Thanks OC, I may run something like that on my 4.1 build, not the 3.8. Let us know how the smaller cam spools for you.
Can someone explain why stage II heads are not streetable?
- Thread starter norbs
- Start date
Thanks OC, I may run something like that on my 4.1 build, not the 3.8. Let us know how the smaller cam spools for you.
fastblackracing
Well-Known Member
- Joined
- Apr 7, 2009
For what its worth, in 99 I put a st 2 headed motor together it was around 250 inches and had many things that were less than ideal. we used a crane street roller 218/218, seems to me lift was 540ish, and the springs were 240# seat pressure. the car had a limit 76 three bolt turbo q trim, 83# injectors and a precision front mount. the block had been welded epoxied sleeved and repaired way more than it should have but none the less it ran and drove on the street surprisingly well. the car was a full weight loaded T with a rollcage and no lightning whatsoever the battery was up front still and the air intake system would not let it make over 22# of boost. the owner had access to these parts and just wanted a street brawler. I ran the car at the track 1 night only and it ran 10.4os @ 134MPH car ran strong in 3rd gear felt like it would never quit pulling
Thanks, fast black I think I am going to order a 218 cam for this, its going to idle for hours in traffic around here with the A/c on and it has to be reliable. I won;t go to the track much, and according to the calcs the cam change is maybe worth 50 hp , and not worth having it run like crap around town. Turbo and head flow contribute to most of the power the cam just lets you get the extra power at higher rpm. I think it will get me a low 9 that should be good enough.
Hey Norbs,
I found a larger billet cam for $25 here on the board, had a small blem, it was checked by Crower and was told it would clean up, got some specs for a 218/218 that DLS uses, having Crower regrind cam at cost of $160
Many of the responses are very old school.
Look at port area on ANY 4 valve motor. They aim for Mach 0.4 max - even turbo motors.
It is the *combination* of head and cam that determines operating range. Big ports need small cams. It works better than small heads and big cam - broader torque curve, better fuel economy, and smoother idle. 2 valve motors generally can't touch the valve area of a 4 valve motor. In this case, we can.
A 3.8L motor hits Mach 0.5 at 8000 rpm, Mach 0.4 at 6450 rpm. A little higher than the 3.8 is meant to run.
Stage heads need a 4" bore. A 4.2 would be my pick. Mach 0.5 7250 rpm, and mach 0.4 at 5800 rpm. A cam in the 260* range should be plenty for a low rpm turbo motor. For a certain power level, you can also use a smaller turbo. A 6266 has made over 700 whp on a 3.4L supra with E85.
Don't forget, WET FLOW is much better in the stage 2 head vs a stock low port. Much better combustion chamber, for quicker burn: better acceleration, less knock. The ports are much more efficient. Efficiency is key.
The problem I am finding the large ports, kill low rpm torque so even though I have a small cam I still have no power under 5500. However I don;t see why I can't run 8000 rpm plus with this setup. I could not make it to the dyno in time last year. This spring I should know the results of the S2 head project.
You say you want more low end torque, and also want to rev to 8000. There's no free lunch. You can't have big ports AND big cam AND big turbo, and expect low end torque. However, big ports and small cam will give you a wider torque band than small ports and big cam. It sounds like you want more streetable power.
The lack of torque is due mostly to your turbo. It's way too big for the intended operating range and HP. The little 3.8L just isn't pumping enough air until 5500 rpm to spin that turbo (especially with your combo). Even a 67 mm turbo will hit hard (very noticeable turbo lag) with stock heads.
You're likely blowing fuel out the exhaust. Too much valve overlap will hurt performance. The smaller cam will also bring the operating range lower - which will help spool and low rpm torque. Ball park 265* advertised on the intake, 275* exhaust, 118* LSA, and the lift will necessarily be lower. It's easier to estimate off a baseline, and the proper data logs.
As big as the ports are, you will pick up air speed with a good valve job and blending. Air speed benefits everything.
1-7/8" headers are WAY too big for your actual HP, and they kill spool. 1-5/8" headers are plenty big for the 3.8 (watch back pressure). A divided manifold will spool sooner. I came across a "quick spool valve" by suprastore...that will help as well (works with an open manifold).
If you want low end torque, you have to do several of these things. You may find that with porting, the right cam, and headers, QSV, that you'll be happy with the GTX4202. If not, consider a smaller turbo. hth
The lack of torque is due mostly to your turbo. It's way too big for the intended operating range and HP. The little 3.8L just isn't pumping enough air until 5500 rpm to spin that turbo (especially with your combo). Even a 67 mm turbo will hit hard (very noticeable turbo lag) with stock heads.
