Joebatz

I know that the intake manifold for an 81 is unique for that model year only. What I don't know is what makes is unique.
I need a replacement manifold and Edelbrock recommends their model 3701. However, my concern is that it will not be
compatible in some way with my current manifold.

Anyway, I have no doubt that someone on here knows exactly what the issues are!

Thanks to all.

Marks69BB

I'm not an expert on later sharks, but since 81 was the first year of the computer chip and that 82 has the crossfire setup, I would say that adding the computer related stuff made the intake unique to that year. Hopefully, someone who has an 81 will comment on aftermarket intake compatibility. Good luck! :cheers:

Easy Mike

Can't say for sure, but the '81s run the electronic Q-Jet. The manifold might have additional fittings for senders/sensors.
:)

UKPaul

I can't tell you what makes it unique as my '81 is normal to me & it's all the others that are different :crazy:
I'm looking at getting a Performer manifold & going by the pictures in the brochures, it looks like my manifold has a fitting for the coolant temp sender to the ECU, that isn't on other manifolds. This is a 5/8" UNF (18tpi) taped hole on the p. side of the stat housing (going from memory). If the performer doesn't have this fitting I was going to get a 1" diameter, 3/8" thick piece of alloy welded to the new manifold & then drill & tap a hole through the whole lot. There are 2 TVS valves (EFE & Purge) in the stat housing, but I don't think that they are unique for '81. I don't think that there are any differences due to the carb.
Hope I've got it right (in that there is just the extra temp sensor), otherwise I may have a few problems when I get my new manifold ;)
:cheers:
Paul

81vette

The 81' had an aluminum manifold, where as previous models were steel. Some early C3 high performance engines may have also came with aluminum manifolds. Someone correct me if I'm wrong on this.

MikeC

I believe everything after 78 had aluminum manifolds. In 78 the L-48 had steel, the L-82 had aluminum. in 79 all were alum.

Easy Mike

The '79 L-48 cars were the last Corvettes to have cast iron intake manifolds. Everything after that was aluminum, including the base engined cars.
:)

81vette

I stand corrected. Thanks.

john's '81 mouse

UK Paul hit the nail on the head!!!! I switched out my stock aluminum intake for a Performer 2101 (don't need to worry about emissions testing here in Iowa), last fall. I did take the new intake to a machine shop, and had them drill & tap for the sensor Paul described. The new Edelbrock 2101 has an indentation cast into the manifold right where this sensor is mounted, so no need to mark the spot, just drill and tap it. I had neither a drill bit that size nor the 3/8" pipe thread tap, so that's why I had a machine shop perform this for me. Only thing was when I went to install, I found that they almost made the hole too big, as I had to use some teflon tape on the thread of the sensor to make it fit tight, but everything worked out. Since this is pipe thread, I think they ran the tap in too far, believe these threads should have a taper to them.

The 2101 otherwise just bolted right up, with no problems. In retrospect, I'm really not sure that the 2101 gives me much if any more performance than the stock aluminum intake, and not sure it's worth the $120 I paid for it, however it looks good!

UKPaul

John,
I spotted that indentation where the temp sensor should go & figured that I could weld an ally disc on top of it to give a nice depth of metal to tap out. As you've done it already, is the manifold thickness at that indentation deep enough to cut a decent thread (getting alloy welding done is a real PITA for me)? I changed my temp sensor on the std. manifold & had to clean the thread out. It was definately a 5/8" UNF tap that I used & the thread wasn't tapered.
I was intending to get the non EGR Performer for mine this winter, but if you didn't notice any performance gains, I'm now wondering if it's worth doing without other mods at the same time. Does the Energizer flow a lot more than the standard camshaft? Have you still got the standard carb?
We once fitted an alloy manifold to an engine in place of the rough cast steel one & didn't notice any difference. After changing the cam & flowing the head we got a huge difference. Later on we put the cast manifold back on while we got the alloy one mirror polished & noticed a drop off in power, which proves that an engine has to be pulling more gas through it, before manifold design starts to make a difference. Looks like I'm gonna have to change the cam at the same time to get the benefit of the manifold. Or is it that the standard '81 manifold flows quite well & doesn't really need upgrading? :confused:
Paul


[Modified by UKPaul, 10:43 AM 11/6/2001]

john's '81 mouse

Paul, I believe there is enough material in the manifold to drill and tap good threads without the welding you are considering, just don't overdo it with the tap and I believe you will be fine.

You bring up an excellant point, that to maximise the benefit of each part, they must be considered in the context of the whole. I suspect that with a more aggressive camshaft, headers, and something other than the OEM Q-Jet I am running, I'd notice a greater increase in performance. I guess the engine does seem a lot stronger now once it hits 3,000 to 4,000 RPMs. I believe the camshaft I am using, 210 duration & 440 lift, compares to 194/204 & 390/410 OEM camshaft, so I didn't go with a big change in this area, due to concerns regarding losing too much low end torque. In retrospect, I probably could have and should have gone with a little more camshaft.

Bottom line, is that I believe an intake manifold change alone won't yeild much of a change, but made as part of comprehensive system package, will improve performance.

