So for the last 6 months I have been testing theory and my knowledge on engines to build my first big block turbocharged engine. The end goal is having the most with the absolute least. I am calling it the Racing Junk/Ebay experiment. The shortblock is figured out and on the way together. 427 tall deck truck block with a fill to the water pump holes, Program caps, Main studs, Billet crank, Manley aluminum rods, JE flat top pistons (8.51:1 compression) with hellfire rings and .220 wall pins. Everything was scored off Racing Junk or Ebay including the pistons ( dealer used an auction to basically advertise, called and got what i wanted for his auction price). Its an overkill rotating assembly for a stock block i know, but my thinking was that if i did everything herhi could to reduce stresses transferred into the block ( aluminum rods, Billet crank that wont deflect and bind) i just might get this stock block to live making high horsepower. 1500+.

The cylinder heads are going to be stock castings. 781's to be exact. Back a few years ago I was lucky enough to work for Brian Tooley at Total Engine Airflow when it was in Bowling Green KY. Using what i learned while i was the Machinist there, I am theorizing that i can get the head to flow about 320-330 cfm at .650 lift while opening them up to 285cc from the stock 265. Exhaust flow will be approaching 300 with a pipe. These numbers were accomplished at least a half a dozen times while i was working there so i feel they are very very obtainable.

Here .is where I feel out of my element. The cam. I've called about 6 different cam companies asking for specs, and recieved the biggest range of specs i have ever encountered for a build. Cammotion was the smallest at 232/224. Bullet gave me the biggest one 260/264.
They all had either a 110 or 112 ICL and a 112 or 114 LSA. They were all given the same specifications for the combination, Peak hp at 6k max RPM at 6500, 3500 pounds TH400 3.42 gear, and a HP goal of 1500-1600.

Brian is a really good friend of mine and we bench race and bullshit at least a couple times a week and he has gotten into researching cams and valve events with a recent build he just completed. a 454 LS7 LS motor with 245cc TFS heads and a 102 fast intake. This engine made 705hp and 630 tq naturally aspirated. it made 600 tq at 4000 rpm all the way to 6200. Its an absolute beast in his corvette, runs 135 mph at 3350 pounds. It was designed to be naturally aspirated and the camshaft has 15 degrees more exhaust duration and its on a 115 lobe separation. That fact is the key to this whole situation. During these bench racing sessions we started discussing the cam for my motor and where the valve events need to be. Specifically the IVC and EVO. Its been my understanding that an engine that has backpressure issues needs to open the exhaust valve later to let the cylinder blow down some to keep exhaust system pressure in check. As far as intake valve close i really have no clue on what my combination would like. With all the talk about how a turbocharged engines cam looks a lot like something you might run for a naturally aspirated setup, Brian starts talking about specing a camshaft that looks alot like the one for his motor. The combos have some similarities, same stroke, Small intake runner for the displacement etc etc. The camshaft we came up with looks like this. 253/260 117 LSA on a 114 ICL. The valve events, Intake open 12.5 Intake close at 60.5. Exhaust valve open at 70, exhaust valve close at 10. thats 22.5 degrees of overlap. These specs are all within 1 degree of the cam in Brians 454 LS7.

Now with that much overlap the conversation turned to reversion. Brian starts telling me about how they've started running 50 degree valve seats to kill flow at .100 lift to help control it. When he pulled the intake off the LS7 there was barely 2 inches of carbon on the intake ports, I honestly have NEVER seen an intake port that clean on an all motor combination. Our theory is that if we run 50 degree valve seats and kill the flow at .100( and be up 20-30 cfm over a 45 degree seat from .300 up), the overlap will Benefit this motor trying to spool what is now a 98mm Precision turbo with a 1.5 A/R housing while still keeping reversion in check, letting the pressures cross over but at the same time having a low volume of exhaust revert. I know with a higher overlap cam the exhaust side MUST be sized right and no restriction what so ever. Planning on 2 inch primaries, 3 inch crossover, the 1.5 A/R housing, and a 5 inch exhaust with a fender exit.

Now are we Effin nuts?? Is that exhaust valve open event even close? We think opening it that soon will create a high level of drive pressure to spool this big turbo. Ive seen guys cams open as early as 62 degrees and they run damn damn good, but i also know 8 degrees difference is HUGE in a camshaft.

