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Forced Induction This section for the traditional Pontiac V8

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Old 10-29-09, 08:29PM   #61
baron_
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...the more I play with this carb, the more I see why carb builders ask 100 details of your engine combo to custom build you a carb


I don't think there's a single hole on the metering block that I haven't changed
LSAB's are the only thing stock at this point
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Old 10-29-09, 10:53PM   #62
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email "tuner" on the turbo forums hes good guy and will help you out.

Hes buddies with Tom V. who would also probably be a good guy to speak with about the carb.
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Old 02-01-11, 01:01AM   #63
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Default carb verses efi

I am just making my way through all this information and I have a couple comments. From 1979 to 1991 I ran a 800 CFM double pump holley with 13 PSI boost. The only modifications I did to it back then was drilled out the power valve orifaces, ran a 2.5 power valve, ran 72 jets on the primaries and 95 jets on the secondardies. I didn't have very much information to go on back then, no internet, only type of cars had turbos so I had to firgue stuff out for myself mostly and make my own parts. The presure box i made for the carb was basicily a standard 14" air filter with no air filter and welded up all the way around to close it up but I also welded in vanes to redirect the air into the carb straight. I getting off topic because the main issue for me back then was how to deal with the denisity change of the boosted air when a carb works on volume of air creating a presure drop at the venturi. The carb has no way of adjusting for density, or at least 20 years ago there was no way that I was able to find, to deal with it. That is why I have chozen to to go with a FAST efi this time because it can be tuned to deal with this issue. It doesn't directly sense air density but by combining boost and intake temp, it can add the correct amount of fuel for all conditions. I haven't got the engine running yet but should be able to start it again in the next few weeks and am looking forward to the adjustablity of efi, the amount of knowledge there is no days on turbos etc (BIG difference compared to 20 years ago) and this time having all the good parts to make thius work reliablely. (the only parts I have reused from the 1980's engine are the head castings, valve covers (with extra thick gskets to clear the roller rockers), brackets for the alternator and the dip stick thats it!
If there is a way to now deal with density change using a presurized carburator, i would be interested in hearing about it. (for old times sake)
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Old 02-01-11, 01:24AM   #64
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John...they use boost referenced power valves in the carb now.
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Old 02-02-11, 11:44PM   #65
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X2
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Old 02-04-11, 03:10PM   #66
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That is really interesting, I was thinking about how to do that back then but didn't have access to a machine shop etc, and never tried anything. My problem was how to get the boost referance signal to the power valve, I was thinking of making a new float bowl etc but it was just too much work. Do you have any pictures of how it is done? It is still not ideal in my mind because you would still have only one point in the density change slope that would be correct, unless they came up with a analog (variable) control for the power valve instead of on/off but it would still be much better then running the 2.5 that I did.
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Old 02-04-11, 07:31PM   #67
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Contol fuel curve with restricted HS bleeds, enlarged/extended bowl vent ?????, and positive pressure to PV vac source port. Enlarging pv channel restrictions as well. Of course boost referenced fuel regulator using high pressure pump.
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Old 02-04-11, 10:04PM   #68
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I dont have any pictures, but if you contacted Kevin at CSU he could probably help you....he builds these things and his product is great. I cant really say how he knows exactly what to do except through experience, but its not just meeting the curve at one point. Basically his carbs are spot on for N/A operation, but as boost is added the carb releases more fuel....Bruce has the basic points listed above. The more boost (air) the more fuel, and somehow he really has it dialed in. With no boost cruising at 2500 rpm I'm right around a 15 to 15.5 A/F ratio. The more I get into it the lower that gets, and under max boost (I've really only opened the car up to 8 psi so far, though I know Mark ran her at 15 a few times) my A/F dropped to 10.2-10.4. Nice and rich, with some room to adjust and tune as I go further. I'll probably move her toward 10.8-11 at 10 psi as time goes on once I have her back together.....still safe.
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Old 02-05-11, 04:39PM   #69
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because I am still trying to firgue out this web site I hadn't see the first messages under this thread and now that I have started from the first one and read all of them it is really interesting to see the development that has happened with blow through applications, back when I did it, I could only read plugs to tell air fuel mixture, so really there was no way of getting into the tune so extensively. What is really interesting is no being on the EFI side and compairing the two, it seems they are very similar now but one side is doing mechaical changes and the other side is doing programming changes. It looks like the denisity change issue has been worked around by changing multiple things. I am curous though these days if both methods are very similar in tuning why someone would choose blow through and have all the work of changing a bleed hole size verses punching in a new number on the computer? Is is the cost completely or is there the fear issue as well, so people are way more comfortable with something you can see and touch vs numbers on a computer. By the way I am using a Fast system and the main reason I picked the fast unit was it, at the time, was the only one that could control boost vs MPH. I had some much problems hooking up back then that this function really impressed me. I plan on not bringing in full boost until at least 70MPH maybe more. (street tires)
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Old 02-05-11, 05:00PM   #70
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Yeah I think its mostly the cost but some are a bit scared of it as well.
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Old 02-06-11, 11:43AM   #71
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Sometimes the cost. Just buying a built carb, even at $1000 is much more affordable using everything else that one might already have. I know looking into EFI several years back, modifications to my manifold for injectors and building fuel rails alone were more than $400. I had an 830 Holley. Sent it to CSU. They made full modifications for $475 and about $20 shipping. So for $500 I was boosting. Of course this does not include the cost for the turbo system, but that cost would be added to both these systems, EFI or carb. The carb also affords a small amount of intercooling thru the carb as well, due to the atomization at the venturies. BUT. The infinite tuning capability of a good EFI system makes the initial outlay of money more than a good deal for a street/strip driven vehicle. Street manners are so much more attainable and easier with proper tuning to make the engine a lamb on the street. The carb, while really good, still is limited. But if I can't afford to move over to EFI I will not hesitate to run my CSU carb. Mark L
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Old 02-07-11, 06:03PM   #72
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Excuse my ignorance Mark but what is a CSU carb? I see your point on costs, I have a speadsheet on my computer in which I filter all the costs on the car into catagories and my fuel injection section is at $4000 but the worse number is $2500 on fuel lines and I haven't updated the speadsheet parts for a long time, I would guess the cost for me to go to fuel injection this time is in the neigbourhood of $7500 but it could be done much cheaper. Those dare steel braided lines and fittings are small costs for each fitting but before you know it they really add up.
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Old 02-08-11, 12:42AM   #73
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OH god dont EVER count the money.LOL
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Old 02-15-11, 01:46AM   #74
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Default Super sticky turbo threads

All sticky thread have been move here
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Old 02-15-11, 02:32AM   #75
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LOL....I guess not
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