i have an 86 z28. i have swapped the 305 4bbl for a 350 4bbl 4 bolts main. pair of aluminum heads and performer intake manifold. i have used the factory distributor and exhaust manifolds. put a hypertech high spark coil on and high flow cat with a dyno max cat-back exhaust.
my question is can i have the stock exhaust manifolds bored out? and can i have a big y-pipe made? if so, will this help my performance at all. im not allowed to get headers, my parents said i couldnt(dont laugh) so i have to think of something to replce them.

im also having as we speak a cam installed and my heads milled and ported. i think the exhaust work is essential. im also thinking of getting annaftermarket chip, or a custom chip.
any comments welcomed

 

Your parents won't let you get headers, but they'll let you shave and port the heads and install a new cam? That's crazy.

You could upgrade to better exhaust manifolds, I suppose, but I've never heard of anybody porting/boring the exhaust manifolds. Getting a custom y-pipe made shouldn't be too hard, though. A local exhaust shop could do it. I don't know of any aftermarket y-pipes for the stock exhaust manifolds.

I think you should knock your parents over the head repeatedly, until they come to their senses.

 

I agree... I don't understand your parents at all..

-LJ

 

Ummm, with all those mods, you're engine is being choked, I say screw your parents, buy headers, and install them, they'll never know

 

Um...did they give a reason for no headers?? Cause that makes no sense that they let you swap in a 350, with new heads and intake manifold, but not allow you to add headers. Are your parents the type that "add gas and push the pedal" or do they know about cars? I'm guessing the former, cause that makes no sense at all, to me anyways. As for your question, I don't think there's much you can do to stock exhaust manifolds, unfortunately. That's why I'm using mine for doorstops . Good luck!

 

Especially since the stock manifolds and y pipe on an LG4 motor are just horrible.

 

thats bad!! parents says he can have a 350 but not headers?
kind of like that kid whos father said he can't have a V8 and had to swapa V6 into a IROC.
biker
if they don't know about cars get headers!!!

 

-LJ

 

Ha!

Oops, that just slipped out.

Okay, seriously, here's what you're gonna do: What you said, but a little different.

Don't bother with your LG4 exhaust manifolds. But, get a set off of an LB9 or L98, and "port" them.

You want the ports slightly larger than the exhaust port of the head, but still sealed by the gasket of course. Clean them up a bit as far as you can reach inside. You're done on the top side.

At the "collector", open them up as much as possible without exceeding the ID of the y-pipe that you got off the LB9/L98 at the same time you got the exhaust manifolds. Again, clean them up as far as you can reach.

Install them with the y-pipe (or, you could have a new one made at this time), a 3" high-flow cat, and 3" cat-back.

I know two guys who run stock-type exhaust manifolds at Bandimere. One is a '90 RS w/ZZ3 that's been highly worked over, and he did the above to LB9/L98 manifolds (but used a factory dual-cat arrangement). Runs low 14's at this altitude, and I think it's got more in it (converts to 13 flat at sea level - he just moved to Fort Worth, guess we'll find out soon). The other is a '37 Chevy pickup (that's not a typo, it is "nineteen thirty-seven") with a huffed 383. He uses similarly ported rams horns on it, weighs 3700 going down the track, runs 13.2's here. He won "Best Engineered" at Division V ET finals in Topeka this year. However, early October the passenger side broke off at the flange (thin from his porting work), so now he needs to do something to get it back together (find another one to port, or go another route).

Or, get headers...

 

hey dont laugh but the reason i cant get the headers is not because of power, but because of noise.
my father is great with cars, but says i cant have headers because there too loud and they will burnup wires just like his did on his blazer.
i need more options please help.

 

Kinda sucks having your parents looking over your shoulder. My dad "had" to put a cat back on my car, but he payed for the high flow cat and the hooker catback + install so I guess I shouldn't complain . It should still flow better than the 2.5" midas crap that was on there before.

If you do what five7kid suggests, you could also run an slp y-pipe. I don't understand why your parents wouldn't let you get headers while your getting port work done and a cam... headers can be a bitch to install but they seem to be worth an extra tenth or two. What point about them do your parents not like? Just about any of the downsides can be remedied with the right headders, Edels and 2055's seem to be easy to install, and the 2055's coated or the edels plated will last for longer than you'll probably keep the car.

Hey five7kid email me next time your down in Topeka, I'd like to see your ride. Haven't found anyone else on the boards that lives here though. My "new" car is definitely faster than my 86 LG4--With the timing way off the 86 ran an 18.14 really pitiful, needless to say I'm much happier with the new GTA .

 

Headers won't make a car overly loud. Obviously you're dad is inexperienced as you can get mufflers that are hi flowing, yet are just as near quiet as stock even with headers.

Ever hear of "sleepers"?

Also, about the wire burning, he has a point there, but wire looms and ceramic coating have solved that problem

 

My parents got me a set of headers for a b-day present lol dunno what I'd do if they told me I couldn't do things to my own car... wait, I'd do them anyway

 

Ever think of Extrude Honing the Manifolds!

 

what is extrude honing?

 

Extrude honing is a proprietary process that forces an abrasive paste through a passage, removing flash and some material to smooth out the flow path. The paste mimics the fluid flow (exhaust, in this case), so it takes off more material where there is a restriction and leaves it alone where there isn't. However, you want to do the rough porting first (like opening up the flange areas), since it won't remove a substantial amount of material.

The guy with the RS that I talked about above had his runners, base, and heads extrude honed together, to give you an idea of what I meant by "highly worked over". This was after the heads were CNC ported.

Things may have improved over the years, but it typically isn't cost effective for one-off work, because set-up is a time-intensive process, but once it's set up, multiple runs are a breeze.

 

i agree, do they realize they are making no sense? i wouldnt spend a dime on the stock ****...

 

yeah i agree try and get some L98 manifolds...

 

Get the headers.. and get a quiet muffler.
Kill the sound not the flow..

 

if anyone is still reading this, i have great news. i showed my parents what you all said and tossed it around. they gave in and bought me headers for christmas. now i have no problems, thanks everyone for your help.

 

swwwweeeeeeeeeeeeetttttttttttttt


headers are good


way to go


good luck

 

Congrats!