how much does timing affect performance in a v6 crossflow

[keefallan]

Just a general question here. I'm going over a 235 trying to get it tuned up on my bass boat. It wouldn't come out of the hole to save it's life and that was with a 25" raker. The gt 150 that came on this 1200lb Ranger(375v 1988) had a 22" raker. SO, there should be no problem with this 235 spinning that 25" prop. I decided to check timing today as along with other things. COmpression is great. I've got 113 as the highest and 104 as the lowest. The motor still only has about 30-40 hours on it. So, I expect compression to still come up a little more.

I decided to check timing just a minute ago using the Joe Reeves method. I found that my timing was only around 20. So I bumped it up to the 24 it's supposed to be(knowing of course that it's still going to creep up to the 28 degrees when running full throttle. So, here's my question to you crossflow wizards out there: will those 4 degrees make the difference in the performance that I'm looking for? And before anyone gives me check this and check that(coils, wires, etc), let's just assume that all that is functioning perfectly. The motor is completely new. The wires were custom made and checked. The coils were checked(ohmmeter). The powerpacks are new. The timer base was checked too. The spark was tested with a spark checker set at 7/16" gap. The carbs are off of the big bore 235(I have a small bore). I worry about the jetting issues later. I'm going to go run it later on this afternoon and see what the difference is with more timing. I'll report back with what I find.

 

[Faztbullet]

Re: how much does timing affect performance in a v6 crossflow

Jetting issues will cause this problem also . Also remember a 235 is only 235 at base of powerhead and just a tad over 200 at prop. The 25 raker is a tad mumuch for that motor, a 24 raker will be pushing it as it will be slow on hole shot but should be at lower end of rpm range.

 

[keefallan]

Re: how much does timing affect performance in a v6 crossflow

Okay. I did go and try the boat. The boat gained 3-4 mph with the same 23" viper prop I used the first time I tested this setup. I don't have gps. But i am using my speedo to get readings. It might be off, but I can still use it to compare. I hit 63-64(rpm's unknown) today whereas I hit around 60 with it the other day(before I tested with the raker). The reason I can't give rpm's is because I don't think it's right. The tach was reading with 5200 trimmed up but not fully out. The tach is brand new. It's a teleflex amega. I have it set on the 6p setting. That's the highest setting on it. It reads right at idle etc. When I ran the boat the first time out(after fully restoring it), I am almost positive that I saw 5400 rpm's on the needle. It hasn't read that since. I've only been able to get it up to 5200(regardless of pitch or amount of people in the boat). I even moved the tach lead to term#2 to bypass the regulator just in case it was the cause. It wasn't, so I moved it back. Clearly the timing was way off. Now, I want to discuss the jetting. The carbs came off of a 1988 gt175(old school 235). They came with 36 idles, 36 mids, and 60's in the mains. I thought it was overfueling a little. I wanted to attack the midrange because it was so sluggish out of the hole. I dropped down to 33's in the mids and left the mains alone. The idles were changed to 30's because of the composite reeds I put in last year. I put in brand new plugs with electrodes so that I could read the plugs better. Normally I'm, running the UL77V's. But for the readings, I like the Ql77jc4's. It was hard to tell the readings because of the plugs being brand new. I only ran it long enough to get the motor warm and let 'er rip. I made 3 passes and shut the motor down with the key right at the ramp and paddled the rest to get it out of the water. The plugs still looked clean. I couldn't read much on anything. It was definately light colored, but I don't know if I saw any white(that's how clean they are). I have forgot to mention that this boat also came with a 6" manual jackplate and the cavitation plate is about 2" above the factory transom cutout(which is about 3-4" above the bottom of the boat). I haven't adjusted anything yet. I just wanted to mention that. It seems to me that I may have to get a 4 blade Trophy(GASP!!) or Renegade to fix the hole shot. I think the porting of the 235 costs some low end grunt. My 150 gets out of the hole faster. It seems to me that I may have more than one problem with this setup. Obviously, I am looking to squeeze every last bit of hp out of this motor and every last bit of mph out this boat. Any advise here is tremendously appreciated. In case anyone missed it, my boat is a 1988 375v Ranger weighing in around 1200lbs. Thanks Fatzbullet for responding already.

