Siamese Intake Sealing Woes

[Rumblin70SS396]

Hello all,

It's been awhile since I have posted here. Unfortunately I have very little time to work on the car so it has been sitting. Any help is appreciated to get this Z up and running again.

A few years ago we replaced the coils, fuel pump, spider and all 16 injectors in this car. The original gaskets had a silicone sealer around each port and the water jackets. I used the paper gaskets available from one of the sponsors here without sealer. Unfortunately almost immediately it was leaking coolant and had a very high idle. After that I shut it down, tucked it in the corner and just got back to it here recently.

Fast forward to present day, I took another set of gaskets and used a non hardening Permatex gasket sealer I have used successfully on other cars. I put the intake back on and torqued the bolts in 20ft lb in the proper sequence. Once the car started, the water issue is gone but the high idle (2k) is still there. I can only assume it's a vacuum leak on the intake as the car never had these issues previously.

What's the best way to seal a siamese intake? Is there something else I am missing? Thanks in advance for any help.

https://uploads.tapatalk-cdn.com/20171015/54656c3a68ec7030226a1aa82ca9e4ba.jpg

Tony

[XfireZ51]

Is this happeningnwhen u first start the motor or its always idling at 2k?

[Rumblin70SS396]

Hello there, it is always idling at 2k and I get a light surge after it warms up.


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[XfireZ51]

Hello there, it is always idling at 2k and I get a light surge after it warms up.


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So it idles at 2k then surges at 2K when warmed up?

[DRM500RUBYZR-1]

Have you blocked off the air horn completely in order to confirm the presence of an intake leak?

Can you isolate it using a propane source and observing engine rpm increase to see exactly where it is coming from?

Where in Delaware?

:cheers:
Marty

[Jitse]

Please check your plenum also for straightness, there can be some problems because of this.
The plenum is cut open , and after it they welded , if they not supported it on a stiff metal plates with the bolt holes tighten to it , it can be that the plenum is bend if this is not done proper.
I had the same issue with my Siamesed plenum, using Jerry’s thicker gaskets, and a bit more torque about 30Nm solved my vacuum leaks.
How did your plenum looks from the inside, did they smoothed it after welding...

[Rumblin70SS396]

Have you blocked off the air horn completely in order to confirm the presence of an intake leak?

Can you isolate it using a propane source and observing engine rpm increase to see exactly where it is coming from?

Where in Delaware?

:cheers:
Marty



Hi Marty,

I will try blocking the air horn, haven't tried that yet.

Never tried the propane trick but I can do that as well.

I am located in Newark Delaware.

Tony


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[Rumblin70SS396]

So it idles at 2k then surges at 2K when warmed up?



I only ran the car for about 15 minutes and once warmed up it idled a little over 2k with about a 100rpm surge.


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[Rumblin70SS396]

Please check your plenum also for straightness, there can be some problems because of this.

The plenum is cut open , and after it they welded , if they not supported it on a stiff metal plates with the bolt holes tighten to it , it can be that the plenum is bend if this is not done proper.

I had the same issue with my Siamesed plenum, using Jerry’s thicker gaskets, and a bit more torque about 30Nm solved my vacuum leaks.

How did your plenum looks from the inside, did they smoothed it after welding...



The plenum was sealed previously so I really didn't think it would be an issue.

I used Jerrys thicker gaskets as well on mine and will have to try the additional torque. The 20ft lbs felt awful tight though and I did re-torque them. Did you use any sealer on them?

I have some pictures of the porting but I don't have them with me. I'll be honest I can't remember if they were smoothed or not but it looked like a pretty nice job.

Tony


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[A26B]

It's hard to seal a full boogie mono runner. Engine de-cel creates very high vacuum and there's simply not much area to provide sufficient clamping friction to keep the gasket in place.

Adhesive:
It makes cleaning difficult, but use an adhesive on one side only, such as the injector housing, so you can apply it easily. Laquer glue gives you more time, super glue is anaerobic and sets quickly.

