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Building an LN3 from spare parts plus a Supercharger


2seater
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I agree, lots of money, too much actually. The donor engine was purchased for a core engine price when what I was after was the supercharger and the associated hardware. As I am now convinced, it is exactly that, a worn out core. The only small possible advantage to the donor engines heads is the roller pivot rockers. Beyond that, the heads are the same. 
 

Yes, I almost never have valves replaced on these low stress applications. The primary reason seems to be rust or something outside of normal operation. I have had guides knurled in the past too but these appear to be beyond that point.

 

 I stripped my original heads this afternoon and they appear pretty nice overall. Definitely cleaner in the ports and chamber to start with. The photo is just as they were removed, no cleanup. The valve guides feel pretty good and I would use them as is. There is some evidence of oil on the intake valves but they would need seals in any case. The intake valves look plenty good to just clean them for reuse. The exhaust could be saved but valves are inexpensive so they may be replaced leaving only the exhaust seats to need some work. There are cheap seat cutting tools on the net but most are not for hard seats. A carbide set with 11/32” pilot and the three angles would be nice but…. Maybe that can be rented or borrowed? Short of something unknown happening, I will touch up and modify my originals for this project. 

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I decided to go ahead and drill the pvc holes into the original LN3 heads. Essentially they are now compatible with intakes for the L27, the tuned port style. In this style pvc, the outside air enters the front head from a passage inside the throttle body and the intake manifold and it is pulled into the engine intake through the diagonally opposite corner. The replaceable pvc valve itself is inside the intake manifold and there is no external plumbing. The spot to be drilled is marked with the silver X on the intake flange of both heads. The hole can be tapped for a pipe plug if desired to go back to the original. 
 

On a hunch, I looked at the rocker arm’s again to see if the late style with the roller pivot could be made to work on the earlier head and it looks like the geometry is very similar. The roller arm is on the right in the photo. It is slightly wider than the LN3 but is otherwise a clone. The problem appears where they attach to the head. The roller arm uses a 5/16”-18 bolt into the head, the LN3 is tapped 3/8”-16 so the bolt falls into the hole. I looked for a thread adapter bushing, much like a helicoil insert, but nothing turns up. Lots of them are available with the correct interior and exterior thread but not on the same piece. Too thin I guess. It isn’t worth the slight possible improvement to pursue it further. 

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I stuck one head on the flowbench today just for a baseline. It was just a rough look at how the port performs which was as expected. I didn’t bother going through the various valve lifts at this point, just a couple of valves stuck in upside down and tape over the exhaust port. The bench is running in the photo but the numbers are a little off as I hadn’t recalibrated and adjusted the scale at that point. After rescaling with 160cfm and 200cfm test plates, the intake port flows 167cfm at 28” of water column. That’s about ballpark for unmodified intake ports. 
There is also a close up view of  the untouched intake port from the chamber side. I keep trying to remember having these heads off the engine but I am sure I have not. These are my original 1990 heads with ~100k miles on them and they are almost perfectly clean. You can plainly see the contours and the surface of the casting. I do not plan extensive recontouring, just smoothing, removing rough edges, narrow the valve guide boss and widen the port a little at the turn. Now to find the ambition to get started on a dirty job🤔

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Set up an area to work on porting the heads, primarily the intakes. Rather than on a bench I am doing them on a set of low sawhorses so I can sit on a short roll around seat, easier on the back. Lined with plastic sheet on three sides and I found a use for my left over Covid masks 🤔 

 

By just testing without valves it allows for quick verification of effects as various areas are addressed. Shortly after starting the head of my 1/4” extended carbide burr snapped off. It had a welded on head so it is more sensitive to getting the tip caught. The distance between the valve guide boss an the side wall of the port is right at 1/4” so it is easy to jam the tip there until it can be opened up. I have a larger headed burr too but it’s too wide to get to the bottom of the trough. New ones are on the way. I did continue for a bit with a burr with a chipped tip which works more slowly. In any case, just doing a mild taper on the valve guide and rounding out the throat just below the valve seat gains 10-11cfm. Removing the sharp edge where the floor of the port turns into the chamber does essentially nothing. Very small gain by smoothing the sides where the mold lines run the length of the port. It looks like improving the bowl below the valve head and massaging the valve guide further are where the easiest improvements lie. As shown in the photo, the flow is about 178cfm. I Need to add a sort of bell mouth to the intake port entrance and better finish the port once the shape is determined. The before and after of the port it is easy to see the vertical sides of the port are almost flat so rounding that a bit blends into widening next to the valve guides.

