I've been reading a lot on engine swaps and the 4.9 looks promising. Coming from an F-body background, all my experience is with the 305 and 350. What I've seen is that the 4.9 makes lots of torque (relatively speaking), but tops out at about 4800RPM. What is the limiting factor here, ie runner length, volume, head design, flow rates, cam, programming, etc? Is it a combination of things? How can this be overcome? I realize there is limited aftermarket support, but some parts must exist, even if one needs to bastardize other GM parts. If I go this route, I'd like an engine I can wind up to at least 6K. Is it possible without breaking the bank?

Remember, this engine was designed for a small engine to pull a 4000+lb car smoothly and quietly in a respectible manner. Like all torque motors, the intake and especially the exhaust ports are very small for a 300 cubic inch V8 engine.

Also, it is a aquare bore engine, an aluminum block with steel floating sleeves, and cast heads.

By putting this engine in a Fiero, you already improve the horsepower. You will give the engine bigger, smoother flowing exhaust with minimun restriction mufflers compared to what was on the Caddy originally. Plus, you remove the power steering pump, which helps a little with hp, also.

I have tried to port the heads, and I did get a small improvement in power, from 220 to 240. But I lost torque from 285 to 240. That would make this motor very much weaker, IMO.

There are a number of things you can do to work this motor to around 300/300, but for the cost of doing that, you would be better off going with an Archies.

Alsao, for around $3000 a stage 1 turbo could put about 8lbs boost on this motor, but there is discussion about the life of the motor set up like this, becasue of the sleeves.

G

That's informative, and where I'd like to see this post go. I understand the benefits of both torque versus hp, but tons of torque does no good if you can't plant it to the ground, or if you're destroying parts.

"Remember, this engine was designed for a small engine to pull a 4000+lb car smoothly and quietly in a respectible manner. Like all torque motors, the intake and especially the exhaust ports are very small for a 300 cubic inch V8 engine."

I kind of expected intake small ports. How much can they be opened? Also, out of the TPI stuff, How long are the runners? It's been shown on TPI's that the runners can be siamesed to increase flow (and hp), without affecting torque. Are the runners (or base) situated in a way that they can be siamesed? Also, are there any rockers that can be used to increase lift? The cam profile on Rockcrawl's site is pretty weak.

More food for thought....

BTW, anyone have a picture of the engine and or intake? Just so I know what the heck I'm talking about

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[This message has been edited by RCR (edited 10-30-2002).]

quote Originally posted by cadero2dmax: a stage 1 turbo could put about 8lbs boost on this motor

You mean something like this?

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LMAO!! you've lost your mind!! let me know when your done!! and PLEASE post a dyno sheet!! OMG!

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I have 2 coins that add to 30 cents and one of them is not a nickle. what are the 2 coins I have?

Wow... turbo 4.9.. Guess this is going to be like juicing the duke. Good luck, if it works, I want one too!!

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

19 Year Old Fierophile.
--1986 GT Daily Driver, 4:10s, NX 50 Shot, Borla exhaust, ported manifolds, and a few other goodies
--1984 SE 4.9, IMSA spoiler, Duel exhuast, GT rear bumper, Konis, drop spindles, Rear adjustable perch, Poly total kit, Poly cradle bushings, Big front bar, Added rear bar, 11.25" brakes on all corners w/SS hoses, Fancy wheels wrapped w/soft rubber, and much much more.

Ah, a pic

Now the intakes, they appear to be wet-style or carburated intakes with bosses machined for injectors. True or false? Is the intake a single plane or dual plane design?

Turbo 4.9...Cool

From personal correspondence with Allen Cline, GM engineer:

quote The 4.x engines had iron heads for structure, noise and to eliminate the need for pressing in valve seats in high volume produciton. Remember, that engine family was developed in the late 70's early 80's and at the time it was not so common to be pressing in valve seats as cast iron heads and induction hardened valve seats were the norm ofr running unleaded fuel. The block was aluminum to save mass and the cross section of the head was very small to eliminate as much mass of cast iron as possible . Aluminum heads back then were just not on the immediate horizon for high volume production. Hindsight being 20/20 it makes you wonder why we didn't use aluminum heads but in the late 70's aluminum heads were still pretty "exotic". If you look at the cross section of the 4.x heads and actually weigh them they are very light as is and actually the savings in going to aluminum was not that great. Pushrod engine heads are like that. When you go to the much larger castings required for overhead cam heads and/or 4 valve heads the weight savings in aluminum becomes much more noticeable.

