Supercharging, revisited

[2seater]

Both are rwd cars and I suspect it may be easier to do, but not impossible for fwd. I do agree it does work. I have imagined how it could be done on our cars more than once. A turbocharger is approximately twice as deep as either the cat. or the muffler. Finding a place to tuck it up out of harms way would be a challenge. Just ahead of the fuel tank where the natural 90* turn in the turbine housing would mimic the first 90* in the piping might work? I hope someone gives it a try.

[Guest F14CRAZY]

I suppose you could hack up the trunk and put it up in there

[Duke]

I'm still confused on why use a supercharger. I was reading this site here. http://reattadudes.entryhost.com/turbo0.htm

Apparently they tried to make a production turbo reatta, but it fell through because it couldn't meet production prices, using stock GN parts. The only question areas I see is the transaxle they used a beefed up 440-t4 with 4th lock up at wide open throttle and I think the gears were changed to end up with a final ratio of 3.73:1, and the possible trouble of ecm and bcm conflicts think something was posted about using a different ecm caused problems. Read this because to me it sounds like a more practical approach especially since GN's are popular and have a nice aftermarket performance part contribution. buy a rebuildable block stuff it with stronger internals buy a upgraded turbo think they used a t-25, change cam, swap injectors for more flow, do some pluming, and then fine tune the ecm. Keep in mind I haven't done this I'm shooting in the dark here, so if anyone knows why this would be harder or not as good as putting a seriesII/III s/c or why it just won't work beat me about the head and shoulders.

[BillNC]

I don't know much about this computer control stuff but here's another possible trick on making V6 supercharging work with the existing ECM/BCM. Basically just use all Reatta's engine controls on a supercharged engine.

To get around the CFM flow limitations either run a different MAF, modify the existing MAF or bypass some of the air flow around the MAF. Example say if 25% of the air flow is bypassed around the MAF. A positive displacement supercharger provides a constant percentage flow increase across the entire RPM range unlike a centrifugal supercharger or turbocharging. So if the engine is supercharged for an extra 50% air flow rate (running it of course with a lower compression ratio etc.) and increasing the fuel flow 50% with injector and pump change. The ECM would think there has been no changes even though there has been over a 50% torque and power increase across the entire RPM band. The transmission would have to be modified for the extra torque.

The main difficulty may be related to increasing the range of the spark advance range (retarding the spark further under boost) although an aftermarket controllable unit or supercharged module unit may be usable or modifiable. The knock sensor may compensate. I don't know the advance curve characteristics of the supercharged lower compression engine pertaining to boost level as compared to the non supercharged engine, it's an area that may need attention.

It seems basically if the engine is crammed in with an extra 50% air/fuel across the RPM range and fake out the ECM data air input and fuel output accordingly, the ECM would never know there's well over 50% more horsepower. Does this make sense or am I missing something?

[padgett]

Remember that while HP determines the top speed, it is TORQUE that gets you there. Look at the 205 HP SII 3800 and you will see that the torque is less than 10% higher than an 88 3800, it just peaks at a higher rpm. What would be nice would be about 250 lb-ft of torque flat from 2000 to 5000 rpm. Of course to do that you would need VVT.

Cam and 10.5:1 compression with appropriate mods to intake and exhaust would do it (supercharger will require premium gas anyway).

Also one iten that seems to have been glossed over a bit was that when Greg converted to a 5-speed he also went to a "L" crate engine so the heads were already right for the supercharger. I do not think one exists for the "C" heads so is going the Park Avenue route, better to swap the whole engine (think bearings were different on L-67 also).

440T4/4T60 is marginal even for a stock engine though the weak area seems to be the differential so if you avoid wheel spin in low gears it will probably last a while. With any power increase, at least a 4T65E is probably a good idea.

AFAIAC the digital dash is a big part of the Reatta image particularly the 88-89 with CRT though if you do not care about that it does not matter.

Still think my 88 has "enough" power, if I were going to mod, would be for 40 mpg at 70+ mph and not more power though would be just about as hard.

Odd thing, all of the computer cars I have had seem to get about the same mpg on the Interstate - around 25 real world, 30 if I work at it. With my day job it is just not that important yet.

