Questions About Boost!

[Guest]

Well, its time to start the project. Started pricing out cranks, rods, pistons, cams, and headwork and then thought, Is the stock block gonna be able to take this? So will it? Also, what compression ratio should I look at going to if I wanna run 15-20psi of boost (at the very max). And any suggestions of companies to look to? Also, is a 2.5 inch exhaust pipe viable for this application? What size injectors should I go with? Any clues on fuel regulators I should use and what how big of a booster fuel pump. And what kinda pizza should I order?

Thanks for the help fellas, its really appriciated.

[2seater]

Disclaimer: These are my opinions only. The basic 3800 has been tested to destruction by a guy on the GN list and extracted over 500hp. before the crank blew out the bottom. More power is possible with a girdle on the bottom end. The crank is similar to the GN crank with the rolled fillets for strength. Judging by the factory 2:1 safety factor and longevity, the rods are probably good for between 300-350 relatively safe horsepower. Hypereutectic pistons should be good to that level also. They offer the advantage of low expansion which allows tight bore clearance which is good for ring stability. Over this level I would look for a forged piston and something like I beam rods. Injector sizing is pretty easy to calculate. Approximate Brake Specific Fuel Consumption, BSFC for short, is generally .57 lb/hr/hp for a boosted engine, or more easily, 1.75hp per pound of fuel per hour. For 300hp, that would be 50hp/cylinder divided by 1.75 = 28.6 lb injectors. This the base sizing assuming 100% duty cycle but if it sees this power level regularly, you would want to add 10-15%. I am using a 190 liter per hour Walbro in tank pump which was a direct replacement for the GM pump with correct harness connections. This is plenty of pump for up to 50# injectors, or about enough for 525hp. Larger in tank pumps are available as well but the current draw is higher and it would be a good idea to upgrade the wiring. The 190 liter pump draws a maximum of 7 amps. I can achieve 8-10 psi boost easily using the stock 2.25" exhaust system (minus the cat). I do not know how much may be left but I would estimate the 2.5" system would be good to 1 bar, or 14.5 psi of boost. All things being equal, one atmosphere (1 bar) will double the output of the engine. There is some penalty to pay in increased backpressure, but it is not a lot, maybe 1-2 lbs of boost to cancel the extra plumbing. Conventional wisdom says lower compression with more boost will produce more power. I would shoot for 8:1 compression ratio as a decent starting point. Mine is 9.1:1 (calculated), which is a little high for turbocharging, and is more prone to detonation problems, but throttle response is very good. A stock dished style piston works good in this application too. I have what the GN guys called a "stealth" fuel pressure regulator which is simply a stock one modified with an adjustable screw inside the vacuum nipple. This works just fine with the bigger pump and I have played with the pressure anywhere from 30-55 psi. I had purchased a billet aluminum regulator but the larger size hit the number 5 injector. It would bolt in okay, but there isn't much clearance to the injector so it is something to be aware of. You will need a fuel management system and probably a timing system to handle anything larger than about 25# injectors and the boost levels you are contemplating. An intercooler will also be a must for that level of boost. Good luck! <img src="http://www.aaca.org/ubbthreads/images/graemlins/grin.gif" alt="" />

[sahein]

The vin 1 block is a beefier block than the vin 3.

[Guest trofeo73]

I know personally these engines are strong, before I bought the riv, I had the manifolds glowing red hot after a hard run; did this many times, no head gasket or valve failure enough to cause serious problems. The transmission should be rebuilt with extra clutches and line pressure, the axles should be fine though. My trofeo easily produced up to around 300 hp, running VERY lean though. A decent turbo, T4 would be what I would use. Make sure the exhaust is well welded. And do a thorough job with lubricating the turbo, poor plumming of oil lines will drive you crazy!!! I would recommend buying the book " Maximum Boost" by Corky Bell. This book will help show you the way!!!!!!Or you could go with 2 garret T3s and run the exhuaust out the front fenders if you were real hard core!!!! Great to hear you are doing it. <img src="http://www.aaca.org/ubbthreads/images/graemlins/wink.gif" alt="" />You wont be disappointed with the performance, but you will encounter some obstacles as noted by Hal and myself.

