Stock 350 Olds EFI intake manifold

[SpeedMan]

Hello,
Cadillac Seville in the 70s, had an 180hp 350 Olds that was Bendix/Bosch port fuel injected.
I first thought it had an regular really low and flat singleplane type manifold, but the manifold is just one giant plenum without runners, just like a blower manifold, is there any thought behind this? I mean, it is Cadillac, the "Standard of the World"..
I would think it is not the lightest car, and no intake runners in the manifold at all would probably not exactly help in torque production..

Have anyone here driven these? Where they afraid of some cylinders going lean/rich maybe? Since I think it is a "fixed parameter" injection system.
They made that engine/injection system for many years, maybe low performance but so was everything else at that time, and it must have worked decent enough for them to keep making it like that?

Seeing some of the stuff from the 70s and 80s I sometimes think there was no tought behind it at all though, but at the same time interesting and some "what if" scenarios.

Olds EFI intake.jpg

[Tom68]

Hello,
Cadillac Seville in the 70s, had an 180hp 350 Olds that was Bendix/Bosch port fuel injected.
I first thought it had an regular really low and flat singleplane type manifold, but the manifold is just one giant plenum without runners, just like a blower manifold, is there any thought behind this? I mean, it is Cadillac, the "Standard of the World"..
I would think it is not the lightest car, and no intake runners in the manifold at all would probably not exactly help in torque production..

Have anyone here driven these? Where they afraid of some cylinders going lean/rich maybe? Since I think it is a "fixed parameter" injection system.
They made that engine/injection system for many years, maybe low performance but so was everything else at that time, and it must have worked decent enough for them to keep making it like that?

Seeing some of the stuff from the 70s and 80s I sometimes think there was no tought behind it at all though, but at the same time interesting and some "what if" scenarios.

Olds EFI intake.jpg

Looks like they were chasing fuel economy and maybe emissions at the expense of everything else, no low rpm power, no midrange power and no upper rev range power.

[dfarr67]

It's MPFI- no need for a fancy manifold.

[SpeedMan]

[/quote]
Looks like they were chasing fuel economy and maybe emissions at the expense of everything else, no low rpm power, no midrange power and no upper rev range power.
[/quote]

How would no intake runners promote economy and emissions? It is not heated either, but of course EGR and probably hot air flap in intake ducting or something similar probably. I think maybe the plenum is not as big as it seems in total volume, since it is so flat, so I guess it is more of an small/normal plenum (volume wise) short runner intake. But I have not one to take a look at in real life.

It's MPFI- no need for a fancy manifold.

So, since it is port injected the runner length does not matter?

[travis]

It's pretty much the same concept on the L31 vortec 350... barely any runner length and a giant plenum with MPFI

[SpeedMan]

It's pretty much the same concept on the L31 vortec 350... barely any runner length and a giant plenum with MPFI

The one that look like a smaller Crossram or Crossfire manifold? That has some runner length, as long as they could be, atleast without turning.
But I am not to updated on all those manifolds.
This Olds manifold har zero runner length, the only runner length is in the cylinder head. Strange, I think the other Cadillac EFI manifolds has runners all the way.

[BOOT]

It's pretty much the same concept on the L31 vortec 350... barely any runner length and a giant plenum with MPFI

The one that look like a smaller Crossram or Crossfire manifold? That has some runner length, as long as they could be, atleast without turning.
But I am not to updated on all those manifolds.

Crossfire/Vortec, one has dual TB top other Port Injection top, basically same base/lower but both with longer cross runners in the intake than that olds one. I'm not an olds engine guy what is the total intake runner track?

[SpeedMan]

It's pretty much the same concept on the L31 vortec 350... barely any runner length and a giant plenum with MPFI

The one that look like a smaller Crossram or Crossfire manifold? That has some runner length, as long as they could be, atleast without turning.
But I am not to updated on all those manifolds.

Crossfire/Vortec, one has dual TB top other Port Injection top, basically same base/lower but both with longer cross runners in the intake than that olds one. I'm not an olds engine guy what is the total intake runner track?

