Question about header flange flatness - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**Yukon Jack** · 09-26-2002, 11:29 PM

How flat should the flange be where the header bolts to the engine?

I just got a set of Dynomax Cermacoated headers for my 454 and I put a straight edge against the flange and it is not as true (flat) as I would have expected. I understand the gasket will be there, but I'm just a little concerned.

*Zkast* · 09-26-2002, 11:37 PM

I wouldnt be concerned really. Those tubes and the flange will give per each cylinder port. It's not like a rigid manifold that wont give and warpage causes the gasket to go.

adamls · 09-27-2002, 01:40 AM

After you put them on, just snug up the bolts every 3-400 miles for about the first 1500-2000 miles. With good gaskets you should see no problems.

JD72 · 09-27-2002, 08:12 AM

An old timer once told me if you cut the flange down the the center and let them have a little give they will seal better. Though I could not see my self cutting a set of ceramic coated headers.

Mike C · 09-27-2002, 08:32 AM

They SHOULD be as flat as the manifolds, but seldomly are. Buy gaskets that have the steel inserts and DO NOT use the bolts that came with them. Buy a set of bolts that came with reduced diameter lock washers. After switching to these, I did NOTHING to the headers on the Jimmy for 8 years.

**Yukon Jack** · 09-27-2002, 09:11 AM

I've heard the suggestion about cutting the flange but was very hesitant with the finish and I'm sure that would void the warranty.

Mike, I have the Percy Deadsoft gasket's and I did buy the special header bolts. The Percy's ought to take care of it, right?

I was like a dang kid at the candy store last night when I was opening all the boxes. I've got quite a task on my hands!

**1970 CST Short Wide** · 09-27-2002, 09:50 AM

Please let me know how they work out. I'm thinkind about a set myself. Do you have AC ? I need to know if they will work with AC. Last ? How many $$$$$$$$$$$$$$$ and whats the reasoning for the ceramic coating.

Thanks
Steve

**Yukon Jack** · 09-27-2002, 10:19 AM

No AC. Got these for the big block for $209.99. My understanding is the cermacoating helps with decreasing the underhood temperature a bit and supposed to be a rust protection. They are coated inside and out. Guaranteed for life, but I'm always sceptical of guarantees!

**1970 CST Short Wide** · 09-27-2002, 11:01 AM

Thanks. Not a bad price, let me know how they fit.

Anybody have any Idea if they make headers for use with Factory AC ?

SoCal71K20 · 09-27-2002, 12:25 PM

This has worked great for me-on non coated headers-I run
Hedman Hedders.
1.Cut header flange.
2.Use copper high temp silicone sealant.
3.Use Mr. Gasket ultra seal header gaskets of choice.
4.Apply copper sealant to both side of gasket.
5.Assemble using high quality American made bolts like
ARP stainless and washers.
6.Keep those header bolts tightened after several heat/cool
engine run cycles.
Never had any gasket blowouts or other problems that you
always hear about after doing this.Pretty common fix with
the weekend road warriors.I've been to cheap to buy a pair
of coated headers,maybe someday,though I get a long life
out of my good' ol Hedmans.

09-26-2002, 11:29 PM	#1
Yukon Jack Post Whore Join Date: Feb 2000 Location: Rose Hill, KS, USA Posts: 12,683	Question about header flange flatness How flat should the flange be where the header bolts to the engine? I just got a set of Dynomax Cermacoated headers for my 454 and I put a straight edge against the flange and it is not as true (flat) as I would have expected. I understand the gasket will be there, but I'm just a little concerned. __________________ 1970 Blazer with a 400 sbc and 4" lift 1980 Pontiac Trans Am, 455 Oldsmobile 2012 Kawasaki Concours 14

09-27-2002, 01:40 AM	#3
adamls Gotta Startem Early Join Date: Oct 2001 Location: Amarillo, TX, USA Posts: 364	After you put them on, just snug up the bolts every 3-400 miles for about the first 1500-2000 miles. With good gaskets you should see no problems. __________________ 67 SWB In Progress, one piece at a time, maybe 3 years I will be finished

09-27-2002, 08:12 AM	#4
JD72 WTF Join Date: Jul 2000 Location: loganville, Ga. Posts: 118	An old timer once told me if you cut the flange down the the center and let them have a little give they will seal better. Though I could not see my self cutting a set of ceramic coated headers. __________________ Some people are wise, some people are otherwise. 72 cheyenne primer factory air lowered rallyes with flat caps flowmasters 12 bolt 3.73 350/350 combo needs rockers . Cowl hood installed. 81 Malibu wagon lowered with 17's bright ass yellow and v-6. 71 225 Electra all original 455/4 81 z28

