Tech questions

T

todd

Member
Hey guys

I need alittle help and since is the guru board of 409's i thought I'd ask ya'll.

One of the unigue features of the 409 is the bore. From my understanding it's oval. Why did they do this when it would increase the manufacturing cost of the engine? Was this to unshroud the valves more to help airflow if not then why?

The combustion chamber is in the cylinder bore. why? Was it a cheaper method of getting a hemi effect or what?

I am either missing this information in the data I have found or I just havent been able to find this yet.

Thank you

todd
 
J

John

Well Known Member
The bore is round not oval and the combustion chamber is in the block and piston combo as the heads are flat. Truck 348 and 409s have a cut away at the top of the cylinder that makes it apear to be oval. John
 
B

bowtieollie

Guest
The combustion chamber was designed into the block to allow for a perfect combustion chamber design for each cylinder.

If thechamber was in the head, the casting variations allowed for different "sizes" for each chamber.

Also, it allowed the designers to tailor the engine to the application by not changing heads - but by changing pistons.
 
tripowerguy

tripowerguy

Well Known Member
Supporting Member 3
It makes you wonder at the intelligence of the Chevrolet high and mighties. When you have the perfect engine and then only produce it 5 years. If they had put as much effort in the W engine as the small block, the big block would have never been born.:p Roy
 
dq409

dq409

Well Known Member
Supporting Member 3
NOW YOU TELL ME !!! DO YOU KNOW HOW MUCH I PAID FOR OVAL PISTONS ?????? ,,,,dq
 
B

bowtieollie

Guest
Before you throw out those oval pistons - they may fit another application.....

No kidding, Honda made an oval piston. It was used in the NR750 V4 engine.

The NR750 was designed to get around racing rules and had EIGHT valves per cylinder. Each piston had two connecting rods.

Essentially, it was a V8 with 4 pistons.

I know you guys are really curious as to how the piston rings were installed - they were a two piece design and appeared as the letter "J". They would interlock once installed.

The bike was (is ) rather pricey. If I recall, they were $60,000us and I believe it was in the mid 90's that they were released. I know of only two in the US and in Canada there are several more.

It was also loaded with carbon fibre and aluminum extrusion materials to reduce weight.

http://www.sportbikez.net/html/showpicture.php?picture=323

for those who would like to see the engine internals.:eek:
 
I

IgnitionMan

Guest
Yes, there have been a few different oval piston setups. first done by mercedes in the early thrities, then Auto-Union, and finally, Honda.

There were two different engine designs in the Honda programs, the NR500 V4 and the NR750 V4. It is a widely known fact that everybody connected with Honda used the term "Not Ready" to identify these engines when not in direct Honda R&D or HRC presence.

Both piston designs are a casting, with two short wrist pins, one fed from each side, and circlip retained on the outer ends, piston boss retained on the inner ends. Crankshaft had two separate throws for each piston, one for each wrist pin, and this gave piston lateral stability in the "bores".

Rings were three piece for oil, one each .040 second and compression, gaps at each end of the oval. Special tools were not needed for installation, done into the bottom of the bore from champher, and using fingers only.

Both piston designs have 8 valve reliefs, one for each valve in its respective combustion chamber.

"Bores" were actually cut with a pantogram mill, tape driven, then the cylinders were Nik-A-Syl coated and then finish pantogram milled for propere clearancing.

Freddie Spencer won a heat race at laguna Seca on a 500 one year, then the bike disappeared into the Honda Secrettent, only to bemade back into a V4 from being a V8 (special heads and round bore pistons/cylinders for that heat race, and slowed back down to droning slow for the actual race.

The NR500 was a real failure, but the NR750, produced as a street bike, and run in endurance racing. was a hitter, good bike, great engine.

How do I know all this? Well, my good freind, Steve Whitelock, current Chief Tech Inspector for World Superbike Championship Racing, was at that time, the head of Honda Racing Corporation, Europe, and brought me a set of each size pistons to play with years ago, still have them around here someplace. I always thought that cutting these pistons up into small pieces and giving them to friends as jigsaw puzzles would be a fun "what is it" Christmas present.
 
I

IgnitionMan

Guest
Nope, the NR500 revved to 13,500, the racer NR750, 11,900 rpms.
 
jim_ss409

jim_ss409

Well Known Member
Supporting Member 5
I was re-reading Todds original post and I think I know where he got the idea that the 409 had an oval bore. With the deck surface being 74deg. instead of the traditional 90deg. the top of the bore would appear oval much like a pipe that was cut off at an angle. This feature allows the use of bigger and staggered valves. One reason that I think 409's are not very detonation prone is the near centre sparkplug location. I wonder what kind of power the W motor would have made with a Z11 style head that also had the exhaust valve tilted so that it opened away from the cylinder wall. More like the later big block.
 
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