Turbo cam question

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Shaker im very interested to hear about this 12.95 run you did. So you were completely stock except for a 2 barrel and a turbo? What carb did you use? How much boost did it take?
 
What is muffler(s) is everyone using for their turbo setups? I've heard not to use flowmaster because they make back pressure which is what you don't want in a turbo setup. So what are you guys using?
 
bblock383 said:
What is muffler(s) is everyone using for their turbo setups? I've heard not to use flowmaster because they make back pressure which is what you don't want in a turbo setup. So what are you guys using?
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Most don't run any, the turbos themselves act like mufflers!
 
Well if I thought I could get away with it or if I had a strip only car but this is a street car so it needs to pass inspection so muffler is a must. I have a cherry bomb 2 muffler on it but its not a straight though muffler and I'm guessing will have the same back pressure problems as the flowmaster. I've heard some people run the race bullet mufflers. It is a straight through design.
 
Any boosted application will require wider lobe centers. Forget everything you know about naturally aspirated engines, as boosted applications require a different throught process.

The reason for wider LC's is to prevent your engine from dumping the fresh [pressurized] air-fuel charge down the exhaust pipe. In short, unless you're running a full on race car (wide open throttle only), you will LOSE power trying to cruise with a cam on tight centers - and it will be a dog on the bottom - and/or very peaky.

I've ran quite a few blower motors over the years (Roots style from BDS) and, yes, the "milder" cams don't have much thump, because there is no reversion (sucking back at the exhaust port due to over lap on the intake and exhaust valves when the piston starts traveling down, and short LC's) with wide lobe centers and a supercharger. However, you can buy blower cams that thump hard - but you'll be wading into "race" territory with your build...

Additionally, your volumetric effiiciency will go up with wider lobe centers as it's not unusual for boosted applications to run over 100% VE.

My advice is to talk to someone who specializes in your application. For roots type blower, I call Craig Railsback (BDS), Don Hampton, etc. For turbo applications - discuss your build with persons specializing in centrifigal blowers. Why gamble when there's a wealth of knowledge from people that have decades of experience ? You'll be much happier in the end. The guys at Comp also sell to the blower crowd and they are very knowledgable - provided they get full disclosure from the builder on intended use.

With blowers, 112-114 centers are the norm. A good "RV" cam works very well with blowers too, on the street. Who needs a thumping cam when you've got that 8MM drive belt screaming, or blow-off valves purging, everywhere you drive it ?

Southernman
 
bblock383 said:
Shaker im very interested to hear about this 12.95 run you did. So you were completely stock except for a 2 barrel and a turbo? What carb did you use? How much boost did it take?
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The 12.95 was not with a 2bbl. It was with a 600cfm Holley DP. The engine was stock except it had shimmed valve springs. It still had the exhaust manifold on it as well. I was running around 21 psi of boost. The car would have gone faster except for the skinny 215/75/14 tires. this was with a 2.5" exhaust system and a stock 87 GN turbo.

I eventually upgraded the turbo, built a header, and put a 3.5" exhaust on the same engine. I put a copper headgasket on the engine and head studs as well. I upped the boost to almost 30psi and the car responded with a 11.77 @ 117 mph shifting at 4700 rpm. Same tires but added 200 lbs to the trunk for a race weight of 3500lbs.
 
I suggest anyone interested in the subject pick up a copy of the HOT ROD article in question.. prob in the HR archieves. Aw, hell I'm in agood mood..here ya go now read and read again .. then when you think you understand.. readit one more time.. not trying to a smarty pants.. just want you to understand.. Note cam info, later turbo design info etc etc.. A 115 on an old to3 or to4b is NOT the same as a BB whatever.. good luck! A little infomation quoted incorrectly is bad info..
 
I tried to attach the complete article.. No go.. file too big.. i am a mental midget when it comes to computter chit.. anyone help upload the thing?
 
Back to the LSA thing, there is another factor with the wider angle that hasn't been mentioned.
Not only does the wider LSA reduce the overlap, but it opens the exhuast valve sooner before BDC. Given that the charge is being forced in moreso than in an N/A application, the exhuast event begining sooner before BDC uses some of the expansion from the combustion to help evacuate the spent charge from the cylinder. (This is also found in supercharger/nitrous specific cam profiles)
The tradeoff with this is that some of the power is bled off at the same time.
In a turbo application, this also has a secondary plus. Since the spent gasses are exiting the engine sooner after the combustion event, they're hotter, and still expanding. This aids the turbo in spooling up. Whereas with a tighter LSA, the turbo is trying to spool boost into the motor, while the intake side is being corrupted by exhuast gas reversion from the valve overlap. So you have pressure on both sudes of the turbo shaft which impeads the turbo from spooling up.
 
