Tune up 83 454 RV engine - Chevelle Tech
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  • 1 Post By hydro462
  • 3 Post By jeff swisher
  • 2 Post By 1975TypeS-3
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post #1 of 14 (permalink) Old Feb 17th, 20, 11:16 PM Thread Starter
 
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Tune up 83 454 RV engine

I really do not mean to intrude into this forum with such a mundane topic...yet at reading so many well founded thoughts on cam/application and reality..i am going to try..

The engine is factory from top to bottom....60k on the odo and it is in remarkable condition.

I will start with this it is what it is and i am not going to let my thoughts run wild. I will be stripping the AIR emissions...adding long tube headers..dual pipes...rebuild the factory rochester....add a intake...new timing chain and water pump..along with recurving the ignition...msd type

So i am looking at this engine and see the cam...it just sitting there and nice cheap flat tappet...then i noticed the heads were what i call marine ovals..781 head large chamber meaning low compression..is what i have found..

So a valve job...milling the down the heads .30...using the right gasket..new springs actually just a whole kit....maybe 500 later (kit) i could have a engine that will breathe above 4000 in current form... its all done at 3200 something now..Living in Oregon steep inclines or passes are part of the journey down shifting into power brings on a whole new meaning..

Does anyone have a profile or a cam type suggestion to make or would care to make...I fully understand how i am limiting things here and at the same time have no desire to go above 5k rpm band. I once played with marine motors and after 5k was the break the wallet time...been there done that..and not again..
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post #2 of 14 (permalink) Old Feb 18th, 20, 7:52 AM
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Re: Tune up 83 454 RV engine

Find a set of L29 heads. They're large ovals with a small combustion chamber that'll bump compression to about 9:1. The other I'd look for are the late 60's semi-closed -215, -290 and -063 castings. They're not much more than 100cc chambers and are also large ovals. You'll get more compression this way without spending a bunch of cash milling heads.

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post #3 of 14 (permalink) Old Feb 18th, 20, 8:41 AM
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Jeff
 
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Re: Tune up 83 454 RV engine

I would leave it alone and just tune the ignition, put a set of duals on it with no X pipe.. After market parts have ruined more decent running motors then anything..

I have a stock 1978 454 with the 781 heads and it runs like a scalded cat and on 87 octane... All I did to it was set the initial timing to 22 and changed the mechanical to 14 with no vacuum advance, ran 2-1/2 dual exhaust with two Dynomax Super Turbos 17749. This winter I am swapping the HEI for a single points triggering an (analog) MSD6AL CD box..
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post #4 of 14 (permalink) Old Feb 18th, 20, 9:07 AM
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jeff
 
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Re: Tune up 83 454 RV engine

I did just about the same thing as hydro462.

I drove a tow truck that was mid 80's with a 350" it got 8 MPG.
I asked the owner of the place where the 454 went that was in it. it was sitting in the corner of the shop he had pulled it because it got 6 MPG.
This was a dually 454 with granny 4 speed and 4.11 gears it was only used in OKC area as a repo truck. so it was usually pulling another vehicle..Had the winch and flat bed on it.

I told the owner I want to stick the 454 back init and I can get better MPG than the 350.

He said do it but if it gets worse you stick the 350" back in.

I set the APT in the Q jet carb to 2.5 turns out from the 4.5 it was at.
Pulled off the vacuum advance and dialed in a quick timing curve which was all in by 2200 rpm.
I used light springs from a curve kit and used the stock GM weights in the HEI.

12 MPG much more power.
I did not mess with the exhaust as it had duals with glass packs so I figured that was plenty good.

There is a lot to be had in a little tweaking.

But if you must pull it apart I would bowl port the heads and go ahead and mill them.
Another swap I have done on 454's was get one of the earlier taller runner intake manifolds for it.
But that was before all of them disappeared from the salvage yards.

If it was mine i would stick a 268H in it Just one of my favorite cams for pulling and making some power and MPG.

If that sounds a little big then a XE256 should bring on the Torque.
You must bowl port the heads.. just easy cheap power to be had there.

Just a simple blend with a hard stone in a drill.
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post #5 of 14 (permalink) Old Feb 18th, 20, 1:39 PM
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Re: Tune up 83 454 RV engine

What you most likely find is a dish piston and Open Chamber head, actual compression will be in the 7.3-7.5:1 area. The 781 are good heads, I would look for something like an Xtreme Energy (Comp Cams) or as mentioned the HE268 that are designed to increase cylinder pressure in low compression engines so they behave more like a high compression engine. Add headers and dual exhaust, put a faster curve in the distributor (lighter spring) and dial down the static timing and get the proper jetting for the combo - they normally came on the lean side.

Back in the late 1970's my father bought a C20 Suburban for towing his horse trailer. He was not happy with the power or mileage so I took the liberty of putting on long tube headers, dual exhaust, recurved the distributor to come in faster and re-jetted the carb. Left the compression where it was, even with the stock cam it would get 13 mpg (TH400 and 4.10 gears) and would tow like crazy. Had to haul a horse from Wisconsin to California, even with a loaded trailer though the mountains you could maintain speed!
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post #6 of 14 (permalink) Old Feb 18th, 20, 5:22 PM Thread Starter
 
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Re: Tune up 83 454 RV engine

