1969 Super BP's, the back of the 1969 APBA rule book

[Mark75H]

The text says new Direct Charging, at least implies the 1968's were regular cross flow. The text also clearly says easy 140 hp in standard configuration (as shown without stacks). These also differ from the 1968's in the mid section; the transmission is attached by studs coming up from the transmission housing and the nuts are accessible in the little scallops in the mid section from the outside.

[Raceman]

Sam, the original BP's in both 1000's and 1250's were crossflows. The Super BP's in both were direct charge. This was the beginning of the direct charge engines and of course the 1150 and 1350 followed as the first production direct charges in 1970 and the 69 1250 was the last of the production crossflows.

Also, the Super BP's had the louvered cowls and racing stripe down the top cowl and down the front of the bottom pan, while the crossflows of 68 had neither. I'm unsure where the change to the second design gearcase took place, but my Super has the second. I was told that some of the regular 1250 BP's had the second design also, but that would be considered heresay at best because of the source. I'm sure Wally would know for sure because he was still at Lake X in the middle of that time.

[Laker]

Can you guys outline the Difference between the Crossflow merc Inline6 and the Direct charge?

[Ron Hill]

I'll guess, from what I've observed... Cross flows in general are like OMC cross flow pistons. In take an an angle up to the dome, down to the exhaust ports.... and out....

Direct Charging, was piston ported, the intake was much like a cross flow, but the baffel on the dome of the piston was more of a damn, than a cross flow... cross flows in, up and down smoothly... Merc pistons were flat except for the "damn/baffle". So, it wasn't an even flow in and out, it was more of a blast in, and the tuner pulled it out...

Ah hell....it seemed easy to explain when I started.....

[Laker]

Im with you Ron and Thanks!
I have had 4 1500s apart and understand what your saying. Much different than my KG4,KG7 KG9 Mk15,20,25s
why did they change?

[Mark75H]

The Direct Charge cylinder intake flow is improved over the regular deflector inlet and the piston surface area is reduced. The large surface area of the regular cross flow piston is one of the design limits for horsepower. The large lumpy dome presents a huge area, maybe twice as much surface as a flat topped loop charged piston, while the regular deflector has the same area under the piston dissapating heat as a flat topped piston. Heat builds up in the metal of the piston crown and if you deliver too much heat and power the piston either has problems expanding or melting.

Reducing the piston surface area and number of lumpy edges also makes for a better shaped combustion chamber for knock resistance (lower octane demand at a particular compression ratio; or higher compression ratio can be used with the same octane).

[Clams Canino]

Can we leap to the conclusion then that the 69 Super BP's were, in a way one of the last true evolutions of the engine (to direct charge)?

The 69 1000BP became the 1970 1150 and the 69 1250BP became the 1970 1350 ? Fair enough?

Now how do we get from here to the 1400 and 1500?? <grin>

-W

[Clams Canino]

Sam? Can I call this a technicly accurate reshuffle of that paragraph? And add it to the DOC?

-W



In the Direct Charge cylinder, intake flow is improved over the regular deflector inlet, and the piston surface area is reduced. The large surface area of the regular cross flow piston is one of the design limits for horsepower. Heat builds up in the metal of the piston crown and if you deliver too much heat and power the piston either has problems expanding or melting. The large lumpy dome presents a huge area, maybe twice as much surface as a flat topped loop charged piston. The regular (direct charge) deflector has the same area under the piston dissipating heat as a flat topped piston. This reduction of the piston surface area and number of lumpy edges also makes for a better shaped combustion chamber for knock resistance, resulting in lower octane demand at a particular compression ratio; or a higher compression ratio can be used with the same octane.

Originally posted by Mark75H
The Direct Charge cylinder intake flow is improved over the regular deflector inlet and the piston surface area is reduced. The large surface area of the regular cross flow piston is one of the design limits for horsepower. The large lumpy dome presents a huge area, maybe twice as much surface as a flat topped loop charged piston, while the regular deflector has the same area under the piston dissapating heat as a flat topped piston. Heat builds up in the metal of the piston crown and if you deliver too much heat and power the piston either has problems expanding or melting.

Reducing the piston surface area and number of lumpy edges also makes for a better shaped combustion chamber for knock resistance (lower octane demand at a particular compression ratio; or higher compression ratio can be used with the same octane).

[Mark75H]

Rewrite looks good, appears to have the same meaning.

Can we leap to the conclusion then that the 69 Super BP's were, in a way one of the last true evolutions of the engine (to direct charge)?

The 69 1000BP became the 1970 1150 and the 69 1250BP became the 1970 1350 ? Fair enough?

Now how do we get from here to the 1400 and 1500??

Yes, the 1350 is directly derived from the 1250 Super BP racing/prototype. The 1000 Super BP did not evolve into the 1150. The 1000 BP and 1000 Super BP were 89 ci to comply with European racing rules that limited motors to 1500cc's (91.5ci). The 1150s are just detuned 99ci motors, simply an extension in the 99ci product line.

The 140 and 150's feature an improved tuned exhaust section. This is probably derived from the original "Twister" racing/prototype motors which you have skipped over.

Back to the 1968 99ci Merc 1250. They use an improved reed valve arrangement. 10 small center hinged reeds and beveled crankshaft for improved intake flow.

[dale robertson]

This is really an old thread. I dug it up because the X-115 thread started me thinking about when I raced in UI back in the early 70's against mostly B.P. powered boats. I really wasn't sure whether they were direct charged or not. I got the pleasure off watching Bobby Drewry drive of into the sunset most weekends. Did Bobby happen to set a UI Kilo record? What was the approx. H.P. of these engines? They should have had an easy 10 or 15 on a good X-115.

[Mark75H]

This is really an old thread. I dug it up because the X-115 thread started me thinking about when I raced in UI back in the early 70's against mostly B.P. powered boats. I really wasn't sure whether they were direct charged or not. I got the pleasure off watching Bobby Drewery drive of into the sunset most weekends. Did Bobby happen to set a UI Kilo record? What was the approx. H.P. of these engines? They should have had an easy 10 or 15 on a good X-115.

Merc said the 99ci Super BP was 140hp without stacks and 155 with. They never commented about the 89ci Direct Charge. An educated guess might be 8% less, just under 130 without stacks.

[2us70]

The combo of Paul Angel and Bobby Drewery was tough to beat. Paul and Bobby stayed in my apartment for the 1970 Nationals. Paul was also generous with info to me on motors, props and setup. I only raced Bobby once. It was the SE finals at the 1973 Nationals. I got out on him in the first heat and broke the 5 mile record. I was feeling pretty good but in the second heat Bobby returned the favor and broke the record again. Second place to Bobby was not too shabby.

This is really an old thread. I dug it up because the X-115 thread started me thinking about when I raced in UI back in the early 70's against mostly B.P. powered boats. I really wasn't sure whether they were direct charged or not. I got the pleasure off watching Bobby Drewery drive of into the sunset most weekends. Did Bobby happen to set a UI Kilo record? What was the approx. H.P. of these engines? They should have had an easy 10 or 15 on a good X-115.

[dale robertson]

I have a newspaper article where he set the SE record in Portsmouth Va. with an Evinrude at 65.54 mph. I found another article from a 1974 Portsmouth race where he averaged 72.87 mph. with the UI boat. Fastest SJ boat that day averaged 71.034mph. Anytime you could run with Bobby you were doing real good.