Difference Between Crossflows?

[amsimonsjs]

I know this has been asked before on the forum, but couldn't find it using the search, so here goes.


I have a bunch of OMC parts laying around in my garage, many carbs, blocks, heads, etc.

I know where each part came from and what motor it goes to, so I'm pretty good there.

Now my question is this: what is the difference between all the V6 crossflows?

I have a 150, two 235s, a 175, and a 200 crossflow.

All powerheads range in age from 1981 to 1985.

I know the motors all had different carburetor sizes and the 235s have the bubble exhaust, but what else besides carburation and heads?

The V6 crossflows all had the same bore besides the 235, which was slightly larger displacement.

So basically, its a matter of difference between the 150, 175, and the 200. They are all the same bore, but have different carbs and different heads. Is there anything else?

I know they had the 185 and the 155, but i've never even touched any of those.

And I had also read somewhere on here that 175s had a bubble exhaust. To my knowledge, the 175s were always flatbacks. The only motors that had the bubble were the Too Thirsty Fives. I may be wrong, but i've gone over BRPs parts list a million times.

 

[Faztbullet]

Re: Difference Between Crossflows?

The 175's from about 1977 to 1985 were flatback 3.5" bore and the 1986-1991 were bubble back 3.625" bore. The early 235's were 3.5 for a couple of years then went to the 3.625 bore. The 2.6 uses a different piston with a scallop cut in skirt. All your heads should be close to the same cc's unless you have some low compression castings. The gt 150,175 flatback are basicly the same block as the 235 has a little but not much different porting to run the bubble exhaust. The carbs are different sizes but the hot rod carbs are the 1 15/16 openings, most are the 1 3/16 and 1 5/16 sizes and a few 1 3/8's.

 

[emdsapmgr]

Re: Difference Between Crossflows?

The early 150 and 175 are the same block, a low-port small bore. These two engines usually share the same heads. The 175 has larger carbs (probably 1 5/6"). The 200 is a small bore high-port block with flatback exhaust and large 1 5/16" carbs. The 200 usually used the 150/175 heads. The 235 during your years was a high port big bore engine with the tuned exhaust, and a different exhaust tuner in the midsection. The 638/639 heads were the good ones for the 235. The 235 used the 1 3/8" carbs. The rubber intake filler blocks were used only on the 200 and 235. but can be retrofitted on any V6 crossflow for 5-8 hp. Most of the early engines ran desirable unlimited rpm power packs, 582138. The heads for the small bores changed during the years of blocks you have. Their compression lowered in later years by increasing head volume and by casting lips in the face of the head by moving the head away from the block. Early small bore 456/457 heads were good. The better was the small bore 235 head, 872/873. Best are the 76 200 uncut heads: 643/644.