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Old 04-08-2017, 11:42 PM   #1
whitedog76
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Mark VI intake

I'm looking at a Mark VI 454 from a motor home.

I've been doing a lot of research, well I'm confused as heck.

Seems like GM had a few different configurations.

Most of what I'm finding are for the pre-75 oval or the 75-94 "peanut port" heads. From what I understand, the Gen V and Gen VI had slightly larger ports.

Can anyone recommend an Intake? I'm really liking the Weiand Stealth, don't know if it'll work without porting.
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Old 04-10-2017, 11:58 AM   #2
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Re: Mark VI intake

Found this pic on another site.

It shows the peanut port, Gen VI, and 8.1 head.

The Gen VI is indeed larger, so an intake designed for the earlier oval ports may work just fine.
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Old 04-10-2017, 02:12 PM   #3
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Re: Mark VI intake

The 96-later Vortec heads have an intake port size that is nearly identical to early oval ports. As such, oval-port intakes bolt up to the 96-later heads just fine.
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Old 04-10-2017, 05:47 PM   #4
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Re: Mark VI intake

That's what I was suspecting. There's a ton of info out there for the earlier engines. Seems to be some confusion when it comes to the later engines.

I guess they aren't as popular as they once were.
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Old 04-10-2017, 11:58 PM   #5
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Re: Mark VI intake

Quote:
Originally Posted by DieselSJ View Post
The 96-later Vortec heads have an intake port size that is nearly identical to early oval ports. As such, oval-port intakes bolt up to the 96-later heads just fine.
^^^ Agreed. A lot of folks will mistakenly call them a peanut port head when they are really close to an earlier oval. Was the engine a fuel injected vortex to begin with? Heres mine before I put the FI manifold back on.

The engine seems to make a bunch of power with the right cam and minimal work on the heads
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52" front and 63" rear spring swap
D44 / 14bff - disc axles
Milemarker 9K and 10.5K hydraulic winches

63" & B52 Spring Install http://67-72chevytrucks.com/vboard/s...ng+swap+thread


NV4500 Reverse Build Thread http://67-72chevytrucks.com/vboard/s...=reverse+build

L29 - 7.4 Vortec Build http://67-72chevytrucks.com/vboard/s...&highlight=L29
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Old 04-12-2017, 11:51 AM   #6
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Re: Mark VI intake

The more I learn about the Mark VI, engines, the more I like them.

With just a cam swap, you can get 500 ft lbs or torque. Just a stock Mark VI can churn 375 HP and 480 ft. lbs. at 3500 RPM

Not too shabby in my book.

I know the LS engines are the popular thing right now, but I'm kind of digging the big blocks.

I can't understand why they fell out of favor.
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Old 04-12-2017, 10:52 PM   #7
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Re: Mark VI intake

Ive heard "rumors" that GM detuned the L29 (Vortec 7.4) in order to not overshadow the LS series engines.... Who knows?

I do know that the one I just put into my '63 pulls harder than I remember any engine that Ive ever had - fuel injected or otherwise. Its got a better cam, injectors and tune than stock. GM left ALOT on the table with this engine.

I like the fuel injection, cam and tune that I ended up with. It pulls like a freight train up to 5500 and still brings a grin when i mash it in 3rd and the 35" tires break loose as if it was a wet street!
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'63 k15 long step
Vortec 7.4 - L29 Blackbear tune, Five 0 Motorsports injectors, Chris Straub Cam, NV4500, divorced 205
52" front and 63" rear spring swap
D44 / 14bff - disc axles
Milemarker 9K and 10.5K hydraulic winches

63" & B52 Spring Install http://67-72chevytrucks.com/vboard/s...ng+swap+thread


NV4500 Reverse Build Thread http://67-72chevytrucks.com/vboard/s...=reverse+build

L29 - 7.4 Vortec Build http://67-72chevytrucks.com/vboard/s...&highlight=L29
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Old 04-13-2017, 10:30 AM   #8
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Re: Mark VI intake

To be honest, I never thought about a big block until recently.

I've read alot of posts of people saying they like the Mark VI better than the 8.1. With that being said, I wouldn't doubt that GM de-tuned them.

Also, when you look at the early Duramax engines, they barely had any more power and torque. (But had a premium price tag.)

We use to haul 20,000 tractors on a gooseneck behind a mid 70's C30. The old 454/SM465 always got the job done. Never had an issue, other than blowing the spider gears out of the diff. I'm assuming they've only improved the 454 since then.

My Mark VI deal fell through, but I'm on the lookout still. I'm going to pick up the SM465 this weekend. For simplicity I'm think of running a FIT or Sniper system, maybe even a carb, unless I can find a whole truck for a donor.
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Old 04-13-2017, 06:52 PM   #9
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Re: Mark VI intake

Quote:
Originally Posted by whitedog76 View Post
Found this pic on another site.

It shows the peanut port, Gen VI, and 8.1 head.

The Gen VI is indeed larger, so an intake designed for the earlier oval ports may work just fine.
Now, it does not. Look at the port spacing. The last head has no cooling passages and an intake port at the end where a cooling port should be. Its not a big block production head thats for sure.
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Old 04-13-2017, 08:41 PM   #10
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Re: Mark VI intake

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Now, it does not. Look at the port spacing. The last head has no cooling passages and an intake port at the end where a cooling port should be. Its not a big block production head thats for sure.
The last head is actually an 8.1 head. Cathedral ports like an LS but will not interchange with any earlier big blocks. There are a few out there who have gotten into the 8.1s with good success. Performance parts might be a little tougher to come by but they're out there. Dirty Larry has tweaked a few and seems to be fond of them. Should check out his builds.
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'63 k15 long step
Vortec 7.4 - L29 Blackbear tune, Five 0 Motorsports injectors, Chris Straub Cam, NV4500, divorced 205
52" front and 63" rear spring swap
D44 / 14bff - disc axles
Milemarker 9K and 10.5K hydraulic winches

63" & B52 Spring Install http://67-72chevytrucks.com/vboard/s...ng+swap+thread


NV4500 Reverse Build Thread http://67-72chevytrucks.com/vboard/s...=reverse+build

L29 - 7.4 Vortec Build http://67-72chevytrucks.com/vboard/s...&highlight=L29
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Old 04-13-2017, 11:32 PM   #11
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Re: Mark VI intake

Quote:
Originally Posted by whitedog76 View Post
To be honest, I never thought about a big block until recently.

