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I have a supped up 70 Riviera with a 455 thats been bored .60 over, has a TA stage 2 cheater cam, port and polish job. Soon I'll be adding some shorty headers, and 3in pipes. The 31 year old Q-jet is still working but since I drove it up to Colorado its been running too rich, I'm leary about putting more money into it since I bet it'll spring a leak soon and its too small a carb for the engine, especially if I go to an aluminium intake. Right now I'm thinking about either a Holley 770cfm Street Avenger or a Edelbrock 800 cfm Performer. Any help or advice would be appriciated.<BR>Thanks,<BR>Will<P>"There is no Replacement for Displacement"<BR>Carroll Shelby

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Carb. to small? Better get the carb number off the side of the carb (stamped vertically on the webbing - 704255 etc.)and do some checking before you spen a bunch of money on a SMALLER carb.<BR> Most late 60s very early 70s big cube motors had 700+ cfm up to the monster 850 cfm Q-jets on them.<BR> Also consider that the original carb is DEVELOPED for that motor not a universal aftermarket that will have to be tuned and "rigged" to replace your original.<BR> I realize you have made some upgrades, but the most your going to need for what you have done is to up the jetting a little. (and that should be based on spark plug readings after you fix the "running rich" issue).<BR> Find a GOOD carb. guy who is fimiliar with late 60s Q-jets and rebuild that monster!<BR>If you have a local drag strip, go and get a baseline then start making changes (ONE AT A TIME) from there. Don't expect huge changes, your original carb is going to be very close and I'm willing to bet it's faster than any aftermarket carb you can put on it!<BR> <BR>From the : "Been the done that" department.<P>Good luck<BR>Dale.

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I checked the numbers its the original 795 Cfm Q-jet, I know they are good carberators but its old and I'm leary about putting money into it, I've already had it rebuilt once but I don't know how much longer the actual body and big peices of the carb will last, I already got really nervous when it removed the jets the first time, I don't know how many more disassemblies it has left in it.<BR>Thanks,<BR>Will

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  • 3 weeks later...

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>I have a supped up 70 Riviera with a 455 thats been bored .60 over...<HR></BLOCKQUOTE><P>bored 60 over shocked.gif" border="0 <P>Wow, I hope you don't run into overheating problems on the street with that setup.<p>[ 09-01-2001: Message edited by: Straycat ]

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I have some problems right now but my fan clutch is defective to I don't move nearly as much air as I should be. I'm going to replace it with a heavy duty one and probably add an extra electric fan to move more air when I'm in traffic and not getting the air flow through the radiator, condensor, and tranny cooler I got mounted up there. I might add an oil cooler as well eventually but then I'll put 2 big electric fans and pull the stock clutched one.

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I used a 780cfm vacuum secondary Holley right out of the box on my 425hp 454 Chev that was bored .30 over. No problem.<P>With regards to the clutch fan, throw it away. If the clutch fails you'll be in big trouble. Replace it with as large a stainless steel flex fan that will fit in your shroud opening. Get the correct spacer so that the fan is about 1" from your rad or as close as the instructions suggest for the particular fan. The flex fan will work fine even with the extra coolers. As a matter of fact you have to be careful that you don't suck any Hondas, Nissans, etc. in.

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Probably quite right on both counts. But unless you have a new clutch in the fan I wouldn't trust a clutch fan after spending all that money on the engine. With a high performance engine with headers the hp loss will probably go unnoticed and you definately won't be hearing the fan too much. Actually the worst I heard for extra noise was the gear drive my buddy had in his 600hp + two NOS kit (one under the carb and one port injected) 482cid Chev street engine. The engine redlined at 8200 rpm. When he'd wind that thing up the gear drive sounded like a blower. Sorry for getting off the topic of the post but just the thought of it brings back some fond memories like being able to spin the 21 1/2" Mickey Thompsons while doing 50 mph. That was without the NOS!

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CTXSLPR ~ You are unregistered so I do not know where you took the car to Colorado from. Most flatlanders fail to realize that Colorado is HIGH and most everything taken to altitude will run rich. I brought 6 cars from the east coast to Wyoming [6000'] and all ran rich. The problem is, adjust them for altitude and they run lean when you go back to sea level.

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I built the car in Bryan/College Station, TX and then drove it back up to school in Colorado Springs, CO. I've pretty much decided to go to a 770 Holley Street Avenger, its gotten high marks from most of the people I've talked to. But I got a new question now, I have TA performance 1.60 ratio rockers in there I was wondering what would be the effect of going to 1.65 ratio rockers.<P>Thanks,<P>Will<P>"There is no Replacement for Displacement"<BR> Carroll Shelby

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Depending on what you're asking the car to do, 770 cfm might not be enough. I've had good experience with 850 Holley's on relatively mild 455's, and I think a modified engine, especially with headers, will like 1000 cfm just fine. I've had great fun with a Barry Grant 1000 cfm carb on my 0.030" over 455, even in a heavy car.<P>Regarding the effect of increased rocker arm ratio, it affects both valve lift and duration, but the change in duration is pretty insignificant compared to the effects of increased lift due to higher ratios.<P>The rocker is just a teeter-totter; if cam lobe lift is 0.300", and rocker ratio is 1:1, then valve lift is 0.300". With the same lobe lift and 1.65:1 rockers, the valve lift is 0.495". 1.60 rockers = 0.480" valve lift, all else the same. <P>The difference in performance isn't easy to guess, because it depends on carb, intake, cyl head, exhaust, etc. If there is a performance increase due to the higher rocker ratio (from 1.60 to 1.65:1), you should expect it will be a small one.

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Its still a street car so I'm thinking either 770 or 870 street avenger, anymore and I'm going to have terrible gas mileage, not good for a daily driver. Ok, now what about the difference between roller and regular rockers, I know the physicals differences but what about performance wise? <P>Thanks,<BR>Will

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