<9:1 and sunoco maximal
928 HP on the chasis dyno today - Thanks Otto
- Thread starter turbobitt
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turbobitt
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- Feb 14, 2002
Update - Talking with Turbonetics on some options. Sounds like the Billet wheel 88 will get me about 200 RWHP at higher boost. Maybe switching to billet 91mm since I don't need to conform to any class rules. Maybe round 3 for the dyno.....
Allan G.
Allan G.
Brian, with that data.... would you deduce that the heads had great flow and that allowed the CFM's that turbo could produce to happen at a lower boost? Another words... if the heads weren't so good.... IMHO.... you might have made it to 35 -36 psi before the compressor was done.
What I see is that the turbo can't supply mass flow over 6600rpm/30psi. The compressor is done. The heads have a lot of flow potential that would need a faster ramp cam and more boost. It will probably peak around 6700 and hold it till around 7000 with 35-40psi if the compressor could keep up
Dusty Bradford
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- May 24, 2001
From my experience the Y2K91mm makes about the same power as an old cast wheel Precision 47-88. The turbine side is great but the compressor housing and wheel aren't. You would pick up power just swapping to an older Precision 88mm. If you went to a new billet wheel 88mm from Precision you would make way more power than a Y2K91.
On the cam. Those old cams in the 260-270 @.050 spooled like crap and were way more cam than needed. We went with something much smaller. It spooled like it was a V8 compared to the old cam and still pulled well to 7500 rpm.
On the cam. Those old cams in the 260-270 @.050 spooled like crap and were way more cam than needed. We went with something much smaller. It spooled like it was a V8 compared to the old cam and still pulled well to 7500 rpm.
turbobitt
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- Feb 14, 2002
Dusty,
I understand your reasoning about the cast wheel Turbonetics vs. 47-88 but Turbonetics assures me that there new billet line of 88 and 91 mm wheels will more than outflow there own cast 88 and 91 wheels at high boost levels over 30 lbs. So to compare apples to apples, I'm sure your experience is based on the Turbonetics cast 91mm version wheel? If so I would agree with your assesment of the situation.
If I were to start over, I would pick the GT4718R T6 flange turbo. The compressor map for this turbo is impressive and the smaller turbine would give me better spool response. I just don't have the cash to fork over for a whole new turbo.
Allan G.
250-260@.050. Damn they must have 330' like ass. This one is about 15-20* less duration than that. Dusty how many lb/hr fuel are the 8.50 cars using with a v6 compared to a v8 with the same race weight non oxygenated fuel?
turbobitt
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- Feb 14, 2002
Bison,
I think one thing we learned is that we undestimated what my current cam would do but also have some direction on what are new cam should be. I think there is some power with more lift but it is hard to say how much. One thing is for sure is that we have not seen the limits of this cam yet.
Allan G.
ttypewhite
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- Oct 1, 2001
I would be very careful in this selection of a newer turbo. IMO I would not focus on breaking 1000 rear wheel hp as the basis of this selection. If this is a true street car you will not have fun with a 47-88 or 91mm. The fun factor with something of this nature would be best enjoyed at the track at full boost with a transbrake. On the street with less boost, whether with alky or just straight pump gas both turbo's listed above would be a dog on the street. The explosiveness will not be there, the fun factor would also be gone. I would tailor your setup to where you would get the best of both worlds. If anyone says a 88 to 91mm turbo is explosive on the street at 17 to 22 psi.........they are not telling you the trueth. You would be hard pressed to beat a low 10sec car on the street that way unless you ran race fuel with lots of boost.
turbobitt
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- Feb 14, 2002
Turbo is already a dog so there is not much more to lose. I believe the 47-88, or 4718R would spool better than my current turbo. Going to a billet 91 vs the cast 88 should not effect spool that much. I would keep the same F189 turbine anyway.
Car is still a lot of fun to drive and not to worried about building boost between lights since it is already a handful to drive. My focus is to maximize this combo while maintaining driveability. And my definition of driveability is my ability to take this to local shows and cruise nights without parts breaking and wearing out parts. Don't like trying to prove anything on the street anyway.
Allan G.
Allan I Know right now where you can get (2) gt4788 turbos at a reasonable price if your interested. One is on the pictures I sent you the other , day, I think it is still for sale. I personally would even go smaller turbo, but that's my preference.
Is it partly due to alot of valve overlap of the older big cams? I would think the high amount of valve overlap would bleed off alot of low RPM cylinder pressure therfore limiting the amount of actual exhaust gasses available to spin up the turbo......making it a dog until the RPMs got on up.
turbobitt
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- Feb 14, 2002
For a turbo cam, the needs are a lot different then a NA cam. For exapmple, The overlap and duration take advantage of the exhaust pulses to scavage the cylinder. With a turbo cam you simply can't have this. In a turbo application, the cylinder pressure at TDC exhaust stroke will never drop below exhaust back pressure. This would make the exhaust closing event important as well as minimizing overlap. So, this would imply that the operating window for the exhaust event is narrow and well defined compared to a NA cam. If you use this logic when selecting lobes, as well as knowing where the cylinder heads flow, things start to fall into place.
So, with all that said, the larger lobes would reduce engine vacuum, reduce much needed low end torque needed to spool a large turbo, and just not perform well anywhere but a narrow high RPM band.
Allan G.
I have to disagree with the statement that you just can't have overlap and accomodate pressure pulse tuning to help cylinder scavenging with a turbo cam. I'm running more duration than what has been discussed in this thread so far, and am not suffering from what I'd call a narrow powerband. On top of that, it is a very streetable cam. A little lumpy at idle, but as soon as the throttle is cracked, the engine smooths out nicely.
turbobitt
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- Feb 14, 2002
Don,
You have to remember that this is all relative. Are you not running some old style M&A's or something like that ? Port flow may be more of a bottleneck with your set-up and therfore would respond differently than a larger port head.
With regards to cylinder scavanging, I've personally seen and run many dyno tests with cylinder pressure transducers, exhaust pressure transducers, valve motion prox's, and many other types of instrumentation. I can tell you that the only pulses in the exhaust are ones that tend to pop the exhaust valve off the seat from another cylinder, by far nothing that would help power or scavange a cylinder. The only thing that one can do is play with header tube volume to change the accumulator effect of dampening these pulses.
Allan G.
You're saying that you don't believe the same sort of pressure pulses occur in the exhausts and intakes of a turbocharged engine that occur in a n/a engine?
turbobitt
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- Feb 14, 2002
Pressure pulses are there, just the base pressure at TDC never drops below Exhaust back pressure. Most turbo's under normal cercumstances generate more back pressure than boost pressure since it requires energy to drive, plus inefficiencies in the system so it is impossible to have scavanging. Controling the exhaust event to minimize EGR effect from the spent gas volume is important. As the piston starts towards BDC, cylinder filling will occure from the winning higher pressure source during the overlap event.
I have seen large swings in exhaust manifold backpressure, mostly caused by opening and closing of the exhaust valves in a small volume manifold. The gas has more energy and volocity with the heat generated from combustion. This is why reading a "gage" type reading can be missleading since it is giving an average and not capturing the high pressure pulses.
Allan G.
Where it comes to using a long duration, high overlap camshaft and taking advantage of pulse tuning with a turbocharged engine, say you don't know how to, and I'll believe you. Say you don't have the resourses to, and I'll believe you. Say you choose not to take advantage of pulse tuning with your engine project, and I'll believe you. But, don't say it's impossible to achieve with a turbocharged engine. That simply is not true.