Now for the 2nd part of this, the horsepower. Brian thinks that this thing will make 1.28-1.3 horsepower per inch N/a. I think that is optimistic. 496 with 8.5 compression making 650 horsepower? Now doing the math for boost pressure, picked 22 psi just for shits and giggles, the calculator on Golenengineservice.com says 1650 horsepower!!?? That is about 300 more than I EVER expected this thing to make. I know Impatient1 makes like 1760 with a stock Mark 4 block in his Drag boat. But really??? Is this really what my motor is gonna be capable of doing? I started this deal wanting 1000 rwhp on pump gas, and now it looks like i could have a serious piece if i really wanted to turn the wick up on it.

Thoughts, considerations, criticisms, all welcome.

John

 

your build is certainly out of my league as far as turbo's go. I have worked on some similar nitrous motors though. I am not sure how much of that would carry over.

Personally I like your camshaft pick more than theirs and here is why. You have a block block trying to push BIG power from it.
There are two ways to make power, and that is RPM and Tq. Both break stuff. so you need to get an idea of what the limits are for your parts.
We know that 1500 Hp is a lot for stock components, I think the nitrous motors I got to help build were making somewhere is the 1250hp range. The biggest issue with the blocks themselves were that they kept pulling the studs from the deck. this is something you will probably need to keep in check, before the fact.

Ok, so what lifts heads? cylinder pressure. and to make big power at a lower RPM you have to have more pressure. and I'm telling you the decks are weak in the thread department. the other way to make HP, yes RPM. so trade some of small cam for a the larger cam like you spec'ed.... larger cam = lower cylinder pressure, more RPM.

so in essence is what I'm saying is by going with a bigger cam you can trade some TQ for RPM. if you turbo's are up top the task.
(this is a 4.310 bore, 4.250 stroke? if so)

the cam i would select would be a 251/251 on a 112, you should peak around 5800, shift around 6350 or so, you might pick up a little rpm and clean up the idle by going a little wider on the lsa, 114 or 15

 

I'm running out the door to the track, but wanted to say this one thing. If you can find one or fab one, run larger than the planned 5 inch exhaust pipe.

 

My experience with turbocharging is limited, but I dove in with both feet (see "Project no-buck" in the turbo builds forum), but I have a decent grasp on engine theory; and I've given this same subject a lot of thought. Here's my take on the cam event effect on a turbocharged engine (and anyone more in the know, feel free to weigh in a correct me as I want to learn):

In an N/A engine, we time the valve events based on the VE being near (usually below) 100%. Also, we have a relatively low risk of detonation, so we tend to run the fastest burning fuel available. We want to build combustion pressure as quickly as we can and take advantage of the piston being near TDC, so the pressure wave is not chasing the piston down the hole. That's why retarding (ign) timing kills power; at high rpm, the piston is effectively out-running comb pressure, and much more of our energy becomes waste heat.

With this in mind, the pressure wave is usually done accelerating the piston by about 90ATDC, but we still have pressure in the cylinder. Opening the exhaust valve early allows the residual pressure to bleed off into the header, which means the piston has less exhaust mass to shove out on the up stroke, generally improving gas transfer and allowing us to open the intake earlier and start pulling fresh mix in. Keep in mind all of these events have to be looked at in the context of VE being at or below 100%...the higher the rpm, the more benefit we get from going in this direction.

Now hang a turbo on that same engine (exactly what our initial tests were)...the early EVO allows the same residual cylinder pressure to hit the turbo at lower RPM, improving spool up. The downside is, now that we have much more than 100% VE, and have probably retarded ign timing and gone to a slower burning fuel, the pressure wave has the potential to accelerate the piston much further down the hole during combustion. Opening the exhaust valve at the same point is now going to release useful pressure levels into the exhaust, especially once we go to a fast ramp roller cam. The ultimate example of this would obviously be a nitro engine, where the combustion event is still happening as the exhaust opens, leading to those massive header flames and noise we all love...

If we want to take full advantage of the turbo's ability to increase VE, we could keep pressing down on the piston and building torque much further into the conb cycle. To do this, we would keep the exhaust valve closed longer to trap cylinder pressure and force it to act on the piston. We would also delay ignition, as we don't have as much of an issue with the piston out-running the pressure wave at higher RPM. We might cut overall cam duration, as we need some bottom end torque to get the turbo spooled in a street type application.

Now the engine is more dependent on the turbocharger(s) to make any kind of power. The more we build the combo around the turbos, the more important turbo sizing and tune become. IF we are building a drag only, anti-lag equipped, leave under boost engine; a lot of this goes out the window, as we artificially spooling the turbo (as AlkyV6 has done an excellent job o pointing out

 

I agree with spinning the engine as fast as you think is possible with your valvetrain. With a balanced rotating assembly there is theoretically to additional stress on the bottom end from higher engine speeds. What does directly effect stress on bottom end parts is torque.

