Crossflow V4

[mjracing]

I need some help trying to make my motor run the fastest I can cause actually I am racing with it here on Puerto Rico. It is a v4 crossflow with high compression heads, and my lower unit is a KR-15 with a 14.5x 25 left clever.. I would like to know some tricks to do to it so it can race more. PLEASE HELP ME!

thanks, Miguel
MJ Racing #44, PR

[terry taylor]

Need much much more information Miguel. = boat, horsepower, set back, and more thanks.

[mjracing]

ok, my boat is a modified donzi(manta) 15 feet long, the motor is an evinrude 100 hp, the carbs are jet to 80, all the electrical system is unlimited, has two power packs.. if need more info tell me! '
thanks very much!

[EMDSAPMGR]

What year?

[mjracing]

i think is like from the 70s to 76s

[EMDSAPMGR]

OMC made a 100 hp engine in the 71/72 timeframe. Those engines were a small bore engine, at 92 cubic inches. While they look idential to the 115/135/140, they have smaller pistons. If you are going to add mods to the powerhead, you may want to start with a 99.6 displacement block for the added cubic inches. All hp engines used the larger 99.6 size from 1979 on.

[mjracing]

oh ok then I would look up for a modern one ! thanks!

[racer]

Also the 71/2 are not as dependable if run at higher rpm but they would have a single power pack and plug wires coming from under the flywheel. A twin box set up started in the late 70s, post a pic and several on here can help

[mjracing]

ok, so the best electric system is the one with one power pack??

[ChrisCarsonMarine]

69-72 used a battewy ignition,prestolite or motorola powerpak,distributor under flywheel,AND an electric shift lower in stock form.73-77 were adi ignitions with a single pak and 1 coil per cyl,Two pak modles began in 78,chris

[scud]

V-4s from 1958 to 1972 use a four spline drive shaft like you would find on the most of the race v-4. 1973 and newer production engines use a 20 spline shaft . Also the bolt patterns for the power heads to exhaust housing go as follows:1958 to 1968
1969 to 1972
1973 to 1977 all v-4 except 140 which is same as 1978 and newer
1978 newer
the 125hp 1971 and 72 is a 99 cuber

[mjracing]

mine gear is a 15 spline shaft! and also is a left hand torque... iam looking up for a cleever o chopper prop for this gear! thanks!

[scud]

I m talking about the drive shaft (vertical or input shaft from the power head ,where the water pump in located) being 4 or 20 spline not the prop shaft. As far as a prop is concerned look on Ebay for ron hill propellers in calif.

[mjracing]

oh my bad! the shaft is a 20 spline

[scud]

can you send pictures of the power head , front ,back,both sides and from top ? If I can see what you have I might be able to offer suggestions on how to increase power .

[racervboat]

A 1978 and newer powerhead will not fit your motor,your best bet is to get a 135hp powerhead.You do not state if there is a cubic inch limit in your class.If your running apba formula vee its 100 ci limit.If your class is open to all modifacations get another motor like 1978 140hp or newer.My modded 1987 90 hp on a 15ft pacecraft gps at 85mhp with 2.0 ratio gase and 26 cleaver.

[terry taylor]

A 1978 and newer powerhead will not fit your motor,your best bet is to get a 135hp powerhead.You do not state if there is a cubic inch limit in your class.If your running apba formula vee its 100 ci limit.If your class is open to all modifacations get another motor like 1978 140hp or newer.My modded 1987 90 hp on a 15ft pacecraft gps at 85mhp with 2.0 ratio gase and 26 cleaver.

And how many rpm,s were you turning to reach 85 mph. gps. thanks.

[terry taylor]

A 1978 and newer powerhead will not fit your motor,your best bet is to get a 135hp powerhead.You do not state if there is a cubic inch limit in your class.If your running apba formula vee its 100 ci limit.If your class is open to all modifacations get another motor like 1978 140hp or newer.My modded 1987 90 hp on a 15ft pacecraft gps at 85mhp with 2.0 ratio gase and 26 cleaver.

And how many rpm,s were you turning to reach 85 mph. gps. thanks.

[Riverman]

Assuming 10% slip, almost 7700 rpm. Must be reeeeeeeeally modified.

[racer]

Was the lower adapted to fit a production mid section? A KR powerhead adapter is different than production, the exhaust bubble feeds the mid further back. More like a V6 except into 1 opening

[racervboat]

Motor is highly modified and spun at 7300rpm and is very reliable.Raced it for 3 yrs and only been reringed 1 time and is still turn key race ready.Boat is for sale at 4000.00 only thing it needs is a lower unit case its cracked by the bearing carrier but still is usable.

[terry taylor]

motor is highly modified and spun at 7300rpm and is very reliable.raced it for 3 yrs and only been reringed 1 time and is still turn key race ready.boat is for sale at 4000.00 only thing it needs is a lower unit case its cracked by the bearing carrier but still is usable.

wow??????

[Umassot50]

i hope to be testing a digital programmable ignition on the OMC V4 within a month. using all stock flywheel, charge coils, and triggers.

[mjracing]

does anyone has a crossflow lighted flywheel ?? Iam looking for on let me know thanks!

[terry taylor]

Motor is highly modified and spun at 7300rpm and is very reliable.Raced it for 3 yrs and only been reringed 1 time and is still turn key race ready.Boat is for sale at 4000.00 only thing it needs is a lower unit case its cracked by the bearing carrier but still is usable.

I think many would appreciate a list of mods. to achieve 7300 rpms. from a 90 hp. cross-flow thanks.

[terry taylor]

Sure would like more information on the above project thanks.