V4 Crossflow - 3.625" bore / sleeve?

**hq_** · 07-21-2017, 07:58 AM

The '89 "90hp" crossflow project I started a few years ago ground to a halt and got buried under a bunch of other projects, but now it seems there might be a chance to finally do something about it.

Everything else is crystal clear ('74 135 heads and carbs, bubbleback, intake stuffers, CCM reeds, toned-down 9 pages port job etc.) but because it inevitably will need new pistons, I've been contemplating about sleeving it to 3.625" 107ci big bore while I'm at it.

The main questions are:

1. What should I expect sleeving to cost? A quick google search revealed sleeves themselves being $100-ish each, but what's the current going rate for having a machine shop install them?

2. What kind of gains should I expect in power/torque? +7-8% more displacement is something and for a "spirited" lake motor a wide usable powerband is always welcome. Skiing, tubing and the usual activities are a consideration and the boat itself is approximately 1000lbs (bare hull) so with the engine, gas and passengers it's no featherweight. 50mph and I'm happy, 55mph+ and I'll be ecstatic.

3. Compared to just one or two size overbore with stock sleeves, is it worth it?

The engine is a keeper so the only major financial aspect is avoiding the purchase of a newer EFI 2-stroke. Recent changes in EU legislation have prohibited installation of higher horsepower engines than the hull is rated for, this one is conveniently a "90hp" boat and while a 90hp Optimax can easily be upgraded to 115-125hp range, I'd hate to spend the money as long as there's a decent - and possibly more powerful - DIY alternative. With the engine and parts I (mostly) already have, no less.

**racer** · 07-21-2017, 05:35 PM

IMO bore it .030 over and go. To install the 3.625 sleeves is a pain on that engine and you will need to get head gaskets made.

**Umassot50** · 07-22-2017, 02:39 AM

I considered this on my v4 project and i decided against it. If you can get sleeves for the bigger bore boring the block will take out most of the aluminum cast portion of the block that surrounds the sleeves.plus modifying the small bore x flow heads for a bigger bore is just difficult. The stock sleeves are cast in and aren't round on the od. Meaning you need to bore them out. All just not worth it. What is the engine your starting with?

**hq_** · 07-22-2017, 06:18 AM

Thank you for the information, it's great to hear experts' takes on the subject. Displacement is always displacement but sleeving is apparently more trouble than I'd deliberately like to get myself into. So a simple overbore it is.

The base engine is a 1989 Evinrude 90 flatback. Go-fast goodies come from a seized 1974 Johnson 135, with appropriate machine and porting work.

**Umassot50** · 07-22-2017, 06:46 AM

Sounds good. There are a couple other threads about building up a a flat back cross flow with 135/140 parts. A couple i commented on.

**FMP** · 07-22-2017, 07:15 AM

Head gaskets the only issue?

**hq_** · 07-22-2017, 02:25 PM

I've browsed through dozens of crossflow threads, trying to figure out what to do, toyed with ideas like resleeving the block and even an EFI conversion. Time after time it comes back to basics. High compression heads, bigger carbs, basic overbore and some careful porting. It would be fun to try something out of the ordinary but it all boils down to bang for the buck vs. elaborate custom work. EFI would be great, though.

IIRC, someone mentioned that head gaskets could be modified from V6 big bore gaskets, which isn't as much of an obstacle as having a machine shop resleeve the block in the first place.

**FMP** · 07-22-2017, 02:33 PM

107ci can't hurt. If you have desire go for it. Slightly larger port area and maybe duration to take advantage of the displacement, you've probably planned it out .

**perfmarine1** · 07-22-2017, 07:27 PM

Originally Posted by hq_

The '89 "90hp" crossflow project I started a few years ago ground to a halt and got buried under a bunch of other projects, but now it seems there might be a chance to finally do something about it.

Everything else is crystal clear ('74 135 heads and carbs, bubbleback, intake stuffers, CCM reeds, toned-down 9 pages port job etc.) but because it inevitably will need new pistons, I've been contemplating about sleeving it to 3.625" 107ci big bore while I'm at it.

The main questions are:

1. What should I expect sleeving to cost? A quick google search revealed sleeves themselves being $100-ish each, but what's the current going rate for having a machine shop install them?