[2seater]

I agree the GN's block is stronger, they can achieve more safe horsepower than we can (probably). Comparing the heads, I believe the later models are superior in design, and I saw a flow test somewhere,(I'll post the link if I find it), a set of stock 3800 heads with mild porting flowed almost as much as Stage 1 heads. Hard to believe but I did see the tests. The port design on the 3800 looks to be smoother and straighter, plus the D-shaped exhausts are supposed to fool the exhaust flow into thinking the inside radius is longer than it actually is. The intake manifold is a little more problematic as it is a one piece design, although the interior volume is decent. The flat back design will cause the air to pile up on the end opposite the inlet, just like the GN's, but there is little that can be done without changing manifolds or modifying it extensively.

[Guest]

You two guys are at the top of my christmas list. Heres what I have so far

Block: Stock

Crank: Stock

Rods: Stock/I-Beam

Pistons: Aftermarket

Cam: ??

Heads: Port and Polish

Injectors: 29lbs/min @ 100% Duty Cycle

Regulator: Stealth

Fuel Pump: Walbro 190L/hr

Compression: 8:1

Other: Intercooler, Boost Controller, Aftermarket ECU/EMS

Few questions: Any suggestions on cams and what grinds? Also, what size injectors for 80% duty cycle? (Not quite sure what duty cycle is but remember a friend saying the lower, the safer) Turbo Location? Im 99% sure my turbo will fit right after where the o2 plugs in on the stock system. Any other suggetions incase that doesnt work out? Also, should the o2 be before or after the turbo?

Transmission: I wanna run a 5speed like Ross, but worried the tranny cant take it even with a good rebuild. Reassure me and tell me just to get it rebuilt really beefy and get a strong racing clutch and go with it. If not, other options?

And Hal, to your disclaimer, I trust your opinion fully, you've got one running and I dont, and I want one.

[padgett]

Smooth power even to 300hp is not going to bother anything, it is shock loads that tears up drivetrains at this level. Worst thing you can do iss to get a tire spinning in dirt or a slick surface and drag it onto a high traction area. Even worse is axle tramp.

I would suggest care in the lower gears with a 5 speed (a fast shift can still be smooth) and a rebuild of the automatic with the extra clutches and a Pontiac valve body for a bit firmer shift.

[Guest]

Any sort of rebuilds for the 5 speed? What type of clutch would you guys suggest?

[2seater]

Padgetts right about smoooooth power delivery, that's partly why I slowed the boost down a bit. My personal opinion about a manual vs automatic is; auto's all the way. The GN guys have tried standard trans on a couple of cars and they went slower. They may feel better, but a good auto. with something like a manual/automatic valve body is hard to beat for speed of shifting plus you get the torque muliplication of the converter from a stop. You could try a higher stall converter but a good one with lockup is $600 plus. The cam spec's for GMRoss's engine should work well although the stock one seems to work okay at the boost levels I am running. For a boosted engine, the exhaust likes to be bigger or more lift/duration in the cam. You've got boost to push it in but there's more to let out <img src="http://www.aaca.org/ubbthreads/images/graemlins/grin.gif" alt="" />

As for duty cycle, 100% is always "on", which is the absolute maximum that can be delivered. At 5000 rpm, there are .024 seconds for every two engine revolutions, or one complete intake, compression, ignition and exhaust cycle. You can read injector pulse width in ED06 in diagnostics. The purpose of making the injector 10-20% larger is to allow some reserve and allow some "off" time to keep the injector from overheating. The stock GN injectors are rated @ 29.5 lb/hr @ three bar or 42.5 psi. You can change fuel delivery rate (within limits) by changing the fuel pressure. the problem with the GN injectors is they won't work in our manifold. They will bolt in okay but besides being too large for our computer to handle in stock form, they require a small "shelf" inside the hole in the manifold to hold the little plastic cap and O-ring on the end. Our manifold is bored straight through so the injector must be of a type that holds the O-ring in a recess in the injector body itself. MSD and others have such injectors, and the ones I have now (24#) are from a Corvette.

I placed my O2 sensor just before the inlet to the turbo. This location keeps it good and hot and it lights off sooner. The turbo takes a lot of heat out of the exhaust and you want to keep it hot. If you can fit the turbo at the stock exhaust outlet, it would be stealthy and it should spool up very well. I am not sure you can get the air in and out of it at that location. The inlet needs to be reasonably large, although it will neck down at the compressor inlet.