[Guest Greg Ross]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">when Greg converted to a 5-speed he also went to a "L" crate engine so the heads were already right for the supercharger </div></div>

Yip, and then went one step further and had the engine torn down and balanced. This was to simplify getting the modified flywheel balanced by going neutral all the way through.

I have a new Summer ride now, blown, 500 sq ft, have a look!

[2seater]

GM did make both rwd and fwd turbocharged experimental Reatta's. The rwd was a GN style engine (I have no idea how they modified the steering system) but strictly speaking, the GN motor isn't compatible with the fwd setup, at least for the hobbyist, and the engine parts do not interchange, for the most part, with a 3800. It really is a less evolved engine, not that it didn't perform, but the 3800 is superior in the oiling system, head flow and the control system. I probably lucked into the T25 trim compressor when I was fooling with assembling my parts, and works great for a low boost application.

The other comments about fooling the ECM about air flow, should work, but it isn't easy. I have been trying to replicate the air flow through the MAF to see what could be done but generating a useful, and readable frequency have proven to be a problem on the flow bench. In the simplest terms, my logic indicates the stock MAF bypass passage needs to be opened up about 30% in area to slow the flow past the sensor to capture my calculated air flow requirement. Work continues.

[luftweg]

>> ...Cam and 10.5:1 compression with appropriate mods to intake and exhaust would do it (supercharger will require premium gas anyway)...<<

So, are you saying that one might as well just use 'old school' engine mods?

The computers would not balk at this in some way?

[luftweg]

>> A positive displacement supercharger provides a constant percentage flow increase across the entire RPM range unlike a centrifugal supercharger <<

Though, if one is keeping the old sensor setup, and with all that talk about 'maxing out MAF' and such -- in a sense -- didn't you just allude to the possibility of a centrifugal charger -- under the right conditions -- being a better option than switching the whole engine (to an SC Series I or II)?

I mean, the old engine already uses the old sensors (of course), and a centrifugal charger can be setup (with appropriate pulley diameters and waste gate 'settings') to provide, say, maximum boost at lower RPM and less boost at higher RPM (is this not possible?).

The greater boost at lower RPM should be less likely to 'max-out' the MAF, since the engine isn't spinning as fast (and thus shouldn't require the same sheer mass of air that it would at higher RPM).

And, if the boost is dumped at higher RPM, again maxing the MAF should be less likely...

I realize there are probably things I missing or overlooking, but not changing the engine (albeit, the drivetrain may be removed for 'beefing-up' and then re-installed) and keeping the sensor setup largely intact seems like an easier route... Of course, the mechanical difficulty of installing the 'jack-shaft' to drive the centrifugal charger would still be an issue...

[2seater]

Dumping or limiting boost isn't a bad idea. The GN type cars had programming to operate a wastegate solenoid to reduce boost in upper gears, but that is usually one of the first things to be deleted The centrifugal superchargers work exactly the same as a turbo supercharger (turbo for short), the drive system is simply different, except the belt drive does operate based on engine speed and not exhaust flow. The turbo wastegate operates just as you suggest, except, it cannot dump more boost than the boost pressure working against the spring in the wastegate. It would require some sort of other type of control to do it and the performance would likely be uninspiring. The car would launch well and fall on it's face, so to speak. If you watch the MAF air flow signal while driving, a normal maximum air flow reading will be in the 125-140 gm/sec range, depending on altitude and such, but it is using a fair part of it's range without boost. At full throttle, mine will go beyond the 170 gm/sec limit in only a few seconds from idle speed. In normal driving, and using part throttle, the car drives normally and air flows remain in the readable range. The response to the throttle is simply stronger, and most people don't drive at full throttle anyway, plus it isn't good for the engine or transmission. If you could figure out how to ramp up boost at first and then reduce it to a few psi to stay within limits of the ECM, performance would still be better than stock. The problem is, once the boost starts working, you won't want to reduce it

[Duke]

Can't the range be changed on the ecm?

wouldn't a program like this one work:

http://www.supportfitness.com/mark/tunerpro/downloadApp.htm

I downloaded an 86GN code from this site and it seems to be able to set psi/rpm for boost or what ever else you can think of. Even had a rev and mph limit function. Only thing I see is no reatta coding.