Standard Adhesive:
Lacquer glues require one side to be absorbent. Gorilla glue looks to be feasible.
https://www.zoro.com/gorilla-glue-all-purpose-glue-4-oz-8-sq-ft-coverage-5000413/i/G0912441/

Anaerobic Adhesive (Super Glue) (#30)
http://www.stewmac.com/Materials_and_Supplies/Glues_and_Adhesives/Glues/StewMac_Super_Glues/StewMac_Super_Glue.html

Recommended procedure:
1. Spray silicone onto only the top surface of the "thicker-3/64" (10168684-X) gasket & allow to dry.
2. Apply the adhesive to the injector housing
3. Lay the gasket in place on the injector housing
4. Mock install the plenum & bolt in place, tightening with the proper sequence
5. Allow 24 hours before removing the mock installed plenum

Now do all the under plenum attachments for final plenum install

The silicone will help prevent the gasket from being damaged during subsequent removal(s) & the adhesive will hold the gasket in place.

added note

Re: Warping from welding. Everyone I've talked to that has built a mono-runner plenum encounters warping. It can be severe and require extensive metal removal during re-machining of the gasket mating surfaces. It needs to be checked with a precision straight edge from side to side and length ways. Gaskets can only do so much to seal irregular surfaces, typically in the 12~20% range. Example, our thicker gasket is 0.046" thick, uncompressed. Maximum irregularity would be in the 0.007"~ 0.012" range.

We had a customer working on a Lingenfelter 415 with a mono-runner plenum, encountering difficulty with plenum sealing. It was severe enough to require gluing/laminating 2 gaskets together & gluing to one surface.

Over torquing can work, just depends on how bad the warp is.

[LGAFF]

I used two gaskets to seal the semi-Siamese intake I had with very little surface area.....is the coolant blocked off?

[LGAFF]

Not much sealing surface and no issues....Gorilla glue is pretty brutal stuff, I used it to bond boards in my back hatch for my nitrous tank install...that stuff will not come off easy

https://uploads.tapatalk-cdn.com/20171015/39e164213d8d49df91561ca7a099c2b4.jpg


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[Jagdpanzer]

Gasgacinch will do the job. Been using it for many years. Nothing else compares.
http://gasgacinch.com/home/technical/


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[QB93Z]

Hi Marty,

I will try blocking the air horn, haven't tried that yet.

Never tried the propane trick but I can do that as well.

I am located in Newark Delaware.

Tony


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If you are willing to drive about 1.5 hours to Westminster, MD I will set up a WAZOO Maintenance Day and we can try to help you get the Z running right. There are a lot of talented ZR-1 owners in the Washington/Baltimore area.


Jim
443-244-1347

[RussMcB]

I can't help with your problem (as much as Jerry and others), but I did want to pop in a say your engine looks great.

[rkreigh]

wazoo to the rescue! with the degree of mods on the mono runner it's not unusual to see them warped a bit

demps showed me a stock intake that was warped enough to not seal and with the amount of cutting and welding on the mono runner they can certainly warp

looks like a great intake!

[rkreigh]

Hello all,

It's been awhile since I have posted here. Unfortunately I have very little time to work on the car so it has been sitting. Any help is appreciated to get this Z up and running again.

A few years ago we replaced the coils, fuel pump, spider and all 16 injectors in this car. The original gaskets had a silicone sealer around each port and the water jackets. I used the paper gaskets available from one of the sponsors here without sealer. Unfortunately almost immediately it was leaking coolant and had a very high idle. After that I shut it down, tucked it in the corner and just got back to it here recently.

Fast forward to present day, I took another set of gaskets and used a non hardening Permatex gasket sealer I have used successfully on other cars. I put the intake back on and torqued the bolts in 20ft lb in the proper sequence. Once the car started, the water issue is gone but the high idle (2k) is still there. I can only assume it's a vacuum leak on the intake as the car never had these issues previously.