You're likely blowing fuel out the exhaust. Too much valve overlap will hurt performance. The smaller cam will also bring the operating range lower - which will help spool and low rpm torque. Ball park 265* advertised on the intake, 275* exhaust, 118* LSA, and the lift will necessarily be lower. It's easier to estimate off a baseline, and the proper data logs.
As big as the ports are, you will pick up air speed with a good valve job and blending. Air speed benefits everything.
1-7/8" headers are WAY too big for your actual HP, and they kill spool. 1-5/8" headers are plenty big for the 3.8 (watch back pressure). A divided manifold will spool sooner. I came across a "quick spool valve" by suprastore...that will help as well (works with an open manifold).
If you want low end torque, you have to do several of these things. You may find that with porting, the right cam, and headers, QSV, that you'll be happy with the GTX4202. If not, consider a smaller turbo. hth
don't l feel like an a$$. l didn't read the whole thread last year, when l posted, and not until just now :/ A low 9 second V6 street car is surprisingly doable.
You have a 270 ci V6: 4.00" x 3.59"
2.10" x 1.625" valves
First, the 232 will behave very differently than the 270. I spec'd a cam for the 231, assuming 2.02" valves. The 270 will run and perform completely differently. You can't cam it and turbo it like a 270 and expect ANY correlation. I think your low end torque issue is the 2.100" valve on a 232
I'm surprised a 4" bore head fit on a 3.8" bore without issues. I'd expect some gasket issue, if not fuel pouring onto the ledge.
Turbos are not power adders...they multiply. So, start off with a naturally aspirated 270ci. You should aim for about 400 bhp @ 6500 rpm (that's only 80% VE). That's roughly 1000 bhp with 29 psig, 900 with 18 psig. The better the base engine, the better the turbo engine.
230/230* 112* LSA 110 Int CL (NOT a turbo cam)
EVO 49*
EVC 1*
IVO 5*
IVC 45*
This motor is basically 3/4 of an LS2...and close enough to an LS3...or LS9. It can be cammed similarly. Take a look at Lingenfelter's LS9 GT9 cam - 215*/247* 121* LSA. It's spec'd to have stock idle, and work with stock heads to 6000 rpm.
EVO 58.5*
EVC 8.5*
IVO -7.5*
IVC 42.5*
Very different than your 230* cam, eh? Notice the GT9 cam opens the intake much later (reduce blow through), and opens the exhaust earlier (quicker spool and blow down). Late IVO will NOT hurt rpm...you need to delay IVC several degrees. Note that it's more accurate to work off of advertised duration.
Can you post ported flow figures when available?
btw, those ramp rates are VERY quick. How is valvetrain deflection with those 240# springs? (i.e. lift at the valve). Comp has some VERY nice LSX cams EHI/EHX that will rev to 8000 and .800" lift with 150# conical springs and short travel hydraulic lifters. Perhaps they can grind you a gentle cam for the Stage II. Hollow intake valves will help greatly.
fwiw, l'm a powertrain judge at a Formula SAE type event in Canada. Undergrads have access to $30,000 engine simulation software, such as Ricardo WAVE and GT Power. I've seen bright students correlate their model with dyno results...with the WRONG cam. They need a LOT of detailed information from expensive sensors. A $500 program has a snowball's chance in hell of being accurate - that's why it's performance "trends". You can learn from it, but don't get hopeful because you get close to a peak number under a single condition.
You have a 270 ci V6: 4.00" x 3.59"
2.10" x 1.625" valves
First, the 232 will behave very differently than the 270. I spec'd a cam for the 231, assuming 2.02" valves. The 270 will run and perform completely differently. You can't cam it and turbo it like a 270 and expect ANY correlation. I think your low end torque issue is the 2.100" valve on a 232
I'm surprised a 4" bore head fit on a 3.8" bore without issues. I'd expect some gasket issue, if not fuel pouring onto the ledge.
Turbos are not power adders...they multiply. So, start off with a naturally aspirated 270ci. You should aim for about 400 bhp @ 6500 rpm (that's only 80% VE). That's roughly 1000 bhp with 29 psig, 900 with 18 psig. The better the base engine, the better the turbo engine.