[2seater]

All the information I have found over the years indicates to extend the envelope the ECM can read requires more than a chip program. I think Padgett has mentioned this before. I don't think it is impossible, but it is apparently deep inside the programming and not resident on the chip. The GN guys have worked on these problems for years, and a lot of people have decoded and modified them in many ways. If we had the same interest in our cars, or similar ones, there would probably be something available. The GN didn't have boost sensing either, but they did have programming to run a wastegate solenoid and allow some effect on boost level based on pre-programmed parameters. I assume the wastegate spring is fairly weak, maybe like the 8 psi one I have, and the ECM was programmed to keep the boost pressure from getting to the wastgate until the programming decided to open or pulse the wastegate solenoid to smoothly reduce the boost level closer to the base setting of the spring in the wastegate "can". I think the "Extender" chip I have seen for the GN's is used in a similar fashion that I am looking at. I believe it is used in conjunction with a MAF translator and probably a larger MAF, so the out of range airflow reading is captured by the translator and reduced to a level the ECM can read and the chip program is matched to the new lower reading. I think there are other "tricks" out there, such as using a two or three bar MAP sensor to generate a signal to the MAT sensor input to change the timing based on false air temperature info.

[Guest F14CRAZY]

This is getting waaaaay complicated

[jonlabree]

http://cgi.ebay.com/ebaymotors/1995-Buic...032532888QQrdZ1

Here's an engine/w supercharger all ready to go.

[BillNC]

Gee, I was checking out that 3.8 supercharged engine with very slight consideration since my Reatta is now showing engine and transmission ills. For what it's worth my thoughts on turbocharging is if a certain amount of throttle is applied to a given level (since the turbocharger being indirectly couple by exhaust) the air flow would increase on MAF with the RPM and TPS being constant with an increase in manifold pressure. A centrifugal supercharger would increase air flow /pressure with the square or cube (don't remember) related to engine speed up to the point the waste gate opens resulting in a similar ECM confusion

An engine has positive displacement like a positive displacement supercharger allowing say instead of a natural atmospheric pressure of say 14.8 PSI it will provide close to constant 22 PSI (depending on drive ratio and supercharger size) over the entire RPM range allowing an easier option of faking out the ECM with air flow bypass and injector mods. It's hard to say how to get around the ECM/MAF air flow issues. Is it easier to fake it out with a mechanical, anolog/electrical or digital solution? My experience is sometimes it was possible solve the same problem 5 different ways.

Padgett's idea is simpler since pushing the torque band higher in RPM range to generate power rather than increasing torque for power would make easier for the stock trans to live. Is the Cadillac late 80's transaxle a bolt in or not compatible? Torque is always fun.

[2seater]

If it was simple, it wouldn't be any fun and everyone would be doing it too. You are right that there are probably many ways to skin the proverbial cat.

[Guest Greg Ross]

I would expect some time late this Summer/ early Fall I'll be driving to NYC for a Long weekend. I think you would benifit from having a spin in Betsy Blue and seeing how an Old Dude/ DIY Guy has used mainly existing technology to make some more HP and enhance Driveability. Least that was the aim!

[BillNC]

That guy ended that auction early on that supercharged engine eBay Motors: 1995 Buick Riviera Motor Engine 3.8 Liter Supercharged (item 8032532888 end time Jan-28-06 05:08:44 PST) It was a consideration for me since it was a local pick up for me and appeared it was going to sell dirt cheap. One time I would have won another dirt cheap auction and the guy canceled the auction seconds before it ended even though I had a bid on it.

I really must do a crazy car project either another V8 mid/rear engine Corvair possibly twin turbo or try a Northstar Fiero swap. When I bought the Reatta cheap I was thinking of doing a Northstar conversion but I didn't know about the mess of the ECM being tied with the BCM which is tied in with the vehicle to such an extreme with no easy solution. It seems like it would be easier to do a brain transplant on someone. I really like the Reatta with it's amazing features but it's constant steam of problems on mine makes me question the logic of pursuing a cool idea of an engine swap especially with my non-familiarity with newer car's computer systems. If somebody was able to come up with a real easy scheme for upping the Reatta's power considerably I think it would actually add value to all Reattas since there are so few of them.

