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Does anyone happen to know how much taller the SBO Ebrock RPM intake is vs. the HSD or have them both to measure?
I'm running the HSD on my 374 SBO build now with ported #6 heads (on my 70 Supreme) but considering swapping to the RPM for more low/mid power and might even upgrade to the new small block Ebrocks once those become available. I'm definitely going to have the Ebrock 1411 750 carb removed and upgrade to the FiTech throttle body EFI like I have on my 442 and just trying to figure out what other upgrades/changes to be done at the same time.
Has anyone (like Mark Remmel for example, Hi Mark!) done any dyno #s on an HSD vs RPM? I'm curious how much more low/mid power the RPM makes and also wondering if the peak hp and tq would come down with the swap.
My concern is I run the factory breather with the HSD and don't want to give that up. To swap to the RPM and keep the breather, I'm sure will require a drop base (like the one on my BBO on my 71 442 w/the Torker) but wanted to make sure it wasn't so much taller that the drop base wouldn't be enough. I'm guessing it's about 3/4" or 1" taller but was hoping to get a confirmation on that.
I pasted the build details and a pic below for reference. It's great for "granny driving" (especially with the Rhoads lifters) as it has little power up to about 4,000 RPM and then lots from about 4500 to 6200. Since it's a fun street car that may go to the track sometime, I think it would be more fun to drive if there was more power down low and mid so you don't have to always rev it up to 6 grand to get to the power. I think it would be perfect as a manual trans car like my 442 but as an automatic even with the 3.90 gears and the stage 2 2004R, it would be nice to have some power down low. To be clear it's great off the line and can do huge burn outs if wanted with the 3.90 rear, 2.74 1st gear and the 3000-3200 converter. This car gets driven by my son, wife, and my 87 year old dad. None of them like to rev it up high so they don't get to experience any of the power once driving the car vs launching from a dead stop. The governor in the 2004R works well for WOT shifts at around 5500 to 6000 but if you floor it and it doesn't down shift, it feels like it has no power because it stays in the lower RPMs. If it down shifts and hits at or around 6k it chirps the tires in 2nd and even 3rd sometimes and you can really feel all the power but it doesn't happen all the time. I can also manual shift it but don't want to always have to do that and my son, wife, and Dad never manual shift. Also if I'm cruising at let's say 20 mph I don't like to ever manually downshift into first unless I'm fully stopped or almost stopped so flooring it in 2nd when it doesn't downshift feels like there's no power also. Anyway sorry for the long explanation but trying to provide the details for why I'm considering the changes. Also I know my current cam choice plays a part in the lack of low/mid power too since it's a wide spread at 235/244 and on a 112 vs something like a 231/235 on a 108 maybe with some more lift too for the port #6 heads....If the RPM is too tall for me to keep the breather even with a drop base, I guess I could always try a cam swap to try to gain more of what I'm looking for even with the HSD. Maybe a tighter cam and the FiTech would help a little with throttle response and low to mid power but I'm guessing the RPM intake would help even more if it's doable.
Thanks in advance for any info, advice, suggestions here!
-Joe
374 Build
Bore 4.125 SRP pistons (.068 over) 21 cc dish
Stroke 3.5 (330 steel w/2” journals)
Rods 6.125 Dyers H-Beam
Holly Street Dominator
Edelbrock 1411 750 cfm 4-Barrel carb with electric choke and bowtie’s adj TV cable for the 2004R, + Solenoid for AC use - raises RPM by about 300 UD HFT 292/300, 235/244, 522/536 (1.6 HS rockers), 112
9.57:1 measured CR 175-180 cranking compression w/Rhoads Lifters #6 heads – 59.5 ccs, 2.07/1.68 valves, crossovers filled, ported 7 QT Oil pan American Racing 1 3/4" stainless headers, 2.5" exhaust (Xpipe, mufflers, tailpipes, & Olds trumpets)
2004R Trans Extreme Automatics Stage#2 w/deep Hughes pan governor set for 5,500 6,100 RPM WOT shifts, R&R 9.5” 3000-3200 non-lockup converter
Last edited by 71 OLDS; January 8th, 2024 at 11:58 AM.
You have the W25 hood and the forced air cleaner in the pic, correct? The RPM is 2" taller than the Performer/stock intake. Not sure on the HSD unfortunately. Many of us hope the new SBO Edelbrock heads eventually show up.
Yes, below is a pic of the car for reference. Hopefully the HSD is an inch taller than the Performer/stock intake because 2" taller may be too much to use the drop base but thanks for providing that info. We went with the #6s vs the Ebrocks because we had the HSD and knew it provided lots of clearance for the breather and would require major mods to get the intake to work with the Ebrocks. But now I was thinking if we could find a way to use the drop base and convert over to the RPM, I could add more mid/low power and maybe upgrade to the small block Ebrocks too once they are available.
I had these olds pics saved from someone who did all the work to make the HSD work with the Ebrocks but after seeing these I think the drop base for the RPM would be MUCH easier and I may prefer the results for my setup more anyway for all the reasons I explained.
Yes, BUT, you have to do some modifying of the air cleaner base. Combination of mallet around carb opening, along with “barrel hooping” and CPR. Basically you need to massage the air cleaner base into a drop base. Limit is the throttle arm and accelerator pump, at least with a Qjet. On a Holley, I guess it would be the fuel bowls/float screws and throttle arm. Wont play nice with an HEI unless you fab a notch in the back, which I did. I had to trim foam down, ymmv.
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Last edited by bccan; January 8th, 2024 at 04:13 PM.
Got it thanks again. I replied to your PM too. We did the drop base for my 442 with the BBO and the Torker so that process can be repeated if it will work.
January 8th, 2024, 11:24 AM
