I have an exhaust leak on my 1988 454 unit. I've read a few items where replacement headers are the way to go. Couple of questions: Is thorley the best bet and what part/style number do I need? Where does one get these installed? any additional stuff needed? and the approx price? I've found them on the internet for approx $375. Any comments would be appriciated. My local gmc truck dealer said they don't do that kinda work.

Probably a 303Y-S, but check their printed catalog or call them to be sure. www.thorleyheaders.com
It will depend on the smog pump/pumps and attendant fittings on the manifolds.

If you are going to remain smog-legal, you will want their heat riser valve, as the stock is too small to flow well. The reducers will connect to a straight 2 1/2 inch exhaust pipe and performance muffler on each side, exiting with a 90 degree outlet just before the first rear axle. If you already have a2 1/2 inch dual exhaust, the Thorleys will connect to the existing pipes. It will be a bit quieter if you have an H pipe installed. Any decent mechanic or muffler shop can do it. Be sure to shield wires and hoses from heat from the headers. Inquire at you local speed shop. You will be very pleased with the results. Before you do this, take a stop watch and climb a hill and record the results. Then do it again with the Thorleys.

Hi KC, It is my understanding that Thorley makes a number of headers that will fit the 454, however, there is just one that is for "our" application. You might also want to check out the Banks system. It is costly be is complete. You are looking at $2500 to $3000 installed. Banks System for '89 454



As far as who could do this installation. Any RV guy or good mechanic. In some areas (not mine) some of the midas muffler guys will do it.



[This message has been edited by davebowers (edited October 17, 2002).]

I'd really think about it before you go to headers.In some cases they may be cheaper, but now you have to modify things.Make sure your really not happy with your engine performance first.The stock manifolds will ussally out last a set of headers,they even offer after market sets that are a lot better than stock(not as prone to warpage and offer better flow).Now if you decide you want to go to headers Dave is right on the money with the Banks system, and the key word is system.This is a engineered system that should be installed completely to receive the best performance.Just my opion hope it's helpful.

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I won't start it here, but several other fora have discussions on Bank$ vs Thorley. For my coach, banks offered headers, tailpipes, mufflers, a K&N air filter element and a flex tube for cold air intake. The K&N is of doubtful value and the cold air intake can be made from a 4 inch dryer vent tube. Both are guaranteed for life. I have a suspicion that the Thorley Tri-Wye design is superior for motor homes over the Bank$ equal tube design, but I can't find the research to prove it. A so-called "desktop dyno" program bears this out at RV RPM ranges.
You will get favorable opinions from users of each. None would ever go back to stock.
The only "modification I had to do were heat shielding of wires and hoses. Easily done with thin sheet metal and hose clamps.

I just checked my 86 p-30 regal my 454 has a bad exhaust leak.I thought it was the right side manifold,but when I checked it out only the donut gasket had blown out.Alot easier and cheaper fix.Be sure to double check it.See ya

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