Individual runner intake manifold for big block Chevy

[GRTfast]

I was reading about the advantages of the individual runner Hilborn electronic fuel injection system. Mainly the fact that with a large cam, you don't get the fouling of the intake charge from overlap that you get with a common plenum intake. Some of the dyno plots show huge advantages in the low end and midrange. Since the Hilborn unit is way out of my price range (8-9k), I was thinking of building my own side draft style intake with individual runners. I would probably use a motorcycle carb on each runner (something like the carbs off late 90's 1000cc sportbikes). I see that this is somewhat popular on small 4 cylinder British sports cars, but I don't see anyone doing it on big V8's. Anyone have any experience with this type of setup? Thoughts on why it is or is not a good idea? Sometimes I get the urge to build something different and make it work. This is one of those times.

[mekilljoydammit]

The big problem is that there's not going to be much motorcycle based stuff that will supply a big enough carb or throttle body. Aftermarket carbs for literbikes top out at around 41mm - in contrast, the individual runner sidedraft manifolds used on smallblock Chevies in the 60s were running 58mm Weber carbs.

Other than that though, nothing wrong with individual runner intakes on big block Chevies - was done with vertical stacks in Can Am in the 60s and 70s, and with crossover horizontal stacks by John Greenwood in the 70s in Corvettes.

[MadBill]

Yes, the problem for IR runners on a big engine is the need for huge flow capability, because unlike a plenum-mounted carburetor, mixture is only flowing for less than 40% of the time. E.g., MFI stacks for Big Blocks run as large as 3"/~75 mm... https://kinsler.com/Shop/manifolds/

[GRTfast]

Yeah that makes sense that it would need huge carbs. Thanks for the quick replies and links. I'm gonna keep looking into it, and probably design something. I'll post pics of the 3D models if/when I do.

[pcnsd]

The largest MC slide type carburetor that I am aware is the Mikuni HSR 48. Slides do not have a butterfly bar to obstruct air flow and so move a bit more air volume for a given depression and CSA.
I estimate the HSR 48 is will flow ~442cfm@ 28"H2O or ~ 377@ 1.5"HG.
Depending on displacement and expected RPM, it may be enough to get you there.

http://www.mikuni.com/fs-carburetor.html

What is your expected bare head flow rate @ pressure?

[Ken_Parkman]

There were IR carb efforts in the late 60's in Trans Am, and Grumpy talks about trying it in PS in his book. I happen to have one of the very few IR intakes cast for the Kaplan AMC Trans Am program in 69 in my shop right now. Holley did make IR intended large Dominators, I remember reading that there was an even bigger bore Dominator IR carb somewhere, but that may be internet folklore.

I'm told the IR efforts in Trans Am were "reasonably" successful, the AMC intake was taller than the Ford and I *think* it worked pretty good, better than the short Ford combo. SCCA outlawed all the wacky stuff for 70. The Trans Am was only a 305 engine of not massive power, and the carb seemed big enough. IIRC Grumpy wrote the carb was simply not big enough for a PS effort at the time; may have worked better on a smaller engine.

You would have to need some kind of massive carb bore for a big block of any rpm.

[mk e]

You could put 2 per cylinder maybe?

I have Ducati TBs on my FrankenFerrari, they are 54mm which might be big enough if you're not planning for more than 75hp/cyl or so..... not carbs though.

[roc]

Another option (which tempts me at times) is buying a used Hilborn MFI intake and converting it to EFI.

[GRTfast]

You could put 2 per cylinder maybe?

I have Ducati TBs on my FrankenFerrari, they are 54mm which might be big enough if you're not planning for more than 75hp/cyl or so..... not carbs though.

I thought about that.... 16 carbs to sync.....



I would look cool AF though.

[GRTfast]

Another option (which tempts me at times) is buying a used Hilborn MFI intake and converting it to EFI.

When my dad was alive, he talked about doing this very thing.

[GRTfast]

The largest MC slide type carburetor that I am aware is the Mikuni HSR 48. Slides do not have a butterfly bar to obstruct air flow and so move a bit more air volume for a given depression and CSA.
I estimate the HSR 48 is will flow ~442cfm@ 28"H2O or ~ 377@ 1.5"HG.
Depending on displacement and expected RPM, it may be enough to get you there.

http://www.mikuni.com/fs-carburetor.html

What is your expected bare head flow rate @ pressure?

Not sure, but they are Brodix race rite bb2 rectangular ports. I think they are 312cc runners. My dad built the motor. It is currently undercammed due to my stupidity (long story). Part of this switch to an individual runner intake would involve a more radical cam choice. It has a comp cams thumpr in it now. I had another thread on here where the expert consensus was that I could use a bigger and better bump stick.

[modok]

Usually IR setups are used on 200-300CI V-8s, making "only" 500 something HP, because that's what size carburetors are common.
Suitable carburetors for larger engines could exist, but very rare, because there has not been much demand at all for them.
Especially today.
I don't mind having two float bowls or even three, but I think 8 is too many
Make it IR throttles and port injection.

[MadBill]

Another option (which tempts me at times) is buying a used Hilborn MFI intake and converting it to EFI.

Kin$ler and probably others offer such converted systems.

[Rick Finsta]

Our Belgian friend Yves has a V8 IR setup on EFI... he's probably a few hours from waking up right now!

[MadBill]

Here's the cross ram that's going on my 495" Can Am engine. It was converted circa 1975 to Lucas mechanical timed injection, via the fabricated TBs (as per left side) and the nozzle bungs visible in each runner. Plan A was to add a vacuum can-operated lean cruise mode to the Lucas system.(Reportedly it delivered < 8 MPG as-was) Plan B was to sell it off for big $$ and convert to EFI using aftermarket TBI-type TBs. Plan C is a pair of 1970 period-correct (as is everything else but the SR cam and gear) Holleys.
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X Ram 001.jpg