Is the late 80's to 90 Cadillac transaxle a drop in when using a supercharged 3.8 or is there a requirement change on electrical control input, axle spline/length, trans mounts, bellhousing bolt pattern, flexplate bolt pattern/balence/ring gear size and starter location/mounting?

I myself would have preferred the Northstar but using the existing ECM/BCM would allow only a V6. With my lesser familiarity on auto computer controls my thoughts was towards going for 50% or more power by torque increase with an objective of trying to simulate close to identical flow characteristics throughout the RPM range as well as various throttle levels as to what the ECM "sees" by not having the ECM's MAF input not see the 50% extra air flow throughout the RPM range. The injector fuel flow would have to be increased by 50% for the same ECM injector output. The tuff part would be what/if are the differences between the crank/cam sensor and ignition timing profile differences. There's risk on the outcome. Just my thoughts for the moment.

[luftweg]

Let me know around that time... would love to see it...

Of course, I would probably come down in my red/tan, which would be out of storage then.

[luftweg]

The following is a reply to an email I sent to some dude selling an item on eBay ( TECH 1 TECH1 SCAN MASTERTECH BCM TROFEO REATTA DIESEL item# 4608147280 )

I have seen something from him before on this forum, so it's probably not all that new:

-----------------------------------------------------------------------------

I also sent you a message that will be posted on the auction, in case other

Reatta folks are interested.

This is a very do-able project. However, it is not without snags. First,

I'll point you to my website where you can see my 88 Supercharged Trofeo. It

is www.theautoshop.net/SuperchargedTrofeo.htm

Next, I need to warn you. There are alot of people out there that will

mislead you on a project like this. There's a bunch of people that can burn

chips for SC 3800's and they'll tell you to use a newer ECM/PCM to run the

engine and an older one to communicate with the BCM. Doing this will cause

problems with the sensor readings and disable many of the diagnostic

functions of these cars.

There are a couple ways to handle this. The stock ECM can be programmed to

work with the newer engine. This has been a surprise to many people, but

most of the sensors will work just fine with the existing 1228253 ECM. You

can use either ignition system (though if you're staying with DIS, I'd

recommend the Delco) and the crank and cam sensors work just fine as is.

You'll have to use the original knock sensor or at least one from an OBDI

engine, but the TPS, IAC, CTS, etc. will work fine. One catch is the Mass

Airflow tables in the older ECM will have to be rescaled to work with the

255gm/sec MAF that the Series 2 engine has. The other problem is the EGR.

I'm not currently running EGR on my engine, but you'd have to come up with

some kind of adapter to run the VIN C EGR, as the 1228253 won't control the

newer EGR valve. That is the only emissions control device I'm not currently

using.

Another way you could do this would be to reprogram the data stream from the

Series 2 PCM to talk to the Reatta BCM. This would be a major undertaking.

I've had a few people ask about doing this, but I've never attempted it. I

do know that with stock software it doesn't communicate. The big problem is

the baud rates, I'm just not sure how you'd get them to synch up. Once you

have that under control, then you need to figure out how the OBDII PCM

handles communications. To be honest, I really didn't see how it was worth

the effort, and I'm not even sure if the OBDII PCM would be capable of

handling the BCM's input for cylinder balance, IAC control, etc. Add to that

the BCM control of HVAC and cruise (varies year to year and models) and

you've got a lot of interfacing and things that don't work right without the

proper communications. Without keeping all the toys, it defeats the purpose

of modifying one of these cars.

Any questions, feel free to ask. The Trofeo and Reatta are quite similar, so

I should be able to help you with most problems in this conversion.

Btw, the Tech 1 scanner is a very handy tool to have for these. I have both

the Tech 1 and Tech 2, you just can't beat factory diagnostics. The one I'm

selling is an extra that I bought for a cartridge it had. It's in very nice

condition, and works great. It has the cartridges you'll need for these cars

(the body cartridge being the big one to have), but if you want full 81-95

support, you'll want to watch for a Mass Storage Cartridge. These usually

sell on ebay for $50-$100. I don't have a spare at this time, otherwise it

would be with it.

