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Edelbrock 3704 vs Holley 300-66

Old 12-17-2018, 09:58 AM
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Edelbrock 3704 vs Holley 300-66

I have the Holley 670 CFM TBI on my stock 305 intake right now and the bore holes are way too small. I'm shopping for a more compatible intake and found the only two are Edelbrock 3704 and Holley 300-66. Edelbrock is 375 bucks, Holley is on sale for 20% off right now making their already cheaper intake down to 215.00. Anyone have any experience with these to parts to donate feedback on them? The Edelbrock is prettier but way more money and I'm all about functionality myself.
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Old 12-17-2018, 11:40 AM
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Re: Edelbrock 3704 vs Holley 300-66

I believe the Holley already has 2" bores which matches your 670. The Edelbrock unit does not but it can be bored out. It's been about 17 years since I used this intake but if memory serves me the Edelbrock is a straight swap (factory provisions for everything) which the Holley requires a few configuration changes to things that mount to the intake. The 670 is too large for anything other than a heavily modified TBI motor, and your'll need something with 2" bores. You may be better going with a carb intake and adapter plate.
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Old 12-17-2018, 12:33 PM
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Re: Edelbrock 3704 vs Holley 300-66

I'm using it on an LT1 350 now, been running well, but when I open it up it seems like there are RPM ranges where it's starving it. It's currently on a stock intake and the holes are too small. The gasket is thick to allow clearance from the undersized holes. I'm hoping the larger bore Holley intake will remedy this. Thank you for your reply Shifty. I'm at work now and I'm anxious to go pop the hood, I can't recall my heater hose location but I think it's already like the Holley. OH, by the way the Holley part number I'm using is the 502-6, thanks!

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Old 12-17-2018, 12:39 PM
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Re: Edelbrock 3704 vs Holley 300-66

Originally Posted by The Big Hat View Post
I'm using it on an LT1 350 now, been running well, but when I open it up it seems like there are RPM ranges where it's starving it. .
That's due to the stock intake manifold which is beyond choking your motor. I assume you are able to tune the EPROM with these changes? That is another huge variable. But you absolutely don't want mismatched port sizes in between the TBI and intake manifold like you have now. The stock intake is even worse if you have flow disturbance in the plenum.
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Old 12-17-2018, 12:44 PM
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Re: Edelbrock 3704 vs Holley 300-66

it has an old hyperchip in it but that means very little. I would like to once i get the correct parts put together have the ecm properly dialed in. I can tell i'm not scratching the surface of this things capabilities, it's not consistent at all.
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Old 12-17-2018, 12:48 PM
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Re: Edelbrock 3704 vs Holley 300-66

Originally Posted by The Big Hat View Post
it has an old hyperchip in it but that means very little. I would like to once i get the correct parts put together have the ecm properly dialed in. I can tell i'm not scratching the surface of this things capabilities, it's not consistent at all.
I would look into EPROM tuning right away before you put anymore parts on the car. At the minimum, correct your intake issue and then get right to tuning. I am surprised it even idles no less run.
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Old 12-17-2018, 01:01 PM
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Re: Edelbrock 3704 vs Holley 300-66

Yah, sometimes it takes a minute for the ECM to figure out what to do when i first start it. Another issue is there is a bit of a brain drain going on these days in my location. I don't know who I'd even take it to to have it tuned. Also, I'm waiting on a TV cable, there is something going on there it's way to hard to pull the thing since I had the tranny rebuild, the adjustable teeth on it are worn off the cable's end. When the cable comes I'm taking it to a different, more reputable transmission shop to find out what the last guy messed up.
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Old 12-17-2018, 07:33 PM
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Re: Edelbrock 3704 vs Holley 300-66

Originally Posted by The Big Hat View Post
I have the Holley 670 CFM TBI on my stock 305 intake right now and the bore holes are way too small. I'm shopping for a more compatible intake and found the only two are Edelbrock 3704 and Holley 300-66. Edelbrock is 375 bucks, Holley is on sale for 20% off right now making their already cheaper intake down to 215.00. Anyone have any experience with these to parts to donate feedback on them? The Edelbrock is prettier but way more money and I'm all about functionality myself.
The Holley appears to have the wrong style EGR mounting pad for a TBI EGR valve. The Holley may not have mounting pads for the AC compressor brace and the EGR solenoid and MAP sensor bracket. Hard to tell for sure because I can't find a proper photo of that side of the manifold.