What's the best way to seal a siamese intake? Is there something else I am missing? Thanks in advance for any help.

https://uploads.tapatalk-cdn.com/20171015/54656c3a68ec7030226a1aa82ca9e4ba.jpg

Tony

Tony,

one other think you may want to consider is elminating the secondaries. It gets rid of the complicated vacuum system under the plenum and helps performance to boot.

I also do a "smoke test" to find vacuum leaks. take off the flex duct and tape up the inlet. find a vaccum port and blow smoke into the engine.

keep a sharp eye out and "smoke signals" will lead you to the vacuum leak

I saw and old mechanic do this and it's pretty cool.

[DRM500RUBYZR-1]

I bought a good smoke machine for our shop a couple of years ago.
It is THE way to locate Evap or Vacuum leaks!
Working on the older Vettes with Vacuum headlight and wiper door systems made having one a must.
"Smoke Signals" sometimes abound. You find one big leak, then once fixed, many smaller leaks. We had a 69 that looked like the entire engine compartment and interior were on fire!
When you see smoke pouring out from under the plenum on the LT-5, you know what's next.
Back to the OP.
It will help to know which runner(s) are leaking, as you then can concentrate your efforts to that area of the plenum. Smoke, or the more dangerous but useful propane method will help to isolate exactly where your leak is coming from.
I would not pass up the offer from Jim, QB93Z, as he has done and supervised more plenum pulls than most other mortals!
Good luck and keep us posted!
Marty

[USAFPILOT]

Obviously the intake is trash. Send it to me, I will dispose of it properly for you.

[Rumblin70SS396]

Guys

Thanks for all the suggestions. I apologize for taking a bit to get back to you but I was in Las Vegas for a conference. I was lucky enough to get BJ on Thursday and saw some of the Z's for sale.

I originally used this sealant with my gasket on both sides.

https://www.permatex.com/products/gasketing/gasket-sealants/permatex-indian-head-gasket-shellac-compound/

After your suggestions, it looks like gasgacinch or the gorilla glue might be better alternatives.

LGAFF,

The coolant is not blocked off. That was a big issue the first time as coolant leaked out. I like your idea of the two gaskets though.

QB93Z/Jim,

Thank you so much for the offer of taking a look at this car in an attempt to get it right. Currently I don't have a trailer and it can't be driven this way. I believe for now I will try some suggestions first and if I can't fix it, we will work something out.

RussMcB,

Thank you! It's really a cool car [emoji41]

rkreigh,

Thanks for the suggestions including the eliminating of the secondaries and smoke machine. I have heard time and time again about the secondaries. I would like to see the impact of the current changes before o go that route though as it requires a retune from what understand and this car has its share of modifications.

DRM500RUBYZR-1,

Again another vote for the smoke machine.....would something like this be sufficient?

https://www.amazon.com/dp/B0746SL9D6?psc=1

Seems like I could use this over and over for this and a bunch of cars including my C3.

USAFPILOT,

I agree, the intake is in the mail [emoji41]

So here's my thinking guys:

Retighten the intake and see if it eliminates the issue.

Buy smoke machine above to see if I can determine leak.

Reseal with double gaskets and gasgacinch or gorilla glue and retest.

If all else fails set up a maintenance day with QB93Z/Jim

Thank you all so much for your help......I'd really like to drive it again.

PS I apologize if I missed anything as I am doing this from my phone and don't know how to use multiple quotes.

Tony


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[DRM500RUBYZR-1]

That smoke machine does essentially the same thing as my commercial version.
You will find yourself using it often!
Good luck and keep us posted on your progress.
Thanks,
Marty

[Rumblin70SS396]

That smoke machine does essentially the same thing as my commercial version.
You will find yourself using it often!
Good luck and keep us posted on your progress.
Thanks,
Marty



Marty,

Based on your feedback I ordered it, thank you.

Should be here next week. In the meantime I will tighten the intake and go from there.

Thank you again,

Tony


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[Rumblin70SS396]

https://uploads.tapatalk-cdn.com/20171029/ffb5cd56c959e29559355b644e6bc7e8.jpg

Well here it is......hope to try it tomorrow.....

Tony


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