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65 Posts
Holly 500 / 38DGAS
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15,217 Posts
A 38 DGAS is kinda small for a decent breathing 2.4. But when properly tuned it will give very good driveability and torque. The one nice thing about the Weber is that it isSO tuneable, but this very same tuneability can make it a pain to get right, as there are too many parameters which can be easily f****d up!
A Holley 500 will make more power however, I've run many of them on 2.0, 2.2, and 2.4 litre engines. (38 DGAS flows 330 cfm BTW). There are a few things that need to be modified to make the 500 Holley 'right' for any 4-cylinder Opel, the carburetor's idle circuits and power valve circuit are literally twice the size as those on a Weber (it was designed for a V8 after all), so it needs some reworking to retain good driveability. When I get home tonight, I'll look up the specs I used on my friend's 2.5 Opel, it should be *close* to what you require. At least it's a starting point for jets, idle circuit passages, power valve passages, power valve vacuum value, etc.
Bob
A Holley 500 will make more power however, I've run many of them on 2.0, 2.2, and 2.4 litre engines. (38 DGAS flows 330 cfm BTW). There are a few things that need to be modified to make the 500 Holley 'right' for any 4-cylinder Opel, the carburetor's idle circuits and power valve circuit are literally twice the size as those on a Weber (it was designed for a V8 after all), so it needs some reworking to retain good driveability. When I get home tonight, I'll look up the specs I used on my friend's 2.5 Opel, it should be *close* to what you require. At least it's a starting point for jets, idle circuit passages, power valve passages, power valve vacuum value, etc.
Bob
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65 Posts
Thanks Bob!!
ill be looking forward to those carb settings!!!
ive ben thinking about the intake setup for the holley....i was considering welding up and porting another manifold for the holley and cutting off the mounting plate for the weber and welding on one for the holley... would this be a better setup than a adapter plate on my existing manifold??
ill be looking forward to those carb settings!!!
ive ben thinking about the intake setup for the holley....i was considering welding up and porting another manifold for the holley and cutting off the mounting plate for the weber and welding on one for the holley... would this be a better setup than a adapter plate on my existing manifold??
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15,217 Posts
Yes, I've tried the Holley 390. You'd need a custom intake of course, I have a prototype made in the early '80's. Still required a ton of work to get good fuel distribution. But, 4-bbls are rated differently than 2-bbls. Multiply 390 cfm X 1.414 conversion factor....you get 551 cfm. Compare that to a 190 cfm Solex.....you can see that it's certainly NOT for a stock 1.9!
Joe, I dug out those specs on the Holley 500. The engine it was setup for is a 2.5 litre (97 mm bore x 85 mm stroke). Compression is 10.5:1. Cylinder head is a 2.4 with 1.94"/1.60" Chevy valves, and is extensively ported. Cam is hydraulic with .465" int/.440" exh lift, 222/218 dur. @ .050", 112 lobe separation. Exhaust manifold is a 2.4 unit, with 2.5" exhaust. Intake was cut open and fully ported. Inside runners were welded to increase the radius. Adapter used for Holley 500. Carb modified as follows:
>10.5" power valve
>72 main jet
>stock pump cam
>.025" pump squirter
>epoxy power valve orifice, redrill to .070" diameter
>epoxy idle circuit passages, redrill to .032" diameter
Hope this helps. I expect you will need different main jets, due to your larger cam, but all in all it would be a good starting point. The Holley was undriveable until all the passages were epoxied and redrilled.
Bob
Joe, I dug out those specs on the Holley 500. The engine it was setup for is a 2.5 litre (97 mm bore x 85 mm stroke). Compression is 10.5:1. Cylinder head is a 2.4 with 1.94"/1.60" Chevy valves, and is extensively ported. Cam is hydraulic with .465" int/.440" exh lift, 222/218 dur. @ .050", 112 lobe separation. Exhaust manifold is a 2.4 unit, with 2.5" exhaust. Intake was cut open and fully ported. Inside runners were welded to increase the radius. Adapter used for Holley 500. Carb modified as follows:
>10.5" power valve
>72 main jet
>stock pump cam
>.025" pump squirter
>epoxy power valve orifice, redrill to .070" diameter
>epoxy idle circuit passages, redrill to .032" diameter
Hope this helps. I expect you will need different main jets, due to your larger cam, but all in all it would be a good starting point. The Holley was undriveable until all the passages were epoxied and redrilled.
Bob
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65 Posts
Thanks Bob...... that should save me alot of stumbling.... i will gather all the parts and get the manifold done... probly install it next fall
In the mean time im going to get the 38 weber jetted just right... i like the challenge!!!
In the mean time im going to get the 38 weber jetted just right... i like the challenge!!!
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1,796 Posts
on a side note
Bob,
Have you ever tried the 38/38 dges carb as a pair on a "sprint" intake? With the simultanious opening butterflys it *should* work, shouldn't it? Probably too much carb for all but an all-out race motor, but would it compare to a long set of side-drafts and maybe take-up less space?
Bob,
Have you ever tried the 38/38 dges carb as a pair on a "sprint" intake? With the simultanious opening butterflys it *should* work, shouldn't it? Probably too much carb for all but an all-out race motor, but would it compare to a long set of side-drafts and maybe take-up less space?
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15,217 Posts
You could use two 38 DGAS's on the Sprint intake, but they actually flow less air than the OEM Weber 40 DFO's. Besides the smaller throttle plates, the DFO's have 30 mm or 32 mm venturis (can't recall offhand without physically checking), the DGAS's only have 27 mm venturis. The other issue is you'd have to completely plug the power valve passages. When using IR intakes (one barrel per cylinder), power valves are not used. The DFO's do not have a power valve.
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1,840 Posts
Holly carb
I use a Holly 650 cfm on a ram intake manifold that is setup
for the Holly 2 bbls.works great . note ( major eng. mods. )
this manifold is hard to find . I have also used the 500 &
agree you will need to play with jetting but is easy to get holly
acc. & reusable bowl gaskets . & you will be impressed with your
time & work invested in the project.
guyopel
I use a Holly 650 cfm on a ram intake manifold that is setup
for the Holly 2 bbls.works great . note ( major eng. mods. )
this manifold is hard to find . I have also used the 500 &
agree you will need to play with jetting but is easy to get holly
acc. & reusable bowl gaskets . & you will be impressed with your
time & work invested in the project.
guyopel
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2,731 Posts
Hey, guyopel, please tell me what is the "ram manifold" you just referred to, just how hard is it to find, and could it be even loosely considered "stock" on an opel GT?
Thanks!!!
Thanks!!!
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1,840 Posts
holley carb 500
Hi , the intake I have is a competition intake manifold built for holley 2bbls . I bought from Pacesetter in 1975 or so . I have used a 500 2bbl , but changed to the 650 2bbl & this has worked the best for me. this manifold has intake runners that are 50% longer than stock & larger port runners , this makes it almost at the heater box .
guyopel
Hi , the intake I have is a competition intake manifold built for holley 2bbls . I bought from Pacesetter in 1975 or so . I have used a 500 2bbl , but changed to the 650 2bbl & this has worked the best for me. this manifold has intake runners that are 50% longer than stock & larger port runners , this makes it almost at the heater box .
guyopel
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15,217 Posts
Ahh, the Pacesetter intake. Does this intake have the Holley carb situated sideways? I have one of those too. I got a chance to throw it on my flowbench once, and as good as it looks, it flowed worse than a stock intake that was ported for a Holley.
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