Speed Demon on a Big Block.....
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Speed Demon on a Big Block.....
Just trying to gauge how much carb I need. For those of you with Big Blocks and a Speed Demon - what type is it ????
For those with small blocks - pick a choice you'd run on a Big Block setup.
Details : 427 / 390hp engine with 2 1/2" exhaust
4-spd M-21 Muncie
3:08 rearend
For those with small blocks - pick a choice you'd run on a Big Block setup.
Details : 427 / 390hp engine with 2 1/2" exhaust
4-spd M-21 Muncie
3:08 rearend
Le Mans Master
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From: Was New Orleans but swam to Baton Rouge LA
Cruise-In IX Veteran
Re: Speed Demon on a Big Block..... (1bad69)
mechanical, no choke
If you have a 4 Speed go with the mechanical secondaries. I have had both and must say that the mechanical has the best response.
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From: NorCal
Re: Speed Demon on a Big Block..... (verskel)
You didn't mention what you would be running for cam, heads compression, etc, so I'll go out on a limb and assume it's mostly stock. I put down the 750 because I've used it successfully on three different mid range performance Ford BB engines. These were either 427 or 428 FE engines in Superformance Cobras with good heads, headers, decent intake with mild performance cams in front of manual transmissions. Performance is very good, the vacuum secondaries make for real smooth transition into the secondaries and my customers even get decent mileage. If you run a real agressive cam, heads and exhaust, then I'd vote for the 850 (or more) keeping in mind that drivability would be secondary to raw power.
These are excellent carbs. My only beef with the ones I have used is the aluminum throttle plates. One decent backfire through the carb and the plates are all junk (bent!). Barry Grant sells steel or brass replacements (available through Summit, etc.) that work great.
Hans
These are excellent carbs. My only beef with the ones I have used is the aluminum throttle plates. One decent backfire through the carb and the plates are all junk (bent!). Barry Grant sells steel or brass replacements (available through Summit, etc.) that work great.
Hans
Melting Slicks
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From: NC USA
Re: Speed Demon on a Big Block..... (Wrencher)
850 here.
I'd say if you are leaving the rest of the engine stock, go with the 750.
If you plan on building it for performance, get the 850.
BTW you'll need a new intake since the stock 390hp one is for a Qjet.
[Modified by Marks69BB, 3:57 PM 3/26/2004]
I'd say if you are leaving the rest of the engine stock, go with the 750.
If you plan on building it for performance, get the 850.
BTW you'll need a new intake since the stock 390hp one is for a Qjet.
[Modified by Marks69BB, 3:57 PM 3/26/2004]
Thread Starter
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Re: Speed Demon on a Big Block..... (Marks69BB)
850 here.
I'd say if you are leaving the rest of the engine stock, go with the 750.
If you plan on building it for performance, get the 850.
BTW you'll need a new intake since the stock 390hp one is for a Qjet.
[Modified by Marks69BB, 3:57 PM 3/26/2004]
I'd say if you are leaving the rest of the engine stock, go with the 750.
If you plan on building it for performance, get the 850.
BTW you'll need a new intake since the stock 390hp one is for a Qjet.
[Modified by Marks69BB, 3:57 PM 3/26/2004]
I'm currently running a 750 holley w/ vac. secondaries. :bb
I Do plan to increase cam size to either a 280 or 292 duration with more lift.
[Modified by verskel, 4:42 PM 3/26/2004]
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Safety Car
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From: South Central Louisiana
St. Jude Contributor
Re: Speed Demon on a Big Block..... (Corey 68)
:iagree: When it comes to carbs, Demons rule. And until Lars proved the theory, many would have said a 750 was all you need..... GO 850 :thumbs:
Instructor
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From: Suwanee GA
Re: Speed Demon on a Big Block..... (LAvetteman)
If you are running the intake for the 365 hp 454, you will need to change the intake to run a Demon. I have a 750 dp BG Carb on my 433 with cam, headers, etc...and it is plenty. The BG carbs flow at least 10% more than their rating. Also, the dp carbs run rich at idle-too rich for my motor. I leaned it some with IFR adjustments. 850 dp too much for your combo.
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From: NorCal
Re: Speed Demon on a Big Block..... (verskel)
'I Do plan to increase cam size to either a 280 or 292 duration with more lift.'
That's still a pretty mild cam for an 850, although there is something to be said for running "wet" (rich). You can run a bit more total timing on pump gas, even with relatively high compression without detonation depending on the lobe centers.
I run the stock 780 Holley on my BOSS 302 with a pretty wild cam, 1 7/8 inch headers, 11.0-1 compression and significant head work, all on 91 pump gas. I bumped the main jets 4 numbers to run it a bit rich, with great results.
Hans
That's still a pretty mild cam for an 850, although there is something to be said for running "wet" (rich). You can run a bit more total timing on pump gas, even with relatively high compression without detonation depending on the lobe centers.
I run the stock 780 Holley on my BOSS 302 with a pretty wild cam, 1 7/8 inch headers, 11.0-1 compression and significant head work, all on 91 pump gas. I bumped the main jets 4 numbers to run it a bit rich, with great results.
Hans
Racer
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Re: Speed Demon on a Big Block..... (Wrencher)
Barry Grant recommends in their literature that comes with the Carbs : 427 to 454 cid with up to 240 duration Cam Cat .050") : 750 CFM SpeedDemon.
I have a 468 cid , 240 duration Roller Cam , 9.6 CR , 4 speed... and am running a new SPeedDemon 750 with mech secs. The difference over a Quadrajet is phenominal. It is a very high quality carb, easy to tune, and comes with a detailed video. Go according to Lars' Demon Setup (bench and on car) List which is available thru him. Its VERY important when you are adjusting idle speed...to adjust BOTH the primary and secondary idle speed screws the same --- this is so the venturi transfer slot is correct, otherwise you could experience a stumble.
You can tell when you are full open on the primarys ...and when you are at that point...the car is really moving ; then....when you bring in the secondaries, its like you have half -a- pedal left ! Youre going to love the SpeedDemon ,for sure.
Dave
I have a 468 cid , 240 duration Roller Cam , 9.6 CR , 4 speed... and am running a new SPeedDemon 750 with mech secs. The difference over a Quadrajet is phenominal. It is a very high quality carb, easy to tune, and comes with a detailed video. Go according to Lars' Demon Setup (bench and on car) List which is available thru him. Its VERY important when you are adjusting idle speed...to adjust BOTH the primary and secondary idle speed screws the same --- this is so the venturi transfer slot is correct, otherwise you could experience a stumble.
You can tell when you are full open on the primarys ...and when you are at that point...the car is really moving ; then....when you bring in the secondaries, its like you have half -a- pedal left ! Youre going to love the SpeedDemon ,for sure.
Dave
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Re: Speed Demon on a Big Block..... (Doug Brandon)
If you are running the intake for the 365 hp 454, you will need to change the intake to run a Demon. I have a 750 dp BG Carb on my 433 with cam, headers, etc...and it is plenty. The BG carbs flow at least 10% more than their rating. Also, the dp carbs run rich at idle-too rich for my motor. I leaned it some with IFR adjustments. 850 dp too much for your combo.
Sorry, my mistake, the intake is off a 425hp 454 vette motor. The 'stock' carb. listed in my book for this engine is the 850cfm Holley DP. :chevy
Right now, I'm suffering from a 'lean' idel with my 3310 which IMO is junk :cuss .....it's about 4 years old with about 6000 miles on it and part of Holley's discontinued Silver Series..... :mad :cuss