First i thank you all for the replies, a long time ago we used the compcam 270 in marine applications just enough bang and a low chance of water reversion...thats a big deal in marine applications...This HE design is it a dual pattern design i assume as much...it seems there is a lot of negative comments on Comp Cams these days..Is that well founded or just part of the backround noise...smiles i mean that respectfully..As to recurving that will be done and headers also....a long time ago headers cracked like glass is that still part of the landscape? There is a lot of price disparity and not to many mfgs for RV's..It seems Thorely headers come up quite a bit...again im not looking for the ultimate by any stretch...just trying to dissipate the heat as quickly as possible..Ceramics are not needed..i hope.
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post #7 of 14 (permalink) Old Feb 19th, 20, 5:24 PM
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Re: Tune up 83 454 RV engine

Since it's a big old tank, I would use a set of Peanut Port heads for even more torque. The only thing you will gain with going to closed chamber heads is spending a lot of money on them as they will need hardened seats for sure and other labor to make them work. The L-29's are a very good choice also.
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post #8 of 14 (permalink) Old Feb 19th, 20, 7:43 PM
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Re: Tune up 83 454 RV engine

Most of the people here who find motor home 454's put them in cars but you're keeping that motor home going ? Is that right OR you have something else to put the 454 in ?
Also don't think those 781's are junk,they are large port ovals that when set up the right way can make some big power gains.
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post #9 of 14 (permalink) Old Feb 19th, 20, 8:21 PM Thread Starter
 
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Re: Tune up 83 454 RV engine

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Originally Posted by 71350SS View Post
Most of the people here who find motor home 454's put them in cars but you're keeping that motor home going ? Is that right OR you have something else to put the 454 in ?
Also don't think those 781's are junk,they are large port ovals that when set up the right way can make some big power gains.
Yes the RV is bit of a barn find...Ive rebuilt the suspension..ive gone thru it lets say...things are good. Actually prior to the 05 crisis i played marine engines quite a bit..i do know there potential and limitations...That however was almost 18 yrs ago times change...I am checking in here simply because the mind and tech changes along with approach towards building. both a marine engine and a rv engines are heady duty cycle motors..the way this engine is setup is mind blowing..it appears that GM tried to use a gas engine like a diesel pusher.

Back in the day i would call this boating on a budget...so to speak. The engine is compression limited yes but as stated it is what it is..I will mill the heads...do a gasket reduction and i believe that 268 will allow this engine to breathe past 3200 rpm making shift transitions much more productive is the word..I could go off on GM looking at this thing... ive never seen such dumbed downed flamethrower...Actually none of that matters..As posted above however i was under a very old impression that after 75/78 all of GMs heads had hardened seats...it was a unleaded gas issue that prompted that back in the day..Maybe not soon i will find out....getting current can be expensive..i am treading slowly.
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post #10 of 14 (permalink) Old Feb 19th, 20, 9:00 PM
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Re: Tune up 83 454 RV engine

Quote:
Originally Posted by 1975TypeS-3 View Post
What you most likely find is a dish piston and Open Chamber head, actual compression will be in the 7.3-7.5:1 area. The 781 are good heads, I would look for something like an Xtreme Energy (Comp Cams) or as mentioned the HE268 that are designed to increase cylinder pressure in low compression engines so they behave more like a high compression engine. Add headers and dual exhaust, put a faster curve in the distributor (lighter spring) and dial down the static timing and get the proper jetting for the combo - they normally came on the lean side.

Back in the late 1970's my father bought a C20 Suburban for towing his horse trailer. He was not happy with the power or mileage so I took the liberty of putting on long tube headers, dual exhaust, recurved the distributor to come in faster and re-jetted the carb. Left the compression where it was, even with the stock cam it would get 13 mpg (TH400 and 4.10 gears) and would tow like crazy. Had to haul a horse from Wisconsin to California, even with a loaded trailer though the mountains you could maintain speed!
1975TypeS-3, Do you own a Laguna, and can you share pics of it? Terry
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post #11 of 14 (permalink) Old Feb 19th, 20, 9:18 PM
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Re: Tune up 83 454 RV engine

There are people here more qualified than me but I don't think you'll need to mess with the valve seats but I think new valves and a valve job will get you down the road without worrying.
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post #12 of 14 (permalink) Old Feb 20th, 20, 3:33 PM
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Cool Re: Tune up 83 454 RV engine

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Originally Posted by 68-13427 View Post
1975TypeS-3, Do you own a Laguna, and can you share pics of it? Terry
I will post some in Projects and Builds - do not want to highjack this one.
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post #13 of 14 (permalink) Old Feb 20th, 20, 3:43 PM
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Re: Tune up 83 454 RV engine

Quote:
The only thing you will gain with going to closed chamber heads is spending a lot of money on them as they will need hardened seats for sure and other labor to make them work
I have never had to install hardened seats in any big block Chevy cylinder I have used and that includes the current engine which runs high 11's in the 1/4 mile with it severely corked up with the stock intake/exhaust manifolds. They are not needed and not worth the potential trouble of a leaking insert.
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post #14 of 14 (permalink) Old Feb 20th, 20, 8:38 PM Thread Starter
 
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Re: Tune up 83 454 RV engine

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Originally Posted by mr 4 speed View Post
I have never had to install hardened seats in any big block Chevy cylinder I have used and that includes the current engine which runs high 11's in the 1/4 mile with it severely corked up with the stock intake/exhaust manifolds. They are not needed and not worth the potential trouble of a leaking insert.
I am quite sure heads made after 75/76 had hardened seats..In the marine industry big blocks and Iconel valves are a standard for reliability..high speed runs for 15/30 minutes is a rather heated topic...8k motor and you skimp on $300 valves...Opps my bad..

I cannot remember any heady conversations on hardening valve seats..Im not to sure one could do that after the fact...i have no ideal.
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