bblock383 said:
Well kid do you think ill have to make any mods at all? I can't imagine having to do any of that with only. 440 lift n stock compression. Also can you elaborate more on having to change the exhaust seats for boost? Do you mean that just new seats need to be put in?
if that's the case then that's already gonna happen with the head rebuild. I plan to do a few things to keep the hot spots down to help with detonation.
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Shaker223 said:
He is talking about hardened seats to run unleaded gasoline. They are not specific to "turbos".
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what he said... the pre-73 "soft seats" were designed to have lead in the fuel which acted as a lubricant between the seats and valve surfaces, without the lead its like running without oil (not that it wont still last awhile) but its a cheap and and must have on any lead free engine...
 
I seen a show on TV where they were experimenting with NOS Grinds for camshafts. They used a fairly agressive cam choice for a NA Engine then a Radical grind for a NA Engine, then lastly they used a NOS Specific Grind camshaft that they "thought" would make alot more power than the other NA Camshafts all on an engine Dyno. They were DEAD wrong. BOTH NA Camshafts made more power than the NOS "Specific Grind" camshaft ever thought about making. This was with a 200 Shot of NOS IIRC.
So moral of the story is just because it is supposed to make more power because the box says "NOS or TURBO CAM" specific does not mean that it always will!!
 
Mad Dart said:
I seen a show on TV where they were experimenting with NOS Grinds for camshafts. They used a fairly agressive cam choice for a NA Engine then a Radical grind for a NA Engine, then lastly they used a NOS Specific Grind camshaft that they "thought" would make alot more power than the other NA Camshafts all on an engine Dyno. They were DEAD wrong. BOTH NA Camshafts made more power than the NOS "Specific Grind" camshaft ever thought about making. This was with a 200 Shot of NOS IIRC.
So moral of the story is just because it is supposed to make more power because the box says "NOS or TURBO CAM" specific does not mean that it always will!!
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so true...

i have an old friend, almost in his 70's now... he built/raced/races kawi triples... he has two boosted bikes, one original top fuel from the 70's (boosted and N02) and a turbo think 500... it runs 60psi boost no lie...

he told me with boost it just needs to get it in... so either alot of lift and no duration, or the other way around... he likes alot of duration because its easier on valve train...

and also scavenging is worthless when you have pressure, dont want it or need it...
 
Valvebounce said:
Back to the LSA thing, there is another factor with the wider angle that hasn't been mentioned.
Not only does the wider LSA reduce the overlap, but it opens the exhuast valve sooner before BDC. Given that the charge is being forced in moreso than in an N/A application, the exhuast event begining sooner before BDC uses some of the expansion from the combustion to help evacuate the spent charge from the cylinder. (This is also found in supercharger/nitrous specific cam profiles)
The tradeoff with this is that some of the power is bled off at the same time.
In a turbo application, this also has a secondary plus. Since the spent gasses are exiting the engine sooner after the combustion event, they're hotter, and still expanding. This aids the turbo in spooling up. Whereas with a tighter LSA, the turbo is trying to spool boost into the motor, while the intake side is being corrupted by exhuast gas reversion from the valve overlap. So you have pressure on both sudes of the turbo shaft which impeads the turbo from spooling up.
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Great post!!! Lots of good information there!

Keep 'em coming!!!:cheers:
 
Another thing I've found with supercharged engines, is that when using a larger (blower friendly) grind, the engine makes more power, and has a reduced boost figure. Boost is only a measure of resistance between the "pump" and the valve. If the engine has a better flowing port, and/or a peppy cam, more charge gets into the cylinder, and less boost is made. Since a turbo's boost is regulated by the wastegate, a better flowing tract will get more charge in and make more power. (Or will make the same power at less boost) Less boost pressure means the charge heats up less. (And it therefore has greater density) and cooler charge is less prone to detonation, and places less stress on everything.

I'm a little bit power mad, but I think it's a sin not to uprate the camshaft when force-feeding.
 
Mag00 said:
I tried to attach the complete article.. No go.. file too big.. i am a mental midget when it comes to computter chit.. anyone help upload the thing?
Click to expand...
Bill, try the march 2008 HOT ROD.. It may be online.. did not check.. email me if you want a scan
 
Mag00 said:
Bill, try the march 2008 HOT ROD.. It may be online.. did not check.. email me if you want a scan
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Thanks, Magoo...

I was the recipient of lots of good advice from folks who had apparently read and digested the contents of that article, and benefitted greatly from Tom Wolfe and Ryan's advice when building our system.

Kudos to those guys for tons of good advice....:cheers:
 
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