I have a cracked driver side exhaust manifold. I have reviewed postings on the topic of replacing stock manifolds with headers and would appreciate any new comments or recommendations. Thanks for any input.

If you reviewed the postings here, you should be pretty well-informed. This is kind of a Thorley fan club.

I can't post anything new.

But just in case:

If you have true duals on your P30, the Thorley headers will match up with band clamps. If you use a heat riser, you will need a larger one than stock.

I thought it showed up as part of my signature but I have a 1985 25' Regal with a 454. And yes I have true dual exhaust. I'm not sure about a heat riser. Can someone elaborate?

I had Thorleys on my '85 Regal (454/P30something) and had no problems. Had to replace the gasket on the passenger side but that was because whoever installed them put in a cheap gasket.
Humbo

I have Thorleys, replaced one set when they developed cracks after about 12 years. May have been due to stresses resulting from loose hangars, etc. New ones are ceramic coated, look good, perform well. Check my posts, I installed them in March, numerous pics.

The heat riser is a valve in the exhaust which forces exhaust through a passage in the center of the intake manifold to warm it up faster. They often stick closed and cause back pressure problems and overheat the manifold. Unless you drive in very cold temps you don't really need the riser.

GM sometimes calls them an EFE valve (early fuel evaporation, I think) same thing. Some have a bimetal spring to move the valve, some have vacuum actuators like this:



Good luck with your header installation.

quote:

Originally posted by Steve VW:


Unless you drive in very cold temps you don't really need the riser.

Being a hot-rodder, I have had a number of vehicles without a heat riser. On colder days (yes, it freezes in Southern California) they required a warmup period. Usually letting it warm up while I wiped the dew off the windows or checked tire pressures was enough time.

You can form your own opinion by wiring the valve open for evaluation.

The main advantage of blocked off heat riser passages is to keep hot exhaust from heating the carb above or the oil beneath. I have torn down a number of engines that had coke deposits built up on the underside of the heat riser passage on the intake manifold.

I can't comment on increased horsepower due to improved exhaust flow, as I can't afford much dyno time. Joe Mondello used a custom made cast iron plug in the passages or the heads, but I don't know if that would show any benefit at MH RPMs.

quote:

Some have a bimetal spring to move the valve, some have vacuum actuators like this:

FWIW, my '84 454 came OEM with a vacuum diaphragm right on the heat riser valve.

Doug Thorley headers ordered. They have a 10% discount promotion online and free shipping.

quote:

Originally posted by Boonton Jim:
Doug Thorley headers ordered. They have a 10% discount promotion online and free shipping.

..
Just for fun, climb the steepest hill nearby, and take note of your speed at a few points.

Then, after the Thorleys are on, do it again and share it with us.

First part of hill climb test completed. Route 280 W in West Orange NJ. First hill from a stop on ramp 55mph at top. 2nd hill 64mph at top. Headers should be installed this week. Will try to repeat test next weekend.

The test was not very scientific but slight gains in mph noted at last mile marker at top of test hills. There was an increase from 55 to 57 mph in the first hill from a stop on the ramp and an increase from 60 to 63 mph at the top of the second hill. I'd like to believe it is the result of the new headers but can't be certain that initial acceleration on first hill or cruising speed at start of second hill were identical with first run.

Very interesting. I would not be surprised if you did see an improvement, the headers are much better than the stock iron manifold. (and so much lighter!)

Thanks for the feedback.

Ambient temperature at time of test can make different results. I have never met a vehicle owner that didn't get improved performance after spending $200-$500 on something.