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Old 04-29-2016, 04:51 PM   #1
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1991 25' Airstream 250
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Headers - help please!

Hi all,

I'm completely confused by which headers to get. I'm not in the market for a Banks kit, my sense is to go for some Hedman Headers, but how do i correctly identify which ones to go for; they don't seem to drive the header part number off the VIN?

The coach is a 1991 P30 250 classic. It has a gen V TBI with 4l80E trans. It has california emissions, but obviously this isn't a managed variant over here, so not too worried about this. I've been looking at these which I could get coated in the UK.

http://www.jegs.com/i/Hedman/500/691...d=#moreDetails

or these:

http://www.jegs.com/i/Hedman/500/691...rentProductId=

or more likely these:

http://www.jegs.com/i/Hedman/500/698...rentProductId=

Elite Ultra-Duty HTC Coated Full Length Headers
1967-92 Chevy/GMC Truck/SUV 283-400
Tube Size: 1-5/8"
Collector Size: 3"
CHEVROLETMOTORHOMECLASS A; P-301976-1991

I am at a loss as to which ones are the right fit and why did Hedman stop making Motorhome headers in 1991? Is it possible that the coach has a set up which will not work with the Hedman Headers due to falling over this boundary and how do i ensure i get the right fit?

I'd be very grateful for any guidance.

thanks!
NR x
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Old 04-29-2016, 05:29 PM   #2
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1974 20' Argosy 20
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Nick,

I bought these Doug-Thorley-Headers thy-303y-c for my 454 Argosy.

My 454 on the test stand.

You can see pictures of the installed headers at post 72 and you can see/hear the engine running at post 75.

I really like the quality and fit of the Thorley headers. Personally I don't think you could go wrong

Brad
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Old 04-29-2016, 05:38 PM   #3
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Thanks Brad - this is included in the description for this Thorley headers

APPLICATION SPECIFICS: 1973-1991 GM Pickup Truck , Suburban, full-size Blazer, full-size Jimmy / 1975-2001 Class A Motorhome, P-30 chassis, 366-454 V8, 2WD ONLY, will not fit D-port cylinder heads, no air injection fittings

It looks like it will fit all P30 chassis 75-2001, which sound good - anyone know if the D port cylinder and air injection comment is relevant?

Thanks
Nick


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Old 04-29-2016, 05:59 PM   #4
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Did some quick searching and can't find much of anything about D port heads. My only suggestion would be to find out what heads were used on your 1991 454 and see if it has oval port heads. I think the vast majority of 454 heads (at least stock heads) are oval or peanut port heads.

My heads were from an early 80s 454 pickup and they were either peanut port or oval heads. I can't remember off the top of my head!
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Old 04-30-2016, 01:45 AM   #5
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Thanks, I'll have a look at that. Clearly, something changed in 1991 because most of the Hedman Headers look to stop fitting the P30 at that point in time. I'll write to Hedman as well and see what they have to say.

cheers
Nick
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Old 04-30-2016, 06:53 AM   #6
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Originally Posted by Boom Sounds View Post
Thanks, I'll have a look at that. Clearly, something changed in 1991 because most of the Hedman Headers look to stop fitting the P30 at that point in time. I'll write to Hedman as well and see what they have to say.

cheers
Nick
The Doug Thorley website says they fit 1975 to 2000 motorhomes.

One thing to keep in mind is the Thorley headers probably perform better than the Hedman headers due to their design.
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Old 04-30-2016, 10:45 AM   #7
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Great - will take a look - do you happen to know if they are a standard length for the P30 454? Thanks.


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Old 04-30-2016, 12:46 PM   #8
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I don't really know if there is any standard length for headers. You can see in the picture below how far behind the back of the engine the Thorley headers extend.

Click image for larger version

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Old 04-30-2016, 01:48 PM   #9
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Headers

Unless you have worked the engine internals like a bigger cam, porting and more compression, you will have minimal if any gain by adding headers. Engine builders will tell you that if your small block Chevy is not capable of 300 hp to not bother with headers. Getting a better y-pipe will gain a little!
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Old 04-30-2016, 03:39 PM   #10
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Originally Posted by mykytiukr View Post
Unless you have worked the engine internals like a bigger cam, porting and more compression, you will have minimal if any gain by adding headers. Engine builders will tell you that if your small block Chevy is not capable of 300 hp to not bother with headers. Getting a better y-pipe will gain a little!
Getting rid of the heat soak from the cast iron manifolds is probably the biggest advantage. That and cast iron manifolds tend to leak a lot and frequently develop cracks.
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Old 05-10-2016, 03:36 PM   #11
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Good looking engine!
Think you are going to have to re-work the exhaust though. It may block getting into the drivers seat...

That said...did you notice a difference in power and/or mileage?

The benefit of eliminating manifold cracks is significant. It would be more than an inconvenience to occur whilst 30 miles up a dirt road...
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Old 05-10-2016, 03:47 PM   #12
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Good looking engine!
Think you are going to have to re-work the exhaust though. It may block getting into the drivers seat...
That's how I plan on heating the cab, it worked (well sorta!) for VWs

Quote:
That said...did you notice a difference in power and/or mileage?
The engine is still on the test stand so I don't have that info. It does sound good though

Brad
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