Here are some pics of a set of full roller rockers on a 4.9. They are Angus Racing 1.6 ratio pedastal mount (FORD) rockers with adjustable pushrod seats. The adjustable seats eliminate the need for custom length pushrods and shims under the pedastals. I machined slots in the stock rocker support rails to eliminate the need for bridges or pushrod guides. The pedastals have two flat sides to fit in the slot. I installed threaded steel inserts to prevent the pivot bolts from pulling out of the aluminum rails with higher lift and spring pressures. I've seen them pull out on stock engines. The stock valve covers don't fit, they will need to be custom made. Unless you can find a used set, these rockers will cost you about $280 for a set of 16, I got mine for $125. I doubt it's worth the money and effort, but it should add about 20 hp.

quote Originally posted by Her86GT: You mean something like this?

WOW, nice job!!Get that working and it will be a screamer. Only difficult problem as I see it will be developing a new program for the chip in the Caddy ECM. I believe that you must use the original ECM as only the Cadillac ECM has the capability to control the special idle speed motor that the 4.9L used.

------------------
87GT 3.4 Turbo Best 0-60 5.2 seconds
http://turbofiero.fierojoe.com/turbo.htm

quote Originally posted by rockcrawl: Here are some pics of a set of full roller rockers on a 4.9. They are Angus Racing 1.6 ratio pedastal mount (FORD) rockers with adjustable pushrod seats. The adjustable seats eliminate the need for custom length pushrods and shims under the pedastals. I machined slots in the stock rocker support rails to eliminate the need for bridges or pushrod guides. The pedastals have two flat sides to fit in the slot. I installed threaded steel inserts to prevent the pivot bolts from pulling out of the aluminum rails with higher lift and spring pressures. I've seen them pull out on stock engines. The stock valve covers don't fit, they will need to be custom made. Unless you can find a used set, these rockers will cost you about $280 for a set of 16, I got mine for $125. I doubt it's worth the money and effort, but it should add about 20 hp.

Where does the extra power come from?
I thought that the stock 4.9 rockers were 1.6:1. You don't expect to get that much power from going to a roller rocker, do you?

Could the stock covers be sectioned and extended in order to work?

quote Originally posted by Dennis LaGrua: Only difficult problem as I see it will be developing a new program for the chip in the Caddy ECM. I believe that you must use the original ECM as only the Cadillac ECM has the capability to control the special idle speed motor that the 4.9L used.

Our 4.9 does not run off the caddy ecm, but uses the common 730 ecm (f-body, IAC for idle) which can be set to run under boost conditions. The re programming will have to be done on our custom Rockcrawl PROM/chip. For that I have already warned Rockcrawl in advance and, I am sure he is capable.

Pete

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I am kinda interested in using the fbody ecm with a caddy motor. I would like to research this a little. Are there any websites or any faq's about this?

quote Where does the extra power come from? I thought that the stock 4.9 rockers were 1.6:1. You don't expect to get that much power from going to a roller rocker, do you?

You are correct, 1.6:1 is the stock ratio. I don't think 20hp gain just from the rockers is an unreasonable expectation, especially considering that the the stock ones are not a high performance design to begin with. I've always been under the impression that changing to full rollers alone will add 15 to 20 hp to a V8. Since you questioned it, and now I'm questioning it, I've done a little reading. It looks as if the reduction in friction is enough to make a noticeable increase in horsepower, regardless of ratio. I'm sure those 40 hp gains are when using higher ratios.

from unknown source... "Aluminum roller rocker arms provide several virtues to the operation of any valve train. Their needle bearing trunnions require very little oil compared to the requirements of conventional "ball" pivot or bronze bearing designs. Accordingly, they have a much reduced "drag coefficient" which reduces the loss of horsepower due to friction."

from Crane Cams... "Needle bearing fulcrum and roller tip reduces friction, lowers engine oil temperature, improves response, increases HP and RPM."

from Harland Sharp... "The unique Friction Free Design has shown average performance gains of 15 to 40 horsepower."

from Comp Cams... "Investment castings, featuring superior ratio accuracy and chrome-moly roller tips. 20 to 30 horsepower gains were not uncommon with this new rocker arm design."

from unknown source... "The needle bearings in the fulcrum also help some in saving wasted mechanical power and some manufacturers claim it lowers oil temperatures as well. It also keeps your valve system more dimensionally consistent in it's operation from valve to valve allowing the engine to operate more like it was designed to. Add that to the fact that the rollers and fulcrum bearings don't rob as much power as standard rockers and it could add up to a significant number of horsepower gains."

