Inline Six...

[LakeRacer99]

Where is a good place to get information on the old inline six race motors xs,bp?, twister?
Like specs, technical specs, pics, differences between stock and racing.
I am sure Raceman and a few others could fill a book with knowledge.
Most of the website I have seen deal with the smaller motors.
Any help would be appreciated.
Thanks.
LR99

[Raceman]

Here's a quick summary:

4 BP's:
1000 BP, 1250 BP, 1000 Super BP, 1250 Super BP. The regular BP's were last of the crossflows, the Super BP's were the first of the direct charges. The 1350 was the first production engine direct charge and the design continues through the rest of the inline 6 production.

Twisters:
Twister, (red stripes) Twister1 (blue stripe). Many people incorrectly refer to the red stripe Twister as Twister 1 also. It was simply referred to as "Twister". Both had side exhaust log extending down and connecting to exhaust housing right above gearcase adapter. This exhaust system was dry and real loud by comparison with today's engines. A very few Twisters and Twister 1's were made with full gearshift lower units for offshore racing. The Twister 1 was the first Merc race engine with a unique crankshaft changing the firing order from it's production counterpart. This of course required different arrangement of passages inside the exhaust log for proper exhaust tuning. This firing order continued through the T2 and T2X.

T2 and T2X:
The T2X may be one of the best looking racing engines ever built by anyone. Ask 10 people who had these engines the difference between the two powerheads and you'll get 10 different answers. Actually with the evolution of the powerheads there probably is no exact answer. They both had 6 one barrel Tillotsens and horizontal reeds. The cranks had main bearings on each journal as opposed to bearings and reed blocks on alternating journals. The T2 was a 15" engine, and the T2X was on a 12" champ housing. Many people don't know it, but Merc actually developed the T3 V6 race engine ahead of the T2X and then adapted the T2 powerhead to the shorter housing, making it available to privateers while the factory worked with the V6. It's generally thought that the X carbs had 2 tubes in the throat while the T2 only had 1. I've heard rumors of T2X's with single ring pistons, but haven't seen one myself. The cowls, while both lift offs are subtley different also.

T3:
The factory guys were fiddling with these in '75 or maybe even '74 under wraps. They were 2 liters and Merc's first looper. The powerheads were very similar to Merc's first production V6, the 1750 nick named Black Max.

T4
3.4 liter race version of the old production 300. The biggest Merc ever made. Some were covertly stretched to almost 4 liters. Probably less than 5 exist in the world today.

XS's:

650XS, roughly half of a T2 powerhead on a 15" center with a production gearcase.

850XS, stone stock 850 powerhead on 15" center section. Nothing special about this engine except red stickers on the cowl and low water pickup gearcase identical to 1500XS's, except had 2.3:1 gear ratio.

1500XS, one of the best Merc's ever in my opinion. Slight increase in exhaust port timing resulted in rating of 155HP.

[sosmerc]

Thanks for the interesting history lesson, Raceman.
Always kind of thought it would have been neat if Merc had taken the inline six a few steps further....lost foam block with integral exhaust and water passages, vee-block reeds in front of the crank, fuel injection, one-piece drop over cowl, mechanical/integral oil injection....when everything is in good order you can't beat the idle quality and bottom end throttle response of the 'ole tower of power!!!

[LakeRacer99]

Thank you for the infomation, as you know it is more than informativeI have some factory specifications from a merc manual for the Twister 2-X with the modern 12" champ bracket, w/center ram trim, Twister 2, and the 1750XS (T3). I think I got them off this site a few years back.
All this information is still soaking in. Was there a 1100XS as well from 1966-70 or around there? Or maybe a 1350XS or bp? I am not real familiar with the BP engines, did they run speedmasters also or shiftable? Did they have lift off cowls?
Well thanks again for the help. You all are helpful.
LR99

[Raceman]

There wasn't an 1100 XS, but rather an 1100 SS. The SS only denoted the change to electronic ignition and had nothing to to with short shaft or super sport or any of those things. The red striped first Twister was sort of a high perf 1350 in a number of ways. Otherwise the 1350's were only available in 15 and 20 inch standard engines. The standard BP had stock cowls, the Supers had louvers like a 1500XS. The Supers also had a small racing stripe right over the top of the top cowl that I don't think Merc ever used on any other engine. The BP's of both varieties also had speedmaster looking gearcases with full gearshifts. They were extremely heavy and extremely weak. They were designed just to meet some class requirement at the time and Merc recommended that shifting with the motor running be avoided when possible. First engines with the liftoff cowls were the T2/T2X's and the XS designation first appeared in '76. I'm e mailing you a copy of a BP brochure, it's too large a file and the board won't let me attach it.

[sosmerc]

a most unusual distributor setup. It would advance the timing quite a bit at first and then as you continued to move the throttle forward it would back the timing off. I believe these engines were only built in 68 and 69. (last inline six that used crossflow pistons )

[Superdave]

If you are looking for the best hi-po block for a "standard" in-line it has a "J" stamped in the side of the block. This denotes the higher port timing for the 1500xs. I had a 1350bp with the bpexh hsng and dual driveshaft lower unit.It wa one of the few race produced lowerunits that had neutral & forward, most were only forward and always in gear. The spark advance could be run way up due to the direct charge pistons. I ran mine at 37* and higher on regular pump gas.....RACEMAN... If I am wrong please correct me.

[Raceman]

Super D, I don't know for sure about the 1350 BP's. I'd heard rumors before, but my old Merc buddy said no. I've never run across any literature on one. The first Twister seemed like an evolution of a 1350 so I always just thought that took the place of one. Just for my own information, are you sure your's came from the factory as a 1350 powerhead on a BP housing? One easy way to tell would be the way the starter mounted if you happen to remember. The 1350 powerheads mounted in a conventional way as do all the later inlines. The 1250 Super BP powerheads mounted more like the older engines with some steel pieces in the brackets. Far as I know the Super BP blocks were the only direct charges that ever mounted the starter the old way. My twin engine Kitson has 1350 powerheads on the standard production type 15" housings with super speedmasters and stacks. It's also got BP stickers on the cowls, so I don't know exactly what I've got as far as the origin goes. I'd really be curious to know for sure if Merc ever made 1350 BP's.