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  1. #1
    FEP Member kingsnake's Avatar
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    Default 351W Swap in 79 Cobra

    I am building a 351W for my 79 Cobra
    I have a 2" Fibertrends cowl hood. Pace car style.
    I was hoping to put an Edlebrock Performer RPM or possibly a Air gap RPM intake manifold with a Holly 4150 on this setup.
    Has anyone tried this? Will there be clearance issues?
    Thanks in advance for any help with this.
    I hate to buy expensive parts and find out latter they will not fit.

  2. #2
    Moderator wraithracing's Avatar
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    I had a 351W in my 85 GT with a 2 1/2" Cervini cowl hood. I ran an ole Performer Intake (this was back in the late 90's) and both an Edelbrock and a Holley. I ran a drop base air cleaner and the convertible motor mounts and had no issues. I ran the solid drop mounts to begin with, but couldn't deal with the added NVH on the street long term.

    The RPM or Air Gap will definitely make things a bit tighter, but you can most likely make it fit. A drop base air cleaner will be a necessity. I would also recommend the 87-93 convertible motor mounts, you can always go solid drop mounts if you need an extra 3/4" drop. You could always test fit the 351W before you buy the manifold and verify how much clearance you have and if the manifold/carb combo will fit. Good Luck!
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  3. #3
    FEP Senior Member 83gt351w's Avatar
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    351 here, with an Edelbrock Rpm intake. It’ll fit.

  4. #4
    FEP Member kingsnake's Avatar
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    Thanks for the advice guys. It always helps to talk to someone who has already been there.
    I know I will need a drop air cleaner for sure
    How much room to spare did you have 83gt351w?
    The Performer Air Gap RPM is another 3/4" taller than the Performer RPM.
    I am guessing the Performer RPM is probably the limit for clearance.
    I thought about putting the engine in without the manifold and taking the measurements, but I really wound like to seal it up.
    I figured someone on FEP would know.
    Thanks.

  5. #5
    FEP Member kingsnake's Avatar
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    How much more clearance do the convertible mounts offer?
    Will headers still clear with them?
    Do they change the drive shaft angle much?

  6. #6
    FEP Power Member Broncojunkie's Avatar
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    Good thread. I'm in the process of building a 351w (408 ) for my 79 cobra. It's originally a v8 car, but I have a stock cut-out hood from a 4 cyl turbo car I plan on using. In my pace car, I have a 302 with dual snorkel air cleaner. It has an edelbrock performer rpm intake with 1" carb spacer and solid mounts. It fits under the scoop just fine, with probably 1/2" or better of clearance. I know there's a guy on here (I think) who has an 82gt with a 460 under the stock hood (cut out with forward-facing scoop) with solid mounts and a little shimming of the k-member.
    Last edited by Broncojunkie; 01-10-2018 at 10:56 AM.

  7. #7
    FEP Super Member erratic50's Avatar
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    K shimming messes with alignment due to geometry at the strut tower. Just keep that in mind.

    There are ways to also shove the K forward then slide the mounts back. More caster and better room for headers etc. do too much and you're modding fenders to make it work. Great way to move the weight balance more towards the back though.

  8. #8
    Moderator wraithracing's Avatar
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    Quote Originally Posted by kingsnake View Post
    Thanks for the advice guys. It always helps to talk to someone who has already been there.
    I know I will need a drop air cleaner for sure
    How much room to spare did you have 83gt351w?
    The Performer Air Gap RPM is another 3/4" taller than the Performer RPM.
    I am guessing the Performer RPM is probably the limit for clearance.
    I thought about putting the engine in without the manifold and taking the measurements, but I really wound like to seal it up.
    I figured someone on FEP would know.
    Thanks.
    Quote Originally Posted by kingsnake View Post
    How much more clearance do the convertible mounts offer?
    Will headers still clear with them?
    Do they change the drive shaft angle much?
    I was able to run 4" tall K&N air filter IIRC with my drop base air cleaner and the 2 1/2" cowl hood without clearance issues. Unfortunately I don't remember how much clearance there was, but again IIRC I couldn't go any taller than the 4" filter without issues.

    If you already have the manifold, then I would just go ahead and test fit as is. I completely understand wanting to seal it up, I would just want to make sure it all fits before buying something that might be too tall.

    The Performer 351W is listed as 4.07" carb height

    The Performer RPM 351W is listed as 4.8" carb height

    The Air GAP 351W is listed as 5.75" carb height

    So there is essentially a 1" difference in manifold height between the RPM and Air GAP, so . . .

    Again it's been a few years since I had my 83 GT, so I don't remember all the details anymore. I can't remember if I had an Edlebrock Performer or a Weiand intake. I know I wasn't running a tall intake manifold, so honestly I would bet my manifold carb height is closer to that of the Performer listed above, keep that in mind.

    The convertible mounts don't really drop the engine, they are just the strongest OEM units and they sit a bit lower than some of the other mounts. No more than say 1/4" in my experience. So they don't really gain you an significant clearance and don't cause header or clearance issues in most cases. I didn't have any drive shaft angle issues either, but I always recommend verifying your angles when making changes like this. Good Luck!
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  9. #9
    FEP Member kingsnake's Avatar
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    Ok got it I will keep all this in mind. Based on your recommendation, I will purchase the convertible mounts for sure.
    Thanks for the help Trey. I'll let you know how it turns out.

  10. #10

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    I had to drill a couple holes in my 82 K frame where the mounts sit. I didnt want to grind off the pegs so I made a couple receiver holes for them. I have a 351W in my car with a Vic Jr intake and it fits under the 82 scoop or pace car scoop I have. Good Luck with it.

    Mike
    1982 GT 351W, retro hyd roller, ported Pro Comp heads, Tremec, M2300K brake kit, Recaros...needs paint!
    1984 LX 5.0 Vert *SOLD*
    1993 Cobra #3971 mostly stock *SOLD*
    1966 FFR Cobra replica 383W, Vic Jr heads, Vortech YS, TFS Box intake, 652rwhp, crazy fast!
    1987 GT in MM&FF May of 97 "Not Fade Away" white and purple. Sold 1999

  11. #11
    FEP Member kingsnake's Avatar
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    Default

    I tried to install the 5.0L convertible mounts on the 5.8L this past weekend. The right one fit the 351w, but the left would not fit.
    Looks like the 351 block is a little wider. this makes sense because the 351 oil pan is wider than the 302.
    The left mount would not push in far enough for the holes to line up without hitting the block.
    I had to cut the back of the left mount on both sides to gain clearance, then weld in new 1/8" steal to retain the original strength of the mount.
    This was a long painful process, as this is heavy steel and requires hot welds for penetration.
    In order to keep from burning the rubber I had to weld small sections and let the mount cool repeatedly.
    Welding both sides of the seams slowed the process even more.
    After all of this, I sure hope it all lines up when I put the engine in.
    I noticed that LMR has urethane mounts that are supposed to fit both 5.0 & 5.8 for $133.
    I tried to save about $100 and bought the convertible mounts from Rock Auto.
    Did not want to send them back so I went ahead and modified the mount.
    I can only hope this does not come back and bite me in the *ss.
    Sometimes it is more cost effective to spend the money!

    Kirk

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