[sglemans]

Will an intake and carb from a 77 Firebird work on a 71 350 engine? Any disadvantages?

[sglemans]

Actually just the intake not the carb sorry for the mistake

[steve25]

Yes it will bolt right up.
It does though have a EGR valve so it’s a tad more restrictive, but I would not worry about that with a 350 cid motor.

The main issue is that a 71 set up would have used a divorced choke which I am not sure the 77 intake does.

[sglemans]

Is the egr valve screwed in to the intake? In other words, can I just put a plug where it was?

[65 Lamnas]

It'll fit and work if you change the valley pan over to the 73-up style. But it's heavier, supports a different style hot air choke system, and your '71 throttle cable bracket boss won't be in the same location on the '77 manifold.

[keith646671]

Trying to figure crux of biscuit in egr interchange issue. Is the 73 up egr passage the small rectangle directly above the square port in the center of the intake flange? My 6x-4's have it, 96 d-ports do not. Does it basically go like this ?? ....

1. Heat from exhaust enters intake thru square center port on head and intake flange. To warm pocket under carb for cold starting and to function choke on "stove-type" manifolds on both egr and non-egr manifolds. Nearly all factory manifolds at least. Called the "heat crossover".

2. An additional smaller rectangular port was added above the center square or round (early) for EGR in 1973up. This egr passage routed to the carb to be reingested into engine thru hole under primaries into air-fuel mixture. Not sure where egr head passage begins?? I see square passage goes into center exhaust port checking with pipe cleaner.

3. My Eddy Performer RPM, Torker 1 and 2 have the flange square passage and pocket under carb to heat carb though T2 has a straight smaller pocket. None have extra rectangle over the square .. likewise the Holley Street Dominator I just got (for old times sake). Victor does not have any of that. Saw on Eddy installation instruction there was both non-egr and egr Performer plain pn's listed but only 1 number for Pontiac Performer RPM intake. Looked like SBC RPM had both. So appears to me most aftermarket manifolds DO NOT have the rectangular exhaust passage to mate to egr head hole factory setup but DO have the square hole warmup passage.

4. Covering the rectangular portion of head with a simple gasket might be ineffective at sealing egr head to non egr manifold since its hot exhaust. Have an Edelbrock gasket that has huge tombstone-like hole allowing rectangle to add to square hole passage after rebounding off intake manifold rail. Not too much perimeter width, looks like would blow out easy. Maybe not much pressure there.



My conclusions ...

Disabling the EGR likely to have limited effect on cooling the intake charge ... ( as an "air-gap" might ) unless larger square passage blocked as well. It may have an effect on diluting it to a degree. My 4x/400 stocker enduro doesnt foul plugs and runs pretty strong though.

Sealing the 1(non egr) or 2(egr) head passages whatever the mix should be accomplished with the "tombstone" gasket .. either egr will function or it wont depending on manifold-head combo.

Dont really understand how indirect path egr appears to take accomplishes any reduction of emissions or reuse of unburnt fuel.



2 friends involved right now ...

- 1. Wants a non egr manifold from my parts stash .. for a 71 2bbl Bonneville street application .. have several egr 4 bbl intakes, likely non-egr on 3 engines I am hesitant to disassemble .. a 72 400, 71 455, 69 350. My thought is for a street car an egr 4bbl intake should be indistinguishable from, and swapping egr intake to non-egr head should be a matter of using a gasket like I mentioned that lets each flow to each other like I mentioned. But see below.

- 2. Has a whistling noise from the 69 GTO he just rebuilt a 0071 block/62 head butler parts 400 for. Performer rpm with 800 Edelbrock carb. Dont believe the RPM would have the extra egr rectangle but might. Weird whistle was thinking possible heat crossover-egr leak. Car runs good but whistles, not an apparent vacuum leak. Said he had to double-gasket intake.

Have messed with mostly 60's stuff and not much of that really, even fuzzier with 70's, any help understanding would be appreciated.

[steve25]

No, starting with the 1973 heads that narrow rectangular slot/ hole above the Exh crossover in each head is actually a dead air space, it goes flat out no where .

It's purpose is to lesson the heat build up the under that valve cover in that spot that was causing oi to burn and contaminate the rest of the oil in the motor as it .

