6 replies to this topic

[sr2]

Hi guys; to come clean this 9 port Holden is not in a Torana but I’d appreciate any advice from the GMH-Torana brains trust – IMOP you guys are the definitive Holden straight 6 guru’s! (Admin – please let me know if I’m breaking the rules here).

I’ve recently purchased an old (no make) triple downdraft Stromberg manifold and a box of what I think are 1 5/32” BVX-2 single choke carbs.

 

 

Plan is to run them on my 186 with counterbalanced crank, Yella Terra head & roller rockers, HID ignition, headers and a mild street cam.

Yes I know it’s an impractical setup but it looks so ‘oldschool’ and feeds my passion for “totally impractical solutions to problems that have never existed in the first place!”

 

If you’re interested in the car it’s going into I have a build thread at….. https://oldschool.co...”-build-thread/

 

Plan is to run the middle carb as the primary with the outside carbs (via a progressive linkage) opening at approx. 65% throttle opening. I’m copying the GM Tri-Power system and suspect that set up properly it will be well behaved in a street car.

Any comments on will it will work, what jetting I’ll need, how to set up the accelerator pumps, etc. will be gratefully appreciated.

 

[yel327]

My advice would be to go and have a read about how the Mopars and Chevys were setup with triple carbs regarding the progressive throttle opening and throttle pumps. L71 and L89 were the Big Block Chevy 427 engines with them. Not sure of what the 440 option codes were. The L71 never opened the outer carbs mechanically, they were open solely on vacuum like a vacuum secondary 4BBL. Not sure how you'd do this without the right carbs? I have also seen a few old grey engines with triples, if it works on them it'll work on a red 6 but probably won't be as street friendly as vacuum operated secondary carbs.

I'd also be making your 186 as many cubes as possible. I assume you are fitting an XT5 3.3 crankshaft with the mains ground down, or did you tunnel bore the 186 for larger bearings?

[sr2]

My advice would be to go and have a read about how the Mopars and Chevys were setup with triple carbs regarding the progressive throttle opening and throttle pumps. L71 and L89 were the Big Block Chevy 427 engines with them. Not sure of what the 440 option codes were. The L71 never opened the outer carbs mechanically, they were open solely on vacuum like a vacuum secondary 4BBL. Not sure how you'd do this without the right carbs? I have also seen a few old grey engines with triples, if it works on them it'll work on a red 6 but probably won't be as street friendly as vacuum operated secondary carbs.

I'd also be making your 186 as many cubes as possible. I assume you are fitting an XT5 3.3 crankshaft with the mains ground down, or did you tunnel bore the 186 for larger bearings?

Hi, thanks for the reply. Apparently the early 60’s Pontiac GTO’s ran a Tripower setup with a progressive mechanical linkage to the outside carbs. From what I’ve read it’s quite commonly to use a progressive mechanical linkage in classic Hot Rods.   My plan is to run a lay shaft (similar to Triple SU setups) but with an adjustable linkage so I can vary the throttle position that the front/rear carbs open at.

I’ve had the the crank mains ground to fit the 186 block with a neoprene rear seal; I’m using Starfire rods and .006” over pistons taking the capacity out to 208 cubes. The crank, clutch and flywheel (standard lightened to 6.4kg) have been balanced as a unit and I’ve got the rods balanced to within 1.5 grams.

[yel327]

Nice, you could have saved a few bucks and used a 202 block but will do exactly the same thing for you.

[sr2]

Nice, you could have saved a few bucks and used a 202 block but will do exactly the same thing for you.

Yes you are right, I have a Blue block I could have used but this old 186 has been in the family for some 35 plus years - I just couldn't throw the old girl out! 

[Bruiser]

Hats off to you for thinking outside the box mate, I love a good idea
Chrysler did the triple 2 barrel thing, too, it’s kind of like a 6 barrel carb with 4 secondaries
But it would have to take you months and months to get those carbs set up that way,
and I don’t just mean the linkage set up
I suppose running on the middle carb could be like running a single standard setup,
But calibrating the 2 outer ones to match would be a nightmare
I mean getting the fuel ratios right across all the operating conditions, and perfect between all cylinders
On a straight 6 manifold
You have to set it all up for Idle, then light throttle tip in transition and low low speed cruise, then higher speed economical cruise,
and then wide open throttle flat acceleration
If all 3 carbs were set up the same internally (jets, bleeds, power valve etc), but set up the tri-power way, I think the moment the outer two came in would be shithousely un-smooth,
plus they’d have to match the middle one anyway to better balance the fuel mix to all 3 ports,
Which I guess defeats the purpose of changing the opening timing at all
It’s tricky enough with just a single 4 barrel with vacuum sec
If you had the gear to read the afr and the stromberg know-how to get this all right,
You could probably dial in those three to run nice across the board all synced up
together as they come.
If the X2 twin setup is better than a single, three would have to be better - the old school grey
motor guys used the setup, and the yanks on their sixes back in the day.
Would have to be far closer to triple su’s than a single anyway, and that
would to be a bonus
Might be better to hunt down a set of those to spend your dough on?
I don’t honestly know the guts of a single throat strommy, I have only ever pissed them off for something a bit bigger
I have seen the specs for X2 carbs, and the internals are a bit different from the usual bxuv-2
But the specs to set three up must be out there somewhere, if you are determined
I’d bet you could set up a 350 Holley to give you half decent economy and power easier than those suckers
with less research and hair pulling

Good luck with your idea, I do hope you can pull it off and prove me wrong

[yel327]

I've never really bothered much with the X2 stuff, GMH replaced it with the single WW for the S engine and it produced better power and drivability. 

 

Pontiac did offer the Tri-power from 1857-1966 but it was replaced by a single Quadrajet in 1967 for better drivability. According to the below link most of the tri-power setups were mechanical linkage only to the middle carb and the other two were vacuum operated, no idle circuit or chokes. Only some manual GTO had a progressive manual linkage to the outer carbs.

 

https://macsmotorcit...ri-power-story/

 

The Rochester 2G is the same family carby fitted to HK-HT 307. Same flange size as a WW Stromberg, but there are larger versions too used on 2BBL 327 and 350 and later engines.