Jag åker med en 650 på min 427 och det är perfekt, felet folk ofta gör är att sätta på en alldeles för stor förgasare till ingen nytta...
Det finna bra fomler för att räkna ut en optimal fugge
/Tommy
Vässade bigblock corvetter
Jag åker med en 950HP som funkar utmärkt, 80/82 Här e ett litet stycke saxat från Corvetteforum.com som e skrivet av Lars Grimsrud.
"Let me do one more post on the subject... notice that a couple of the experienced guys who are running fast cars lean towards the bigger carbs....
First, I just want to make sure you realize that I don’t pull this stuff out of my butt. I’ve been racing and building cars for 30 years. I put myself through 8 years of college and a PhD through street racing, with winnings totaling over $100K. I hold 2 NHRA Super Stock records (SS/KA). My Doctorate is in Medical Engineering with an emphasis in Thermodynamics (which includes concepts like internal combustion engines). I taught at the GM training center in Salt Lake as an advanced instructor for Carburetors, Ignition Systems, and Automatic Transmissions. I have been restoring and modifying musclecars since 1974, and currently own a large automotive restoration facility in addition to my job as the Manager for the Lockheed Martin Space Systems Propulsion Laboratory. I have rebuilt over 400 Q-Jet, Holley and Barry Grant carbs over the last 5 years. I am the carb builder for the 2000 and 2002 Bonneville World Speed Record Holder in the Stock Body Class. I’ve done extensive actual dyno testing with Hot Rod Magazine and Dougan’s Engine Service at the Westech facilities in Los Angeles to compare and verify the things I talk about regarding carbs and ignition systems. I smoke cigars and I drink beer. I know what I’m talking about. So here are the facts:
First, regarding vacuum secondary carbs: A vac sec carb, even with the lightest spring installed, will seldom, if ever, actually get the secondaries wide open. In dyno runs, I consistently see that a 650 or 750 vac sec on a 350 will open the secondaries about halfway, even with the lightest spring. Forcing the secondaries manually open during the dyno run produces a massive power gain. Vacuum secondary carbs are nice for 4-wheel-drive vehicles where you don’t want to suddenly pop the secondaries open while you’re bouncing across rocks and trees. They’re also nice for motor homes and trucks with horse trailers where you don’t want to force the secondaries open under low-rpm load-pulling conditions. If you’re going to pull a horse trailer with your Vette, get a vacuum secondary 650.
Carbs are cfm rated at a given “Delta Hg” pressure. In other words, with a given pressure differential between the top and bottom of the carb, the carb will allow a certain amount of air to pass through. There are all kinds of graphs and formulas for figuring out how many cfm your engine needs. But fact is, at WOT (wide open throttle), your engine does not produce the Delta pressure that the carb is rated at. So the carb flows a bunch less than its rating. You can successfully “over-carburate” an engine and actually get a performance improvement – even at low rpm. We have proven this on the engine dyno over and over. Look at the guys who are running fast: They’re not running 550 or 650 cfm carbs…. I’ve run carbs as big as 1050 on a small block, and they idle just fine with no off-idle stumble once set up right. No… they don’t run rich because they’re big…
Keep in mind through all this that GM installed 750 cfm Q-Jets on engines 250 cid and bigger (the OHC Pontiac was 250 inches with a 750 Q-Jet). I spite of common misconceptions, the Q-Jet is NOT a vacuum secondary carb: It is a mechanical secondary carb with an airvalve to allow the secondaries to come in without the use of a secondary accelerator pump (a secondary pump would cost more).
I have run back-to-back tests of 650 and 750 carbs on engines down to 302 cubic inches (take a look at this month’s issue of Hot Rod Magazine: There is an article in there by Matt King on computer simulation versus actual power. The engine in the article is a 302 Ford. We ran that engine with a 650 and a 750 BG mech sec carb. The 750 consistently produced 5 more hp across the rpm range, and the results in the article are with the 750 mech sec carb as shown in the photo). Dyno runs typically start the pull at 3000 rpm, where the engine is placed under massive load and the carb is popped right open to WOT. On every run I have made, a 302, 327, 350 and 383 will take a 750 mechanical secondary carb slammed right open to WOT at 3000 rpm without any bog or hesitation, and it will consistently produce better power across the rpm range than a 650 carb.
