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How to best restrict an oversized Holley Dominator style throttle body for better response?

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Hello team,

I enjoyed attending the throttle body webinar very much, but unfortunately my question posted was cut off and incomplete.

From ~380hp to ~640hp naturally aspirated 468 cubic inch V8 engine, horsepower varies because of elevation range where car will be used, from sea level states to 11,000 feet + in Colorado, USA.

The engine has a carb-style open single-plane intake with a dominator (4500 Holley) large square flange, and there weren’t any 1,000 cfm throttle body choices available fir the dominator flange, and the only one I found with a progressive linkage to the secondaries was from Edelbrock (part no 3888) and flows 2,000 cfm, or 500 cfm per throttle bore.

I was thinking of best ways to make the throttle more linear and progressive and not let the engine make full power at 1/2 throttle on just primaries.

So far, either blocking off one side primary butterfly completely, or installing restrictors on both primary bores are my best thoughts on this.

I think that completely blocking off one primary bore would be the most linear power curve at less than 1/2 throttle when the secondaries open, but I would also like to hear other thoughts and opinions about restrictors and any other ideas. Being an air door only for a single plane intake, and having the injectors plumbed for normal placement near the head, I wouldn’t think there would be any mixture variations from cylinder to cylinder caused by the offset open bore.

Thoughts?

I think using restrictors would limit total airflow, but with large throttle bores opening a small amount, the restrictors would quickly max out and still wouldn’t allow a linear throttle to power relationship curve.

here is a link to the throttle body I have:

https://www.summitracing.com/parts/edl-3888

i think i would seriously be changing down to the https://www.summitracing.com/parts/edl-38783 if possible as adding restrictors will be a nightmare i would think we run class restrictors here in nz in different dirt track racing with reasonable results but i think for what you are doing i would be downsizing

Regards Ross

Greetings Ross, and thanks for your direct perspective. That is the exact problem, that only the 4150 carb-flange size throttle bodies are 1,000cfm as in the kind you linked to.

We don’t have room for an adapter-spacer to go from a Dominator (4500)intake flange to a square bore (4150) flange for a smaller throttle body.

Exactly what manifold are you using? That it's designed for a Dominator suggests race only for BIG engines and turning a LOT of rpm - TOTALLY unsuited for your application.

I STRONGLY suggest getting ride of it, and the throttle body you have (words fail me on how stupid using that is!), and fitting something sized for your engine size and power levels - you will gain everywhere and actually be able to fit a suitably sized throttle body - probably something in the 750-850 range will be ample (back in the carb' days NASCAR engines were running the equivalent of 390 CFM in restricted races, and still making around 700hp!). I would also give serious thought about a dual plane - there are some very good products that will give up a little at the top end but give a lot more back in the mid-range and also better response - but some head designs and/or deck heights may limit options.

As for mixture distribution - you're correct in that the fuelling will be equal to each cylinder BUT the air to the cylinders is going to be anything but uniform, so the individual AFRs are going to be out.

Greetings Gord,

We are using very obscure/rare cylinder heads for an Oldsmobile V8 (Batten heads) that have a completely different port layout and bolt pattern than a normal Oldsmobile V8 head.

There was only one intake manifold cast for a Big Block Oldsmobile using Batten heads, and it is a large single plane intake with a Dominator Carb Flange. I believe we found the last rough casting about 3 years ago now, and I haven’t seen another in that time.

These heads outperform other Oldsmobile aftermarket heads with quite a bit of development, typically making another 40-200hp more than other heads are capable of, depending on level of modification.

This is a large single plane intake, and it is actually a very good design that runs good even at low RPM, but it is also tall, and we won’t have room for a spacer or flange adapter really to go to a smaller throttle body size.

Those are the reasons why we are “stupidly” forced to use this manifold and large pattern throttle body. I agree it is frustrating, and I tried to fit the smaller pattern 4150 style throttle body on it, which is what I had before this one.

I am looking into some rare new old stock model of Dominator sized throttle bodies that flow 1,300cfm, but there are a few drawbacks to this model, and it may not have progressive linkage for easy street use.