230/230* 112* LSA 110 Int CL (NOT a turbo cam)
EVO 49*
EVC 1*
IVO 5*
IVC 45*
This motor is basically 3/4 of an LS2...and close enough to an LS3...or LS9. It can be cammed similarly. Take a look at Lingenfelter's LS9 GT9 cam - 215*/247* 121* LSA. It's spec'd to have stock idle, and work with stock heads to 6000 rpm.
EVO 58.5*
EVC 8.5*
IVO -7.5*
IVC 42.5*
Very different than your 230* cam, eh? Notice the GT9 cam opens the intake much later (reduce blow through), and opens the exhaust earlier (quicker spool and blow down). Late IVO will NOT hurt rpm...you need to delay IVC several degrees. Note that it's more accurate to work off of advertised duration.
Can you post ported flow figures when available?
btw, those ramp rates are VERY quick. How is valvetrain deflection with those 240# springs? (i.e. lift at the valve). Comp has some VERY nice LSX cams EHI/EHX that will rev to 8000 and .800" lift with 150# conical springs and short travel hydraulic lifters. Perhaps they can grind you a gentle cam for the Stage II. Hollow intake valves will help greatly.
fwiw, l'm a powertrain judge at a Formula SAE type event in Canada. Undergrads have access to $30,000 engine simulation software, such as Ricardo WAVE and GT Power. I've seen bright students correlate their model with dyno results...with the WRONG cam. They need a LOT of detailed information from expensive sensors. A $500 program has a snowball's chance in hell of being accurate - that's why it's performance "trends". You can learn from it, but don't get hopeful because you get close to a peak number under a single condition.
This thread is interesting. From what I've already seen you'd need to know the intake pressure and the exhaust back pressure to be able to nail cam timing events. Reducing overlap with fast ramps while opening ex sooner and closing ex at or near tdc has worked for a long time on turbocharged engines. Spreading the lobes for a given pair of lobes spools slower but is required In a lot of instances to help with valve events. There's a crap load of data out there on 400-500ci v8 applications and not so much on v6 applications. A 1200hp 500ci v8. Meh. You could make all kind of mistakes and still make the power.
Nail on the head. Most of this thread is above my knowledge, but I'm getting there slowly. But, that's why these cars give you such a sense of accomplishment; not everyone is capable of getting them to run the number.
turbobitt
Well-Known Member
- Joined
- Feb 14, 2002
Cam is not as aggressive as you think. I've analyzed those lobes and they loose intensity on a Buick cam core. I made 900+ hp on what you would refer to as "not a turbo cam" and from the same lobe family as the mentioned cam at the same spring loads.
AG
Like I said before stage 2 heads have a gazillion hours of R and D in them. My first stage 2 heads were originally priced for $10000. I would love to run a set of unported stage 2 on the street, I wonder how the flow #'s would compare to a set of raised port GN1R's. I wonder if the same principle that has been applied to making the GN1 and TA heads so fast and competitive in TSO be applied to a set of unported stage 2's. I am sure that someone has done this, I just don't recall ever reading anything.
Large diameter 240# springs, super long pushrods, 11/32 stems, solid roller - 1960s BBC tech. That's what Smokey had when he developed the Stage ll in the early 1980s. Modern lobes rev to 8000 rpm with hydraulic rollers and 150# seat pressure (this is VERY impressive).
So, how did you analyse your lobes, and how do you qualify an "aggressive" cam?
While 900+ bhp is very impressive, you seem to imply the "900+" is the most it could have made. There's a Procharged Chevelle that ran at Bradenton last year. It went from a 4.4x s 1/8th mile to a 4.1x with JUST a cam change. That works out to 20+% more hp. So yes, l have strong evidence to believe in a "turbo cam".
rag231: The tools available until recently were very primitive. I challenged the maker of swirl and tumble meters to admit that they don't work. He admitted that you need CFD to see what air/fuel is doing in a running engine - and those tools are still available mainly to OEMs. I'm super impressed with the gen v 4.3L V6; and there's still room for improvement.
turbobitt
Well-Known Member
- Joined
- Feb 14, 2002
I have not yet even began to turn up the power and exploit the potential..... But then again, what do I know. Only ran 8's on my first try @ heavy 3650#. Guess not good enough.
BTW - 900+ was all it could have made on the old junk turbo. I have enough data to support that its not camshaft related restrictions.
I'll just step aside and let the experts do the talking.
AG.
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Those lobes were some of the most non aggressive lobes we've seen.
