new engine new carb?
Thread Starter
Le Mans Master
Joined: Jun 2008
Posts: 5,284
Likes: 235
From: Rockledge FL
new engine new carb?
Ok so my new crate motor will be here friday. The old engine has a speed demon 750 vacuum secondary for the time being will go on the new engine.
the techs at barry grant told me that my current speed demon would be "at its max" running the new motor but the next size up the 850 speed demon would be too big.
the motor itself is going to be a 454 crate motor with the GM oval port heads 2.19/1.88 valves.
cam is the comp cams roller cam
xr276hr
compression is 9.0:1
duration 276/ 282
at .50 224/230
valve lift .51/.51
lobe lift .301/.301
LS6 dual plane intake
headers
2500 stall
3.55 rear end
is my current 750 speed demon sufficient or should I look at something bigger.
the 825 mighty demon maybe?
the techs at barry grant told me that my current speed demon would be "at its max" running the new motor but the next size up the 850 speed demon would be too big.
the motor itself is going to be a 454 crate motor with the GM oval port heads 2.19/1.88 valves.
cam is the comp cams roller cam
xr276hr
compression is 9.0:1
duration 276/ 282
at .50 224/230
valve lift .51/.51
lobe lift .301/.301
LS6 dual plane intake
headers
2500 stall
3.55 rear end
is my current 750 speed demon sufficient or should I look at something bigger.
the 825 mighty demon maybe?
Last edited by baxsom; Jul 22, 2009 at 08:37 PM.
Le Mans Master
Joined: Jun 2004
Posts: 6,231
Likes: 65
From: Seattle WA
St. Jude Donor '14
IMHO, that's a relatively mild 454 and should do fine with with your existing carb unless you're going drag racing. It's definitely going to need a tune.
If you're turning the engine past 6K, then I'd say a new carb is in order. Where's your power peak?
If you're turning the engine past 6K, then I'd say a new carb is in order. Where's your power peak?
Thread Starter
Le Mans Master
Joined: Jun 2008
Posts: 5,284
Likes: 235
From: Rockledge FL
peak torque at 3500
i planned on driving a while and then a dyno tune.
i just wanted to make sure it wasnt limited by anything.
Thread Starter
Le Mans Master
Joined: Jun 2008
Posts: 5,284
Likes: 235
From: Rockledge FL
cool,
i was thinking i could use it and be fine but here is exactly what the tech at barry grant told me
The 850 annular is going to be too big and the 750 annular is just borderline big enough for it. The Speed would be fine up to .240 @ .050 and definitely a vacuum secondary since the converter is less then 3000. If I thought there were going to be changes made later I would go with the 800 Mighty Demon which is good up to .260 @ .050 and would be suitable for other combination changes as well.
Thank you,
i was thinking i could use it and be fine but here is exactly what the tech at barry grant told me
The 850 annular is going to be too big and the 750 annular is just borderline big enough for it. The Speed would be fine up to .240 @ .050 and definitely a vacuum secondary since the converter is less then 3000. If I thought there were going to be changes made later I would go with the 800 Mighty Demon which is good up to .260 @ .050 and would be suitable for other combination changes as well.
Thank you,
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Keep the one you have and see how the dyno tuning goes, if the engine is not getting 'fed' enough, they will let you know and advise you on what you should get. My 'guess' is that the 750 will be enough for your engine. If you can borrow a larger carb from a buddy...just for the dyno run....you can know for sure if the engine is leaving anything on the table with your present carb.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
A 750 will be plenty for anything short of running 6500+ all day. I had a 750 on my 69 for quite a while, then went to the 850. Lost a little bit of down low grunt, but picked it up on the upper end. I'm running a mechanical secondary (manual trans) so it pops a little harder when you jump on the go pedal. The vacuum carb would have been my choice with an auto.
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Drifting
Joined: Apr 2008
Posts: 1,540
Likes: 51
From: Lexington Park Maryland
Keep the one you have and see how the dyno tuning goes, if the engine is not getting 'fed' enough, they will let you know and advise you on what you should get. My 'guess' is that the 750 will be enough for your engine. If you can borrow a larger carb from a buddy...just for the dyno run....you can know for sure if the engine is leaving anything on the table with your present carb.