The Holley will need modifications to the heater hose system.

The Holley pushes the TBI too far forward. You could have fun getting the throttle, cruise control, and Trans TV cables adjusted properly.

The Holley is apparently drilled for older heads where the six bolts per side go in at the same angle. You'll have to dick with that if you've got the newer heads that have the center two bolts on each side more vertical than the rest. The Eddy has the two center holes suitable for the OEM heads.

No promises on the ignition coil mounting posts on either the Eddy or the Holley. They look too close together to fit the TBI coil bracket to me.

For sixty bucks, you'd save a number of headaches buying the Edelbrock.
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Old 12-18-2018, 12:58 PM
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Re: Edelbrock 3704 vs Holley 300-66

Originally Posted by The Big Hat View Post
it seems like there are RPM ranges where it's starving it.
Ranges? Plural? MORE THAN ONE??? First Guess: NOT an airflow problem.


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Old 01-09-2019, 10:59 AM
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Re: Edelbrock 3704 vs Holley 300-66

Wow! Thanks Schurkey! That is a lot of useful information. Greatly appreciate it. I'm already fighting cable issues just with the Holley TBI on the stock intake. The bracket actually puts it back. I ended up cutting the end off the throttle cable and wrapping it around the stud and fastening it with an e-clip with a washer under it. clamped the cable's loop with a screw down barrel fastener. As for my cruise I haven't even begun that battle but yes, it is going to be one. Then for another thread... the TV cable is WAY to hard to pull I barely gas it and only drive it because it's my only transportation but it will not downshift on it's own.
Back to the airflow question it starves when opened up in the high RPM's. That's why I figured the butterflies being much bigger than the stock intake ports weren't doing me any favors.

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Old 01-09-2019, 12:26 PM
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Re: Edelbrock 3704 vs Holley 300-66

Originally Posted by The Big Hat View Post
I'm already fighting cable issues just with the Holley TBI on the stock intake. The bracket actually puts it back. I ended up cutting the end off the throttle cable and wrapping it around the stud and fastening it with an e-clip with a washer under it. clamped the cable's loop with a screw down barrel fastener. As for my cruise I haven't even begun that battle but yes, it is going to be one.
I have a Holley TBI, but I've never installed it. I wasn't expecting the throttle bracket to require different cable ends. I figured the stock cables would plug right into the Holley arm.

Originally Posted by The Big Hat View Post
Then for another thread... the TV cable is WAY to hard to pull I barely gas it and only drive it because it's my only transportation but it will not downshift on it's own.
Defective cable, or stuck valve in transmission. Cable should pull EASILY.

Originally Posted by The Big Hat View Post
Back to the airflow question it starves when opened up in the high RPM's. That's why I figured the butterflies being much bigger than the stock intake ports weren't doing me any favors.
Anything is possible, but lack of airflow is the LAST thing I'd suspect.

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Old 01-09-2019, 01:40 PM
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Re: Edelbrock 3704 vs Holley 300-66

The end of the cable fit on it fine but i only had about a quarter throttle. There was too much slack in the cable. On the starving at high RPM question, what would you suspect? Timing? Tune?
I also want to add: thank you very much for your input, I really do appreciate it. Not many older car guys where I'm at!
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Old 01-09-2019, 08:17 PM
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Re: Edelbrock 3704 vs Holley 300-66

Originally Posted by The Big Hat View Post
On the starving at high RPM question, what would you suspect? Timing? Tune?
I don't know what "starving" means, so I can't help other than to offer guesses: Not enough fuel, not enough exhaust system. Possibly weak ignition. Worn cam lobes, not enough valve lift.

What is the intake manifold vacuum at WFO-maximum RPM? Should be lower than 2". Lower is better.


Originally Posted by The Big Hat View Post
Not many older car guys where I'm at!
"Older". Yeah, I guess that describes me.

