L head turbo build

[RMS]

it's not a L series its a L head and it seems to be the least modified motor out there, well some times you'll see a couple extra carbs and some zomies but nothing super wild, no EFI or forced induction and only on super rare occasions will you see them turning at 6000rpm. well 6000rpm is really fast for a motor with a 4 1/2 in stroke that is usually governed at 3400. after months of trying to gleam hot rodding tips out of others with the same motor to no avail i thought i would try here.

what im trying to do is make up for the power loss i got after changing the gears on my 52 dodge m37 from 5.83 to 4.89 about 20%.
the motor in my truck is a chrysler 251 L head also known as a flathead. in the stock configuration it makes 200 foot ponds of torque and 105hp @ 3400 with its 6.6to1 compression ratio. everyone i talk to says why bother just install a small block but being a datsun guy i love inline's and im always impressed with the power you guys get out of your L's and KA's.

I managed to get my hands on the holy grail of L heads. the chrysler crown marine 265. : with its 4.75 stroke 3.436 bore stelite seats, sodium filled valves, bronze valve guides and huge barring surfaces it has a lot of good things going on. the block im working with has been decked and is a standard bore to give me lots of meat between the cylinders. it has been converted to full flow filtering. line bored on the mains, three angle grind, stainless sodium exhaust valves and a shadbolt cam(profile unknown) Im going to send the crank, rods and flywheel out to be balanced. I have some good quality chrome rings and some "roto caps" for the valves(not so good for gas but apparently good for propane?)i have spare rods from less stroked motors and can increase the rod length if i can find a piston that will work. here is a thread i made on another forum packed with all the info i could find along with pics of what i have:http://www.g741.org/PHPBB/viewtopic.php?f=3&t=5180 even with running twin carbs and exhaust i dont think it will make up the 20% im looking for. even if I bump the compression to 9to1 i dont think i will see the gains im after.

So being a datsun guy my first thought was lets add a turbo. I know what I'd like it to be like but don't know how to get it there. its in a 6000lb 4x4 that i bounce around in the bush i was thinking about propane to get away from float/vent problems on severe grades also with the long stroke it should run better on high octane with its slow burn and i wouldn't have to build a box for the carb. there is lots of room under the hood for plumbing and coolers. with that being said and knowing how i drive my truck the turbo has to work a certain way (i think). the turbo should kick in real fast like @ 800rpm to 1200rpm and run out of poke by 3400-3600rpm so im not tempted to keep spinning it up. then when i take my foot out of it it should dump really fast.

any help on this project would be greatly appreciated
cheers
Robyn

[okayfine]

Increasing compression by almost 50% would do quite a lot in theoritical terms. I don't know anything about the 251 to say if it would give you a 20% gain in power/torque, but I would be shocked if that were not so. Are there people with 251s that have similar compression and can give you first-hand advice with regard to how your goals would match up to their reality? If the rest of the engine would be happy with the comp. bump, that's a lot simpler than adding at turbo system.

Interesting project.

[RMS]

Interesting project.

thank man

inliners making speed keep their cards close to their chest and are reluctant to share anything. granted there is a lot of mods and info for the Hudson motors but they go with belt or shaft driven blowers and its a different animal.
there are flow issues around increasing compression in the Lhead due to the layout. with the valves being beside the piston the space between the valves and piston is quite large and the only thing that can be done to my knowledge is to shave the head. witch is limited due to valve shrouding. the current motor in my truck is 40 over and the head is off a smaller stroked car. the head has also been milled to the max and gives me around 8.2-1 im pushing about 120bhp. there is one guy in California who makes a hi comp aluminum head witch should give me 8.5-1 but it costs around $1000.

for pure esthetics i think it would look supper cool to have two small turbos off a 1.3L sprint each feeding a impco 125 on my duel cast manifold with a bunch of stainless and brass tubing

[andrew.lori]

I have an 1955 M152 with the same 251 engine. A friend of mine with the identical truck ( one digit in vin between our trucks ) found a Crank and Rods out of a 265 flat head. I wish I could remember what old Mopar or Chrysler Industrial engine he found the parts out of. When he built his motor he installed a vintage Offenhauser Head and Shadbolt cam dual down draft carbs with the 2 into one exhaust it was Amazing how much better his truck performed over my truck also with a fresh 251.

[datzenmike]

The flat head is very inefficient in design. The trick to getting the most work out of a given energy supply is that as much heat as possible is put into expanding the air in the cylinder above the piston. Ideally no heat is absorbed by the piston or the head/cylinder surfaces. To do that the head surface must be minimal so heat isn't absorbed. The flat head combustion surfaces could be ceramic coated. I know, kind of high tech but every % increase counts.

Maybe twin turbo twin carb. (very small turbos so they spin up fast on a 4 liter 6 cylinder) If the valves are shrouded the turbo will force them to breath better so I would bring the compression up two points to 8.6 at least. This will bring up the efficiency maybe 8% or so alone.

Are these pistons hyper-eutectic or forged? This motor is going to make a lot more heat.

