions; the more you trim off, the more likely cold air will be sucked into the exhaust manifold, which will destroy the exhaust valves.