I run a 750 Speed Demon mechanical sec carb with no choke on my stock 350 in a ’64 Roadster. It’s jetted to its out-of-the-box specs with a nice blueprint setup by yours truly. I can run this 4-speed car at 1000 rpm and punch the throttle wide open without dropping the clutch with no bog or hesitation (this is a much more adverse condition than an auto trans car with a 2000 stall stock converter). Performance off idle is identical to a vac sec carb, but at WOT, the mech sec carb walks away from the vac carb. No contest. I have shown this on the dyno and on the street repeatedly. My 23-year-old daughter drives this car with no problem. She has never been able to stall it or bog it. Guys - please tell me you’re bigger men than my daughter.
Of key importance on any BG or Holley carb is the initial bench setup of the throttle blade angles. This does NOT come set up right from the factory on either Holley or BG carbs. This involves setting the primary throttle blades to expose .020” of the transition slot, and then setting the secondary blades to match the primary blade opening exactly. Any idle speed change must involve re-setting both primary and secondary blade angles equally to produce equal air flow and bleed through all 4 corners of the carb. Failure to do so results in poor idle quality, improper mixtures (“This big carb runs too rich!”), and off-idle stumbles (“the carb must be too big”). I outline this in my BG Tuning article – contact me by e-mail if you want a copy.
Run a 750 on the 350. Run an 850 on anything bigger than a 427. Run a 650 or a 750 vacuum sec carb on your motor home and Dodge 4X4 truck. If you can’t get the carb to run right, send it to me, and I’ll set it up for you.
If you really want to run a 650 or a 750 vac sec carb, I'm sure you'll be just fine. I'll take your money from you at the next stoplight."
"Let me do one more post on the subject... notice that a couple of the experienced guys who are running fast cars lean towards the bigger carbs....
First, I just want to make sure you realize that I don’t pull this stuff out of my butt. I’ve been racing and building cars for 30 years. I put myself through 8 years of college and a PhD through street racing, with winnings totaling over $100K. I hold 2 NHRA Super Stock records (SS/KA). My Doctorate is in Medical Engineering with an emphasis in Thermodynamics (which includes concepts like internal combustion engines). I taught at the GM training center in Salt Lake as an advanced instructor for Carburetors, Ignition Systems, and Automatic Transmissions. I have been restoring and modifying musclecars since 1974, and currently own a large automotive restoration facility in addition to my job as the Manager for the Lockheed Martin Space Systems Propulsion Laboratory. I have rebuilt over 400 Q-Jet, Holley and Barry Grant carbs over the last 5 years. I am the carb builder for the 2000 and 2002 Bonneville World Speed Record Holder in the Stock Body Class. I’ve done extensive actual dyno testing with Hot Rod Magazine and Dougan’s Engine Service at the Westech facilities in Los Angeles to compare and verify the things I talk about regarding carbs and ignition systems. I smoke cigars and I drink beer. I know what I’m talking about. So here are the facts:
First, regarding vacuum secondary carbs: A vac sec carb, even with the lightest spring installed, will seldom, if ever, actually get the secondaries wide open. In dyno runs, I consistently see that a 650 or 750 vac sec on a 350 will open the secondaries about halfway, even with the lightest spring. Forcing the secondaries manually open during the dyno run produces a massive power gain. Vacuum secondary carbs are nice for 4-wheel-drive vehicles where you don’t want to suddenly pop the secondaries open while you’re bouncing across rocks and trees. They’re also nice for motor homes and trucks with horse trailers where you don’t want to force the secondaries open under low-rpm load-pulling conditions. If you’re going to pull a horse trailer with your Vette, get a vacuum secondary 650.