[RMS]

it interesting you should mention having the head ceramic coated. i mentioned that to a buddy just the other day not for thermal efficiency but as an alternative to having his head milled to raise the compression........hmmm.. thanks mike ...i wonder could i carefully take a die grinder to the head and hog out the area above the piston and have the entire combustion chamber on the head ceramic coated rather than just the valve relief area? (pic below) typically how thick is the ceramic coating in a combustion chamber? or is it "the thicker the better"? i have a bunch of heads so i can easily find out how much meat i have to work with.

Are these pistons hyper-eutectic or forged

i can barely pronounce eutectic... the Canadian army eme for the truck just says "aluminum alloy" i imagine they are junk. i have seen old school forged racing pistons come up on youpay for $150 a set. i was thinking of running the longer rod out of the 251 in my 265 and finding a piston with modern rings and a higher pin height. the vw pistons that came out of a z22 turbo block are close but i would have to go with the 8inch rods out of a 236 and I think the skirt should be a bit longer. whatever piston i end up running i should send out for some trick coatings
the po of some of my parts did a nice job with an aluminum boss on the oil pan. it is located at the lowest spot on the sump. could it be used for the turbo oil dump or is it best to have the oil pour on top?

i like the idea of two turbos but i haven't even tuned twin SU's before. im not afraid of making a manifold. it could be done out of schedule 40 with 1inch flanges. weight is not an issue. plus my buddy Mr wolf said he would use his years of experience as a food safe pipe fitter to tig up a manifold for me.
i took some time to process a reread of the first five pages in turbo q&a last night and played around with drawing a layout for an inter cooled turbo propane setup i hope to be able to use a air suction valve off of a subaru ASV system to replace the road draft tube and crank case breather. drawn in green

[RMS]

I have an 1955 M152 with the same 251 engine. A friend of mine with the identical truck ( one digit in vin between our trucks ) found a Crank and Rods out of a 265 flat head. I wish I could remember what old Mopar or Chrysler Industrial engine he found the parts out of. When he built his motor he installed a vintage Offenhauser Head and Shadbolt cam dual down draft carbs with the 2 into one exhaust it was Amazing how much better his truck performed over my truck also with a fresh 251.

i like the radio vans i had a m43 that i started to convert into a camper but by the time i got some goodies in it there was no room for me at 6'1". i sold it to a buddy who's 5'7". 265 are out there you just have to be willing to drive to the prairies and pull one out of a combine. if it has a full flow block its likely a 265 or if its a crown marine m47 made after 54 link http://www.mrbtech.com/ChryslerEngineSpecs.pdfim in the process of pulling a m47 out of a boat. it is not a fun operation. the boat is in the water and i will have to get the 600lb short block on to the dock with out a crane. are you on the G741 forum?

[andrew.lori]

My van is just a Utility Van I have owned it since 1979 and restored it 12 years ago and maybe have put 20 miles on it since. My friend converted his into a Radio Truck over a 3 year period there are pictures of it on the web link below pictures at bottom of the page and some interior shots of the Radio Setup about half way down the same page. He sold it to a fellow in Maryland for a Pile of USD.

http://www.signaltelecom.ca/M152%20III.html

I have been away from the Military Truck circle for Years so Nope Im Not a member of the G741 forum ... maybe I should join for some motivation.

[RMS]

you should get back into the m152, military dodges complement 510s very well because after you take the dime out for a rip and get held back from having any fun by traffic and speed laws. you can jump into your single line brake 8000lb truck and have some white knuckle fun 10k under the limit. 80k in my m37 feels like 100mph in a 510 with blown tie rod ends

[andrew.lori]

I never left the M152 world my truck is a Keeper .... you describe EXACTLY what its like between the two. I will post a pic later when I find one of my old beast the buddys call the War Wagon .

[datzenmike]

it interesting you should mention having the head ceramic coated. i mentioned that to a buddy just the other day not for thermal efficiency but as an alternative to having his head milled to raise the compression........hmmm.. thanks mike ...i wonder could i carefully take a die grinder to the head and hog out the area above the piston and have the entire combustion chamber on the head ceramic coated rather than just the valve relief area? (pic below) typically how thick is the ceramic coating in a combustion chamber? or is it "the thicker the better"? i have a bunch of heads so i can easily find out how much meat i have to work with.

Are these pistons hyper-eutectic or forged

i can barely pronounce eutectic... the Canadian army eme for the truck just says "aluminum alloy" i imagine they are junk. i have seen old school forged racing pistons come up on youpay for $150 a set. i was thinking of running the longer rod out of the 251 in my 265 and finding a piston with modern rings and a higher pin height. the vw pistons that came out of a z22 turbo block are close but i would have to go with the 8inch rods out of a 236 and I think the skirt should be a bit longer. whatever piston i end up running i should send out for some trick coatings

I don't think it's applicable for increasing the c/r although it probably will slightly. It's a ceramic dust or paint that is fused onto the head material or piston tops. Basically it acts like pink insulation. It it does not retain heat, so the incoming fuel/air can't absorb heat and push closer to detonation. Any heat released by burning gas and air helps expand the air increasing the push on the pistons and is not wasted heating the head and piston tops.