Scott Pearson

The Auto Shop

www.theautoshop.net

Phone: 563.886.2821

Fax: 563.886.6127

[2seater]

I may have discovered something useful regarding air flow measurement, and quite by accident. I should know more tommorrow, after further testing. I have related that I am testing a MAF on my flow bench, to establish a good baseline for the frequency output vs actual air flow, so future changes can be compared. While searching the 'yard for a 3" MAF sensor, (came up empty), I found several MAF's for the '93 Buick 3300 engine, the little brother to ours. I pulled one sensor for a friend's "granny Buick" work car. While working on my test hookups on the flow bench I decided to try the 3300 sensor to be sure it was good. Much to my surprise, it required about 30% greater air flow to generate the same frequency output. I don't want to jump to conclusions, there may be some other reason, but this could be useful for compressing the actual air flow into the range the ECM can read. More to follow.

As regards output increase of 50% requiring 50% more of everything isn't quite true. There is some excess capacity in the injector flow rate and the ECM air flow scale, the stock configuration isn't using all of it's capacity. The injectors do need to be upsized, and by a little more than the air flow increase. The BSFC calculation for a forced induction engine is a little higher than an N/A engine. A good rough calculator is 2hp. per pound of fuel per hour for a naturally aspirated engine and 1.75 hp per pound for forced induction. Plus add 15%-20% to keep the duty cycle down around 80%-85%. Something around 28#-30# per hour for a 250hp engine.

[Guest Greg Ross]

I conversed with Scott quite a bit about a year ago and posted his links on this Board. I believe he's the real deal. He's been running an S/C Trofeo with Getrag 5-Spd about as long as I have had mine. He was offering these conversions at one time but I don't know about now. And I agree with his comments about the Slick Willys' offering reprogrammed 3800 Chips, they're dangerous!

[manikmekanik]

There is a TECH 1 mastertool scanner on eBat right now!!!

Price is @ $65, shipping is @ $20. With many cartridges!

[BillNC]

Hi luftweg,

Thanks for the info. For a few minutes I spoke with Scott Pearson of The Auto Shop. What a very interesting knowledgeable guy. His comments on using the series 2 supercharged engine with the existing Reatta's electrial/ECM/BCM is that it's not all that difficult. Most things are compatible except you have to use the original knock sensor, EGR and reprogram the ECM for the 255gm/sec MAF and with new tables which he has on file and can do. He said the 4T65e trans series 2 engine isn't compatible and the Reatta's 4T60 isn't strong enough stock which is why he went to a Getrag 5 speed which presented axle computability problems. He said someone was able to get the 4T60 to survive the supercharged engine after major strengthening. I asked him about the compatibility of the V8 FWD 80's Cadillac with the Reatta's 3.8 and he didn't know.

I seen on a Fiero board the trans used with the Northstar engine (I believe 4T65 type) isn't compatible with the marginal Fiero axles which uses the Getrag trans but the 4T65 trans axles splines should be the same as the Reatta's.

Well, to make a long story longer here's another thought I was curious about. How about the Pontiac G6 6 speed manual trans which has larger axles than the Getrag and if GM's famous interchangeability continues there's a chance it would be compatible with the Reatta's and be the correct length. Who knows maybe there's a slight chance on the G6 3.9 engine could be workable?

So the end result of all this is the series 2 supercharged engine shouldn't be all that difficult to use in the Reatta but the trans is a problem. With the following transmission options: Any thoughts?

1. Highly modify the Reatta's

2. Pontiac's G6 6 speed maybe compatible

3. Maybe there's a year the 80's FWD V8 Cadillac trans are compatible it might be a 4T80 type.

Here's some picture's on eBay of the G6 trans and engine.

http://cgi.ebay.com/ebaymotors/PONTIAC-G...1QQcmdZViewItem

[BillNC]

Hi Greg,

Scott sure does seem like the real deal and helping. I talked to him a few minutes and asked him a couple questions including a couple problems I had and he replied with very informative answers. He's really sharp, knowledgeable and knows his stuff.

[padgett]

Keep in mind that with forced induction a lot of the N/A rules go by the wayside. To increase power you lower the compression and increase the boost.

For any particular engine combination/state there is a maximum chamber pressure. Beyond that and multiple flame fronts form (detonation), temperature goes up and power goes down (and unless the engine is built like a diesel, things break).