The total length from valve seat to plenum opening? I will have to measure an Olds head, but runner length in cylinder head is an relative "normal" length maybe. But in the intake manifold you have room for somewhat longer runners, if you want to, compared to f.ex. an SBC intake since an Olds intake is a bit wider.

[chevyfreak]

I had one of those 350s. Came out a eldorado. Very low output engines. Low everything. Block has window webs. For a engine it works like a engine, but its just built as an engine, As a performance setup, there is waaaay_yyy beter out there.
Intake only has to move air.
I experimented with mine, again , nothing special happened. Made a adapter to mount a 4jet and cut the throttle body pad open to suit. Closed that up and mounted 2 x 2jet inline with the ports.ran the same.

I suspect it was made just to get it emissions compliant and cadillac being cadillac, went their way of doing it. And the caddy owners i know cruise their cars, they never race it, like rolls royce drivers. If it was really the hot ticket it would have been used longer. Just my thinking. From what i remember Only cadillac used it for a brief time.

Olds 307 still used a carb (ccc type) thru the 80s where others were using tbi etc.

Chevyfreak.

[SpeedMan]

Chevyfreak.

Interesting, I would bet it would work better with just the normal dual plane. It is a strange design. I cannot see it having any benefits to anything at all, except equal cylinder filling for the fixed injection to work good and equal for each cylinder. Hood clearance I would think would not be an problem on the Seville either.

Did you weld in the manifold? I was thinking about trying to use this type of manifold it as an base to make my own intake manifold.

[BOOT]

The total length from valve seat to plenum opening? I will have to measure an Olds head, but runner length in cylinder head is an relative "normal" length maybe. But in the intake manifold you have room for somewhat longer runners, if you want to, compared to f.ex. an SBC intake since an Olds intake is a bit wider.

Yah to where the runner starts inside the plenum, sounds like it's gonna be short. Intake runner length tuning. Still like mentioned doubt it's really that great for an old intake.

[nhrastocker]

The Oldsmobile 350 EFI has been very competitive in NHRA Stock Eliminator with Bob Shaw with the car running mid 13's in the 1/4 mile.
In Stock Eliminator you have to retain the original intake and throttle body.

The are other racers that run the engine in Super Stock class going very fast in the 10's.

[chevyfreak]

Interesting, I would bet it would work better with just the normal dual plane. It is a strange design. I cannot see it having any benefits to anything at all, except equal cylinder filling for the fixed injection to work good and equal for each cylinder. Hood clearance I would think would not be an problem on the Seville either.

Did you weld in the manifold? I was thinking about trying to use this type of manifold it as an base to make my own intake manifold.

No welding done. I just messed around with it using carbs , didnt want to go efi. Traded it with my buddy. He fitted a std qjet intake.i drove it there after, to me its better down low.

Chevy freak.

[P R S]

The Oldsmobile 350 EFI has been very competitive in NHRA Stock Eliminator with Bob Shaw with the car running mid 13's in the 1/4 mile.
In Stock Eliminator you have to retain the original intake and throttle body.

The are other racers that run the engine in Super Stock class going very fast in the 10's.

Bob Shaw later talked Bob Dennis into this combo for super stock.Bob Dennis ran the engine with the STOCK intake at first and went well into the 10’s before modifying a Holley street dominator to accept the injectors.I ran Bobs Olds Achieva S/S back in 2010 or so with that engine and went 10.50’s at 3100 lbs but that one had a Hogan’s sheet metal intake,which did not run any better than the modified Holley intake.....you know there are 2 different sized TB’s for that engine also......Victor

[BOOT]

There are plenty of examples of people going fast with(around) a bad part But it's a lot of work/money in other areas! Kinda done it myself I have a TPI car.

Plenty of old threads with people talking bout an older part that works good IF

So if you don't mind spending a lot of time figuring it out... Or just want something unique.

Just remember most brand dual planes intakes have essentially became the same thing. That's what I like bout the LS cuts out a lot of old engine BS!