Mods to 95 Venom 200hp

**96Javelin409** · 08-18-2022, 03:34 PM

So I'm looking to get some more performance out of my 200hp Venom on my Javelin 409 bass boat. I tracked down a set of 2.7 heads and have read some info on methods for blocking idle reliefs. I guess here are a few concerns/questions I have:

1: My boat is definitely heavy for a bass boat, if I did the idle relief block off AND the 2.7 heads would that be too much compression for a heavy(ish) boat? Should I just do one or the other? Also at what threshold does 93 octane become a necessity?

2: I've read about some type of mod to do on the 2.7 heads since they are off an open deck block and going on a closed deck block? It has something to do with the center cylinders and making a dam or something? Also I've seen mention of running 70hp thermostats from an early 90s outboard instead of the thermostats that are supposed to be on the head? Yet when I looked up a random 92 70hp engine online I got the same part number as what's already on the heads. I also read drastically different experiences/suggestions with the 2.7 heads as far as the cooling dam with marine tex. Some people said slap them on it's fine and others said it will get cylinder temps up and destroy the engine, I have to imagine these were differences in uses but heck, if I can buy some marine tex and find out where to put it on the heads to help with cooling that's a no brainer from a cost/work perspective.

3: Does anyone have any jetting suggestions for the 2.7 head upgrade or idle relief plug off or both? I'm not asking for a definitive answer but if somebody has seen a similar set up it would be nice to at least get in the ball park on my first rejet, those little things are expensive these days and hard to find and not sure about drilling any out as I've read mixed things. I've got a set of 65's and 67's but haven't ordered any others yet. Seems like the larger the jet the harder they are to find.

Thanks for any insight, oh and also right now my compression is around 90psi on all cylinders.

**mrichartz** · 08-18-2022, 05:07 PM

Don't drill the jets.
I would just do the heads if its that heavy.
I think its 130 135 for 93 oct but not positive looking for my notes.
150psi+ is where you're going to need more than 93 oct
Should be 2 sizes up for the heads.
Are gutting the air box or drilling the exhaust?

The damn for the heads is between the top and bottom of cylinders..

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Thermostat... modded cooling so you dont need the fittings

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Did or are you drilling the 2 reliefs in the top of the block?
Lets all the Air out of the block and running water lines..
Blue hose in the side

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**96Javelin409** · 08-18-2022, 06:27 PM

Awesome thanks for the info. I hadn't planned on gutting the airbox or drilling the exhaust. What all is involved with drilling the exhaust and what benefit does it have, less back pressure maybe? And is gutting the airbox worth it? I'm sure that needs even bigger jets after doing that too with more air coming in right?

So if I'm looking at that photo of the head right, is the dam just filling in that area between the cylinders and diverting the water off to the sides? Also any special prep work before the marine tex? Maybe like a 60 grit cartridge roll on a die grinder or something to clean the metal up?

**mrichartz** · 08-18-2022, 07:01 PM

reason i asked about gutting it was jetting and yes supposed to be another 10 for no or gutted airbox.
Drilling tbe exhaust is just drilling holes in the lower unit
Dont mind the mid exhaust have custom mids w off shore exhaust.. its the holes in the lower

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The damns in the heads hit it with the die grinder lightly and clean it up really well..

And yea i actually ended up with tons of jets only because i bought his entire stock when i was looking for the 80s i needed for mine.

**mrichartz** · 08-18-2022, 07:09 PM

Oh yes the heads yes thats all it is.

**96Javelin409** · 08-18-2022, 07:18 PM

That's a wicked looking setup! Thanks again for all the info I really appreciate the clarity on the dams I was having a hard time figuring out what the actual goal was so I didn't mess it up haha I have a spare airbox so I could gut that one, is there much of a difference between the gutted air box and no air box at all? I guess the odds are pretty small but I would probably feel a little "safer" with the gutted airbox vs no airbox just so there isn't a straight shot into the carbs/engine...knowing my luck I'd suck something in there somehow but if no airbox is way better than gutted airbox I could persuade myself.

What size are the holes in the lower unit? Looks like maybe 1"? And is the placement super critical or just about where yours are?