 

Exwest, I know forced induction engines work on the piston longer than N/A engines, But how much more? Could we calculate it? Estimate it? In my mind the IDEAL exhaust valve open point is the point where the acceleration of the piston has dropped off. It might still be working on the piston BUT that exhaust pressure would be better served being diverted to the turbine of the turbo instead of the top of the piston. I have a hard time correlating things with all the nomenclature so, how does 90 degrees ATDC correlate with 70 degrees BBDC? just trying to get this picture right in my head by using all the same factors.

I am not going to be using a system like Alky has because this motor is going to be a blowthrough carb setup. I might be able to figure out how to employ the afterburner once you guys figure out how it might work on its own using compressed air and fuel through a nitrous nozzle with either retarded timing to light it off or a spark plug. That being said, This is a 500 inch motor, it should spool pretty damn good WITH THE RIGHT CAMSHAFT. I want this camshaft to be absolutely perfect for this motor, and i thought coming here and asking input from Tom, Andy, Donnie and all the other people that know way more about this than me.

As far as Torque, the last thing i need to to concentrate on making it below 4500 rpm. 500 inch motor with a 4.25 stroke with a cylinder head thats only 280cc is gonna make boatloads, well probably WAY too damn much torque to be even remotely manageable. The chassis is a 2nd Gen Fbody thats going to be a 12 point cage or 25.5, stock suspension with caltrac bars, and a 10.5 slick. The LAST thing i need is low end torque. I will have problems getting this thing outta the hole without overpowering the tire i know. Brians camshaft made peak torque in his 454 at 4700 rpm. Theorizing a 1200-1400 rpm powerband, making peak torque at that same RPM will give me peak HP at 5800-6000 and hold good power to 6500-6700. I am afraid of spinning this thing 7000+.

Andy Excessive torque is something i am trying to address and stay away from in the lower RPM ranges. I wont be able to utilize it so why worry about making it right? BUT i am scared of shifting that powerband TOO high into the RPM because this motor does NOT have enough intake port on it to go Very high. What are your thoughts on this 4700-5000 Peak torque point i have in my mind? Peak Horsepower by 6500??


I really want to know where the exhaust valve open point should be. That is my key to the whole camshaft. Once i know that the durations can be worked out which will make all the other things fall into place.

Again, all thoughts Critiques comments are welcome. Information is power. need as much of it as i can get.

 

Nomenclature

73maro,
To understand the nomenclature, just think about what the piston and crank are doing at that particular point in the cycle... For instance, at TDC we say the crank angle is zero, and the piston can only move down, so we are either 0ATDC or 180BBDC... At 90ATDC, we are also at 90BBDC. In your example, 70BBDC is also 110ATDC. Everything will add up to 180. How we look at it depends on which cycle or cam event we are trying to figure out. Exhaust opens as the piston is moving down. It is headed to BDC, so we express the event as 70deg BBDC. On the intake, the opening event is happening as the piston is moving up so we express the opening as Xdeg BTDC.

 

I am not familiar with those heads so I can only make the general statement that I would put the biggest cam I thought I could get away with with those heads.

Also since it sounds like you will have a low restriction exhaust I would not use a cam with less exhaust duration than intake duration.

 

Ok now ive got it straight in my mind. I have read in more than one place than a turbo motor can exert usable energy 20 degrees past where a N/A setup could, and 10-12 more than a nitrous engine. The more i research the more its looking that the EVO can be in the 65 to 70 BBDC range so the biggest amount of exhaust energy could be transferred to the turbine.

Andy, the valvetrain isn't going to be too extravagant. The cam will be solid roller, Comp lifters, nice big diameter pushrods and typical stud mounted rocker arms. I have a set of Crane Golds setting on the shelf i thought about using with a girdle. Not gonna get crazy with the lift on the lobes, or with the spring pressures. Planning on around 225 pounds on the seat and 700 or so over the nose with .650 or so lift.

781 castings are some of the better flowing stock Oval port BBC heads out there. Very small cross sectional area so they will have to be opened up significantly to work. I am expecting to take at least 20-25cc of material out of the ports taking them to 285-290 from the stock 265. 325-335 cfm is easy. Ive heard of 350 once. Exhaust port is the same way, good but can be improved on to flow 300 cfm or so.

