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do 8v gasoline heads fit on a diesel block?
by
voodoo
on 23 Oct, 2005 11:32
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do 8v gasoline heads fit on a diesel block?
why do I want a gas head on my diesel?
because I want to lower the compression from 23:1 to 15:1
compression makes heat, I want to have cool egt so the pistons don't melt
I checked, 8v gas head has about 28 cc chamber, shave a little and its 25cc, plug into compression formula gives 15:1
some gas head flow better than diesel heads, more air = more power
big intercooler, big turbo, lots of fuel, lower compression to reduce heat.
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#1
by
Master ACiD
on 23 Oct, 2005 11:57
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gas heads dont have provisions for glow plugs, pre chambers, injectors, etc. maybe you can figure out a way to make everyting fit through the sparkplug hole!
i dont think it could work, but let us know if you get anything done.
if you want to lower the compression just flycut the cylinder head a tick, or even the piston tops.
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#2
by
vwmike
on 23 Oct, 2005 12:01
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It's great you're thinking and all, but the gas head has no prechambers. no place for the injectors to bolt in, and no place for the glow plugs. Yes, some DI engines making big power are running ~15:1 compression, but I doubt you'd like how that drove (if it drove) on the street. It would be a gutless wonder until it got under boost.
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#3
by
QuickTD
on 23 Oct, 2005 12:08
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I think we've been over this before... Lowering the compression ratio will have little effect on EGT. High EGT's are the result of overfueling. Lowering the compression allows you to run higher boost without excessive cylinder pressure, this enables you to run more boost before something physically breaks. It will help with head gasket failure, piston breakage or rod bending problems, it will not lower EGT's.
Where will you put the injector and glow plug in a gas head? How will you start and idle a small diesel with 15:1 compression? The 14 litre 6cyl (900hp, 1500ftlb) cummins that you used as an example in your last post on this subject will not start in the cold with 15:1 compression, it must be plugged in for several hours. A smaller engine with a higher surface area to volume ratio will be significantly worse. You'll have to push it to get it to start, preheat it to near operating temperature or use cases of starting fluid to warm it up like the tractor pullers...
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#4
by
voodoo
on 23 Oct, 2005 16:44
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good answers. more responses not needed
turbo's are good for melting pistons, no really after reading thousands of mitsubishi , honda, turbododge posts I give up.
most often read turbo post: there was a 3 second boost spike and my $500 forged pistons melted.
list of gear already in possesion:
5 thunderbird turbos, garret t3's .48 ex .63 cp good for about 250 hp ea
2 megasquirts
4 intercoolers
3 2.4L dodge 16 valve motors, one built for turbo
4 2.0 motors
5 transmissions
1 neon that laughs at me
14 440 cc injectors
1 laptop
1 wideband o2 box
$50 takes all
gas is $3 a gallon making me not want to drive a 12 mpg turbo car
also in possession: a 1.6L na vw diesel not for sale
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#5
by
vwmike
on 23 Oct, 2005 17:08
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good answers. more responses not needed
turbo's are good for melting pistons, no really after reading thousands of mitsubishi , honda, turbododge posts I give up.
most often read turbo post: there was a 3 second boost spike and my $500 forged pistons melted.
list of gear already in possesion:
5 thunderbird turbos, garret t3's .48 ex .63 cp good for about 250 hp ea
2 megasquirts
4 intercoolers
3 2.4L dodge 16 valve motors, one built for turbo
4 2.0 motors
5 transmissions
1 neon that laughs at me
14 440 cc injectors
1 laptop
1 wideband o2 box
$50 takes all
gas is $3 a gallon making me not want to drive a 12 mpg turbo car
also in possession: a 1.6L na vw diesel not for sale
Haha...well, if you're close then consider it sold!
Really, in the last 5 years I've burnt one set of rings, and melted one piston in a turbo CIS Rabbit. A lot of people melt pistons - mostly because of inadequate fueling on gas engines. Mine was due to a stupid wiring issue with the fueler the first time and a heat soaked intercooler the second time. It's really not nearly as common in diesels and it is actually much more difficult to break the engine as knock isn't really a concern.