09-27-2002, 08:32 AM	#5
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,715	They SHOULD be as flat as the manifolds, but seldomly are. Buy gaskets that have the steel inserts and DO NOT use the bolts that came with them. Buy a set of bolts that came with reduced diameter lock washers. After switching to these, I did NOTHING to the headers on the Jimmy for 8 years. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

09-27-2002, 09:11 AM	#6
Yukon Jack Post Whore Join Date: Feb 2000 Location: Rose Hill, KS, USA Posts: 12,683	I've heard the suggestion about cutting the flange but was very hesitant with the finish and I'm sure that would void the warranty. Mike, I have the Percy Deadsoft gasket's and I did buy the special header bolts. The Percy's ought to take care of it, right? I was like a dang kid at the candy store last night when I was opening all the boxes. I've got quite a task on my hands! __________________ 1970 Blazer with a 400 sbc and 4" lift 1980 Pontiac Trans Am, 455 Oldsmobile 2012 Kawasaki Concours 14

09-26-2002, 11:37 PM	#2
Zkast Account Suspended Join Date: May 2002 Location: Olathe, Kansas Posts: 929	I wouldnt be concerned really. Those tubes and the flange will give per each cylinder port. It's not like a rigid manifold that wont give and warpage causes the gasket to go.

09-27-2002, 09:50 AM	#7
1970 CST Short Wide Senior Moment Join Date: Mar 2002 Location: Pittsburg Ca Posts: 4,101	Please let me know how they work out. I'm thinkind about a set myself. Do you have AC ? I need to know if they will work with AC. Last ? How many $$$$$$$$$$$$$$$ and whats the reasoning for the ceramic coating. Thanks Steve __________________ 1970 CST LS 1 6 speed Ford 9 inch Detroit Tru Track, Dakota Didgital, Vintage Air, QA1 Coil Overs Front & Rear Lots of FUN 2013 GMC PU, Oldest Son 71 GMC LWB. QA1 Suspension, Angry SB. Youngest Son 2019 GMC Diesil Dually. Youngest Son 2017 Toyota SUV Daughters car 2018 Traverse , Wife’s Ride Pittsburg Ca 94565

09-27-2002, 10:19 AM	#8
Yukon Jack Post Whore Join Date: Feb 2000 Location: Rose Hill, KS, USA Posts: 12,683	No AC. Got these for the big block for $209.99. My understanding is the cermacoating helps with decreasing the underhood temperature a bit and supposed to be a rust protection. They are coated inside and out. Guaranteed for life, but I'm always sceptical of guarantees! __________________ 1970 Blazer with a 400 sbc and 4" lift 1980 Pontiac Trans Am, 455 Oldsmobile 2012 Kawasaki Concours 14

09-27-2002, 11:01 AM	#9
1970 CST Short Wide Senior Moment Join Date: Mar 2002 Location: Pittsburg Ca Posts: 4,101	Thanks. Not a bad price, let me know how they fit. Anybody have any Idea if they make headers for use with Factory AC ? __________________ 1970 CST LS 1 6 speed Ford 9 inch Detroit Tru Track, Dakota Didgital, Vintage Air, QA1 Coil Overs Front & Rear Lots of FUN 2013 GMC PU, Oldest Son 71 GMC LWB. QA1 Suspension, Angry SB. Youngest Son 2019 GMC Diesil Dually. Youngest Son 2017 Toyota SUV Daughters car 2018 Traverse , Wife’s Ride Pittsburg Ca 94565

09-27-2002, 12:25 PM	#10
SoCal71K20 Registered User Join Date: Jan 2002 Location: Lemon Grove, California Posts: 152	This has worked great for me-on non coated headers-I run Hedman Hedders. 1.Cut header flange. 2.Use copper high temp silicone sealant. 3.Use Mr. Gasket ultra seal header gaskets of choice. 4.Apply copper sealant to both side of gasket. 5.Assemble using high quality American made bolts like ARP stainless and washers. 6.Keep those header bolts tightened after several heat/cool engine run cycles. Never had any gasket blowouts or other problems that you always hear about after doing this.Pretty common fix with the weekend road warriors.I've been to cheap to buy a pair of coated headers,maybe someday,though I get a long life out of my good' ol Hedmans.



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