Jon

quote Originally posted by Her86GT: You mean something like this?

No one likes a tease.... Give us some details!!

Specifically What size turbo is that (please don't say T3!!) Also what sort of boost will you be running?

Intercooler? anything done to retard spark on detonation?

Thanks!

quote Originally posted by rockcrawl: You are correct, 1.6:1 is the stock ratio. I don't think 20hp gain just from the rockers is an unreasonable expectation, especially considering that the the stock ones are not a high performance design to begin with. I've always been under the impression that changing to full rollers alone will add 15 to 20 hp to a V8. Since you questioned it, and now I'm questioning it, I've done a little reading. It looks as if the reduction in friction is enough to make a noticeable increase in horsepower, regardless of ratio. I'm sure those 40 hp gains are when using higher ratios. from unknown source... "Aluminum roller rocker arms provide several virtues to the operation of any valve train. Their needle bearing trunnions require very little oil compared to the requirements of conventional "ball" pivot or bronze bearing designs. Accordingly, they have a much reduced "drag coefficient" which reduces the loss of horsepower due to friction." from Crane Cams... "Needle bearing fulcrum and roller tip reduces friction, lowers engine oil temperature, improves response, increases HP and RPM." from Harland Sharp... "The unique Friction Free Design has shown average performance gains of 15 to 40 horsepower." from Comp Cams... "Investment castings, featuring superior ratio accuracy and chrome-moly roller tips. 20 to 30 horsepower gains were not uncommon with this new rocker arm design." from unknown source... "The needle bearings in the fulcrum also help some in saving wasted mechanical power and some manufacturers claim it lowers oil temperatures as well. It also keeps your valve system more dimensionally consistent in it's operation from valve to valve allowing the engine to operate more like it was designed to. Add that to the fact that the rollers and fulcrum bearings don't rob as much power as standard rockers and it could add up to a significant number of horsepower gains." Jon

Yeah, but those tests are typically done to show the best results, which means aggressive cams with high valvespring loads, high valvetrain friction and high RPM.

The 4.9 has a mild cam, soft valve springs, and low RPM capability. I don't think it'll gain that much from roller rockers. It's already got a roller cam, doesn't it?

quote The 4.9 has a mild cam, soft valve springs, and low RPM capability.

Maybe yours does, but not the one I'm building. Anyway, I already admitted that it's probably not worth the money and effort spent to do it. And the truth is we'll probably never know how much it does, because the engine will have lots of other mods done at the same time. It's just something I wanted to do. They're obviously good for something, why else would everyone be spending $200-400 on them? Sure they look cool, but only until they get covered.

Yes, the 4.9 already has roller lifters.

quote Originally posted by PBJ: Our 4.9 does not run off the caddy ecm, but uses the common 730 ecm (f-body, IAC for idle) which can be set to run under boost conditions. The re programming will have to be done on our custom Rockcrawl PROM/chip. For that I have already warned Rockcrawl in advance and, I am sure he is capable. Pete What you are saying is that you use the F body throttle body which has the more traditional IAC and that all engine managemnt is done via the Chevy ECM. As you are aware the 730 ECM should have everything that you need to control a turbocharged engine and it can accept the knock sensor ESC signal. That ECM is a good choice. But how far the 4.9L engine can be pushed seems unknown at the present time. I would initally go a bit conservative on the boost. On the chip program using perhaps 2-3* retard per pound of boost from the base settings and cutting in the power enrichment cycle at 2000 RPM. I would be very cautious about boosting this engine, since the stock 4.9L has 9.5:1 compression. Too much boost and/or too little fuel or insufficinent timing retard and cylinder temperatures will soar through the roof. With this much compression you may wish to consider alcohol/water injection system. I'm building a system right now based on a $60 high pressure 12V sprayer pump from Northern Hydraulics. The reservoir is a common radiator overflow tank and the jet is a $4 .75 gph small brass oil burner nozzle which would flow about 1/3 oz. per minute. An adjustable pressure switch will energize a relay which will start the pump when boost reaches 6 psi.

------------------
87GT 3.4 Turbo Best 0-60 5.2 seconds
http://turbofiero.fierojoe.com/turbo.htm

quote Originally posted by Her86GT: You mean something like this?