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#6
by
QuickTD
on 23 Oct, 2005 17:09
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turbo's are good for melting pistons, no really after reading thousands of mitsubishi , honda, turbododge posts I give up.
most often read turbo post: there was a 3 second boost spike and my $500 forged pistons melted.
There is your problem, all your examples are of gasoline engines. Excessive boost combined with high compression in a gasoline engine results in detonation, the mixture fires before TDC due to heat, pressure etc, this melts pistons.
A diesel engine has no fuel in the intake charge, it therefore cannot detonate during compression. The fuel is injected near TDC and fires due to the heat of compression. Diesels depend on controlled detonation to run. You could run 30:1 compression and 50psi of boost if you could get a head gasket and rods strong enough to hold it, it would never melt due to detonation.
Forget what you know about turbocharged gasoline engines if you want to build a powerful diesel, none of it applies.
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#7
by
Patrick
on 23 Oct, 2005 18:23
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Where will you put the injector and glow plug in a gas head? How will you start and idle a small diesel with 15:1 compression? The 14 litre 6cyl (900hp, 1500ftlb) cummins that you used as an example in your last post on this subject will not start in the cold with 15:1 compression, it must be plugged in for several hours. A smaller engine with a higher surface area to volume ratio will be significantly worse. You'll have to push it to get it to start, preheat it to near operating temperature or use cases of starting fluid to warm it up like the tractor pullers...
Welll..............................
Yes but................
Drove an 855 cummins, Big cam 1, 400 horse, about 1100 ft/lbs if memory serves, big holset turbo with 14.5 to 1 compression for a lot of years, about 700,000 miles worth. truck was overfueled about 30% courtesy of John ter Horst. Started okay down to about -5c without being plugged in. Couple hours on the plug at -40. No glow plugs on this engine.
Present truck is powered by Perkins, NA 354ci, no glow plugs, 16.5 to 1 compression. Use the "Thermostart" (single glow plug/fuel injector on the intake manifold) almost all the time, wwinter or summer. Need it less if the factory timing is used, but the truck smokes more. Will start down to -30 without beinng plugged in, but doesn't like it!
Depends on a lot of variables.......................
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#8
by
QuickTD
on 23 Oct, 2005 21:17
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Depends on a lot of variables.......................
The most important being direct vs indirect injection. Large direct injection engines have lower surface area to volume ratios. They also do not have a prechamber to add to the surface area. Prechamber turbulence also contributes to poor starting because the turbulent air gets more exposure to the cold combustion chamber walls. All these factor make it necessary to run relatively high compression to insure reliable starting. Big DI engines seldom need glow plugs to start reliably.
Drove an 855 cummins, Big cam 1, 400 horse, about 1100 ft/lbs if memory serves, big holset turbo with 14.5 to 1 compression for a lot of years, about 700,000 miles worth. truck was overfueled about 30% courtesy of John ter Horst. Started okay down to about -5c without being plugged in. Couple hours on the plug at -40. No glow plugs on this engine.
Present truck is powered by Perkins, NA 354ci, no glow plugs, 16.5 to 1 compression. Use the "Thermostart" (single glow plug/fuel injector on the intake manifold) almost all the time, wwinter or summer. Need it less if the factory timing is used, but the truck smokes more. Will start down to -30 without beinng plugged in, but doesn't like it!
I'll give you the cummins, they will start down to -5ºC if they are in a good state of tune, but they blow clouds of acrid white unburnt fuel for 15 minutes... I've gotta call BS on the perkins though. We've had a fair number around, 4.236 and 6.354, both turbo and NA and one thing they cannot be accused of is being terribly eager to start. The "normal" 17.5:1 compression version isn't bad but -30º is out of the question. Haven't had much experience with those "thermostart" things. They are used on most of the T4.236 powered aircraft ground power sets I've worked on but have never had any cause use them. The airports need engines that start, so they keep them plugged in. They must work some kind of great if you can get that 354 to fire at -30...