I've read alot of posts of people saying they like the Mark VI better than the 8.1. With that being said, I wouldn't doubt that GM de-tuned them.

Also, when you look at the early Duramax engines, they barely had any more power and torque. (But had a premium price tag.)

We use to haul 20,000 tractors on a gooseneck behind a mid 70's C30. The old 454/SM465 always got the job done. Never had an issue, other than blowing the spider gears out of the diff. I'm assuming they've only improved the 454 since then.

My Mark VI deal fell through, but I'm on the lookout still. I'm going to pick up the SM465 this weekend. For simplicity I'm think of running a FIT or Sniper system, maybe even a carb, unless I can find a whole truck for a donor.
I got pretty lucky with mine. Traded some LS parts and got a complete L29 - accessory brackets and all. Didn't find out until at the machine shop that it really didn't need a rebuild even after 80k. I have had a Howell harness floating around the house for years and the original "black box" ecm that I sent to have tuned. If I were to do it again, id probably opt for the 0411 pcm and have the harness built to match.

I see the 1996-2000 7.4s going anywhere from 5 - 800 around here, complete.

From what I can tell, the manifold breathes about as good as the heads (which isn't great but they can get to @5,500 rpm without any head work. If you're looking at higher RPMs, look at different heads and intake. Even bigger injectors and a tune will really help it out. A cam change can be amazing. The heads, while still a little restrictive in the ports seem to benefit from the fast burn chambers even though the "heart shape" seems to limit the engine to around 30 deg adv total. Roller cam is cool. Lack of fuel pump boss is not cool for the carb guys. One piece rear seal, again very cool.

To answer the original ? though, yes an early oval manifold will fit. Ive seen a few people run them on the Vortec head Big Block.

Good luck. Hope you find one for a deal. Id like to find another car or truck to stuff another one in!
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'63 k15 long step
Vortec 7.4 - L29 Blackbear tune, Five 0 Motorsports injectors, Chris Straub Cam, NV4500, divorced 205
52" front and 63" rear spring swap
D44 / 14bff - disc axles
Milemarker 9K and 10.5K hydraulic winches

63" & B52 Spring Install http://67-72chevytrucks.com/vboard/s...ng+swap+thread


NV4500 Reverse Build Thread http://67-72chevytrucks.com/vboard/s...=reverse+build

L29 - 7.4 Vortec Build http://67-72chevytrucks.com/vboard/s...&highlight=L29
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Old 04-14-2017, 12:47 PM   #12
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Re: Mark VI intake

Quote:
Originally Posted by '63GENIII View Post
The last head is actually an 8.1 head. Cathedral ports like an LS but will not interchange with any earlier big blocks. There are a few out there who have gotten into the 8.1s with good success. Performance parts might be a little tougher to come by but they're out there. Dirty Larry has tweaked a few and seems to be fond of them. Should check out his builds.
Seriously? mind=blown
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-98 c1500 x-cab: 5.7L, 17" rims, 5/6 drop, flowmaster, helper bags,NBS rear disk brakes.
-02 Suburban 4x4: leveled front
-CBR600F4i, CBR600RR, CBR1000RR, and standup skis
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Old 04-14-2017, 04:50 PM   #13
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Re: Mark VI intake

Quote:
Originally Posted by Tom View Post
Seriously? mind=blown
Yea, dirty larry has posted that pic about a dozen times
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Old 04-14-2017, 05:32 PM   #14
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Re: Mark VI intake

Quote:
Originally Posted by '63GENIII View Post
I got pretty lucky with mine. Traded some LS parts and got a complete L29 - accessory brackets and all. Didn't find out until at the machine shop that it really didn't need a rebuild even after 80k. I have had a Howell harness floating around the house for years and the original "black box" ecm that I sent to have tuned. If I were to do it again, id probably opt for the 0411 pcm and have the harness built to match.

I see the 1996-2000 7.4s going anywhere from 5 - 800 around here, complete.

From what I can tell, the manifold breathes about as good as the heads (which isn't great but they can get to @5,500 rpm without any head work. If you're looking at higher RPMs, look at different heads and intake. Even bigger injectors and a tune will really help it out. A cam change can be amazing. The heads, while still a little restrictive in the ports seem to benefit from the fast burn chambers even though the "heart shape" seems to limit the engine to around 30 deg adv total. Roller cam is cool. Lack of fuel pump boss is not cool for the carb guys. One piece rear seal, again very cool.

To answer the original ? though, yes an early oval manifold will fit. Ive seen a few people run them on the Vortec head Big Block.

Good luck. Hope you find one for a deal. Id like to find another car or truck to stuff another one in!
I think saying that the chamber "limits" you to 30 degrees of timing is a misstatement. The port and chamber design is actually so much more efficient that you only need 30 degrees for a complete burn. One of the magazines did a swap of these heads onto a late-80's low-comp engine and they said they picked up about 40ft/lbs of torque when they pulled the total timing from 36 down to 30.

I'm looking for a set of heads to do this same swap on my 87. The smaller chamber also bumps compression by about a full point. Now if I find a complete engine with harness for a reasonable price, then...
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