Hi there,

thinking about swapping my exhaust mfld to newer ones, I've read in the Camaro performance book by David Shelby, that the stock ones after 89 flow pretty well for stock, cuz headers are not allowed overhere. What heads can you recommend which work fine with stock exhaust mfld, I was told the L-31 will not fit. What hp gain can I expect ?

1985 IROC-Z28, LG-4, Q-jet, double airsnorkel, no cat., Flowmaster, Edelbrock perfomer mfld., dyno 193hp / 150rwhp

 

What is the reason that headers are not allowed there? You have eliminated your cat. (That is a big no-no here in the states)
Why couldn't you buy emissions legal headers? As long as they have the O2 sensor bung and the A.I.R. tubes, you should be good to go. Edelbrock, Hooker, Heddman, and quite a few others make emissions legal headers for these cars.

The reason the L31 (Vortec) heads don't work, is that you would have to plumb your egr from your exhaust (ie: air tubes). They also take a special intake manifold because of their very different bolt pattern. You could try to find a set of L98 aluminum heads from a corvette. They are the pre 87 intake bolt pattern, are 58cc's and have d-shaped exhaust ports for better flow.

If you are dead set on just replacing the manifolds, you might try to find a set of 4th gen (rams horn) manifolds. They flow alot better than the log-type manifolds that our cars come with, and they have the d-shaped exhaust ports, too.

 

The reason overhere is almost everything needs to be proofed and be ready for the MFK which is similar to the German TÜV, I know it sounds weird, headers are not allowed but cars before the year 89 don't need a cat. That even means every single car which was imported before 89, cat needed to be removed, it is really crazy. In general altering your car with parts that can be easy recognized as non original is pretty difficult. For my Centerlines I received a permit, also for the Eibach Pro-Kit, which was from the company who built those parts. To be honest the amount of US-cars especially 3rd gen Camaros is pretty small overhere, cuz they were not officially imported for some years. So the US companies are not that interested in paying for those tests just to support the customers overhere with permits, which I can understand. We have to let the goverment check our cars every 3years (rust,electrical stuff, mech. functions, brakes and much more...) I need to change my muffler for every inspection, also removing my tailightcovers etc., so I would like to get some heads which fit to the 305 and also don't need to much altering for using stock exhaust manifolds. By the way my car was bought in Canada and it doesn't have the A.I.R. tubes, will I ever find without tubes which flow better than the original ones on my car ? You guys overthere don't know how lucky you are altering your cars, the way you like. I could have headers, but it would cost about $4000-5000 just to get this tests and this is tooo muuuch. Anyway hope you somehow understand my way of explaining in English.

 

Hey swissiroc - don't worry, your English is great - better than some Americans' I've read...

Hey, I don't know if you're aware of it, but there's a process called "Extrude Hone" which forces an abrasive paste through a part in order to smooth internal surfaces and/or open it up to flow more air... This way, the part (in your case an exhaust manifold) looks completely normal on the outside, but flows significantly better than stock... Unfortunately, I don't have any info on pricing, but you should be able to get more info at one of the two links below...


Hope this helps!

 

Hey V8Rumble,

thank your for telling me good news about my English and my exhaust maniflods. .
To be honest, a friend of mine was also talking about the "Hone" stuff. I'm going to inform myself, what price level this will be.
That means I will not find any 89-92 manifolds which don't have the A.I.R. tubes ? What about the L-98 heads, will they fit "normally" ? Will there be a gain of 20-30 HP ?

 

L98 iron heads (14011083) are 64cc, whereas your 305 heads are 58cc, so your compression will drop. On a side note, the valves are bigger: 1.94in 1.5ex. These heads use the 87-up intake bolt pattern, but that is easy to get around, by elongating the 2 center intake bolt holes or either side.

The L98 Aluminum heads (10088113) are 58cc, and have the same pre 87 intake bolt pattern, so they should match up perfect. They are also 1.94in 1.50ex. The only real difference that I see is that they are angle plug design.
If you port these heads, and use a thin head gaket, then you should see a pretty good boost in HP.

Do you think it would be okay for you to use the stock LT1 manifolds (rams horn), or would there be problems with that too? If you are not interested in the AIR tubes, just plug them off.