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#9
by
VWRacer
on 24 Oct, 2005 06:31
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Not only will the 8v gas head fit a diesel block, but it would make a heck of a NA racing engine at 15:1 CR. Of course, you'd have to run minimum 110 octane leaded racing gas in it, at about $6.75/gal, but it would work fine. If you ran 116 leaded racing gas you could even turbocharge it... :shock:
FWIW, for a number of years the dreaded GM diesels of the 80's were sought after by drag racers. Drop on a set of gasser heads and intake and you have a bullet-proof combination for very little money.
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#10
by
veeman
on 24 Oct, 2005 07:54
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>>turbo's are good for melting pistons, no really after reading thousands of mitsubishi , honda, turbododge posts I give up.
If I'm reading this thread and the other you started correctly, your prinicipal fear is melting pistons on a turbo engine...
Before you give up, have you tried driving a bone stock vw TD (IDI) engine?
As many have suggested on this board, I'd recommend you get a "baseline" for your project first. Try out a 1.6 or 1.9 TD, install a thermocouple and a boost gauge, make sure the timing is dead on and see how it behaves.
It might not be a rocketship, but you'll gain a ton of experience from putting everything together AND you'll know how the thing was designed to run...wtihout melting anything. This is where I'm at right now...
Once you drive the car for a while, then you can start tuning, plus you'll have the gauges / know-how to do it. Check on this board. There are plenty of examples of how people have made safe modifications to net some impressive power gains.
Another strategy would be to build the motor with the head studs / machine work, injectors, turbo, etc that would make it a performance engine, then tune it "conservatively" at first. Keep an eye on things as you break it in and if something is wrong, you'll see it.
As you mentioned, EGT's are important to watch. Pulling up a large hill, EGT's can spike while keeping in the boost... another situation why a good stock "baseline" can help.
I'd encourage you not to give up on your idea just yet... It's clear you've done some thinking and reasearch and that your motivation is there. I'm relatively new to the diesel worlkd and this board and others like it have plenty of info that applies directly to these engines.
Best of luck.
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#11
by
Patrick
on 24 Oct, 2005 14:00
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Depends on a lot of variables.......................
I've gotta call BS on the perkins though. We've had a fair number around, 4.236 and 6.354, both turbo and NA and one thing they cannot be accused of is being terribly eager to start. The "normal" 17.5:1 compression version isn't bad but -30º is out of the question. Haven't had much experience with those "thermostart" things. They are used on most of the T4.236 powered aircraft ground power sets I've worked on but have never had any cause use them. The airports need engines that start, so they keep them plugged in. They must work some kind of great if you can get that 354 to fire at -30...
\
I did say it doesn't like it! Takes a lot of messing with it, crank, stop and wait, crank again, etc. Truck's got two 1000 amp batteries too. Only done it a few times when absolutely had no choice. MUCH prefer having it plugged in! Thermostarts a good thing, but it takes fuel pressure to push fuel through (crank it) and really good batteries/starter/cables. The thermostart will actually throw flame. (ask me how I know!!) :oops:
Don't know why, but it's actually better at -25 or 30 than at -5-10.
Drier denser air maybe???
As for the white smoke out of the cummins, I know what you mean! Some are a lot better than others though, I think it depends on where the timing is set.
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#12
by
Master ACiD
on 02 Nov, 2005 18:12
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theres some diesel truck drag racing club around here that frequents the local drag strip.
one guy with a dodge cummins is claiming over 80psi of boost. he claims to have a stock bottom end too, but i sure would like to see what he did to that top end!
one of my friends is in that club. hes got a 4 wheel drive ford diesel dualy with some slick as snot banks turbo kit and a bunch of other upgrades. he can light up all 6 of his wheels all at the same time and leave a 6 wheeled burnout.
kinda makes my little 1.6D seem insignificant.
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#13
by
greggearhead
on 02 Nov, 2005 21:25
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Yes, the gas head will fit on the Diesel block. As a gas engine. The land speed Rabbit truck used a diesel 1.5 with a few different Gas heads to run around 16:1 compression (usually on pump gas no less). Block had to be notched for the valves - wasn't ideal on a couple levels, but can't argue with the results. Several records.
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#14
by
935racer
on 02 Nov, 2005 21:47
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Land speed rabbit truck? what class? how fast? more info needed :twisted: