mpfi injection/turbo -> spfi pistons

[bgd73]

I looked closely through tech manual for a 1989 sube. Upon finding a mpfi turbo driveline cheap, I thought of the swap of normal 7.7:1 turbo pistons onto the spfi engine's pistons of 9.5:1 (lower end/block).

By swapping heads, intake,ECU wiring etc.

I found subtle differences:

the pistons for spfi==9.5:1 and a diameter .0005 inches different (smaller) than a mpfi 7.7:1 piston.(Could spfi pistons handle a pound or two of turbo?)

the final drive hypoid gear for mpfi is 3.475, the 2wd swap would be 3.7 (2wd takes off faster-- possible welcome torque kill?)

thoughts of a heavy duty radiator neither car has would be a great idea too (should have two core soon enough)

 

Other than this, I don't have any other facts, as I would need to look at both blocks to find other stuff. Anybody done this? It really got me pondering a unique setup, as I am itching to take my old ea82 apart for bearings, or possibly another, and keep my old one running for now.It is so ridiculously possible, I am thinkin as if I had the stuff already

[mikeshoup]

Are you talking running a turbo setup with an SPFI block?

 

My XT Turbo's engine was built like this. It gives it plenty of low-end torque, and more power for when the turbo kicks in. Its running stock boost, and I wouldn't run anything higher than that.

 

Largest problem with it so far was a head gasket blew in fairly short order. Not entirely sure the cause of it. It most likely was due to overheating from neglect on my part.

 

If you do this, keep that thing running cool. Run ONLY premium. It WILL knock under boost otherwise. You may even have to retard the timing. What helps me is I live in a higher altitude. The lower air pressure means less air is being force fed to it. I recommend an intercooler if you don't have one. (I plan to throw a SAAB 900 IC on it soon)

[bgd73]

Are you talking running a turbo setup with an SPFI block?

 

My XT Turbo's engine was built like this. It gives it plenty of low-end torque, and more power for when the turbo kicks in. Its running stock boost, and I wouldn't run anything higher than that.

 

Largest problem with it so far was a head gasket blew in fairly short order. Not entirely sure the cause of it. It most likely was due to overheating from neglect on my part.

 

If you do this, keep that thing running cool. Run ONLY premium. It WILL knock under boost otherwise. You may even have to retard the timing. What helps me is I live in a higher altitude. The lower air pressure means less air is being force fed to it. I recommend an intercooler if you don't have one. (I plan to throw a SAAB 900 IC on it soon)

 

hey thanks-- I was sure it could be done with the expense of a bit more heat/strain. If the single core all metal radiator can handle most anything, the double core should be very good. If a few other factors come together in coming weeks, I will know.

 

I would like to kill boost if possible instead of retarding timing -- even if it is next to nil. My spfi pings now randomly, and I aint budging anymore. I am not even interested in adding IC (may not even run turbo). You're xt must haul rump roast-- is it 2wd? the turbo gears (3.475)?

[mikeshoup]

So you're just going for a N/A MPFI motor then? So, in otherwords just an N/A XT? Sounds fun. (All XTs are MPFI by the way and so are all Turbos)

 

If you run the turbo, the only way to reduce boost is to put a weaker spring in the wastegate. Otherwise, you're stuck with the stock 7psi. Which isn't much btw.

 

Oh yeah, and my XT does haul rump roast. Its 4WD with the 3.7 gearbox. I eventually plan to get a 3.7 rear LSD in it, then a FT4WD gearbox.

[NorthWet]

...I would like to kill boost if possible instead of retarding timing -- even if it is next to nil. My spfi pings now randomly, and I aint budging anymore. I am not even interested in adding IC (may not even run turbo). You're xt must haul rump roast-- is it 2wd? the turbo gears (3.475)?

Last things first. The final drive on turbos is an effective 3.70; the front ring and pinion set combined with the reduction in the tranny shafts works out to 3.7, which is what the rear diff needs to be on 4WD versions.

 

There is a way to reduce boost dynamically based on a knock sensor. SAAB uses this method in their APC system on turbo'd SAABs. For your app, you would still need to do some mods like mikeshoup said in order to get a lowered minimum boost, but the APC allows the boost to be higher than the minimum wastegate setting.

 

And, yes, the SPFI and Turbo pistons are supposed to be physically interchangeable (I have not done so yet, so can't say from experience).

[bgd73]

Last things first. The final drive on turbos is an effective 3.70; the front ring and pinion set combined with the reduction in the tranny shafts works out to 3.7, which is what the rear diff needs to be on 4WD versions.

 

There is a way to reduce boost dynamically based on a knock sensor. SAAB uses this method in their APC system on turbo'd SAABs. For your app, you would still need to do some mods like mikeshoup said in order to get a lowered minimum boost, but the APC allows the boost to be higher than the minimum wastegate setting.

 

And, yes, the SPFI and Turbo pistons are supposed to be physically interchangeable (I have not done so yet, so can't say from experience).

 

The driveline this came from is a 1988 GL-10 -- the final hypoid gear ratio is written as 3.475 for 1989, I would hope yours is correct (3.475 is odd to majority). Another note, 1988 was a year mpfi gl-10 wagons had 7.1:1 compression according to cars101.com. I am shrugging this off as a written error, as a tech book for this shows it at the common-for-all 7.7:1

 

mikeshoup: If the xt @ 3.7 hauls, I wonder what a tin-can sedan is gonna do being a bit of steel lighter...

 

Swapping ecu stuff Q-- there is 3 more injectors , a different ecu, and knock sensor(?). How difficult is wiring, I am hoping many things overlap the same.

