compression effects.

kskfordfleet · Jul 6, 2009

hello, got a question that maybe some of you diesel perfomance guys can help me with.

basically i need to understand what the effect of running an higher compression ratio from a NA engine with a standard turbo.

example (1st gen) 4b with 18:5 compression, and somthing like a H1C or Hx35/hy35 turbo.

vs standard turbocharged compression of 17:5.

i understand that boost by itself dose not make power, that fuel provided in combination dose.
but will the higher compression cuase EGT problems?..limit the amount of fuel i can dial in? will it be nessary to limit boost via a waste gate?

condsidering that the higher cr ratio should increase power at low end when not on boost, would it help to run one of the larger Cm exhuast housing on the turbo? like 18-21? to reduce boost psi lower rpm.

i am aware of the possiblity of swaping pistons, what i would like to hear or understand is the theroy or best guesses.. as to how this would effect the running of this engine or potential for catostophic failure.

thanks, all opinions apreciated.

GOT-Torque · Jul 6, 2009

what's the engine going to be used for? That's pretty close to stock. It will have higher cylinder pressure which would lead to producing more torque at lower rpms. Is this a performance build? O-rings and head studs? If you aren't going crazy with rpms or fuel, I'd say the slightly higher compression would yield more low end and miles per gallon.

You could always put a bigger head gasket in it to offset the higher C/R...

kskfordfleet · Jul 6, 2009

the 4b ..converted to 4bt is going in a 4x4 crawler truck (76 ford 3/4 ton highboy with an fj45 cab on it.)
limited road duty.

i'm looking to get the anemic 76hp/ 185 tq up to around 100-120 hp / 250+tq.

nothing to radical.

i'm concerned about peak cylinder pressure, and high egt's,
i have no idea what the cam profile is like in this engine.
hopfully its not a real narrow lsa on a small duration (peaky clinder pressure on the low side)

thanks for the reply.

carcrafter22 · Jul 6, 2009

Those are stock numbers on a 4bt so just adding the turbo and messing with the fuel will get you there or more.

toss on an hy35 add, a fuel pin, 3200 spring, decent injectors and you will be around 250hp and still very reliable. Look at 4btswaps.com and you will see alot of post like this.

kskfordfleet · Jul 6, 2009

no adverse effect's running a full compression ratio higher than a stock 4bt?

carcrafter.. i did ask a question similar to this on 4btswaps.. the consensus answer ...go buy a road engine rather than convert.

witch is not the route i want to go, $1500-2500 for a worn out twinke truck motor or $300 for a complete industrial 4b with less than 400hrs on it.
theres a lot of $ to spend between those extremes..lol

pump mods are not as simple as a VE.

i'm in tractor territory with a Cav Dpa..

i have figured out how to adjust my fuel output.. by adjusting the plate through the inspection cover.. the governor is a little more intersting.
as i have not found replacement spring, and i'm not 100% sure the dpa uses a veriety of springs vs the same spring used in differnt mounting locations.
via a chart i have that decodes the pump #'s, it changes tension on the spring and resistance agianst the fulcrum point of the govenor arm
(think shifting weight up and down a teeter totter lol) not sure how much rpm i can get looks like 2750-3500 is possible.. but i'm still researching it.

anybody know for sure if there is a difference in the ring style or gapping
between N/a and turbo piston applications?

carcrafter22 · Jul 6, 2009

Sorry you got that answer over there, alot of folks there are stuck on one speed when it comes to modding things (wierd since its a conversion website LOL).

Have you considered looking around for a junk 4bt so you can steal the injection system off of it? I have talked to lots of guys that have found them complete and rebuildable for around $500. I know there is a company that sells core motors on ebay, I looked at a complete 4bd for $600.

I dont know much about that injection pump but I am sure someone here would know, have you tried posting pics and part numbers here in the tractor section?

Is there a full power screw on it anywhere?

Do you have any pics to post up of it?

kskfordfleet · Jul 6, 2009

no power screw, i'll try to describe how you add fuel,

when you look at a dpa pump, theres a two bolt side cover, you remove that cover. inside there is the twin plunger ring, holds the plungers in a radial fashion. and a drive plate splined on the shaft, the drive plate is bolted to the drum with two bolts. each of the pump plunger has a half moon tab that limts its out ward travel (limiting the volume of fuel) the tabs ride in a slot in the adjustment plate that is samwiched between the drive plate and plunger drum. the slots in the adjustment plate taper from a small opening to a larger opening top control the amount of travel of the plungers
to increase or decrease fuel
you loosen the bolts on the drive plate and bump the adjustment plate in the direction of rotation to increase fuel (big end of the slot), against rotation to decrease fuel (small end of the slot).

the draw back is you cant do it while the engine is running and you have to drain and prime the pump each time you adjust.
all i know is i can add more fuel than it injects right now..but i don't know what the limit is for max fuel this pump will put out.
when i do set up the turbo it will be trial and error with the pyro.

yes i'm interested in a bosch set up and junk road engine for parts, when operatunity knocks..lol

but its kinda fun trying to figgure this dpa out in the meantime.

tractor forum you say? must have missed that..maybe they can answer some of the govenor question i have with this pump. thanks

VMacKenzie · Jul 6, 2009

The question is does the non-turbo 4B have piston cooling. . . if not then you're limited on the amount of fuel/power you can get out of it before melting pistons.

kskfordfleet · Jul 6, 2009

good point,

B series with piston cooling, uses squirter tubes off an oil galley running thru the block? or is a squirt hole in the big rod end?

well i'll just have to drop the pan and have a look.

Begle1 · Jul 6, 2009

Up until the common rail, the piston cooling nozzles thread into the main bores. (Slide 43)

kskfordfleet · Jul 6, 2009

interesting.. visuals
thank you.

compression effects.

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