Gator81

Paul & John,
I've got the 3701 on my '81, and all of the original fittings, etc., attached with no mods required. There were several holes (all tapped) that required the purchase of threaded plugs, as the holes were not needed for installation of the '81's parts. I also fabricated a block-off plate for one of the EGR attachment points. The manifold has two of them, and you obviously need just one. Edelbrock supplied a blockoff plate, but it was cumbersome, so I made one out of simple aluminum bar stock.

As far as I know, based on my experience, the '81 manifold is NOT unique, at least in so far as it's replacement. There may be something about the original GM item that results in the '81 having a unique part number. But it looks just like every other aluminum intake I've seen on '78'-'81 Corvettes.
:seeya

UKPaul

John,
Thanks, that's a real relief. Getting aluminium (aluminum?) welded locally is a real PITA but cutting threads, etc is no problem for me though. Regarding camshafts, Gator81 put me on to Crane Powermax emissions legal camshafts which give more exhaust scavenging while keeping a high vacuum for the ECU to remain happy, so I'm looking at fitting one at some point (hopefully when I fit the manifold).
Gator,
Hi, how are you? I'll probably go for the 2101 (non-EGR) so may have to drill & tap a hole for the temp sensor. Just to be different I was also thinking of polishing the manifold & then getting it anodised (less effort then involved in keeping it clean. Lazy, Moi? :) )
:cheers:
Paul

Dalannex

Paul, what are you running for a cam now? I thought about changing intake when I put my cam in, but after talking to MANY people on the subject, they all said to leave the intake alone, and if I wanted to change something else make it the heads, and exhaust manifolds. But, as far as manifolds go, my 81 has that same temp sensor that Paul and John talk about, and from looking at a friends performer manifold (not sure which no.), it does have the spot to drill and tap out for this sensor. Shouldn't be much trouble to switch, but is it really worth it? I guess that's up to you.

Dalannex

Paul, by the way, as far as welding aluminum goes, most places make a bigger deal out of welding aluminum than they have to. I think it's a money maker is all. If you have access to a TIG welder with high frequency that's all it takes to weld it up, or an AC/DC stick with TIG gun and high freq attachment, but that's all the same, just different. :crazy: Of course, it sounds like you don't need it now, but for in the future, it may be useful information. MIG with a spool gun and 100% argon works well too. It's a little messier, that's why I recommend the TIG. Of course, I would practice on some scrap before tearing into a manifold because it's a little different to get used to. Anyway, that concludes today's session of useless information for the day. Class dismissed. :D

UKPaul

Hi Delannex,
At the moment everything in the motor is standard. Winter has started in earnest today (it snowed :( ), plus I've finally been paid, so I'm thinking of changing my cam & maybe the manifold. All I've got to look at visually are pictures of manifolds in brochures. The EGR Performer looks to have all necessary fittings (which Gator81 has just verified) & the non-EGR version seems to have a spot in the correct position for the sensor, which sounds like your friends has. I don't expect any huge performance gains (maybe none at all) by just changing the manifold, but combined with a better cam it should hopefully help (if it doesn't improve over the standard one, then at least I'll be able to impress people by having the word "Performer" written on the engine :lol: ). I figured that by changing the cam, the manifold will have to come off, so it would be a good time to fit a new one. I still haven't decided for sure, so any experiences of whether it would help with the type of power output I want would be welcome (300 - 350HP). The "Compucams" that Gator81 pointed me in the direction of look to be a good option for an ECU driven motor - just got to choose the one I think I'd be happy with. If I can get the motor to pull as well at mid to high rpms as it does at the bottom end, I'll be well happy with it :) Until, that is, I want more power ;)
Alloy welding :mad Seems that you have the same breed of welders there as we do here! Ask them to weld ally (even when fully cleaned & ready to weld) & they act like they're doing you a big favour. Lots of intakes of breath through clenched teeth, the shaking of the head, the muttering & tutting sounds, moaning & groaning, etc! And after all that you still have to wait about 2 weeks & pay through the nose. As luck would have it I'm helping a guy build his engine & he used to be a professional welder. He has his own MIG so (assuming the engine holds together when I've finished :lol: ;) ) I'll ask him a favour. He told me last night that his welding equipment supplier has told him there's a new system out for welding ally with an Arc welder. As long as the current can be turned down low enough, you can apparently weld ally with Arc! Whether it's a new system or the guy has only just heard about it (making it new to him), I don't know but I'll try to find out more.
Did you change valve springs or anything else when you put your new cam in? Keep the useless information coming - I'm finding it useful, welding is a black art to me! :)
:cheers:
Paul

Dalannex

My cam change was just the cam and lifters. I had just overhauled the motor, so the timing set was new, or I would have changed that as well. Heads, springs, pushrods, valves, rockers are all stock. When I overhauled the motor a friend of mine gave me a cam out of his personal stock that he said would be great. It was too large. I only had 3 hg of vacuum. The carb can't make it run at less than 1700 RPM with that low of a vacuum at idle. I went with a comp cams on the advice of several people here, and it is perfect. I just love it. Of course, you remember some of my carb problems that I had after that, but now that I got that fixed, it's great. Idles nice, sounds super, and has really good power. I have never run it over 4000 RPM, but it has REAL good power up to there. I think alot of the carb problems were a result of Bubba tuning. It was messed with pretty severe. The cam my friend gave me was the same one that I took out of the car, so somebody tried messing with the cab before to get it to run. I think the stock carb would run OK with this cam, but, you've been through your carb enough that you can tune it just fine, so that's no biggie.