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Old 01-18-2019, 08:00 AM
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Re: Edelbrock 3704 vs Holley 300-66

By "older", I was referring to the car! For that matter, I'm 41 and too old to make any digs myself! Moreover, where I am few people run anything over 4 cylinders.

I think you are on the right path with cam related issues, I have what I believe is a lifter that is knocking when the engine is cold. It is accompanied by a miss that then turns to a partial miss, then stops missing when it runs a while. Maybe a weak lifter I figure. It sat for about 7 years. Maybe put some sea foam through it and if that doesn't clear it up pull the intake and replace the lifters?
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Old 01-18-2019, 08:04 PM
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Re: Edelbrock 3704 vs Holley 300-66

You could always have your stock intake bored to match your 2" TBI
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Old 01-19-2019, 06:30 PM
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Re: Edelbrock 3704 vs Holley 300-66

Best intake upgrade for a TBI is, a 4-bbl intake, and an adapter. You'll want an adapter that puts the TB back in the stock location, NOT the one that moves it forward or to the rear. I think the Holley is the one you DON'T want but I could be wrong.

For your situation I'd suggest a Performer intake and an adapter. Efff the EGR.

Meanwhile, the intake is NOT The Bottleneck in your motor. Its shortcomings are, in order, exhaust (every piece from heads to bumper), heads, & cam. THEN AND ONLY THEN will an intake make any material difference. Power comes from BURNING FUEL, but you can only get that to happen along with AIR FLOW, because you can't get the fuel to burn unless it's mixed with the right amount of air.

Think of your motor as being like a series of pieces of garden hose all strung together. Imagine you have a 25' piece of " followed by a 25' piece of " followed by a 50' piece of ". Now tell yourself, HOW MUCH MORE will that whole setup flow, AS A TOTAL SYSTEM, if you increase that " section to 1"? Or even to 1" or 2"? REALLY?

That's exactly the situation you are in now. Unless you have already cured The Bottlenecks as described above, dinking with the intake is just ... putting lipstick on a pig.
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Old 01-21-2019, 09:37 AM
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Re: Edelbrock 3704 vs Holley 300-66

Originally Posted by sofakingdom View Post
Best intake upgrade for a TBI is, a 4-bbl intake, and an adapter. You'll want an adapter that puts the TB back in the stock location, NOT the one that moves it forward or to the rear. I think the Holley is the one you DON'T want but I could be wrong.

For your situation I'd suggest a Performer intake and an adapter. Efff the EGR.

Meanwhile, the intake is NOT The Bottleneck in your motor. Its shortcomings are, in order, exhaust (every piece from heads to bumper), heads, & cam. THEN AND ONLY THEN will an intake make any material difference. Power comes from BURNING FUEL, but you can only get that to happen along with AIR FLOW, because you can't get the fuel to burn unless it's mixed with the right amount of air.

Think of your motor as being like a series of pieces of garden hose all strung together. Imagine you have a 25' piece of " followed by a 25' piece of " followed by a 50' piece of ". Now tell yourself, HOW MUCH MORE will that whole setup flow, AS A TOTAL SYSTEM, if you increase that " section to 1"? Or even to 1" or 2"? REALLY?

That's exactly the situation you are in now. Unless you have already cured The Bottlenecks as described above, dinking with the intake is just ... putting lipstick on a pig.
Having upgraded numerous TBI engines my order is a bit different. Exhaust, then intake manifold, then cam, then if it is still not enough power the heads. I have had a stock long block 350 gm goodwrench engine for a telephone company 1-ton van make 200 HP and 300 TQ to the wheels with headers, exhaust, and performer rpm intake.
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Old 01-21-2019, 11:51 AM
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Re: Edelbrock 3704 vs Holley 300-66