With that custom intake that Rockcrawl made for Her86GT, that should be a 350hp motor (accroding to the desktop dyno run we made at 8lbs boost). The intake that is shown here should have added several ponies in itself, just as the Allante does.

Below is a 4.9 with a stock Cadillac 4.5 Allante intake, on the engine of the 4.9-in-a-Fiero originators (Team Python). That, too increases the performance by about 20hp without affecting torque.

Hope this helps

G

[This message has been edited by cadero2dmax (edited 10-31-2002).]

quote Originally posted by Will: From personal correspondence with Allen Cline, GM engineer: [QUOTE]The 4.x engines had iron heads for structure, noise and to eliminate the need for pressing in valve seats in high volume produciton. Remember, that engine family was developed in the late 70's early 80's and at the time it was not so common to be pressing in valve seats as cast iron heads and induction hardened valve seats were the norm ofr running unleaded fuel. The block was aluminum to save mass and the cross section of the head was very small to eliminate as much mass of cast iron as possible . Aluminum heads back then were just not on the immediate horizon for high volume production. Hindsight being 20/20 it makes you wonder why we didn't use aluminum heads but in the late 70's aluminum heads were still pretty "exotic". If you look at the cross section of the 4.x heads and actually weigh them they are very light as is and actually the savings in going to aluminum was not that great. Pushrod engine heads are like that. When you go to the much larger castings required for overhead cam heads and/or 4 valve heads the weight savings in aluminum becomes much more noticeable.

[/QUOTE]

What other 300 cubic inch V8 engine do you know of that weighs 381 pounds ready to install? That is almost 200lbs lighter than the SBC 305 of the same era, and almost 150lbs lighter than the 302 Ford - with the same configuration (a'c compressor, flywheel, induction, manifolds, etc.)

So, contrary to what this engineer has to say, there must have been substantial savings in the aluminum block/cast head configuration over an all cast setup!!

G

[This message has been edited by cadero2dmax (edited 10-31-2002).]

The turbo is from... no it is not a T3. I will tell you all about it in the spring. And you can see it for yourselves at Carlisle PA.

Pete

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a turbo trans am? about the same size engine. maybe a grand national?

quote Originally posted by Dennis LaGrua: WOW, nice job!!Get that working and it will be a screamer. Only difficult problem as I see it will be developing a new program for the chip in the Caddy ECM. I believe that you must use the original ECM as only the Cadillac ECM has the capability to control the special idle speed motor that the 4.9L used.

Wrong!!

The ECM from a GM 305 will also work on this engine - - I know, I have that setup on my car.

G

quote Originally posted by cadero2dmax: What other 300 cubic inch V8 engine do you know of that weighs 381 pounds ready to install? That is almost 200lbs lighter than the SBC 305 of the same era, and almost 150lbs lighter than the 302 Ford - with the same configuration (a'c compressor, flywheel, induction, manifolds, etc.) So, contrary to what this engineer has to say, there must have been substantial savings in the aluminum block/cast head configuration over an all cast setup!! G

"Contrary"? What are you talking about? How are you reading this differently than I am?

quote Originally posted by RCR: I must be beating a dead horse here.... I've done a little more research and turned up some pics from The Alternate V8 page. These two pics show what I believe to be the two different intakes (PFI and TBI). Both are essentially the same and don't show much room for porting, without doing a lot of welding. It's hard to give up 100ci by going to a "more" popular swap, but I guess you get what you get...Still would like to see more tech mods, though... Any idea why GM is using cast iron heads on an aluminum block? Beancounter strategy?

Looks familiar!

The 4.9 is not EVER going to be up to par with most other V8's...namley SBC's and similar

The floting sleeves and restricted headers make it unique as a Low reving high torque V8 which nothing much, in terms of mods, can be done. It is also very odd because of the great difference between BHP and Toruqe on the motor...you usually get a MAX of 20 hp Difference from the Torque raiting, however, this seems to be odd that there is a 70 ft/lbs of toruqe difference from the HP raiting (man i make NO sense do i!)

I'd tend to believe that the restricting factor here is the beauty of the Aluminum block and oddley designed heads. I do not believe that the aftermarket high performance parts upgrade for this engine in particular is very vast AT ALL, however, if anyone would ever be willing to experiment, i'm sure this engine has some untapped power somewhere...without loosing it's low reving toruque and light weight...

