87 Burb

Need some advice from some seasoned boosted engine builders.

In the process of rebuilding an '87 4-bolt 350 LO5 with a spun rod bearing. Machinist inspected and says .030 will take care of the bores. I'm already running Vortec heads and a RamJet manifold controlled with a port modded EBL with tables up to 15psi or 200kpa. I also converted this to a roller motor by tapping the center oil gallery bosses and installing a factory roller setup.

Will be putting a turbo on this motor sometime this year. The RamJet is already fitted out with low impedance 55lb injectors (good for around 830hp with gasoline), and a 2-bar map sensor. Installed a wideband LC-1 O2 sensor and a single Walbro GSS340 in the tank.

When I install the turbo, I plan to add a second GSS340 with a Y block and a new 1/2 inch supply line to the RamJet. I'll use the existing 3/8 and 5/16 lines for return (fuel filter removed on the 3/8).

The goal is to build a solid, reliable engine with decent off-boost power to move a heavy vehicle, ('87 Suburban, 3/4 ton, 4x4). I'm in Colorado at 6600ft, and use the vehicle for camping, towing, and crawling over rocks up to 14,000ft. Fuel injection is hard to beat for this application.

While I'm not looking to build a 9 second third-gen, if I used this engine in a properly set up car, it would have this capability. Under boost, I would like this engine to be capable of producing 700-900hp on E-85 or C16. I realize if I set up VE and spark tables to run E-85 and want to hit 700-900hp, I will need larger injectors.

The Suburban has a TH-400, NP208, and a 14-bolt semi-float rear axle. The driveshafts are pretty beefy. The TH-400 will need a rebuild at some point, but it seems like I've got the right transmission to handle the power if I set it up properly. I have a pair of one-ton axles (full float 14-bolt rear/Dana 60 front) waiting in the wings if these 3/4 ton pieces are not up to the task. Brakes have been converted to hydroboost (powered by the power steering pump, not engine vacuum).

Planning to go with a 383, all forged bottom end. CNC-Motorsports offers a variety of balanced kits, mostly from Eagle. They seem to have a pretty good reputation and decent prices, but I'm open to other vendors if you have suggestions.

I'm looking for some advice on compression ratio and cam selection.

CNC has a forged kit with 31cc inverted dome 5.7" rod SRP pistons (148750) which would put me around 8.5:1. This seems like a decent compromise for boost and off-boost towing. If I wanted to go with a 6" rod, I could upgrade to some 28cc JE pistons (170817) that would be a touch higher in compression. The JE pistons are made from a different aluminum alloy and are said to be stronger than the SRPs, although the piston pin with a 6 inch rod intersects the oil ring so you would need to run oil rail supports. The JE piston alloy also expands more when heated so they need more clearance (read clattering pistons until they warm up). Not sure how big these issues are, some people say "stay away". What do you think? 6 inch rods with better pistons, but oil rail supports and large clearances, or 5.7 inch rods, high silicone forged pistons with tight clearances and a solid oil ring groove? (The picture of the SRPs seems to show the pin intersecting with the oil ring groove so this may be an issue either way). I've also heard the JE and SRPs don't hold up well under boost. Not sure if this is the case, chime in with your experiences...Both of these pistons are indicated by JE and SRP as being ready for boost, (SRP-moderate levels of boost). Who offers a better boosted piston than JE and SRP?

Rings: Both of these pistons run 1/16, 1/16, 3/16 rings. Are 5/64 rings better for boost? For boost, I've heard people recommend gapless top, gapless second, don't run gapless, run plasma moly, run Hellfires with boost, don't run Hellfires they'll wear out your bores in 20k miles. Some guidance here would be helpful...

Both pistons seem to yield a decent compression for both towing and boosting, but I'm wondering if a touch higher would build better off-boost torque and power. It seems important to consider the cam and compression at the same time. I do not want the engine to perform like a slug off-boost, but I would like to have a low enough compression to get some serious power with a properly matched turbo.

I currently have a RamJet/HT383 roller cam which seems to work pretty well with the vortec heads.

On the RamJet, they run a 9.4 CR with this cam and 1.6 rockers. On the HT383, they run this cam at 9.1 with 1.5 rockers. I'm running 1.6 Pro Magnums. At 8.5 CR, how much low-end am I going to give up? (Remember, I have a serious need for off-boost low-end torque, 383ci will help, but I don't want to cripple this engine with too low of a CR).

