i'm starting a new "budget" build on a new car and i've pretty much decided to stick with exhaust manifolds for this build. it's not supposed to be a super crazy fast car, just a nice cruiser. i've read in several different places that the l98's got a better manifold, which would make perfect sense, but i'm curious about the other manifolds out there. specifically the l69 manifolds. any info will be extremely helpful.

 

I have a 91 w an LB9 tpi 305 and put the duel cats off my bros 92 l98. the manifolds are differant and it was better for performance. the outlets are 2.25" on the l98 vs 1.75" on the LB9 stock singel cat set up. but the l98s restrict down to 2.0 just before coming out on the pass side. So i think the power increce was from the duel cat set up more then the manifolds, as well as the size of the pipe's. So if i had my stock manifolds on there and did a duel 2.5" set up i think it would have been the same or better. But i dont like to deal w blown gaskets so no headers for me, but cheap 90$ summit headers are going to be better then any manifolds. Just my input.

 

well, i'm gonna build a new y-pipe with mandrel bends and a real y-junction, and i've currently got a set of lo3 manifolds. in your professional opinion, do you think it'd probably be fine? i don't want headers cause it won't get the effect i'm going for when you open the hood. i want the engine bay to be "stock appearing"

 

On a dyno where you are going for every tenth of a horsepower, the L98 manifolds will make a different over the TBI manifolds. On a "stock" engine where you arent going for the 1/4 mile ET record, it wont make a noticeable difference. If it was me, I would search for L98 manifolds, but since you already have the L03 manifolds, its up to you.
L69 manifolds are different in that there is a place for the EFE valve on the passenger side. Otherwise, I believe they're the same as the L98 manifolds with the larger outlet.

 

Down a bit in the following link:

https://www.thirdgen.org/forums/exha...-question.html

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The manifolds themselves are the same. The L69 uses an EFE valve, the L98 a spacer. The L69 driver's side manifold will have a heat stove (carbed car), the L98 won't.

JamesC

 

i think i'm gonna continue my search for l98 manifolds then. no cluncky EFE valve and better overall design than my lo3 manifolds.

the goal is to have a moderately cammed 350 in the car, with stock appearing engine bay that clicks off high 13's. a "stock" car that can compete with the stock cars of today.

 

An FYI: The spacer used in the L98 was essentially the EFE valve without its butterfly.

JamesC

 

can you by chance get any pics of this spacer for me?

 

The following pic is of the EFE valve (sorry, best I could do). The spacer doesn't have the butterfly or the vac apparatus that closes the butterfly:

https://www.thirdgen.org/forums/atta...ll-me-file.jpg

JamesC

 

the spacer on the l98 pass side is not a spacer more of a donut adapter but makes a cone to make the seal but does come off and it's the same l98 or lb9 tpi 305.

 

I haven't seen all TPI cars, of course, but the ones I have seen include the spacer that I've described above. I'd love to see a pic of what you're talking about.

JamesC

 

the silver ones are l98's and the others are LB9's
look down the l98 port (pic 2) and you can see how it neck down to 1.75"
just click to inlarge

 

 

Kevin91Z, are the `89+ L98 exhaust manifolds supposed to be an improvement over the `88 and older?

 

not sure jimdutro
The pass L98 kicks out more, so in a swap the LB9's are better for clearance, like in an s-10, or i'm going to use these in my jeep since the l98's that are on there come close to the frame. look at pics 3, 6, & 9.

 

As far as I know, the 87-92 L98 exhaust manifolds are all the same.

 

Interesting. Your info about the donut goes along with info in the link above. I assume (and you know what that means) that the EFE valve, the spacer, and the donuts are essentially all the same size?

JamesC

 

'91-'92 LB9 single cat manifolds are the same as LO3's. '86-'90 LB9 should be the same as L98.

L69 would flow the same as early LB9 & L98, but would also have the heat stove on the driver's side.

 

i'm picking up a set of l69's next weekend. got a killer deal on them (free) so i can't complain.

 

I used L69 manifolds, Y-pipe, and intermediate pipe on my old LG4 (along with a high-flow four-bolt cat) and was very pleasantly surprised.

JamesC

 

i'm actually gonna build the y-pipe for this one. true 2 1/4" pipes into a 3" all mandrel bent. i can get all the materials together for this for ~$100+my time. i think it'll be very nice

 

Was gonna say Matt i have my old L98 manifolds sitting in the garage, havent posted them up for sale cause i dont care to ship these heavy things but if your interested, ill sell em to you cheap. The air system has been plugged.

 

pm me a price bro

 

Heat stove being the "aluminum" tube that goes from the manifold to the air cleaner, right? And the EFE valve is on the passenger side?

I am pretty sure the 85 TPI has the L69 manifolds, which would be the same as the L98's from 87-92. The 86-89 I am not sure, but the 90-92 LB9 automatics definitely have the L03 TBI manifolds. The 89-92 dual cat 5-speed LB9's have the L98 manifolds, as well.

 

Yes.

JamesC