[[HTi]Savage]

that should work dude. iam running an SPFI block with turbo heads MPFI intake and stock bost in my 87 RX. its ballsey. but it blows head gaskets.

the stock gaskets cant handel the high compression and the boost.

But the high compression needs lots of air densety or else it lacks power, its a pain in the rump roast but it works. Use Fel-Pro gaskets mine have worked so far.

iam running with no thermostat so it runns cooler. give it a try.

[kingbobdole]

Mikes car is very fast, even up here in CO... He needs to intercool it tho, so that when we race I dont totally kill him in my XT, just smoke him:lol:

[bgd73]

Savage']that should work dude. iam running an SPFI block with turbo heads MPFI intake and stock bost in my 87 RX. its ballsey. but it blows head gaskets.

the stock gaskets cant handel the high compression and the boost.

But the high compression needs lots of air densety or else it lacks power' date=' its a pain in the rump roast but it works. Use Fel-Pro gaskets mine have worked so far.

iam running with no thermostat so it runns cooler. give it a try.[/quote']

 

By chance are you running the 2 core radiator with your setup along with no thermostat? I like having the thermostat, it is actually a balancing junction for what the heater box can cool too....

If you are, I don't want to attempt the high comp MPFI turbo setup :cool:

[NorthWet]

By chance are you running the 2 core radiator with your setup along with no thermostat? I like having the thermostat, it is actually a balancing junction for what the heater box can cool too....

If you are, I don't want to attempt the high comp MPFI turbo setup :cool:

IMHO, running without a T-stat is a bandaid. Once a properly functioning t-stat hits operating temp, it becomes a non-issue. If the car is going to overheat it will do so with or without the t-stat, or whether it is a 160 or 192degreeF t-stat. No t-stat, or a cold one, will just increase engine wear, fuel consumption, and emissions.

 

Make sure the rest of your cooling system is first rate. A 2-row-core radiator is good, cheap insurance.

[bgd73]

IMHO, running without a T-stat is a bandaid. Once a properly functioning t-stat hits operating temp, it becomes a non-issue. If the car is going to overheat it will do so with or without the t-stat, or whether it is a 160 or 192degreeF t-stat. No t-stat, or a cold one, will just increase engine wear, fuel consumption, and emissions.

 

Make sure the rest of your cooling system is first rate. A 2-row-core radiator is good, cheap insurance.

 

I agree about the overheat with or without. With pushes it into another route (the heater core) without, sends most to radiator and hardly anything to h core and its lines. I want it dispersed all over every square inch it can go to, it is common sense stronger cool, even if the same reading shows up on the guage. A true experiment would be to shut the car off after full temp, and check it just 20 min later- same guage same readings yet engine stays warmer longer without thermostat and guage verifies it is still warmer after same time shut off.I just did this not long ago. I swore it was running cooler without, and I was quite wrong, plus there was no heat at all-- that is NO indication of cool engine, most likely the opposite. I installed a "stant" replacement due to the slime stuck on old one (again the sealant additive - it is what clogged my rad.) The stant is quite small in comparison to oem, seems faster reacting, non- yoyo'd.

 

I am sure the 2 core could handle the setup.. just second guessing everything before it is a waste of time in my mistakes.

[mikeshoup]

2 core can definitely handle the heat. Mine never reaches above 212 (I have a mechanical gauge) on uber hot days. 212 is about half on the gauge I think?

 

The old radiator I had from when the head gaskets blew was an old one core that was clogged to hell.

[bgd73]

2 core can definitely handle the heat. Mine never reaches above 212 (I have a mechanical gauge) on uber hot days. 212 is about half on the gauge I think?

 

The old radiator I had from when the head gaskets blew was an old one core that was clogged to hell.

 

The one cores love to clog in the exact wrong places - where the most air hits them consistently. Will be getting brandy new 2 core this week-- it is ashame it is already getting into the 40's at night, so I may not know true test until I drive to hot weather, or wait til next year .

I am guessing 195 thermostat still opens in normal time, and really hangs on to a steady ambient for the engine - another plus along with cool enough.That MPFI turbo parts car is still sitting there tempting me at this moment..I am ready to play around with the old ea82's more than I have been.

[[HTi]Savage]

I am only running a single core rad. if i had the 2 core rad i would put the t-stat back in. also when winter commes around i,am puting the t-stat back in.

also if i stay off the gas i have gotten 31 mpg. but iam always driving balls out its the only way to drive a sub. more power this way.

[bgd73]

Savage']I am only running a single core rad. if i had the 2 core rad i would put the t-stat back in. also when winter commes around i' date='am puting the t-stat back in.

also if i stay off the gas i have gotten 31 mpg. but iam always driving balls out its the only way to drive a sub. more power this way.[/quote']

 

I bet the flow of turbo pressure vs just n/a vacuum acts as a coolant pump on its own...pushing it to only 2 destinations (rad/h core). The n/a really doesn't flow coolant well without it.My bigger cfm DL carb drove ok without -- that is when I put the guess together about cfm and all the channels nearby, and what they do as a reaction. Simply put-- high vacuum intake (like spfi) likes to slow coolant, slow vac pressure, fluid pumps, an invisible physic -- what a strange thing I learned about the old sube :-\ . May put no thermostat to action with first runs of bigger intake.

On another swap note-- there is a recent post about cams being different from mpfi->spfi. Should I use the spfi cams on mpfi heads?

[[HTi]Savage]

My car has always ran it 1/4 the way up the guage. the original t-stat was 185 degree t-stat. the high compression block runns hot. sometimes too hot.

with the t-stat out it runns the same temp as with it in. However it takes a little longer to get up to operating temp, but not much longer. When it runns too hot it looses power as with any engine. any thing past half temp is too hot for my engine, thats what u have to consider with the high comp block

among other things.