I know the motor is going to need Duration with the small head being 500 inches. Is it going to take a cam in the 260/270 range? i really didnt want a cam that big, and yes i know how Big inches calm down huge camshafts, but this isn't a 100 percent track car. I would like to cruise this car on occasion.

 

Cam selection, as I understand it, has to do with making the most of pressure differentials. With a turbo, we cut down on overlap, as there will typically (NOT always) be higher pressure present in the exhaust than in the intake. So, we have delayed the EVO to take advantage of cylinder pressure, AND we've cut overlap to prevent EGR. We only have so much crank rotation to play with, so that means overall exhaust duration HAS to be less than we would want with a N/A engine.

On the intake side, we are only concerned with how much air mass we can get into the cylinder. If we have a big healthy cylinder head, we can move a lot of air without much manifold pressure (high HP at lower boost pressure), BUT we are sacrificing N/A torque; so spool time (and RPM) will be higher than with smaller heads. On the flip side, smaller heads will build torque (and spool), but it will take more boost pressure to move the same air mass into the cylinder. Boost equals heat, so higher boost pressure means we have to do more to overcome density loss, detonation potential, etc.

As far as cam selection goes, we still don't want a lot of overlap, so we will likely delay the IVO event (compared to a N/A cam). We can push air in later on the compression stroke (esp. with high boost pressures) so leaving the intake open longer can be beneficial to a point. Usually we see exhaust duration cut more than intake duration compared to N/A cam profiles. All this adds up to a wider lobe separation angle (LSA). Some of the most successful (small-block) turbo cams are out in the 116-117deg LSA range, compared to 110 or less for a high HP N/A cam used in the same engine.

 

Exwest, Everything you just said applies to the thought process we had when picking these events. the Intake centerline is pushed back 114. Lobe separation angle is 117. the cam doesnt have a lot of overlap, but its hard not to have some when you have 250-260 degrees duration. I posted the exact events we came up with in the first post. When you have Excessive exhaust side pressures is when you really need to cut down on your overlap to prevent EGR. IF you can keep your drive pressures in check, say less than 1.5:1, you can put more overlap into the cam to help spool and response.

 

The cam we just installed in the 350 project has -8deg overlap, 218/[email protected] duration on a 114 LSA. Not a "turbo" cam per se, but definitely moving in the right direction from the one we had in there. I agree with your idea that if we can keep the exh/boost pressure ratio fairly well in check, we can benefit from a "bigger" cam like what we would typically see in a N/A engine.

As far as I've seen, usually the exh pressure/boost ratio is affected most by the plumbing, A/R of the turbine, and turbine trim. If the exhaust housing, etc. is small enough to get good spool, it tends to get pretty high pressure ratio as total airflow goes up (high RPM and boost). Thus far we have no way to monitor exh pressure/boost ratio on the dyno. That's something I'm working on along with everything else...

 

I'll share the thought process that I went through in picking my camshaft and maybe you can find it usefull in translating some of it over to your application, I hope.
Let me add that I did have the help of engine analyzing software to help with my choice. I would not try to do it again without the feedback that I got from the simulator.
How do I start this. Good parts in the bottom end is very smart. That gives you a good foundation to play with. The heads and the cam selection should be treated as one. In other words, the cam must carefully match the heads you've picked AND the intended window of operation (rpm operating range) and usage (street, drag, both).
My project revolved around the choice of using the first set of aftermarket heads made available for the Buick V6. Much better heads are now on the market, but they're the heads I had purchased for the project long before other heads hit the market.
These are production/stage I style heads, not the more elite Buick Motorsports Stage II heads.
The heads I'm using have 1.835" int, 1.5" exh size valves. They've been max ported, but these valve sizes were retained. The cylinder bore is under 4 inches and I wanted to avoid shrouding problems.
The intake flowed 210 cfm on the flow bench. Yuck. From what I've learned from reading numerous publications on the subject, a head that flows below what should be required to meet a certain power target can be somewhat compensated for by camshaft events. Duration and lift being important to accomplish that goal.
To be continued.