[johnta1]

Jim Hand wrote this many years ago:

Exhaust Cross-over Comparison
(middle part of page)

[keith646671]

Thanks for correction. Had checked thru Jim Hands book and not found that explanation of crossover matching before posting. Printed out article and added to my copy. Examined Butler site, found a variety of intake gaskets, many with block off plates I believe to handle any 65-up intake to head mating scenario, as well as block off-normal earlier. Will likely consult/buy gasket set from them when I need to mate heads with whatever intake.
Like to match/blend the intake ports joint insuring gasket causes no flow disruption .. be nice if intake port edges of gasket had smooth metal for less flow resistance and to wick heat from charge .. also make sure I properly seal or block off the crossover.
Appears EGR does not have its own port in head/intake joint. Is taken off tap into heat crossover within intake. Brought out to a vacuum operated valve that shuts it off for idle and various other conditions. Feeds into area below carb primaries when valve opens. Could only see it detracting from performance as it dilutes and warms the charge.
Looks like the Edelbrock tombstone gasket sticks out excessively .. maybe made for Edelbrock heads not factory?? water crossover hole on both ends?? I might have wrong one . I do have a Fel Pro MS 90123 looks like a tidier gasket and appears to be coated steel (for (65-71) where Eddy is not.

[Kenth]

Originally Posted by sglemans

Will an intake from 77 Firebird work on a 71 350 engine? Any disadvantages?

Yes, no disadvantages. Use 1972-up intake gaskets. Original valley pan will be fine.

[keith646671]

77 intake would have egr circuit that would need to be blocked/used within intake wouldnt it? Could get heat crossover blocking gaskets as well?

[steve25]

If your going to use a carb from a intake that was running with EGR then your going to need to fatten up the jetting to get out of a lean condition it will have otherwise.

Same goes for even just not hooking up the EGR to a vacuum source..

[77 TRASHCAN]

Originally Posted by keith646671

77 intake would have egr circuit that would need to be blocked/used within intake wouldnt it? Could get heat crossover blocking gaskets as well?

The 77 intake has 2 round holes in it, to the EGR valve. One will take a 1/2" freeze plug. The other hole is slightly larger, if I'm remembering....

I have a 78 intake on my 1970 350, that's in my car right now. Having the round holes that connect the EGR valve made it super easy to plug them off. I think Chevys have one round hole, and one Squarish...

I am running the stock 1970 350 valley pan with the 77 intake.

You only need the later valley pan with the 73-75 intakes that have the huge EGR sump on the under side of the intake.

Hope this helps you out!!!

If you've got a 77 Quadrajet, I'd use it to, a very good carb!!!

Looking forward to your progress!!!

[keith646671]

Well I have 4 outside, neglected, to get apart and see if I can save as many parts as I can ... .intakes on 3, pistons in all 4. 72 400/7k3 still has original tranny on back, 76-79? 400/6x, 75? 400/5C (had 5C ) .. 69 350/47. If I can get pistons out will try to make a bake/bead/mag package deal at local machine shop .. should learn the p's and q's of egr doing up that bunch. Do have a 400/4x in my enduro but runs too good to mess with, can try to eyeball the 73-74 difference on next time I run it. Has a lifter tick I believe ... disappears when warm. Should be good for another enduro

[sglemans]

Originally Posted by 77 TRASHCAN

The 77 intake has 2 round holes in it, to the EGR valve. One will take a 1/2" freeze plug. The other hole is slightly larger, if I'm remembering....

I have a 78 intake on my 1970 350, that's in my car right now. Having the round holes that connect the EGR valve made it super easy to plug them off. I think Chevys have one round hole, and one Squarish...

I am running the stock 1970 350 valley pan with the 77 intake.

You only need the later valley pan with the 73-75 intakes that have the huge EGR sump on the under side of the intake.

Hope this helps you out!!!

If you've got a 77 Quadrajet, I'd use it to, a very good carb!!!

Looking forward to your progress!!!

Thx, good to know you don't need to change the valley pan. What would happen if you just decide to use an egr valve instead of blocking it off?

[Skip Fix]

HO used to sell a SS piece to adapt early crossover to later heads -used one with my 72 SR intake on my 78 original motor. Laid the EGR in the area so it looked "correct" for smog
Also the FelPro 1233 gasket looks like the one insert will seal for both also, or use the complete block of insert.

[77 TRASHCAN]

Originally Posted by sglemans

Thx, good to know you don't need to change the valley pan. What would happen if you just decide to use an egr valve instead of blocking it off?

Nothing would need to be done. Fully functioning EGR would work fine.