I'm sorry and I appreciate your input but I have some discrepancies here. I never said I had stock exhaust, in fact I never said what my exhaust was at all. I have edelbrock headers and Y-pipe running into 3" then to a three chamber flowmaster with 2.5" tailpipes, the converter is a free flow restrictionless. I agree fuel provides power but not by burning it, but by combusting it. Hence, fuel injection is superior to a carb in the respect that it offers far superior atomization - this is from a guy who can rebuild a double pumper blindfolded. To go with the idea of improved combustion I have also added a high voltage coil and a 6AL box. I appreciate a good carb setup but more for an old school build. I believe I may have seen this Sofaking post and it's pretty old. New products have been released for fuel injection since then. In my case I have to dig to confirm it but I think my lifters are possibly sticking or worn out or both because the car did sit for years, has a knock that goes away and the miss that accompanies it goes away with it. My TBI is rated at 670CFM and is enough to support more than 200HP, moreover an edelbrock 4150 should be able to make more than 200HP. If I want more than 300 heads and cam in that order I believe would be a better choice for me. A stock 350TBI truck motor makes 210HP and 300pnds of torque. Given those stock numbers I am hypothesizing I should be able to get much better HP and torque with a 670CFM TBI, Vortec heads and a well matched cam than stock.

I'm open to better suggestions if anyone has them, I could be wrong and objective to insight on this topic. Thank you.

I scrolled up, the post is 13 years old.

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Old 01-21-2019, 11:55 AM
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Re: Edelbrock 3704 vs Holley 300-66

Not too bad an idea, especially on a budget. I may talk to a machine man about that. Thank You!

this message for DMcain, i'll have to work on figuring out the functions of this site better! Apologies!

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Old 01-21-2019, 02:31 PM
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Re: Edelbrock 3704 vs Holley 300-66

Originally Posted by The Big Hat View Post
I'm sorry and I appreciate your input but I have some discrepancies here. I never said I had stock exhaust, in fact I never said what my exhaust was at all. I have edelbrock headers and Y-pipe running into 3" then to a three chamber flowmaster with 2.5" tailpipes, the converter is a free flow restrictionless. I agree fuel provides power but not by burning it, but by combusting it. Hence, fuel injection is superior to a carb in the respect that it offers far superior atomization - this is from a guy who can rebuild a double pumper blindfolded. To go with the idea of improved combustion I have also added a high voltage coil and a 6AL box. I appreciate a good carb setup but more for an old school build. I believe I may have seen this Sofaking post and it's pretty old. New products have been released for fuel injection since then. In my case I have to dig to confirm it but I think my lifters are possibly sticking or worn out or both because the car did sit for years, has a knock that goes away and the miss that accompanies it goes away with it. My TBI is rated at 670CFM and is enough to support more than 200HP, moreover an edelbrock 4150 should be able to make more than 200HP. If I want more than 300 heads and cam in that order I believe would be a better choice for me. A stock 350TBI truck motor makes 210HP and 300pnds of torque. Given those stock numbers I am hypothesizing I should be able to get much better HP and torque with a 670CFM TBI, Vortec heads and a well matched cam than stock.

I'm open to better suggestions if anyone has them, I could be wrong and objective to insight on this topic. Thank you.

I scrolled up, the post is 13 years old.
Headers, Performer RPM intake manifold with a 454 TBI on a marine adapter got me ~255 crank hp from a stock 8.75:1 compression ratio HD 190 hp factory rated 350 TBI long block. Same engine with 0.015" shim head gaskets, 1.6:1 full roller rockers and a factory GM LT4 camshaft put out 250 RWHP or about 320 HP at the crank with stock swirl ports.

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Old 01-21-2019, 02:38 PM
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Re: Edelbrock 3704 vs Holley 300-66

How much torque? Big Blocks aren't high rpm engines typically. I figure you had a nice amount of torque coming from that motor.
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Old 01-21-2019, 08:28 PM
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Re: Edelbrock 3704 vs Holley 300-66

Originally Posted by The Big Hat View Post
How much torque? Big Blocks aren't high rpm engines typically. I figure you had a nice amount of torque coming from that motor.
Small block 350 engine with a 454 TBI unit on it not a big block engine.