 

You've already picked your rpm range and usage. That will dictate much of your cam specs. For instance, you wouldn't want to run big lift on a street engine unless you like adjusting, inspecting and replacing valve springs often. The operating range and components you've picked look good, although I've gained a good amount of respect for shaft mounted rockers over stud mounted.
From what I've learned from reading numberous publications, a poor flowing head in relation to a particular goal can be compensated for with the camshaft to a point. Duration and lift are key to that point. Area under the curve being important with the lift figure. More duration will allow higher lifts without a lot of strain on the valvetrain allowing more reasonable ramp speeds.
The work that I did on the sim has shown me that the intake duration is key to picking the power band of the engine. That should be picked first. The exhaust duration picked afterwards to compliment the intake duration, balancing the flow.
The overlap is tricky. It would be nice to know ahead of time what kind of int boost/exh bp ratio you're going to have before picking an overlap and LSA. In my case, I had the goal of obtaining a better than 1:1 crossover before I picked my cam specs. That would allow exceptional efficiency on the top end, but it did kill spool up time. Since nitrous was also part of the plan, I really wasn't too concerned with the spooling difficulty part of the equation.
To be continued.

 

I picked .714" lift at the valve as a figure that would give me the best area under the curve, but still maintain a sane amount of durability of the valvetrain. I'm going on over 3 years on the same set of valve springs. They are due to be changed, though. The seat pressures have dropped to a point where I'm nervous about that now.
A .714" lift matched perfectly with the amount of intake duration that I wanted to use to give me my power band of 4500-7800 rpm. What I mean by matched is, the amount of duration allowed for an aggressive amount of ramp speed to give me my .714" lift keeping ramp speed within acceptable maximums. Less wear and tear on the valvetrain.
The intake duration I picked was 242 on the intake and 250 on the exhaust. The amount of duration worked good to make up for the short comings of the heads, AND to help control cylinder pressures (as mentioned above by another) at mid-range rpm levels if I had happened to install a turbo that would provide me with a good amount of boost early in the powerband. That turned out not to be a concern with the 91mm. Although, with the T76 and the nitrous, it certainly was.

 

Lobe separation angle, overlap and installed intake centerline were picked solely from the work I performed on the engine simulator. You'll notice that I haven't offered much in the way of exact camshaft event numbers for your setup. The sim work has spoiled me a bit. I highly suggest that if you're serious about getting the cam as close as possible to perfect that you get yourself a reputable sim and spend many, many hours playing with it. Just remember, garbage in, garbage out. If your entries are accurate, you should be able to use the results of the sim as a good guideline. Not gospel, just a guideline. Advice you get from very experienced individuals with a combination similar to yours should also be thrown into the hat. Although, if I had listened to my peers about camshaft selection, there are some discoveries I'm pretty sure would not have happened.

The flow balance with my cam is 80% exh to int.
The overlap is 32 degrees @ .050", if I recall correctly.
Intake centerline installed 4 degrees advanced.
Lobe separation angle is 110 degrees.
The cam looks pretty much like a good n/a cam, except for maybe a couple extra degrees on the LSA. Again, this cam was picked with the intention of achieving a better than 1:1 crossover ratio. What's most important is this cam allowed for the discovery of the Nitrous/Methanol Drag Turbo Anti Lag System.

 

I also hold fast to the theory that you can obtain pressure pulse tuning with a turbo setup. Some think that the higher pressures in a turbo system negate pressure pulse tuning. I argue that it does occur, just at higher pressure thresholds. My whole combination was setup on a simulator with the hope of obtaining the help of pressure pulse or resonance tuning. Another reason why I went with the amount of overlap and LSA that I did.

 

Which sim did you use? Engine analyzer pro? I scored a copy of it and threw around some numbers playing with it trying to learn it. Thanks to slow67 for taking the time to run my combo through the program and sending me the file. I had to leave for work the next morning after I got it so I did not get to play around with the cam numbers yet like I want to. One thing I noticed that made me think I'm somewhat on the right track is the flow percentage #. 79 percent. Since I've been out on the road this last week I've been able to build an info sheet on duration and lift numbers for Comps XESR lobes so that my inputs will be an exact match to what I can actually get. I don't want to hafta lash valves every time I wanna drive the car so that's one reason I picked the extreme energy street roller lobe. 254 duration ( they don't have a 253 lobe) gets me .660 with a 1.7 and .698 with 1.8. 260 exhaust lobe gets me .668/.707. I'm still interested in hearing opinions on my EVO point. I'm starting to think it might be too early. I think my 114 Intake centerline might be pushed back too far as well.

 

what would really be nice is to figure out how to change the cam timming on the fly like the V-tech or simmilar setups do on the smaller engines. we could the put a smaller cam in there to help spool then advance it to help build power in the later RPM ranges. Any one looked in to how this could be done? mabye with some sort of centrifical device?

 

Nitrous.