Here's a little description of my cam 14097395:
----
This hydraulic roller design is used on the 383 truck and Ramjet 350.
The duration at lash point in degrees (intake/exhaust) is 288/308; duration at .050" tappet lift (intake/exhaust) is 196/206 and maximum lift with 1.5:1 rocker ratio (intake/exhaust) is 431/451. Valve lash is zero/zero and lobe centerline is 109 degrees.
This camshaft is a great upgrade for 1996-2000 Chevy/GMC trucks equipped with the L31 Vortec 350 Engine. This cam is great for additional bottom end torque. If installed in one of these trucks, a custom computer re-program is needed.
----
The lift with 1.6 rockers is around .459/.480. Doesn't sound like much lift, but it has been said vortecs do not flow much more with lifts over .500. I suppose the steeper ramp to reach .525 or .550 might result in more flow since the valve has to open faster to reach greater lift numbers. The tight LCA of 109 seems a little narrow for a turbo application, but with the mild lift and mild duration, I'm guessing there is not a lot of overlap which is what we are trying to avoid with a turbo application with increased exhaust back pressure. Is my thinking on track here, or am I off-base?

What are your thoughts on using this cam in a turbo application? Do you have a better hydraulic roller suggestion that will still provide good off-boost low-end? I've heard my factory roller setup is limited to .570 of lift. Also, any more lift than the RamJet cam with 1.6 rockers will require a spring/retainer upgrade on the vortecs. I'm prepared to do this if need be.

Cam, compression, pistons, and rings: What should I do?

Sorry for the long-winded post, just trying to provide enough details to get solid responses to the questions I've asked

xpndbl3

iTrader: (5)

that NP 208 won't like all that power with an aluminum case and a chain + case flex = boom. Lift on vortecs is limited to .460 maybe .480 at the most without cut guides and spring pockets opened up. For a cam, call comp and they'll custom grind you one.

87 Burb

Yep, an NP205 would allow me to engage 4wd for more traction under boost. Then the weak link becomes the 10-bolt up front. Solution: Dana 60 with 35 spline Dana 70 stub shafts. It's just sitting there, begging to be installed.

If I'm not engaging 4wd or low range, I believe the NP208 is a straight through design, unlike say a Dana 18. In 2H, This removes the load on the chain and most of the load on the case. It may be able to handle the torque in 2H, we'll see. Good point.

junkcltr

iTrader: (1)

The 55lb/hr will not get you 800+HP on a turbo engine. Not even that on a gas engine. Keep in mind the 10% ethanol. You are also over estimating your BSFC.

The NP208 will not handle that much torque. The NP205 won't either for the torque and HP you are talking about.

The Dana 60 will break axles unless you go with aftermarket axles and u-joints. The 10-bolt will break with 300HP.....seen it happen many times.

You want 800-900HP and low RPM spool. You only get one or the other unless you build a sequential turbo setup.....and that isn't going to happen. Since it is a 4x4 then go with smaller turbines and settle with 600HP. Get the low RPM torque you need. When you hook a large tire at that HP level the driveshafts are going to twist.

The cam is the last thing on your list to worry about. Once you figure out what you really want that is realistic then choose the cam. I would run between 8 to 10 CR depending on what you choose for spool RPM and max. HP.

87 Burb

Injectors: You may be right, some say 830 some say less. Duty cycle is pretty easy to monitor with an EBL. I'll go larger if need be.

Drivetrain: You're right, the 10-bolt front axle is inadequate for increases in torque or larger tires. I'm not looking to run 4wd with the 10-bolt under boost. NP208, same situation. NP205, they can handle quite a bit, especially with upgraded output shafts.

The real key to drivetrain survivability is how is this vehicle going to be used? I'm not looking to hook an impressive launch and land a great 60 ft time. This vehicle may never see the quarter. Until the rest of the drivetrain is upgraded, serious power can be reserved for 3rd gear in 2wd and the drivetrain can live "as is" after a tranny build and an appropriate converter.

Keep in mind, the stock 300ft/lb engine in first gear, low range puts out 1,941ft/lbs to the drive shafts (2.48 x 2.61 x 300ft lbs) and that doesn't take into account the torque multiplication of a slipping converter. When the front axle is on snow or mud, going up a steep hill and the rear axle is on dry rocky ground, and the pedal is mashed at 3000 rpm, (something that happens here in Colorado) nearly all the torque finds its way to the rear axle. The rear tires either break traction, or the vehicle leaps forward. It's often the latter. Now this isn't a true apples to apples comparison, but you can see these truck drivetrains are designed to handle torque, towing, etc. If the power can make it past the transmission in 3rd gear, 2wd, the rear axle and driveshaft will hack. NP208 in 2H, maybe. If you want to do 4-wheel smokey burnouts, or try to launch with a trans brake in 2 or 4 wheel drive, then yes, upgrades will be required.