 

 I received the new exhaust valves yesterday and did a quick lap on one of them. The location on the valve is pretty good but the contact area is right at the service limit of .110”. Buicks do use a wide seat  but it would be nice to narrow them a bit, preferably by widening the 60* angle below the actual seat. 

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This is pretty much a non-topic post, but it is a head scratcher. The good news is the wandering crank sensor showed up this afternoon as well as the new extended length carbide burrs from McMaster Carr. After my rant about deliveries in another thread, McMaster, based in Illinois and shipped UPS ground, has always been outstanding for delivery. 

The head scratcher part is regarding the flowbench or at least the results so far. I mentioned I needed to add a sort of bellmouth to the intake port for proper flow testing. To do that I just add a small self adhesive D shaped rubber strip around the port, like used for misc. sealing projects, but I was out of it. Today I bought a small roll. All it does is provide a smooth entrance rather than the hard square edge. In any case, I installed the strip and tried the head flow again, and lo and behold it was now in the mid-180cfm range, a pickup of 8-10cfm. This seems like good news but that meant my baseline untouched results were inaccurate. With that in mind I added the D-rubber to the untouched head to hopefully reset the baseline number. On the bench, the unmolested head flows about 174 cfm, mirroring the cfm increase on the worked over head from adding the D-rubber. To verify, I stripped it off the untouched head and the flow dropped into the mid 160's, so at least that part is verified.

All of the above is still somewhat predictable and I could live with that for this purpose where the numbers are helpful, but I am mostly looking for a trend without getting bogged down in the details. The reason for the head scratcher part mentioned at the outset, it seems like flow rate indications seem to be increasing on their own. After going back and forth between the two heads, it appears the head I am working on is now aver 190cfm without doing anything other than add the D-rubber?? This is very puzzling as this is a very simple design with water filled gauges to measure suction pressure and flow, no electronics involved. It could be accounted for if there is an air leak ahead of the sensing area, but nothing appears there, at least not so far. Testing for leaks is also dirt simple: cover the hole in the bench where the flow enters, crank up the suction, and if there is any indication of flow, there is a leak. I guess I should have suspected something was out of whack when I woke up the bench after a couple years being idle and I had to adjust the indicator scale for the inclined flowmeter. This has always been rock stable in the past and never varied more than one or two cfm using the machined test plates to check calibration. I know I am rambling on about this, and I want to save time by only going for the low hanging fruit regarding light porting, but I guess the GIGO adage is still true. It doesn't need to be spot on accurate for this part of the project but it must be repeatable or not worth checking. Maybe I have a mouse nest floating around inside🙃   

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I did take the bench unit apart to check for the correct measuring orifice and look for a stray mouse nest and everything looks just fine. A few fasteners could be snugged up a bit but nothing out of the ordinary found. Tried both heads on the bench again and going back and forth between them a couple times the results repeat so that is a positive. Ordinarily I test with the valves in place and go through the lift progression, so the large increase in flow without valves made me question myself. Below is a pic of an intake valve inserted into my 200cfm calibration plate. It is a knife edged hole in an aluminum plate, dimensions are on the plate. Our intake valve nominal size is 1.72”, so it almost passes right through the orifice plate with only the valve margin showing. It graphically illustrated to me that a hole that size is capable of the flow rate I am seeing. In any case, the only item limiting air flow through the intake valve opening into the chamber is the valve stem. Indicated flow is 196 cfm that increases to 200cfm if the valve stem is withdrawn to be flush with the valve guide. At some point I will go through the calibration process on the bench but at this point I am confident it is working consistently for my present purposes. With that in mind I copied my original reshaping to the other two intakes in the first head.

One other item for the heads is to see about reshaping an old exhaust valve to use as a tool to narrow the exhaust seat. 