A Stage 1 Turbo or a 50 shot of N02 can be added to this motor, however, there has always been a question of engine integrity especially with regards to the head gaskets which seem to be a particular weekness on this motor.

If my suggestion matters AT ALL i'd have to advise aginst doing any majoy modifications to this motor if you are not very machincally inclidned

Cadero
PBJ
Rockcrawl

Are all EXPERTS in the Cadero Field, however, i don't think this engine will ever put out more then 320-330FT/LBS with the MOST of mods

I'm going to keep mine ORIGIONAL

EDIT: to add some jargin

------------------
Steven Rossi
2M4 Cadero Converted GT

[This message has been edited by stevenrossi (edited 10-31-2002).]

quote Originally posted by stevenrossi: Looks familiar! The 4.9 is not EVER going to be up to par with most other V8's...namley SBC's and similar The floting sleeves and restricted headers make it unique as a Low reving high torque V8 which nothing much, in terms of mods, can be done. It is also very odd because of the great difference between BHP and Toruqe on the motor...you usually get a MAX of 20 hp Difference from the Torque raiting, however, this seems to be odd that there is a 70 ft/lbs of toruqe difference from the HP raiting (man i make NO sense do i!) I'd tend to believe that the restricting factor here is the beauty of the Aluminum block and oddley designed heads. I do not believe that the aftermarket high performance parts upgrade for this engine in particular is very vast AT ALL, however, if anyone would ever be willing to experiment, i'm sure this engine has some untapped power somewhere...without loosing it's low reving toruque and light weight... A Stage 1 Turbo or a 50 shot of N02 can be added to this motor, however, there has always been a question of engine integrity especially with regards to the head gaskets which seem to be a particular weekness on this motor. If my suggestion matters AT ALL i'd have to advise aginst doing any majoy modifications to this motor if you are not very machincally inclidned Cadero PBJ Rockcrawl Are all EXPERTS in the Cadero Field, however, i don't think this engine will ever put out more then 320-330FT/LBS with the MOST of mods I'm going to keep mine ORIGIONAL EDIT: to add some jargin

Nope - - not an expert. But I have made that statement many times, including in my original post to this thread.

I am not an engineer. The only way I got the heads flow benched was because the owner of the shop owed me a favor or two. He took a pair of heads - from an "extra" engine I had lying around - and he tried various tricks that normally opens up most motors.

The shop did different things to each single cylinder (except one which was left stock, for comparison purposes). Like I said earlier, the best they were able to do was to extract a little hp, but lost a lot of torque.

Then, in the make believe world of one of the best desktop dyno setups available, all kinds of things were done to extract power.

Without nitrous (I am not sure how the floating sleeves would hold up under a very big shot)we got almost 400hp with about 450lbft at 6000 RPM. But to do that, the engine was modified a BUNCH (punched to 5.0, supercharged, etc). That engine is probably a ten grand motor, in addition.

Now answer me this, how much could you get for 10 grand from a SBC? I'll help you. My son has a 377ci SBC in one of his Camaros. He built it up from an 400ci SBC out of an old GMC 3/4 ton, and he did it for an out-of-pocket of about 6 grand total. This motor now has a little more than 600hp & 450 lbft of torque at the shaft (dyno'd), and is a very streetable engine, even if it is normally aspirated

For an additional $4K, he could throw a wilder breathing set of heads, supercharge, and work that same motor some more - - and get close to a thousand hp and a thousand lbft (and a not very streetable motor).

If I were wanting power, which would I want for my same investment? 400hp or a thousand hp??? Hmmm. let me think - - - -

I will repeat my thoughts about this 4.9 engine. If mid 13's (with mileage in the mid 20's), smooth power, and a light to light performance that impresses all but the big bucks street racer - all for a minimal investment - will satisfy your needs, go with the 4.9. If you want more, go with a SBC.

Yes, there are things that can be done to this engine. If I had Rockcrawl's knowledge and skills, I might persue them. But for me (as well as the "average" Cadero owner, I would like to think) the costs would outweigh the gains. In other words, what it cost for me to get 300/300 from this engine would buy AND install a good Archie's SBC with far better numbers and performance.

G

[This message has been edited by cadero2dmax (edited 11-01-2002).]

PBJ, Cadero, RockCrawl,

I've gotten the bug to do this swap and a friend just so happens to have a 93 Sedan DeVille sitting behind his shop that he says I can "take what I need". Can one of you E-mail, or pm me a list of what I need to get started? I have an 86 S/E 2.8 with a 4-Speed. I'd like to keep the 4spd if possible.

