ramongloria

does anyone know if lt1 exhaust manifolds will bolt on to l98 heads?
can the manifolds be ported out for better flow?

VetNutJim

They will bolt on.
However the LT1/LT4 exahaust ports are square. Most of the later model L98 exhaust ports are D shaped.

The original L98 exhaust are really close to 'shorty' header style.
They can be ported to an extent also.
The flanges can be ported and matched to the exhaust ports.
There's alot of 'meat' on the L98 exhaust flanges but there is NO excess metal in the actual pipes.

The collector of the original L98 exhaust ports can be ported also.
There's not alot there to take out but there is some.
The exhaust pipes are 'necked down' where they brought all four into the collector.

I don't think you'll gain anything changing over to the LT1/LT4 exhaust manifolds.

Changing the exhaust system downstream of the manifolds to the LT1/LT4 system is a good thing to do.
Replacing your L98 manifolds with longtube headers is also a good thing.
Hook the headers up to the LT1/LT4 exhaust system. Without spending big bucks for 5 more HP, that's the way to go for an L98... IMHO.

STL94LT1

LT1/4's have D-shaped exhaust ports.

CorvAdel

I agree...
The LT1 engine I have sitting on my w/shop floor has D-shaped exh. ports, which is the same shape as the exh. manifold, 36mm wide x 33mm high.
The Hooker-style headers I have hanging off my w/shop roof are to suit L98s and they are square, in fact, a little more rectangled, 33mm wide x 40mm high.
Another set of stock 98 exh. manifolds are square...31 x 31mm.

ramongloria

the headers you have on the wall are they shorties?
would you part with you l98 exhaust manifolds?

garkahn90

I am just finding out that LTx's exhaust manifolds with bolt up to your L98. But there is not an EGR fitting on the LTx's. On an LTx the EGR and AIR aparently share the same plumbing.

FELNGR8

Yes, the LT1 EGR hangs off the back of the intake manifold. The AIR pipe is dual purpose to route exhaust gases to the back of the intake manifold from the center of the pass side exhaust manifold. And for the first 4 minutes of engine operation the AIR blows fresh air into the center of each exhaust manifold. I got a good look at a bone stock LT4 two weekends ago and the pipe construction is identical, with the difference being no EGR on the back of the intake, just a block off plate.

Farnkly I don't know why someone would want to replace L98 mainfolds with LT1 manifolds. The L98s are essentially shorty headers and the LTx are heavy, cast, more restrictive, manifolds. One reason GM went to the LTx design was to quiet the underhood noise for picky new car buyers.

juanathandavid

question: what about the collector sizes on the manifolds?

Don't the L98 manifolds jave a 2.25" collector, whereas the LT1 manifolds have a 2.5" collector?

wouldn't a true dual 2.5" exhuast be better than a stock L98 exhaust?

VetNutJim

That is correct but.... the EXHAUST MANIFOLDS DO NOT have the "D" shape ports.

I have a set of LT4/LT1 manifolds ..... and the ports are square.
Have I got a some special ones or something?

The head ports went to D shape in what..1990? That's when the '113' heads came out, I think.
The '128 heads will 'mate up' better to the LT1/LT4 EXHAUST MANIFOLD ports.

Here's the reason NOTto change from L98 to LT1 exhaust manifolds:

If you just want a nice cast iron manifold then the LT1/LT4 exhaust manifolds WILL bolt up to your engine.
If you're willing tomake that change you probably won't be concerned about NO EGR and getting the A.I.R system hoocked up to them.
AS far as the EGR tube is concerned, you could easily drill a new on in the manifold if you HAD to have it.


MIS-MATCHING the exhaust ports by using a larger exit port on the manifold than the exhaust ports on the head is used to create an 'air dam' that 'can' reduce intake dillution charge from the exhaust side.

Changing to the LT1/LT4 exhaust manifold will be a total waste of energy if you're doing it for increased performance.

Read my previous post. 'Bout everything you need to know is in it.

STL94LT1

Looks like you got the rare non D-port manifolds.