[Guest]

Did some looking on the net, can someone give me bore/stroke numbers of the engine and anything else I will need to know when looking for pistons/rods ect. Also, GM Ross or whoever else knows, what is the grind of your cam and who supplied it to you?

[Don B.]

After putting an '80s 252ci turbocharged engine together, and

installing it in an 'H' body I have an opinion.

The GN motor will not bolt up to the standard front drive trans.

Compression is usually good a 9:1.

The supercharged 3800 is prepped for the Reatta and just as

strong as the GN 3.8.

About 10 years ago Buick had a catalogue the you could order

Stage 2 V6 engine parts, anything from aluminum heads to a steel

cut crank or Tunnel ram intake. An engine built from this book

could make 600 or more horse.

Other locations to look would be KenneBell for 3.8/231

SLP for 3800 FWD.

I've seen GN's, Grand Prix hit high 12's in the 1/4 mile.

I've also seen full frame Skylark GS's and Wagons do low 8 seconds.

[Guest Greg Ross]

Don,

That GM Catalog is still available, or at least was last year. Stage II components were still being offered, even a long block as I recall.

Red Reatta, The Cam is from Crane Cams in Florida, my history file is out in the shop but I'll dig out that info for you. The process was to send Crane a 3800 stock Cam, they build it up and reprofile the lobes.

[2seater]

Bore is 3.8" and stroke is 3.4". I can't find my rod measurements but I believe they are considerably longer than the older 3.8's. The compression height is also quite a bit less that the 3.8's too. If you set the pistons side by side, the 3800 pistons look like race parts. The stock replacement pistons are #1738 in Silvolite hypereutectics and I used #1744's which are .050" taller compression height. They are the replacements for the later model 3800, like 91-94. The UEM website for the piston maker is down right now but just search for Silvolite and the United Machine website will come up. One other caveat, the older 3.8's have the same displacement, but most of the parts will not interchange with the 3800. The bolt pattern for the bellhousing is different between the rwd and fwd engines as well.

[Guest]

Thanks Hal and Ross.

Don B. Im not putting a GN motor in my car. Im building a new turbocharged engine.

[Don B.]

You don't have to look for it.

I have mine somewhere. I just want to give

suggestions on the posting. I am suprised

it was still around as of last year.

[2seater]

Just a couple more numbers for you: The stock piston dish shows a volume of approx. 26cc's. They were pretty consistant as they are fully machined. I had tried three different piston makers before I settled on the the Silvolite's, but the dish averages 4cc's more volume than the stock ones, which does lower the compression ratio. Others were much worse. I asked about .020" oversize stock pistons but was told they did not exist, at least at that time. Do not believe the specifications in a catalog, measure them yourself. You will find the catalog specs are an approximation at best. A fully machined piston will be better, but the standard replacement types are "as cast" in the dish area. In this respect a good forged and machined piston will be better although probably not necessary at a 300-350 hp level. The piston pin measures just over .90" and the compression height measures 1.49". When searching for pistons, watch for a note that may say something like "destroked .020". I found that the aftermarket piston makers must assume you are going to deck the block, so they shorten the pistons. These small amounts do not sound like much but they add up. For example, with a common destroked replacement piston, the dish a little larger than stock and a FelPro headgasket (which has a cylinder hole which is too large), the resulting compression ratio would have dropped to less than 8:1, even with a .020" overbore. My original target, which was calculated at 9.5:1 wound up at 9.1:1 because of the larger dish in the piston. The only other dimension I have is the heads cc'd between 38 and 39 cc's. As you can see, they are small chambers, about 1/2 of what a common 350 Chebbie 76cc head has, and you can get some really high compression ratio's with a flat top piston and a nice squish piston to head clearance of .035"-.040". High compression ratios are not desired for boosted applications in any case, but this illustrates what small differences can do. I also mentioned the FelPro headgasket only to illustrate that even a quality manufacturer may not have the correct part for your goal. The FelPro cylinder hole measured almost exactly 4.00". The maximum recommended bore diameter for my engine is 3.840" so that is WAY too big, not only a significant reduction in compression ratio but a nasty area where unburned stuff will build up. By contrast, the stock GM gasket measures 3.850" and is a nice graphite coated steel. If you plan on a lot of boost, you may consider having the block O-ringed <img src="http://www.aaca.org/ubbthreads/images/graemlins/grin.gif" alt="" />