My Road Trip Motor Progress
Dalland:
Hey Rick, I have no experience about the old big block engines, mostly because I'm only 22.
But I am lucky to have a good friend and teacher that must be one of the smartest engine developer in Europe.
He told about the amcar thinking about valve design and that they believed that slow rpm engines don't have the same "problem" with dynamic compression and that the inertia of the air will work against them and not with them as in high rpm engines. So thereby the used large valves to to have "all" the air it need ready behind the valve for the down stroke.
But then again, what is low rpm when it comes to the inertia of air?
It would be interesting to see tests from different valve size and designs on low rpm engines, but i will still believe that small valves and high air speed is the way to go.
When my teacher was working for Porsche in the eighties this was one of the things he was working with, and he is also a strong believer in small valves...
And than it is the question of the air/fuel mixture quality when the air speed slows down..
But please do some mileage tests, for what its worth my 2275 with 42mm valves and much squish runs 46 mpg on longer trips.
andy198712:
46mpg?!?!?! Blimey! What's the details??
Yes what is low rpm? I'd be tempted to say most car engine are low rpm when compared to rpm's spun by bikes...?
Dalland:
Quote from: andy198712 on January 27, 2013, 20:49:53 pm
46mpg?!?!?! Blimey! What's the details??
Yes what is low rpm? I'd be tempted to say most car engine are low rpm when compared to rpm's spun by bikes...?
Hey Andy, no fancy parts just a good tune. parts listed here: http://cal-look.no/lounge/index.php/topic,18639.0.html
To take an example from my new workplace, the Rolls Royce boat engines that are built runs normally at around 800-1100 rpm and they use as small valves as necessary...
Some of the reasons are already mentioned but it is also a thing to know that big valves are hotter valves because the seat area is the cooling area (yes also the stem), this is also one of the reasons that all car engines went from 2 -> 4 valves per cylinder, this was also around the same time as leaded petrol disappeared...
rick m:
Dalland....
My intakes are 42 and exhausts are 37.5. When speaking low rpms....we are not really that low when you consider most diesels are truly the low rpm motors. My motor runs great between 2000 and 5000 rpms. What kind of cam grind are you running? I am curious about the 46mpg. The best I achieved so far was about 33mpg on a 1915 I built with an engle 110 in it and dual 40IDFs. I could have achieved better had I put my 36 Dellortos on it.
I can only go by what I know and that is how the car drives and performs. That is my test bed. I will have to mount my video camera in the car and take it for a drive to illustrate the driveability and power down low.
RM
Dalland:
Quote from: rick m on January 27, 2013, 23:34:19 pm
I can only go by what I know and that is how the car drives and performs. That is my test bed. I will have to mount my video camera in the car and take it for a drive to illustrate the driveability and power down low.
RM
You can't show drive ability one a video, dyno that shit and we know what you got. ;)
(well I am not the guy to talk since since i still haven't tested my engine)... ;D
Camshaft is a FK-8, all specs is in the link before..
As your topic name suggest, this is my road trip engine as I have been all over Europe with it and my old caravan. ;)
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