The piston on the right is a fully floating kind? I see clips to hold the pin inside the piston.


Aluminum alloy could be just that. Forged pistons are. The only problem with aluminum is it's huge increase in size when heated, about twice that of the iron block and head. Cold start-ups are noisy until the piston swells to proper clearances at operating temperatures. Most pistons today are hyper-eutectic or alloyed with another material beyond the point where it can naturally absorb and hold it in suspension. In this case silicon is mixed into the aluminum and it's eutectic point is about 12%. Beyond this (hyper) the silicon can fall out of suspension and form lumps like gravel in concrete. Aluminum can be 'forced' to accept 14% to 16% (even to over 20%) silicon content and this reduces the aluminum's expansion rate from heat and this is turn allows a much closer cold tolerance between the piston and the cylinder wall. A drawback is that the piston, though strong and hard is very brittle. I suspect your pistons are just aluminum alloy and probably rattle when cold.

[RMS]

the piston pin is a full floating type with a bronze bushing in the rod ?
the book says the piston fit should have a 5-7 pound pull @ 70deg. is that a lot?
below is a pic of a good used stock piston and a set of rings. check out the lobes on that cam



if my pistons rattle i cant hear them over the 6 blade 18inch fan and the 5 feet of 3 inch non baffled stainless.



after reading and re reading some of the info hear on the realm and reading your post

Aluminum alloy could be just that. Forged pistons are. The only problem with aluminum is it's huge increase in size when heated, about twice that of the iron block and head. Cold start-ups are noisy until the piston swells to proper clearances at operating temperatures. Most pistons today are hyper-eutectic or alloyed with another material beyond the point where it can naturally absorb and hold it in suspension. In this case silicon is mixed into the aluminum and it's eutectic point is about 12%. Beyond this (hyper) the silicon can fall out of suspension and form lumps like gravel in concrete. Aluminum can be 'forced' to accept 14% to 16% (even to over 20%) silicon content and this reduces the aluminum's expansion rate from heat and this in turn allows a much closer cold tolerance between the piston and the cylinder wall. A drawback is that the piston, though strong and hard is very brittle

i feel farther behind. So lets see if im on the right track (and if i can be followed) concerning my build. so i want to normalize my flow and maybe add a couple atmosphere's. but in doing so heat is created. which i can use to help the cause. but to use the heat every part has to be able to take the heat and the more heat that's lost by absorption the less effective the build will be. now the hard part balancing what can be done vs what i can afford to do.

if i get forged pistons they will have more mass and have large clearances when cold, rattling more than the stock pistons. with the low eutectic value of the stock and old school pistons they absorb the heat and expand i can beef up the stock pistons but problems are said to happen with some of the fancy coatings and I imagine adhesion is compromised by things expanding . once i considered the expansion of things i realized i was very wrong. imagine if I had a big chunk of ceramics in the head and it let go.

cool looking thin coatings http://swaintech.com/

[Byron510]

... check out the lobes on that cam

Yep, certainly not a stable profile for a rev'er, that's for sure...

Byron

[datzenmike]

the piston pin is a full floating type with a bronze bushing in the rod ?
the book says the piston fit should have a 5-7 pound pull @ 70deg. is that a lot?
below is a pic of a good used stock piston and a set of rings. check out the lobes on that cam



if my pistons rattle i cant hear them over the 6 blade 18inch fan and the 5 feet of 3 inch non baffled stainless.

As a rule fully floating pins free up a small amount of power.

after reading and re reading some of the info hear on the realm and reading your post ...

i feel farther behind. So lets see if im on the right track (and if i can be followed) concerning my build. so i want to normalize my flow and maybe add a couple atmosphere's. but in doing so heat is created. which i can use to help the cause. but to use the heat every part has to be able to take the heat and the more heat that's lost by absorption the less effective the build will be. now the hard part balancing what can be done vs what i can afford to do.

if i get forged pistons they will have more mass and have large clearances when cold, rattling more than the stock pistons. with the low eutectic value of the stock and old school pistons they absorb the heat and expand i can beef up the stock pistons but problems are said to happen with some of the fancy coatings and I imagine adhesion is compromised by things expanding . once i considered the expansion of things i realized i was very wrong. imagine if I had a big chunk of ceramics in the head and it let go.

cool looking thin coatings http://swaintech.com/

You can use either, both have advantages/disadvantages Forged are stronger and will take more abuse and heat like in a turbo application. You need more cold piston to cylinder wall clearance than the hyper-eutectic pistons. Forged are more expensive they are not necessarily more heavy.

As to exotic coatings the heat loss saved may add 2-5% more power. This might be something that racers could afford where every hp is needed for an edge over the competition.

[datzenmike]

... check out the lobes on that cam

Yep, certainly not a stable profile for a rev'er, that's for sure...

Byron

Byron, keep in mind that the fathead cam almost pushes directly on the valve stem. No push rods, rocker arms. I imagine there is provision for clearance adjustment and valve lifter but this is close to OHC DE head