Have you seen some of these full size boosted gas trucks (not talking about the diesels) ripping off 12.9 second quarters, launching in 4wd? Take a look at the videos at the link below. It can and is being done with transfer cases far less durable than an NP205. Is this guy producing 7-900hp? Probably not. The drag saavy guys here can probably look up the weight of his truck and use the et's and mph from the videos below to calc hp.

http://www.ststurbo.com/z71_videos

My agenda is a little different than most members of this forum and I'm not looking to do what this guy does. Let's not get bogged down on drivetrain.

"You want 800-900HP and Low RPM Spool": Didn't say that. I'm looking for good OFF-BOOST low end torque. I want the engine to run like a strong naturally aspirated 383 until 3000 to 3500 rpm, then I want it to spool and produce serious power from there on. This is why I'm concerned about compression ratio and cam. I don't want the engine to be a slug until it spools, but I don't want to have so much compression I can't produce serious power with the turbo. I don't think the two are incompatible, they just need to be carefully balanced. That's the central question of this thread.

The critical factor with this project if I can get compression, cam and turbo right, will be tuning. Getting the right tune is the key. I'm going to need help, and I'll need to spend some time with the right people on a chassis dyno. But that's another thread for another day.

Right now, I need to pick the right parts, get them ordered, get this engine assembled, and installed. I'm looking for some good advice on pistons, rings, compression ratio, and cam.

Here's another link to stimulate conversation. In this article, they take a ZZ383 with aluminum fast burn heads, fairly high compression, and a couple of different hydraulic roller cams, using both pump and race gas. They bolt on a Vortech Gen II supercharger, play with pulleys and nearly hit 750 at the flywheel. Now granted, I think there were some pretty smart guys setting everything up, but it shows big power can be had without huge levels of boost. They give peak hp and torque in different configurations, too bad they don't show the whole curve from 1500 rpm if the dyno can measure that low.

http://www.gmperformanceparts.com/_r...344_eprint.pdf

junkcltr

iTrader: (1)

I think I understand you a bit better now. If that was my setup I would go with 9:1 CR or slightly less. Use a dish piston and small chamber heads (better efficiency, more low end torque). I would install a 224@.050 duration, 114* LSA cam in that 383ci for low end torque and good high RPM boost HP. Having the turbos spool around 3500 RPM will allow for good sized turbines and 800-900 BHP.

It isn't a matter of what people say the 55 lb/hrs will support. It is what YOUR application will allow them to support. Using a 90% DC, a .58 BSFC shows that they are good up to 680HP. With a good head design and decent turbines you might do better with the BSFC so 720HP may be possible.

Yes, I have seen gas boost rigs at the track that are not diesel. I wouldn't run 4WD just to get a 12.9 ET. Better off with some DOT slicks in 2WD. That is drivetrain stuff so I will not go into details.

The car magazine setups usually aren't that smart of people, but they do have an endless cash supply to bolt stuff together and play around. If they do something exotic, they usually have someone else come in to figure it out.

87 Burb

With the ZZ383, the magazine says they are running 9.7 CR. GM tech specs below say 9.6. Sounds like a high compression ratio to be running boost, especially with hyper pistons...

http://www.gmperformanceparts.com/En...8772&engCat=sb

The dyno curve on this motor with the factory roller cam shows nearly 400 ft/lbs at 1500 rpm. Plenty of off-boost low end torque. This is what I'm looking for.

http://www.gmperformanceparts.com/En...8772&engCat=sb

They run the ZZ383 up to 7.5 psi with all factory parts, let's call it 9.6 compression and 91 octane and get 636hp at 6,400rpm with a vortech drawing power from the crank and no intercooler. Hmmmm....how much farther could they have pushed the factory roller cam with higher octane fuel like they did after they swapped in the Comp cam? How much farther with a cooler, denser, intercooled charge? How much farther with a lower compression ratio and forged pistons? How much more power would a properly sized turbo produce not taking power from the crank? No, a turbo is not free horsepower, but for a given level of boost, more power makes it to the flywheel than with a belt driven supercharger.