Now peak pressure is a function of chamber volume. Increase the chamber volume and increase the boost and the peak pressure stays the same, however with an increased charge volume, the *average* pressure during the power stroke increases and so does the power output.

Now like anything else there are limits and other factors (e.g. stroke, flame path length) come into play but *in general* a 7.0:1 cr will develop more peak hp than an 8.0:1 engine of the same geometry given the same peak chamber pressure but you must have boost to achieve the same pressure with the lower cr.

This took me quite a while to wrap my mind around but makes sense when you consider that it is the chamber volume that is important.

------------------------------

Transmissions: the 4T65E (all "E") transmissions are designed to be controlled by the ECM and these subroutines do not exist in the 88-90 ECM hence they are "incompatable" electrically but I suspect might be adapable *mechanically*.

The 93-94 supercharged Park Avenue ECM should be compatable electrically (has the E-transmission routines) and already have the high MAF tables plus is still P4 (OBD I ?). What would need to be changed is the ALDL subroutine to match the data stream expected by the BCM. The alternative is to reprogram the BCM to accept the later data stream but that is really unknown territory.

Unfortunately if anything my workload is going to be increasing this year but shouldn't be that difficult for someone with a Reatta willing to learn the machine language for a Motorolla 68HC11 processor. There is a lot of information available and I would be willing to *advise*.

[2seater]

I agree with the boost vs compression ratio. Generally the GN and nitrous guys have found the same thing, lower compression and more boost, or NO2, and the power goes up. There is probably a lower limit as to how low to go on compression ratio, as the engine will be soggy when off boost if too low. If I cannot get the higher compression ratio engine to run without substantial knock, the old engine will returned to use, with a lowered compression ratio, maybe 7.5-8.0:1.

[BillNC]

It's tuff to do on fuel injection engines but for amusement this is what I tried in the olden days on turbocharging while maintaining the existing high compression. To somewhat limit maximum chamber pressure as boost begun was to increase the density of the mixture. By increasing richness of the mixture to an extreme there was a small window between too lean (preignition) or too rich where the engine would skip. The 9.25 compression ratio engine on 94 octane was able to run 15 pounds of boost. It resulted in about doubling the power to the rear wheels and with the foot out of the throttle there was no noticeable change in gas mileage before the turbo was installed. I also tried water injection where the water injection level would increase relative to the amount of boost but I couldn't achieve as much boost do to difficulty I had trying to ignite the mixture. There is yet another method which would allow high compression, almost constant maximum chamber pressure while increasing boost, with little pressure retard needs. Unfortunately none of this is easy and is obsolete with nowadays fuel injected engines.

[BillNC]

The old 1976 Porsche 930 Turbo Carrera had 6.5 compression ratio and still was surprisingly good on gas mileage for it's day.

http://www.conceptcarz.com/vehicle/z9985/Porsche_Baby%20Turbo/default.aspx

[Guest imported_dantm4]

Your link is slightly wrong - day snuck in at the beginning - in case anyone else clicks on it. Just erase that part.

-Dan

90' Black/Tan Coupe

[BillNC]

Thanks damtm4,

Don't know what happened but the post is fixed now.

[BillNC]

Would say the conclusion considering there's no MAF/ECM flow limitation and a E type trans in a 91 Reatta it would just be best to put a series 2 supercharged 3.8 only in a 91 Reatta sidestepping the main two problems and not bother to consider the 88-90?

[Guest F14CRAZY]

That's right. A '91 would be simplest, whatever "simplest" really means in an engine swap like this.

[Guest F14CRAZY]

Back to the Series 1...

One way or another, I'm going to research this. Come on, we're talking 255 hp that bolts on in like a day with perhaps a $500 investment.

An L67/4T60e swap is out of my league as far as know how and labor, and Ryan wants about $6k to do it.

We need to know if the heads and upper end will bolt on. The harmonic balancer was mentioned too

[Guest Greg Ross]

You or your Dad have an acquaintance working in a GM Dealer Parts Dept? Get them to order in the two sets of head gaskets for you, lay one over the other and make a command decision.

[Guest F14CRAZY]

Ha! Aw just RTV it

I'm exchanging emails with maybe2fast, and we figure that yes, series 1 supercharging hardware will bolt on. Have that, underdrive pulley, rockers, and maybe a cam job and I'll be pulling hard