 

[Faztbullet]

Re: how much does timing affect performance in a v6 crossflow

The 175 is a big bore and jetting is different. What is the carb size as it will be stamped minto front of carb? You could bre to rich and washing plugs that why they are white and rpms are low......

 

[keefallan]

Re: how much does timing affect performance in a v6 crossflow

They are the big carbs(1-3/8). The 1979 235 had them too. I did step the mids down 3 sizes from what came on them(36 to 33's). I didn't want to touch the mains yet because they only have 60's in them. My gt 150(with 1-5/16 carbs) has 30 or 31's in the mids and 65's in the mains. Those are all stock jets except for idles because of the composite reeds in it. A stock 150 has 59's in the mains.
I went and looked into the '85 235 jetting and it has different jetting(I know the carbs are slightly different, it doesn't have that needle that sticks into the airflow(mids)). Anyhow, the jetting on it was something like 31's in the mids and 63's in the mains. Doesn't the motor pull from both the mids and mains at wide open throttle? WHat is your advise?
I guess what my thinking is this: if it's running fat, wouldn't it be in the mids? That's where the stumble is. Jetting is all new to me. I can build the motors and even port them(a 150) but I've never delved into this until now. Thanks again for your input in this Faztbullet.

 

[phillnjack2]

Re: how much does timing affect performance in a v6 crossflow

why not look at what the engine realy is/was, look at the year of it and the spec of it ,as in the big bore little bore etc, jet it to what it originaly was when it left the factory.
you've got over 10% difference in the compression, that's a lot for a rebuilt engine, I could understand it being low till run in,
but the difference is a bit much. was this rebored or honed ?
if rebored is it 20 over or 30 over ? this could make a difference slightly to jetting.
The timing if 4 degree's out will make huge difference to performance on any 2 stroke, and these like to be bang on with timing.
have you done a lync and sync as well ? this will make a difference to hole shot.

what is the gear ratio of the gearbox ? is it original gearbox ? this again could also make a difference to what prop it can push.
I would expect a 235 to atleast push a 27 pitch prop never mind a 25 and at least 70mph on that boat,
you should easily be able to get 5500 rpm maybe more.


phill

 

[emdsapmgr]

Re: how much does timing affect performance in a v6 crossflow

You did not state which year 235. Up through around 79, they are small bore (149 cubic inch.) After that they are 160 cubic inch. Makes a difference. They are both high port engines, which don't have the holeshot of the 150/175 small bore low port blocks, even with high compresison heads and intake stuffers. So, you need to get the rpm's up during holeshot. You won't get that with the raker, even with the bleed holes in it. Go with a 4 blade renegade bass-it'll do a better job of getting the rpm's up from initial holeshot. Maybe a 25 renegade bass. You need to be somewhat careful swapping carbs and jetting. Carbs are different internal designs and jetting is different between years. The same jet can perform differently in different carbs. 235 small bore carbs will work differently in a 235 big bore. Rather than swap carbs, maybe best to go back to your the stock ones-the will match your heads, etc. I think you are correct to have moved the timing up, but may want to start running premium fuel, as the net effect will be for it to actually be running at 28. Small bore stock 235's run 120 lbs compression. Big bores about 10 lbs less. Compression can vary around 5 lbs between heads, depending on how they were bored at the factory.

 

[keefallan]

Re: how much does timing affect performance in a v6 crossflow

The engine was a brand new 1979 block right out of a box. All I had to do was run a dingleberry hone thru it to clean it up. It was sitting in it's box for 30 plus years. I stumbled upon it for 600 bucks and decided to build one!! I found the intake fillers. The block already came with the exhaust fillers. I found a freshwater donor 235 midsection and bubbleback. I had the intake already. The carbs for a '79 235 I COULD NOT find. I wanted to run the fuel primer choke system anyways(but after all this pain of jetting, I'm rethinking that one. I'll gladly put on a choke solenoid system). I found a set of 1988 gt175 carbs which is nothing more than a big bore 235. That's why I'm having the jetting issues. I just think those carbs are too fat in the midrange. I don't want to mess with the mains yet when they only have 60's in them. My '88 150 carbs are set up much different. They have 30's in the mids(I think) and 65's in the mains. And they are only the 1-5/16 carbs