Carbs are cfm rated at a given “Delta Hg” pressure. In other words, with a given pressure differential between the top and bottom of the carb, the carb will allow a certain amount of air to pass through. There are all kinds of graphs and formulas for figuring out how many cfm your engine needs. But fact is, at WOT (wide open throttle), your engine does not produce the Delta pressure that the carb is rated at. So the carb flows a bunch less than its rating. You can successfully “over-carburate” an engine and actually get a performance improvement – even at low rpm. We have proven this on the engine dyno over and over. Look at the guys who are running fast: They’re not running 550 or 650 cfm carbs…. I’ve run carbs as big as 1050 on a small block, and they idle just fine with no off-idle stumble once set up right. No… they don’t run rich because they’re big…
Keep in mind through all this that GM installed 750 cfm Q-Jets on engines 250 cid and bigger (the OHC Pontiac was 250 inches with a 750 Q-Jet). I spite of common misconceptions, the Q-Jet is NOT a vacuum secondary carb: It is a mechanical secondary carb with an airvalve to allow the secondaries to come in without the use of a secondary accelerator pump (a secondary pump would cost more).
I have run back-to-back tests of 650 and 750 carbs on engines down to 302 cubic inches (take a look at this month’s issue of Hot Rod Magazine: There is an article in there by Matt King on computer simulation versus actual power. The engine in the article is a 302 Ford. We ran that engine with a 650 and a 750 BG mech sec carb. The 750 consistently produced 5 more hp across the rpm range, and the results in the article are with the 750 mech sec carb as shown in the photo). Dyno runs typically start the pull at 3000 rpm, where the engine is placed under massive load and the carb is popped right open to WOT. On every run I have made, a 302, 327, 350 and 383 will take a 750 mechanical secondary carb slammed right open to WOT at 3000 rpm without any bog or hesitation, and it will consistently produce better power across the rpm range than a 650 carb.
I run a 750 Speed Demon mechanical sec carb with no choke on my stock 350 in a ’64 Roadster. It’s jetted to its out-of-the-box specs with a nice blueprint setup by yours truly. I can run this 4-speed car at 1000 rpm and punch the throttle wide open without dropping the clutch with no bog or hesitation (this is a much more adverse condition than an auto trans car with a 2000 stall stock converter). Performance off idle is identical to a vac sec carb, but at WOT, the mech sec carb walks away from the vac carb. No contest. I have shown this on the dyno and on the street repeatedly. My 23-year-old daughter drives this car with no problem. She has never been able to stall it or bog it. Guys - please tell me you’re bigger men than my daughter.
Of key importance on any BG or Holley carb is the initial bench setup of the throttle blade angles. This does NOT come set up right from the factory on either Holley or BG carbs. This involves setting the primary throttle blades to expose .020” of the transition slot, and then setting the secondary blades to match the primary blade opening exactly. Any idle speed change must involve re-setting both primary and secondary blade angles equally to produce equal air flow and bleed through all 4 corners of the carb. Failure to do so results in poor idle quality, improper mixtures (“This big carb runs too rich!”), and off-idle stumbles (“the carb must be too big”). I outline this in my BG Tuning article – contact me by e-mail if you want a copy.
Run a 750 on the 350. Run an 850 on anything bigger than a 427. Run a 650 or a 750 vacuum sec carb on your motor home and Dodge 4X4 truck. If you can’t get the carb to run right, send it to me, and I’ll set it up for you.
If you really want to run a 650 or a 750 vac sec carb, I'm sure you'll be just fine. I'll take your money from you at the next stoplight."
Kasta inte bäver i trähus.
-
StingrayRacing
- Corvetteexpert
- Inlägg: 755
- Blev medlem: lör okt 25, 2003 16:51
- Ort: Västerås
Lars inlägg är beundransvärda, fastän det är en kaxig liten norrman! 
Annars kan man läsa detta: http://www.barrygrant.com/demon/default.aspx?page=5
Om vi nu ska diskutera storlekar....
Annars kan man läsa detta: http://www.barrygrant.com/demon/default.aspx?page=5
Om vi nu ska diskutera storlekar....