Torque was over ~300 ft/lbs at the tires from 2,500-4,500 with about 320 ft/lbs @ peak around 3,000.
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Old 01-22-2019, 07:48 AM
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Re: Edelbrock 3704 vs Holley 300-66

I see, it sounded like you were comparing a 454 to a 350. I don't dispute that at higher rpms a carb does make more hp because it's dumping more fuel. That's the upside to the carb. In my case, I don't want to go through the trouble of switching for one. Traditionally fuel injection offers better low end torque and hp that's been the trade off as I have understood it, especially in terms of TPI. I just want to get the most out of my current setup. A carburetor only needs 4-8 pounds psi, my electric pump pushes much more than that and would have to be either regulated, which I'd think would cause the pump to burn out fast or eliminated and I'd have to run a mechanical pump or inline electric. along with the mods needed to do that. Another concern I actually do have because I drive it every day is fuel consumption. I get about 25mpg on the highway now, Being that gas is expensive and I'm not racing I enjoy the cheaper fuel bill.
Since I have you though, what about boring out the stock manifold? At least I could just bolt the TBI on without having to use a thick gasket that funnels it down to a smaller intake hole.

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Old 01-22-2019, 08:31 AM
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Re: Edelbrock 3704 vs Holley 300-66

Originally Posted by The Big Hat View Post
I see, it sounded like you were comparing a 454 to a 350. I don't dispute that at higher rpms a carb does make more hp because it's dumping more fuel. That's the upside to the carb. In my case, I don't want to go through the trouble of switching for one. Traditionally fuel injection offers better low end torque and hp that's been the trade off as I have understood it, especially in terms of TPI. I just want to get the most out of my current setup. A carburetor only needs 4-8 pounds psi, my electric pump pushes much more than that and would have to be either regulated, which I'd think would cause the pump to burn out fast or eliminated and I'd have to run a mechanical pump or inline electric. along with the mods needed to do that. Another concern I actually do have because I drive it every day is fuel consumption. I get about 25mpg on the highway now, Being that gas is expensive and I'm not racing I enjoy the cheaper fuel bill.
Since I have you though, what about boring out the stock manifold? At least I could just bolt the TBI on without having to use a thick gasket that funnels it down to a smaller intake hole.
I also never said I ran a carb. I used a Performer RPM intake manifold + Mercruiser Marine TBI to Carb intake adapter + 454 TBI unit on stock small block 350 with headers. The only time I would ever waste my time boring a stock intake is if I were trying to maintain a stock appearance for something like emissions compliance in a state like California.
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Old 01-22-2019, 03:05 PM
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Re: Edelbrock 3704 vs Holley 300-66

OK! I'm embarrassed now but I will own it! You have my apologies! I got the impression you were saying to switch over to a carb and you are absolutely right, that's not what you were saying! OK, that idea I can go with, putting a TBI on a carb intake would be economical as well from price standpoint and I have more than enough cowl to accommodate that setup. That is a good idea. Sorry, I completely overlooked your meaning that's my fault. Thank you for what actually turned out to be a really good idea. I'll even finally get to make better use of an obnoxiously high cowl hood that the car had on it when I got it. No hard feelings I hope! Thanks again!
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Old 01-22-2019, 03:19 PM
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Re: Edelbrock 3704 vs Holley 300-66


For simplicity and perfect fit id just have the stocker bore to 2in bores. That's what ive done with mine to set on my L98 I plan to drop in maybe in the spring. If youre only making 200-275 hp ive heard this intake is not a bottleneck.
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Old 01-24-2019, 10:55 AM
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Re: Edelbrock 3704 vs Holley 300-66

Originally Posted by dmccain View Post

For simplicity and perfect fit id just have the stocker bore to 2in bores. That's what ive done with mine to set on my L98 I plan to drop in maybe in the spring. If youre only making 200-275 hp ive heard this intake is not a bottleneck.
From my experience even bored out the TBI manifold is a noticeable restriction in power even on a stock engine.. That was also using the taller factory Van manifold casting. The low-rise car manifolds are even worse in terms of flow. Using the 454 TBI unit on both the performer rpm with the marine adapter was a noticeable bump in power across most of the rpm range.

The performer rpm/marine adaper made a good bit more power than the bored 3704 I ran back to back with it. Both were well dialed in as well. Performer RPM had just as much off-idle torque and the throttle response of both were great once the AE fuel was dialed in properly with each. For that matter even a single plane intake has good low-end power and throttle response whe it is dialed in correctly.

Last edited by Fast355; 01-25-2019 at 05:47 PM.
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