So here is a hydraulic roller cam with a torque curve that I'm looking for.

Camshaft duration (@.050 in):
222 degree intake / 230 degree exhaust
Camshaft lift (in):
.509 intake / .528 exhaust
Camshaft Part Number:
12370846
Camshaft type:
Hydraulic roller


Compression ratio:
9.6:1


How is this setup different than what I'm putting together?

Fast Burn Aluminum Heads vs. Iron Vortecs: Aluminum can explain a good portion of the compression they are able to run. Fast Burns also have bigger valves, a larger 210 cc intake runner and a larger 78cc exhaust port. Slightly smaller combustion chamber. When they flow Fast Burns vs. 170cc iron Vortecs, they generally don't outflow the Vortecs by much if at all at lower levels of lift.

Higher Compression Ratio: 9.6 or 9.7.

Okay, we can upgrade the vortec heads to handle this higher lift cam. The question becomes, how much can we lower the compression of this motor before we lose substantial amounts of torque from 3000rpm and below? We may get more low end torque with the iron 170cc vortecs compared to the Fast Burns for a given level of compression, so this may work in our favor. Cam guys, feel free to chime in here.

The other question that comes into play is supercharger vs. turbo. How would this cam handle the exhuast back pressure and possible reversion of a turbo?

This same analysis could be applied to the Comp Cam they swapped in. The problem here is without a torque curve to look at, I'm guessing it had less low end than the factory cam because they got 11hp more peak NA. Since we don't have the full curve, we're speculating. How do these cam specs work in a turbo?

Calling all serious cam guys that know something about turbos and the effect of compression on low-end torque...

As this relates to this project, which cam, which compression ratio will retain most of the cam's low end torque, but still provide an opportunity to generate serious power with a turbo?

xpndbl3

iTrader: (5)

www.theturboforums.com


read for 40 hours, read some more, then post something on there. It'll have all the data you'll ever need on that site and typically they bite heads off if noobie questions are asked before researching.

Edit: seen you already posted on there without looking around first. Hopefully they're nice to you

87 Burb

I've got 40 hours or more over there. Takes about that long to read Marty's "Grenade" post.

Did find a few gems about turbo cams here and there. Most guys over there are looking for 1000rwhp and don't care much about low end, off-boost torque. They just slap in a high stall converter and spool it up ala flyin' hillbilly. A lot are looking to go 8.5 CR or lower. Mine isn't the question that has been asked 100 times. Not many people are looking to do what I'm planning with a tight converter.

AutoRoc

iTrader: (1)

I don't see a problem with a 383 Ramjet/Vortec head combo but a complete build up and you are looking at and contemplating using an off the shelf crate engine cam? Do it right and call a custom cam maker like Cam Motion, Camshaft Innovations, Bullet, etc. It's not going to add much to the budget but it should definately make a boosted engine run it's best. I'd shoot for 9:1 compression and hope for the best. It would be ideal for alum. heads, irocn might want less if you really plan on a turbo combo capeable of big power. I'd do an S400 turbo(75mm compressor, 1.00+ A/R). 2800 stall...again custom made for the application.

JE and Diamond make great pistons and can suggest what ring to use for their piston in your engine.

87 Burb

Good suggestions. Thanks. If I can educate myself a bit more on the cams before I talk to these folks, I might have a more productive conversation.

I've read here on thirdgen that some of the cam makers are not real knowledgeable with turbos. Call them for a recommendation, write it down. Call them two weeks later after they've forgotten what they told you. Give them the same specs, and you get a radically different cam recommendation. Like they really don't know cams for turbos, but give you an authoritative answer anyway. I didn't see those manufacturers in your list of suggestions, looks like you're steering me towards productive conversations.

Been reading what Vizard says about cams and cams with turbos. Pretty enlightening stuff. I will say I've read the first 6 chapters of his Chevy Cam book twice, but it will probably take 3 more times to actually comprehend 80% of what he is saying.

He starts out the book saying there is way more to cams than you think. When he gets to turbo cams, he then says these are way more complicated than even nitrous or supercharger cams, which are more complicated then NA cams.

Well maybe this partly explains why I'm not getting the lively discussion I hoped for with this post (aside from being a really long post with lots of detail and multiple questions).

Vizard is on the GFN boards. Maybe I'll read his book a few more times, then ask him the cam/compression part of this post and see if he responds.

Once I've gotten a better handle of what to look for in a cam for this unusual application, I can truly comprehend what these guys at the cam makers you are recommending might tell me.