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Ah, my apologies, I was thinking BBC +60 for that displacement.

However, I would iterate that is the wrong package, with the heads now being included, for what you're apparently using it for as it would be intended for a RACE application and totally unsuited for anything else. Trying to work around the limitations for 'street' use is, putting it politely, foolish.

I'd be looking at something along the lines of - https://mondelloperformance.com/2018/11/mondello-edelbrock-aluminum-cylinder-heads/ , with a - https://mondelloperformance.com/product-category/intake-fuel-systems/ topped off with a https://www.edelbrock.com/throttle-body-4150-for-universal-4150-style-4-barrel-4150.html - I couldn't find anything smaller, but it does have the progressive linkage, etc, which should be a decent compromise.

There are a lot of people still using Old's based drag engines, or who are enamoured by flow numbers, and I expect you can sell what you have to them for a decent price which will go a long way towards the better setup.

Gord, we aren’t changing the engine all up. It makes monster torque from 2,500 to past 4,500... over 600 ft lbs.

It is fresh built and Dyno’d, and we have plenty of torque converter to handle the cam size as well... 8 inch converter.

let’s just say I am not new to engine building, but to matching throttle bodies for EFI USE on these engines...

Since you mention that you have port injectors.... Any chance you could modify (or fabricate) one of the single throttle body adapters to fit the 4500-style flange, then use single 90mm throttle body (or DBW throttle body that would allow you to have any pedal map you want).

https://www.summitracing.com/parts/edl-3847?rrec=true

Apparently they do make 4500 style intake elbows (not as low profile as the one above however...)

https://www.summitracing.com/search?SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=4500%20intake%20elbow

OK, here's the lowest profile 4500 intake elbow I could find:

https://www.stevemorrisengines.com/carbs-hats-efi-elbows-and-throttle-bodies/throttle-body-elbows/sme-billet-dominator-4500-efi-elbow-low-profile.html

Ah, as it's not your first rodeo, and you're otherwise happy with it, some possible suggestions, in what may be the easiest to hardest options.

If your ECU allows drive-by-wire, convert to an electrically operated throttle as you can map the pedal-throttle positions for progressive operation.

Adapt a progressive cable lever for fitting to the current linkage - something like this https://www.weberperformance.com.au/product_info.php?products_id=837 You should be able to fabricate something for your application, just make sure the cable travel and operating travel for the lever match. I have such a lever somewhere I'd send as a sample to you, as it wasn't suitable for purpose, but low-key searching for the last 8-10 years hasn't unearthed it yet :-( .Depending on your particular application, you may find you can make a change to the pedal end for a similar affect.

Modify the manifold you have by machining off the 4500 flange and welding on a fabricated 4150 pattern flange, with a surface skim to ensure the pad is flat.

Sleeve the 4500 TB and have new butterflies made - easy enough for the latter, but a bit of a pain with the aligning/drilling for the throttle shafts.

CNC machine, or 3D print, your own TB body - maybe using the 4500 shafts and linkages (for bore spacing) with smaller butterflies.

I wouldn't be too keen on a progressive linkage between the shafts because of the variation in air flow distribution within the manifold versus fixed fuelling.

[edit] David's suggestion has merit as you aren't restricted to the after-market, but can easily fabricate your own if clearance is a problem.

Thanks so much for the good ideas Gents!

It looks like I will have to try a creative solution like the single throttle body adapter and only after a while if we don’t like using what we have....we only have an older MoTec M8, so DBW is not in the cards for us.

This is a budget build over a looooong time as a Father-son project, so I am trying to get it going before it is too late for my Dad to ride in it with me.... he suffers from Dementia and has always been my partner on car builds and automotive projects.

I will report back for others knowledge if this is not a drivable setup as-is and if I make changes to it.

If you use a cable throttle, then you can use a progressive throttle pulley that has a "scroll feature", a large radius for the initial throw, so it take more travel per angle change, then a shorter radius for the open throttle. You can make your own, or I have found that there are some you can buy...

Here are some examples:

https://www.efihardware.com/products/c93/Pulleys