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This is an interesting read 2seater. makes me keep thinking that 5 years ago when we did the engine in the Red I thought about doing this also. However with gas hitting $4.00 a gallon [for regular and not premium which a super charged engine requires] I'm now glad I didn't. Gas can be $5.00 a gallon by the 4th of July and with the miles I drive, quite expensive...

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43 minutes ago, DAVES89 said:

This is an interesting read 2seater. makes me keep thinking that 5 years ago when we did the engine in the Red I thought about doing this also. However with gas hitting $4.00 a gallon [for regular and not premium which a super charged engine requires] I'm now glad I didn't. Gas can be $5.00 a gallon by the 4th of July and with the miles I drive, quite expensive...

I am with ya there. I am thankful I drive few miles myself, plus hoping my hybrid shows up within a year. Do you suppose the mileage deduction allowance will increase?

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To put the sidetrack about airflow anomalies to bed, I just did a couple of things I should have done before wasting everyone's time.

 

First, I arbitrarily clamped the intake valve at .400" lift, close to the maximum of an '89-'90. Nominal valve lift for intake is .400" '89-'90 and .433" for '88. I ran both the untouched head and the ported head on the bench and the results are much more in line with expectations. Untouched head, 160cfm on the dot, ported head, 175cfm, a useful increase without a lot of work. I then pulled out my records of the last heads I did, the '88's I received from Daves89. That was a more serious porting attempt, partially due to rust issues, but with just a scrape and brush of the intake port, .400" flow was right at 160cfm, after porting, there are several readings of 182-185cfm at the same lift as I was experimenting with back cutting valves. There are also notes about the port with no valve, just as I have been doing now. Result: stock 194, ported 202.🤢 

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7 hours ago, 2seater said:

I am with ya there. I am thankful I drive few miles myself, plus hoping my hybrid shows up within a year. Do you suppose the mileage deduction allowance will increase?

I would think that the government would have to be convinced that the price of fuel has to stay high before they would make an adjustment.

I have read that fracking might start up again because with the higher barrel prices it would be more economical

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Between yesterday and this morning I finished roughing in the intake porting on both heads. After that was done I went to double check my work on the second head and something happened inside the vacuum chamber of the flowbench, a sort of whump sound and the flow indication dropped off. Investigation will have to wait and is just as well so the rest of the project keeps going.

 I am in the process of cleaning up and lapping in the new exhaust valves and touching up the original intake valves. I did double check the intake porting as I went through removing sharp edges inside the exhaust ports with no actual reshaping as they are pretty good to begin with. I found the exhaust valve made a handy gauge for judging the “roundness” of the intake throat, it fits almost exactly into the bowl of the intake, something I didn’t notice before🤔 

The photo below is of the intake valve at maximum lift of .400” just to illustrate why this engine is a non interference type. Because of the upright ten degree valve angle, coupled with modest lift, the valve protrudes only a small amount below the head. The head gasket plus the piston down in the hole adds another .100+” and the quarter inch deep dish in the piston does the rest.

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I know porting is going to help, but for a low RPM 3800 do you think you will be able to feel much more seat-of-the-pants acceleration over the stock heads?

 

Just wondering because if I ever build a similar SC engine I probably wouldn't go to the trouble of porting the heads. My die grinder died and my burrs and stones are shot from doing rough grinding projects. The stones look downright pitiful. 🙂 

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3 hours ago, Ronnie said:

I know porting is going to help, but for a low RPM 3800 do you think you will be able to feel much more seat-of-the-pants acceleration over the stock heads?

Just wondering because if I ever build a similar SC engine I probably wouldn't go to the trouble of porting the heads. My die grinder died and my burrs and stones are shot from doing rough grinding projects. The stones look downright pitiful. 🙂 