Problem is, I need to get these parts ordered, installed and get this vehicle running. It's easier to slide a cam in now while the engine is on a stand, and verify the con rods clear the lobes. Changing the cam is doable later, but changing the pistons is not. Unfortunately, cam and compression should be decided together.

Little side note: It took me 6 months to get Vizard's Cam book from Amazon. He's got another book on Chevy Pistons, Rods and Crankshafts. Thought this might be a good read considering what I'm trying to do. This book seems to be out of print and hard to get like the cam book. It was around $20 new, and the going rate for used copies of this book is often around $140. Anybody read this book? Is it REALLY that good? I have a hard time understanding the $140 price for a used book, but apparently the demand for this book has driven prices up this high...

bl85c

iTrader: (2)

I think you need to take a look at what you plan to do with this thing. Lots of towing and occasional 1/4 mile runs I'd say look for higher c/r and quick spool with less boost. Less towing but you plan on heroic 1/4 mile runs I'd look for slightly less c/r, higher boost and delayed spool so you don't break traction (and parts).

What part of colorado are you in?

87 Burb

I'm over on the western slope, not too far from Aspen. Took the kids skiing again today. Best snow in decades.

I hear what you're saying. I really don't want the engine to be gutless off-boost. I'll give up some top end to get things moving down low. The elevation already takes away a fair amount of power. I'm really trying to figure out how to capture the lion's share from both ends if possible. I do believe with a turbo it can be done, you just need to know what you are doing.

Junkcltr and AutoRoc are recommending 9:1. I think they are right. Vizard says you can run 12 psi and maybe a bit more at 9:1 with pump gas IF you set it up right. 9:1 seems like it would provide better off-boost low-end torque than 8.5:1, but I really need to think this through in conjuction with the cam (DCR, overlap, etc.). Vizard put together a 1000+ hp turbo sbc. The cam specs are very different than an NA motor (35 degrees of negative overlap). I'm curious how something like this might run at low rpm, off-boost. I really need to come up the curve on cams, then talk to the experts at various cam grinders as AutoRoc suggests.

Assuming 9:1 is the right level of CR, I've been looking for off the shelf d-cup or inverted dome forged pistons that would put me at 9:1 with Vortec heads. Want to run a .035 to .040 quench. Haven't found a lot of options. Not really wanting to go the custom piston route, mill the heads, install thick gaskets, or run the short 5.56 400ci rod to make some of the off the shelf piston offerings work. Looked at JE, SRP, Wiseco, Diamond, Arias, TRW, KB, Probe, Mahle. Doesn't seem to be a lot of options at 9:1. Looks like Mahle has some, but they appear to be dish, not d-cup.

I may be putting the cart before the horse. It may make sense to let the cam's DCR/IVC drive the piston choice/CR.

On the other hand...in low traction situations off-road (snow, mud, ice), if the torque comes on like a freight train down low, it can be difficult to get a vehicle moving. I've got a V10 Excursion, love the low end, but it can be tricky to get it moving in deep snow. The tires simply break loose and dig in. This might be an arguement in favor of a lower CR which would leave more room for boosted top end.

I was looking at the CRs for the different GM truck engines offered in '87 just to get a read on GM's thinking at the time. Most 350s were 9.3, mine was 8.6, and the 454 (not offered with 4wd) was 7.9. Off road, and pulling away from a stop light, my 8.6 CR TBI wasn't too bad, good low end, but not so much you break traction with the automatic. Not real peppy, but user friendly. Top end was pathetic, which is what sent me in this direction in the first place.

The 7.9 on the 454 is interesting. I'm guessing for a hard working tow rig, they wanted low compression for durability, but low end torque was key with this engine. If I recall correctly, this motor was a dog on the top end, but with 7.9 factory compression, seems like a candidate for a cheap big inch turbo build. Leave the factory heads on and boost it. The lesson here is low end torque and low compression are not mutually exclusive. Again, need to understand the cam.

The cam advice from Corky Bell's turbo book was not real deep. IIRC, it basically said it is hard to do better than the factory cam, which is why I started out looking at the mild RamJet cam I already have.

Onward...

bl85c

iTrader: (2)

I'm over in denver. Snowed alot this year, I'm not exactly happy with it though. My camaro's my daily driver right now, so driving anywhere looks a bit like this. -> Picture clumps of snow flying everywhere .

You should look for atleast .04" quench on a boosted engine with forgings. Watch out for piston slap.