High compression & jetting?

[B.Mac]

2.5 200 7 petal front, boyeson reeds, exhaust chest cut, velocity stacks, 35 cc heads (141-147 lbs comp.), just rebuilt @ 8 hrs break-in time.
Carbs are WMH's (pumpers) presently running 0.66 mains........

Should I bump up to 0.68's for insurance before i get on it?
B.MAC

[VectorPat]

I am doing a 91 2.5 with some light porting and had 72 in it and was way too fat.. Went 68 and is much better but still fat...This motor had the sleeves with the notch in the exhaust port and now it has 3 new sleeeve with out the notch and compression is about 15psi higher on them, so I am plannig on putting the 66 on the lower comp. cyl and the 68 on the high ones..I think it should hit it right on the money then..

[B.Mac]

My motor is identical to yours only it was the prototype ('89) to the production '91 2.5 / 200. It has the exhaust relief slots that are suppose to make it difficult to make good compression.

Merc parts express lists the mains as 0.64's in the '91 V-200 so I believe the 0.66's may have been a precaution installed by the previous rebuilder. (Not this rebuild) Parts express also shows the '91 as a 5 petal, what is yours? Do you have WMH pumper carbs?

What kind of compression are you running? I know that higher compression equals more BTU's = more heat= the need for more cooling (fuel). I had 125 accross the board before the rebuild, now have 141-147.....what's your compression on the slotted exhaust ports -vs- non-slotted? What heads cc?
B.MAC

[Jay Smith]

Please read "HEADS" by STEVEN ,

Sorry , I got tired fingers....

[VectorPat]

This is a 7 peddle motor and it has 3 cyl. with the slots the other 3 are sleeved with no slots.. The heads are cut to 33cc and it has 135psi on the slotted and 150psi on the new sleeves.. Only thing is yesterday it went bang and now has a couple holes in the front side..havnt taken it down yet to see what happened...I dont think it was from being to lean..This motor has been a real SOB since we started playing with it..It was running strong and had made acouple mid 90mph passes and broke while cruising at 80..

[Reese]

got too much compression for a heavy hull...but it's your call, I'm just not that brave...there is probably less than 5 hp difference between 135 and 147...but a good deal more secure.

Don't want to preach cause you already know my opionion on jetting and compression...heavy hulls need more conservative setups.

At least consider changing the specs on #4 with regards to compression and jetting...good luck.

[B.Mac]

I agree completely.........
I had no idea she'd go that high with 35 cc heads but you gotta consider the motor only has 8 hours total run time.
35cc's should put me between 135-140 after fully broken in.
I expect some decrease in compression once she peaks (I hope she's peaked )
My target compression is 135-140 X 6

Right now shes running 141-142 X 5 cylinders and 147 on #4
Dont forget #4 is .030 over (additional 5 lbs?)

Mercury parts express calls for .064's in this motor stock.
I've been running .066's (same as Skip)
The hipo 245 carb motor calls for .068's

I just picked up .068 jets for all 6 cylinders to make sure I'm running fat and I'll be running 40:1 100% synthetic after another tank of crude oil. If it blows up it wont be from runnin' lean.
After about 20+ hours I'll start checking my piston tops for an idea where I am and MAYBE come back down to .066's on all but #2 & #5 if it's wet. I'm looking for a wide margin for error here you can believe that!!!

VectorPat sorry ta' hear about yer mota', I hope you can salvage most of her.........What were you running that motor on getting 90's??? I wish I could "just cruise @ 80"
B.MAC

[VectorPat]

Luckily for me it wasnt my motor, it was a friends.. He was running it on a Mirage..He had broke 100mph with it before..Like I said we have been fighting this motor or maybe I should say it has been fighting us for sometime and it finally bit it bad enough to where we will be moving on the something bigger and better... Oh yeah and BADDER