Im not exactly sure, can someone explain?

 

Exhaust manifolds usually refer to the cast iron log style with holes where each port's gasses pass through a short run into a main chamber which leads to the exhaust pipe. In the broadest sense an exhaust manifold is a term that covers the device connected to the exhaust ports that directs gasses away from the ports, which includes headers.

Headers consist of iron or steel tubes from each port that join together at a collector from which usually a single tube leads to the exhaust pipe.

Headers can be of several designs, shorty, long tube, stepped and equal length.

L98 exhaust manifolds are actually shorty headers since they consist of short SS tubes from each port that connect in a collector which is connected to the front Y pipe. These flow pretty well but are not especially tuned to our motors.

Long tube headers, such as TPIS offers, are usually the L98 upgrade path as they are tuned to a certain RPM band. Also they are larger in diameter than the stock shortey headers, which aids in reducing restrictions in the exhaust system.

This should give you at least an overview on the topic.

 

Concur all the above. Headers will allow the engine to breath better too. A Big boost in HP if used with the right exhaust system. Warning headers reduce the room you will have in the engine compartment, a mother to install, and often have to tighten up the system every 6 months or so. If you are lazy like me..stay with the original crap.... if you love tinkering then go for it...

:flag

 

I understand that full length headers on a L98 will gain about 5 hp. I think you could gain more putting in a mandrel bent front y-pipe and gutting the cat. Big HP gains aren't in the cards for L98 Vettes because the original manifolds are so good.

I also did some clean-up work on my 86 exhaust ports when I put the 90 motor in and I'd bet that headers would gain me hardly anything. Grinding down the AIR tube intrusions into the exhaust stream should gain you a bunch. While I was in there I smoothed out the flow at the collectors and port matched to the heads.

 

Where'd you get that? The header designs for most new cars free up more room than the huge stock castings. I know my hooker headers cleared up a LOT of room under my hood. Then there are the F-bodies, anything is better than their stock manifolds. Hell on them you cannot do the spark plugs, when you take it to the dealership they drop the motor out of the car to do it. With headers it's a 30 minute job.

Also if you use the right bolts, tightening is not an issue either.

BTW, headers on the vette are cake to install. 1 full day tops.


[Modified by Nathan Plemons, 3:34 PM 8/10/2002]

 

Our L98s have effectively shorty headers that realy don't take up much room under the hood. So I think on an L98 full length headers would indeed take up a little more space just from the longer tubes. From build up data on a '90 L98 Vette TPIS headers netted about 15hp (from trap speed data) over the stock front Y. Indeed going to a mandrel bent front Y and cleaning up the stock shorties may get very close to that figure; this is the route I've taken.

I believe the LT1s have the log style cast manifolds that are bulky. When I replaced the cast manifolds on my IROC with full length heades it realy opened up some space and made the plugs much easier to get at. It also gave me a nice boost in HP.

 

Full headers release about 10-15hp on L98s, with as much as 20-25hp from a good catback combo. The exhaust manifold is the most restrictive part on the L98.


[Modified by vader86, 5:34 PM 8/10/2002]

 

Yea, I would say you pick up some good power. Check out my sig. I figure I boosted factory power output by about 20% with little more than a full on exhaust system.

 

Exhaust manifolds are the factory connection from the exhaust port on the heads to the y pipe (or to the exhaust pipe in duals). They are usually cast iron and their job is to be quiet, not break and seal well.

You can also get tubular shortie headers. These are usually made from tubular steel and are much lighter than stock cast manifolds. They may have a larger inside diameter and care may be taken with bends to insure smooth surfaces with little restriction. Weight savings is a major benfit of shortie headers.

Long tube headers are usually made from tubular steel and are also much lighter than the stock cast manifolds. The advantages however of long tube headers is the tuning of the exhaust pulses to the advantage of scavanging exhaust gases from the combustion chamber (can actually provide a vacuum to the open exhaust valve/combustion chamber). This tuned effect, similar to the long intake runners on an L-98, can effect an increase in HP across a range of RPM. Properly designed and fitted to an application the results can be quite impressive. Improperly designed (or "1 size fits all" products) long tube headers offer only slight improvements beyond "shorties".

 

The LT1 manifolds on 92-96 vettes fit very well in the engine compartment. They have heat shields and bolts that stay in. They are very well designed so perfromance gains from substituting long tubes are not as much as they are when headers are put on engines that have the F body manifolds.

Many aftermarket headers (especially true for stainless steel ones) have bolt loosening problems the first few miles because of the expansion properties of the flanges. Thicker flanges can help reduce this problem. Most aftermarket headers don't come with heat sheilds, don't clear heat sensetive places very well and rust like you would not believe after a while. Virtually ALL aftermarket headers (measure them and you'll see what I mean) do not have equal length primary tubes so the tuning affects from them are never realized. The actual gains come because the stock manifolds were really bad and or the rest of the system that got replaced to put the headers on was really bad.