2. What kind of gains should I expect in power/torque? +7-8% more displacement is something and for a "spirited" lake motor a wide usable powerband is always welcome. Skiing, tubing and the usual activities are a consideration and the boat itself is approximately 1000lbs (bare hull) so with the engine, gas and passengers it's no featherweight. 50mph and I'm happy, 55mph+ and I'll be ecstatic.

3. Compared to just one or two size overbore with stock sleeves, is it worth it?

The engine is a keeper so the only major financial aspect is avoiding the purchase of a newer EFI 2-stroke. Recent changes in EU legislation have prohibited installation of higher horsepower engines than the hull is rated for, this one is conveniently a "90hp" boat and while a 90hp Optimax can easily be upgraded to 115-125hp range, I'd hate to spend the money as long as there's a decent - and possibly more powerful - DIY alternative. With the engine and parts I (mostly) already have, no less.

Best thing to do is find a 140 crossflow and switch covers and plate and you are set. Then go from there. Leave the port heights alone and just square up the ports, if you want to have bottom end, and or add finger ports. They will be your best gain in power. Changing a flat back to a bubble back,although can be done is a lot of work. You will need a reference motor to do it. I don't know about over there but here in the states those early 80's 140 crossflows are a dime a dozen. Good luck with it.

**hq_** · 07-23-2017, 04:10 AM

FMP: That's the major paradox. In absolute terms any added displacement == better. In relative terms I'm torn between the gains vs. cost and effort required. Trading close to $1k to maybe five horsepower under the power curve. In a racing engine I'd do it in a heartbeat, but this will only see recreational use.

perfmarine1: I wish it was that simple. Serviceable 135 and 140 crossflows, even newer 110:s and 115:s, aren't very common around here and it took me quite a while to find even a seized one for parts. I measured the port size/diameter/timing on the 135 block and posted them in another thread a few years ago. There's a major difference to 90 block and, if I've interpreted the diagrams correctly, the 9 pages mainly combines 235 (135, 140) port timing with larger, more squared port area. The 90 ports are so tiny that it'll leave lots of room for shaping everything to perfection, working towards the desired shape little by little.

Finger ports on a crossflow seem to be an elephant in the room. I've seen them mentioned every now and then but failed to find any definitive information, details or measurements on the subject. If they have a major impact on performance, I'm not surprised that experts are wary of publishing any specifics?

I'm by no means a pro but I've done quite a bit of 2-stroke porting between early-mid 80's and late 90's, mainly on dirt bikes and Jet Skis. Removable transfer covers and open tract to exhaust ports make the crossflow design so accessible that it'll be hard for even me to screw it up...

**FMP** · 07-23-2017, 07:25 AM

OK, so you have unconvinced yourself and it's as clear as mud what you're going to do.

**Umassot50** · 07-24-2017, 01:55 PM

had you seen this? i built it 4 years ago. yes ive been slacking on my projects too. plan now is to make it efi. throttle bodies.. http://www.jenvey.co.uk/

**FMP** · 07-24-2017, 02:05 PM

Did you happen to see the post in the Yami V4 thread a few days ago about an injection setup. How big are those bores ? Looks good!

**Umassot50** · 07-25-2017, 12:40 AM

Originally Posted by FMP

Did you happen to see the post in the Yami V4 thread a few days ago about an injection setup. How big are those bores ? Looks good!

It will use taper bored throttle bodies. 42mm at the intake. I didn't see yamaha post. Ill check it out.

**hq_** · 07-25-2017, 05:04 AM

Originally Posted by Umassot50

had you seen this? i built it 4 years ago. yes ive been slacking on my projects too. plan now is to make it efi. throttle bodies.. http://www.jenvey.co.uk/

Wow! Very nice! Any thoughts on what ECU, trigger, injectors etc. you're going to use? EGT? Narrowband/wideband lambda? Will the ECU control ignition as well? Something like this would definitely give old crossflows a new lease of life. 42mm throttle bodies are WAY larger than 1 3/8 carbs, almost 45% more flow and, as it seems, shorter straight tract to the reeds, so combined with precise fuel metering this may result in a metric crapload of power and incredible power/torque curve.

Current 100hp+ outboards tend to weigh from 370lbs on up so a 300lb V4 EFI crossflow is an awfully tempting proposition. Especially if it can be stretched all the way to 150hp or more. Getting rid of imprecise fuel mixture of carbs and common ignition advance variations with stock coil and power pack CDI can have a dramatic effect on reliability, too.

You got my full attention now.