Lasse E
Corvette BigBlock 468 Coupe '72
454 +.060, Crane H.roller 226/234@.050, 288/296 adv .587/.610 lift 112 LSA w stud girdle, GM tuned 990 / 118cc, SRP forged pistons, forged rods & crank. Perf. RPM Air-Gap. Shaved Holley 850DP. MSD-6AL limit 6'
Corvette BigBlock 468 Coupe '72
454 +.060, Crane H.roller 226/234@.050, 288/296 adv .587/.610 lift 112 LSA w stud girdle, GM tuned 990 / 118cc, SRP forged pistons, forged rods & crank. Perf. RPM Air-Gap. Shaved Holley 850DP. MSD-6AL limit 6'
Grabbar grabbar.... I rest my case.....
VEM har sagt attjag åker med en 650 vac ? Nej då, en 650 DP sitter det i.... men det skulle räcka med en 570 cc fugge eftersom jag ALDRIG varvar mer än 5000 rpm och jag rejsar inte....
Läs artikeln igen och förstå att grabben snackar om att trycka plattan i botten utan problem... visst kan jag göra det också med en 850 och det bara sörplar till men jag pratar inte om det utan jag pratade om ekonomi.... Men gör som han säger så kan vi läsa av era stift tillsammans sen MoaAhaHahA
VEM har sagt attjag åker med en 650 vac ? Nej då, en 650 DP sitter det i.... men det skulle räcka med en 570 cc fugge eftersom jag ALDRIG varvar mer än 5000 rpm och jag rejsar inte....
Läs artikeln igen och förstå att grabben snackar om att trycka plattan i botten utan problem... visst kan jag göra det också med en 850 och det bara sörplar till men jag pratar inte om det utan jag pratade om ekonomi.... Men gör som han säger så kan vi läsa av era stift tillsammans sen MoaAhaHahA
-
StingrayRacing
- Corvetteexpert
- Inlägg: 755
- Blev medlem: lör okt 25, 2003 16:51
- Ort: Västerås
Fick du med koppling adaptern eller kör du automat?! Jag höll på att shoppa en 502 för ett par vinterar sedan från Scoggin Dickeys, men det blev lite dyrt då dollarn stod runt 10:-, så jag renoverade 468:an som jag har nu.frisk skrev:Motorn e på väg över vattnet. Det blev en ny 502:a
Hur gör ni med vevhusventilationen? Jag kör med helt öppna som mynnar ut vid sprängkåpan, men det blir skitigt i längden så jag funderar på någon annan lösning... Är det bra att ansluta den ena till insuget, eller finns det nackdelar med det?
Lasse E
Corvette BigBlock 468 Coupe '72
454 +.060, Crane H.roller 226/234@.050, 288/296 adv .587/.610 lift 112 LSA w stud girdle, GM tuned 990 / 118cc, SRP forged pistons, forged rods & crank. Perf. RPM Air-Gap. Shaved Holley 850DP. MSD-6AL limit 6'
Corvette BigBlock 468 Coupe '72
454 +.060, Crane H.roller 226/234@.050, 288/296 adv .587/.610 lift 112 LSA w stud girdle, GM tuned 990 / 118cc, SRP forged pistons, forged rods & crank. Perf. RPM Air-Gap. Shaved Holley 850DP. MSD-6AL limit 6'
Jag kopplade min vevhusventilation som den var original, med pcv-ventil i vänster ventilkåpa, och slang för vakum i insuget, slang från luftrenaren till höger ventilkåpa. Eftersom jag har rullvippor så har jag Moroso ventilkåpor som är lite högre. Kopplingen i ventilkåpan sitter nog precis där det sprutar olja, för jag fick en väldigt hög oljeförbrukning. Så tills jag kommer på någon bättre lösning så har jag bara dragit in slangarna i luftrenaren, det går ju bra så länge motorn är frisk och inte sölar ner. På en sliten motor med mycket vevhusgaser så skitar man ju ner förgasaren, och det påverkar även motorgången. Finns många mer eller mindre sofistikerade lösningar på detta.
"Janne 289"
"Janne 289"