Mercrusier 898 intake and exhaust upgrades

Hi all- I have a 1978 Mark Twain that is in really great condition. It is my "knock around" boat..I want to replace the intake with a 4 bbl intake and run one of my Holley on it. Will a square bore Eldebrock aluminum work? Also want to convert to through hull exhaust but the only thing I can find for it is a Captain" Call kit which is $$$ and switches between std exhaust and hull sxhaust..I am not interested in being able to go back and forth, anyone have any ideas?? Thanks for all the advice..

Re: Mercrusier 898 intake and exhaust upgrades

is it a marine carb? what size engine? think that a boat is cheap? they dont sell marine parts at the auto parts store for a reason. thier special! and safe. square bores are generally for higher rpms. the missing planes dont give a good idle. plus they usually come with big cams that make the engine lope, roller rockers, roller cams, main studs not bolts, forged pistons, i could go on... what size is your cam? do you know? dont be fooled by the 4 bbl makes me go faster myth...how many cfm is that carb? what was the origanal carbs size? is it marine? besides, the square bores dont build power untill at least 2500 rpms. and thats the cheap one (i think thats the torker 2.) i put square bores on roller motors with h beams, not boats with stock junk oh and the thru hull is alot louder. especially for the guy behind ya!! its just a open header. higher end square bores go from 3500 to 9000 rpms. is that in your operating range?

Re: Mercrusier 898 intake and exhaust upgrades

and run one of my Holley on it.

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I Agree with lilmandavis up to the point of his Questioning whether it's a Marine Carb or Not.......<br /><br />After That,.... I have No Idea What He's Talking About.........<br />It Seems he's confused the vertures of Single-plane,+ Dual-plane manifolds with Square-bore, Vs Spread-bore manifolds......<br /><br />I only Question WHY you'd want to Cobb a Holley to a Mercruiser,.... When it was Never offered by Merc....... That's Alot of Creative Engineering for Nothing......<br /><br />A Edlebrock Preformer is a Carbon Copy of the Merc./Weber carb that's been used for Years......<br />The 600cfm copy would be Perfect for your 305cid motor..........

Re: Mercrusier 898 intake and exhaust upgrades

Yes it is a marine Holley- and yes I know all about the torque/hp curve thing- I do run a vintage boat restoration shop-I have built several motors for the Gar Woods, Chris's and Centurys that have come thru here...<br /><br />The reason for the upgrade is that the factory Carter is pretty sloppy in spite of only 300 hrs- I suspect it was "swapped" out at some point...<br /><br />I like the sound of the open exhaust but we have been running the inline mufflers and they attenuate the high noise but still keep that V-8 rumble...<br /><br />I am planning on running a Weiland dual plane- the motor is WOT at 4800 so with a curve of 2500- 5000 rpm it should be fine-<br /><br />What I am looking for is a way to seal off the exhaust riser tube to the lower unit- I have thru hull exhaust here (we stock em for the woodies) and I have silicone exhaust tubing (yup stock it too)<br /><br />Ok thanks for the primer but-

Re: Mercrusier 898 intake and exhaust upgrades

Oh yeah- the Holly is 600 cfm- I am thinking that I could get similar throttle response and such like I do when we put them on the Woodies- I had some problems with the Performer carbs- but that could have been due to the inclination angles that the motor was sitting- it was a v drive motor with a short return so the motor sat steep (enough we had to modify the oil pick up)

Re: Mercrusier 898 intake and exhaust upgrades

Well John,..... It sounds like you Already know your way around a Boat,+ it's Motor.......<br /><br />The Best way to cap off the Y pipe is at the junction with the transom plate,........<br />Get Rid of the Y pipe altogether..... I built my own little Aluminum Block Off Plate.....<br /><br />Does that old boat have Logs, or Center Riser manifolds,.??...<br /><br />Mine are center riser manifolds... I just went Straight Out off the end of the factory Risers,... At the Same Angle......<br /><br />If they're Log Manifolds,.... I Don't Know if you can get Riser to go in the direction you need.....

Re: Mercrusier 898 intake and exhaust upgrades

Hi you know- I had just about decided to make a stainless block off plate- I have a guy that laser cuts stuff for us from time to time but was kinda hoping for an off the shelf thing, oh well...<br /><br />It has log type manifolds now but I have a set of center risers I can use I think that way I can get the bazooka mufflers on it between the center outlet and transom they need 11 1/4"<br /><br />Of course all of this is gonna lead to putting a 350 in the dang thing I bet...oh well- like I said, it is my knock around boat

Re: Mercrusier 898 intake and exhaust upgrades

yep.. id just drop in more displacement. with those parts, that carb is good for that manifold. save the dollas and go big 350 baby lol! put a cam in to heck!!! adjustable rockers. 1.5-1 are good enough. make sure the springs are good though i always put in oversized pushrods just to be safe!! (thicker) plus i was thinkin that it was a single plane. another thing i do sometimes is lol... on the plane seperator grind a 2" long by 1" deep gap in it. makes it idle rough but on the dyno gave it about 75 more horse at 5200 ?!?

Re: Mercrusier 898 intake and exhaust upgrades

but thats automotive stuff