All good points. I have no dyno sheets or anything to prove one way or the other. Way back, before any of the boosting, I acquired a cam, lifters, exhaust manifolds and few other items from a 3800 that was being rebuilt at a semi local shop that specialized in taking in the customers car, truck or van, pulling the engine, rebuilding it, and reinstalling, all for a reasonable price. I knew nothing about the '88 engine being slightly different until much later. If memory serves, and this is 25 years ago now, I think I was just after cast off parts to experiment with and I was given more than I expected. I think my first project was hogging out the rear manifold, removing the heat shields and having ceramic coatings done inside and out, Titanium Gray. I still have them hanging on the wall. That was also the period where I tried cold t'stat's, enlarged throttle body, computer chips, cone air filters etc... At the time, I was using a G-Tech for acceleration runs, and there were small improvements to be sure. Then I discovered I could use the MAF as a sort of indicator of better airflow, and hence better performance. At the time, it seemed a stock Reatta would see about 125gr/sec peak on the MAF. My fooling around got that up to the low 130's, and I figured that was proof that it all had a purpose. I remember asking for anyone else to try the MAF test and report back. I remember Padgett reported in the mid or upper 130's for MAF, and I was no longer so proud. I did a crude measurement on the camshaft I had snared from the rebuilder, discovered it was a bit more aggressive, in my mind anyway, and eventually it went into my original 1990 engine. Subsequent testing showed air flow up around 140, so it seems the can did indeed help. The formula from that time is 1.32 x MAF reading = ~HP.

 

Fast forward and along the way, I built a flowbench. It can be used for lots of things but it is usually cylinder heads in the engine industry. Of course that lead to experimenting on a used junkyard engine I picked up, and porting was a natural extension. One of the things I discovered, ported or not, the heads flowed more with increased valve lift. Not great gobs, but it didn't plateau. Now the stock arrangement can accommodate a .500" valve lift at which point the keeper hits the valve seal. I know I am making lots of assumptions, but my reasoning is, if it can flow more at a given lift and rpm, it likely will do more than not? I figured the '88 cam was a useful improvement, factory developed and approved, so why not use the best (IMHO) if possible. The other thing I hear over and over, build a good N/A engine, then boost it. Porting just became something I do when it is all apart anyway, but it is more optimizing what the factory provided rather than serious and all out "porting".

 

Oh yah, tools. My old Makita electric dye grinder is getting a little loose and will vibrate at certain speeds. I have tried air grinders, but they freeze my hands with extended use and they are noisy. I don't have any stones, only carbide burrs in various shapes and diameters, plus a selection of cartridge rolls for sanding out the worst of the grinding marks. Much like the flow bench, it is home brew and keeps a few synapses still working. 

 

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Your posts got me to wondering what I actually have left so I dug them out. Not much left really. I've loaned a lot of stuff to friends that I never got back. Threw a lot of worn out stuff away when I moved from my last house. Seems like there is a lot of small stuff missing that I might have stashed away somewhere and forgot where I put them. The die grinder that I liked best was the pencil type powered with a flexible cable. The drive cable inside it finally started binding up and vibrating so I threw the whole thing away when I moved.

 

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For some reason my photo didn't show up in my last post. I fixed it.

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9 hours ago, Ronnie said:

For some reason my photo didn't show up in my last post. I fixed it.

Stuff like that never goes bad. Who knows, maybe could be used for artistic talent you don't even know about yet. 

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All I can tell you is that after I ported and polished my heads,

intake manifold, supercharger, and exhaust manifolds, I felt

an increase in acceleration and torque.

But until I increased the size of my exhaust,  (1/8" to 2 1/2")

I felt the real increase in power.

It will now light up the front tires from a stop.

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Want more power ? 1989-1992 Allante 4.5 V8. 91-92 is easiest, get tranny also.

Edited by Padgett
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I did make an approximate sixty degree face angle exhaust valve using my vertical lathe, aka, drill press😎 While it does contact the wide exhaust seat, and would probably narrow the 45* part, it would take forever as a valve grinder rather than an actual cutter, so I scrapped that idea. 
I reassembled the heads this morning after a little spritz of black paint. Of course they look just like when I started from this angle. Retirement party to go too but maybe heads get installed tomorrow 

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Heads went on today. Uneventful, but while I am sure the torque/angle type of installation is more accurate, it is tedious and clumsy. I do have a tool for that but trying to keep in position to read it while applying considerable force is a job for a contortionist.

 I installed the new crank sensor and the plastic splash shield plus the new damper. I started assembling the brackets for the front accessory drive. The large bracket on the left side was cracked and the belt tensioner on the lower left was broken probably from the ham handed engine removal at the junkyard.  This will be a mix of new and used parts. One item to note is the large bracket partially overlaps the water pump. I was going to leave the old one in place to try it as it is an easy replacement but it will get a new one if that big bracket must be removed.

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