**mrichartz** · 08-18-2022, 07:48 PM

I dont run airboxes.. but I don't go around recommending it just because thats when someone would suck something in like you said...
Just remember for everything theres more jetting.

My motors are 148 or 152psi depending on which gaskets i use.. right now 152 ..with other stuff done so ive got 80 jets and the timing is 16btdc not 18 because of comp
My motors have all the sleeves in opposite sides so the idle reliefs are blocked and decks are milled w the heads

Your comp. Should go up about 15 psi w the heads.. do you know which ones you have theres actually two different..
You also want to make sure the motor will turn at least 5700 or 5800 or more wot..I think i remember Al says 6000 or more is better.. if its only 5500 is definitely not good...
And yes its usually just a couple of 1" holes on each side where the exhaust comes down..

**96Javelin409** · 08-18-2022, 08:18 PM

Got ya, yeah it'd be all fine for me until one day I was in a hurry and had a rag or something cleaning up something under the cowl and forgot it and well....

The heads should be here Saturday so I'll know more then, I do know the casting # is 3311490. Definitely noted on the rpm. I am only at around 5500 right now but I'm not sure once I have a little more power if it'll be able to spin up more, if for some reason it is still too low I'll make sure to change my prop up, I'm considering going to a raker 22 or 24 anyways. Have a 26 pitch renegade right now.

I'm gonna go ahead and start the search for some bigger jets. So with the heads, exhaust holes (no idea if this effects fueling), gutted air cleaner...I'm thinking I'll need a jet range from 70-72 maybe?

**96Javelin409** · 08-18-2022, 08:40 PM

One other thing, just trying to wrap my head around the cooling system mod. So that fitting is added at the top of the block into the water jacket on both sides, then the hose runs from the starboard side fitting to what looks like a blowoff valve delete which is basically just a plate with fitting to replace the factory valve. What about on the port side? I can't quite make out what's going on there, also is the thermostat deleted? I think part of what might be confusing me is I don't actually have the 2.7 heads here yet.

**mrichartz** · 08-18-2022, 09:52 PM

You have to decide exactly what you're going to do and add up for jets... Rough idea is 2 for heads 10 for gutted airbox..
Whats in there now And are the bottom two bigger?

yes blocks are drilled on each side with a water line run down the side and out the pan/cowl same w the blowoff delete so i have three hoses coming out of my cowls... So that way i can see whats flowing..
And yes you use thermostats.
Thermostat going to need a stainless steel spring in each side.. see if i can find a pic but i have them and can send you measurements ..have a box of them.
Dont buy the ridiculous priced ones they sell just because they say marine...

**mrichartz** · 08-19-2022, 11:13 AM

Oh you might what to look into doing 106 pullovers too.
Basically makes it start pulling from the high speed jets a few 300 to 400 rpms sooner.. most likely will have to make them but easy to do.. you might find some but good luck... Why i just make them.

Also what head gaskets do you have now? Theres two Sizes the newer years thinner ones are good for 5 lbs usually.. but think you motor probably has them already.
But just realized if you're at 90lbs now maybe not

**96Javelin409** · 08-19-2022, 03:08 PM

How do I go about making 106 pullovers? I've also got some smaller intermediate air bleeds I scooped up on ebay a while back for cheap since I knew I was going to be doing some modding and they might come in handy. I think I have the new style head gaskets since my outboard is a 95 but I guess I won't know for sure until I pull the heads off

**mrichartz** · 08-19-2022, 03:25 PM

I use old jets drill and smooth them out and either grind them down or thread the hole in the carb to take the thread.

**96Javelin409** · 08-19-2022, 03:43 PM

Ok cool and is the .106 the inside diameter? and do they have to stick out any or should they be flush or what? does it matter how far down into the tube they go?

**96Javelin409** · 08-19-2022, 03:49 PM

One other thing I was wondering, since obviously I'm going to be changing a lot of stuff and will be trying to get the air fuel ratio right again. I have tuned several cars and have an aem wideband setup I use for those, would that be helpful at all with dialing this in? I figure it would at least let me know where I'm at while I'm actually in the throttle, was just trying to figure out the best place to drill and tap for it if I did.