Thanks

Glenn

quote Originally posted by FieroV6Dude: PBJ, Cadero, RockCrawl, "take what I needa list of what I need to get started

check out these sites www.fieroaddiction.com and http://members.fortunecity.com/bubbajoexx/

also do a search using "4.9" in key words in technical are under subject only

that will give you days of reading

Pete

quote Originally posted by FieroV6Dude: PBJ, Cadero, RockCrawl, I've gotten the bug to do this swap and a friend just so happens to have a 93 Sedan DeVille sitting behind his shop that he says I can "take what I need". [b]Can one of you E-mail, or pm me a list of what I need to get started? I have an 86 S/E 2.8 with a 4-Speed. I'd like to keep the 4spd if possible. Thanks Glenn[/B]

Ohh boy how many times have I BUGGED PBJ asking this question.Although you didn't ask me i'll tell you what i used to do my swap.

I used
~Oil cooler
~Carb (2bbl)
~High performance Starter (had to cut bell housing a little to make room)
~Stock Fuel Pump (PFI takes more)
~Flywheel (1994 CAV Z24)
~Cav Z24 Clutch (Holds up GREAT to a 4.9)
~Standalone tachometer

Oddly enough if you get a cavalier Z24 Flywheel and Clutch from 1990-1994 model it will do just fine

Obviousley i'd recomend a custom made Flywheel, however, If properley machiened and refaced the Flywheel works great. The clutch also handles the power of the 4.9 very well.

------------------
Steven Rossi
2M4 Cadero Converted GT

Off topic

quote Originally posted by 1FST2M6: I have 2 coins that add to 30 cents and one of them is not a nickle. what are the 2 coins I have?

Two canadian quarters... Hey you asked

Back on topic

Kudos to all of the Cadero pioneers!

Rockcrawler is ploughing some new ground with his 'all out mod' approach and as with all good R&D, good info will come out of it for others. Keep it up.

Hey Jon, Youre not allowed to help other people with their turbos! I hope you guys read compressor maps before choosing a turbo.

Let me know if you want some help with the spacers because we have a CNC machine in the lab.

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

Howard, someone was telling me about a guy who put a turbo on his car and it made the car slower. I asked if the guy's name was Howard Haha, just kidding. I'm not in charge of designing the PBJ 4.9 turbo, I'm just here to prevent him from melting the pistons. Wether or not it adds power is not my problem I doubt you'll ever see a turbo on any of my cars. Turbos suck! Hehe, kidding again!

CNC?? Now that'd be cool if I knew how to create a CAD document. I'm picking up my Bridgeport mill and some other machinery next weekend.

quote Originally posted by rockcrawl: CNC?? Now that'd be cool if I knew how to create a CAD document. I'm picking up my Bridgeport mill and some other machinery next weekend.

I'm fluent in AutoCAD. My services are at your disposal.

Autocad isnt that tough Jon. I can do it! Thats awesome youre buying a mill. Full size or a mini? Bridgeports are good equipment. I milled our rear uprights last year on one.

Hey Will, do you use MasterCAM? Ive just started myself. If so, we could import that directly into the CNC. No more G code!

Yikes I thought the compression ratio was too high on those motors to put in turbo ?

quote Originally posted by Howard_Sacks: Hey Will, do you use MasterCAM? Ive just started myself. If so, we could import that directly into the CNC. No more G code!

Nope, but if you donate a copy, I'll learn

I'd love to get my hands on a ProEngineer package, but I don't have the 60 G's lying around for that

It is nice to read the many creative and positive comments on this post about the 4.9L. I believe that for the best bang for the buck, this engine has much to offer.
Without some serious modifications, I would leave this engine normally aspirated. An engine like the 4.9L with 9.5:1 compression pistons is not the best good candidate for adding a turbo.I would estimate that adding anything over about 4-5 psi boost; you'll have a tough job controlling cylinder temperatures and detonation. Of course you could cut the timing way back but this will defeat the turbos purpose as it will really cause a sharp decrease in horsepower. Alcohol/water injection could help but this would be a band aid fix to a bigger problem.
The most power with a turbo engine is usually generated with higher boost and lower compression and not the other way around.

------------------
87GT 3.4 Turbo Best 0-60 5.2 seconds
http://turbofiero.fierojoe.com/turbo.htm