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Thread: What intake/parts to use?

  1. #1
    Senior Member
    Join Date
    Feb 2009
    I've got a stock 1988 Hardin Marine 350 Chevy engine. It is supposed to have 260hp. Specs are as follows: 4.00 bore, 3.48 stroke, 9:1 compression. A max of 4400 rpm. The other engine they offered was rated at 280hp, and had a max rpm of 5000. Every thing else is exactly the same, except timing, which is 12 BTDC@700RPM instead of 10BTDC@700RPM. Obviously, I don't know that much about engines, but i can change parts like a mutha. What is different about the 280hp, that gets it the extra 20hp? They have 600 Holleys. What kind of upgrades could I "bolt on", to give me some more HP? I'm not looking to change crank,rods,pistons, just the best bang for the buck without getting crazy. What type/model intake? More torq, rpm's would be great. PS: I don't what to swap to a big block yet. Thanks guys

  2. #2
    You can do as little as change the intake and carb, to as much as a complete top end kit; heads, cam, intake, carb, rockers, etc...everything you need in a matched combination for your exact application, or any variation of the above. Really depends on how much power you want, and what your budget will allow.

  3. #3
    Senior Member
    Join Date
    Feb 2009
    What kind/model intake would i want?

  4. #4
    Don't know the Hardin engines but the Merc 260hp 5.7 used a GM low rise quadrajet intake. Changing this to a GM Bowtie (it's like an Edelbrock RPM but cast iron), Edelbrock RPM, RPm Air Gap, or etc,etc is worth 15-18hp. I've done this to many small boats with Merc I/O and speed gains show that hp.
    What intake does Hardin use ? Is the Holley a square bore or spreadbore carb ? Does it have electric choke or heated choke ? Do you mind losing the choke if need be ?

  5. #5
    Without getting crazy, I'd suggest an Edelbrock RPM Airgap intake manifold and an MSD ignition box...
    The difference between the 2 engines is most likely the camshaft. To add a small boost to your camshaft, you could swap your stock 1.5 ratio rocker arms to 1.6 This will increase the lift and open the valves faster which makes the engine think it has more duration. (example, a .450 lift cam with 1.5 rockers will be .480) You could also upgrade to roller rockers at the same time. There are a couple things to watch for when doing this however. First, with the increased valve lift, the valves may hit the pistons, and without tearing the engine down to check, you wont really know how close they are coming. This is not very likely considering your engine is stock. More of a problem with high lift cams and high compression pistons, but you should be aware. The other thing to watch out for, is the pushrods having enough clearance in the slot they come up through in the cylinder head. Sometimes the slot has to be opened up enough, and you cant do that without pulling the heads, which I assume you dont want to do at this time.
    These are my suggestions for bumping up a stock engine without doing a rebuild or pulling/swapping the cyl heads...

  6. #6
    Senior Member
    Join Date
    Feb 2009
    I don't exactly know how to identify, but the manifold is cast iron with a septum front to back, port side being deeper than starboard side of hole. The rear of the hole has larger round holes than front. I believe this is a "spreadbore" manifold? The Holley, has 4 holes on the bottom, that are all the same size. I just had it rebuilt. When looking for a marine rebuild kit, it came up as for a "marine 351 ford application" approx: 600cfm w/electric choke.By the way, thanks to all you guys for being patient with my ignorance, I truly value you taking the time to respond.

  7. #7
    Considering the choke, unless you really need it, block off the heat crossover port. It saps performance and how often do you drive your boat in cold weather where a choke would really be needed? There are metal blockoff plates that go into the manifold gaskets...

  8. #8
    Careful about buying a manifold for that engine, in the late 80's (86 or so)Chevrolet changed the mounting pattern so that the center two bolt holes on each side that hold the manifold on are at an angle as opposed to the other bolts, and then in the 90's they changed again to the vortec style of head. I don't know if they make a performer RPM (which would be my choice) for that style of head. You can modify the manifold to work by redrilling the center two holes on each side. Edelbrock does make a performer manifold that is made for that style of head, if that's what you have, although it's probably not much more than what you hve now. You would need to get a casting number off of your head to determine what you have. My boat started with a similar engine, 260HP but a couple years older, a cam with .480 lift didn't come anywhere near hitting the piston when I swapped out the stock one for a Comp Cams.

  9. #9
    Yeah, you will want to double check the actual year of your engine as from's a link to a manifold
    BTW I had about .486 lift on a 327 SBC and flat top pistons with no worries about hitting, but it is something to keep in mind...

  10. #10
    Your pic in post #6 shows you have 87-95 late model centerbolt (non-vortec) heads and what appears to be the GM Bowtie intake. The GM Bowtie intake is a killer piece - it makes same hp as Performer RPM and equivalent aftermarket intakes.
    The pic looks just like the Bowtie piece for 87-95 heads. To clarify you have this, look at the stampings just behind the carb on the carb pad. There should be a Chevrolet Bowtie emblem cast in. Just before this is the #'s 14096242.
    If this is what you have - again the pic looks like it - then another intake is not going to do much if anything. I love these things and use them all the time.
    Oh, if the carb pad looks like the below photo, then you def have the Bowtie intake for the only other cast iron intake (low performance, production car one)has 4 throttle bore holes for a quadrajet carb.

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