VetNutJim

NOPE!!! I'm just WRONG as HECK.Those are just like the ones I have.... I just remembered them WRONG.
I got to be getting that oldtimers disease.
#%@%!@$ I hate it when I'm wrong.


Mia Culpa,Mia Culpa.

I just got back from the garage where I checked and MEASURED the port sizes on the LT1/LT4 exhaust as well as the L98 exhaust manifolds.

Here's the LT1/LT4 exhasut port sizes.
Yes, there is a GIGANTIC middle port that would be split by the seperator in the head....

LT4/LT1 both end ports... 1 7/16 x 1 9/16
Middle Port.....................1 9/16 x 2 1/2
Exit Port at the collectors.... 2 1/2"

L98 ALL ports 1 1/4" kind of square... round edges in the corners
Exit Port a the collectors.......2 1/4"

L98.....There are TWO of the tubes (on each header) that are squished down looks like to clear the heat shields

The LT1/LT4 exhaust manifolds DO LOOK, TO ME like they would flow a little more than the L98 shorty manifolds.
A LOT more maybe????

The L98 headers are poorly made with a lot of weld covering the port in the exhaust manifold. I don'y know how much there is to gain by cleaning that up but I did it to mine. Probably about 1/2 HP gain for all 8. Not worth all the grinding and sweating, LOL.
The LT1/LT4 exhaust are a lot nicer made piece IMHO.

The LT1/LT4 exhaust manifold HAS a center port 'injection' fitting for the A.I.R. system. I only checked one of mine but I think they have 'one each' of these holes in both manifolds.

Knew I had those back for there for something, guess I just forgot what they looked like and I still don't remember why I have them. Must's been planing something for my L98.

Sorry for the erroenous info above guys. Memory ain't working good as it used'ta.


OH, head port exit sizes..I almost forgot.... I JUST measured these also.

128 Head Exhaust ports..... 1 3/8" x 1 5/16" 'Square" ports....rounded a little in the corners
113 Head Exhaust ports...... 1 1/4" x 1 1/4" "D" shaped ports.

Again, sorry for the wrong info I posted, guys.

89onlyZ51

Are the collector end of the LT1/4 and L98 the same size as well as the bolt pattern? I know the LT1 manifolds will bolt up to my 113 d-port heads just fine, but I'm wondering if they'll also bolt up to a stock (or Corvette Central "true-dual") exhaust system.

I haven't had the opportunity to hold both types of manifolds at the same time. By the crude measurements I was able to take of each at different times, it seemed the bolt pattern of the LT1 manifold was slightly larger than the L98.

Tom

VetNutJim

Tom, I'll check that and post the info back here tommorow.
It's about 12:30 am here so it's too late to go out there tonight.

Jim

VetNutJim

Tom, you are right.

I measured the collector bolt spacing between the L-98 manifold and the LT1/LT4 manifold.

They are close to the same but not quite exactly.
This distance is from any one bolt to the next bolt.
Here's the measurents:

L-98.............. 3 5/16

LT1/LT4 ...... 3 1/2"

89onlyZ51

Thanks, Jim. With your measurements, I took the risk and picked up a set of LT4 manifolds, and it looks like they'll swap in for the L98's. They both have a 3" collector, and the flange angles/heights seem to be exactly the same.

I figure that by slightly elongating the bolt holes in the down-pipes with a dremel, the LT4 will be a direct swap for the L98 manifolds. I'm not sure if it will buy anything, but having only 1 1/4" (with the welds) openings on a 1 1/2" exhaust valve on the L98 can't be good for upper-end breathing.

Tom

bill mcdonald

I dont know if the LTX manifolds have this issues, but I removed a set of cast iron manifolds from an old truck I have to repair some head gaskets, and I could not get them back on. I had to drill out the holes on the manifold to get them back on. I think they heat up and move on you.

89onlyZ51

Not so much an issue with the LTx's as they have a support bar between each of the inlets. I know it won't be a problem with mine as they are new