30 replies to this topic

[salamiman]

Bit of help needed if possible.

With a bit of decent headwork on a 9 port Hi comp head & the right cam in a 202, what is the approx upper limit of HP expected from a set of 1 3/4 SUs @ the flywheel?

[Bruiser]

I know of a fella who was determined to get as much as he
humanly-possibly could out of 1 3/4", in spite of all the
knowledgeable guys telling him to go 2"
Was a clever dude himself, achieved 200ish rwhp
and mid 13's in the quarter in an old holden

Ended up going 2" though, was serious about
going ever quicker

[salamiman]

Thanks for that Bruiser.

Id like to acheive around 250+ at the flywheel & have seen 265+ from an engine on youtube by powerhouse engines, it sports a small 4bbl holley & they mention alot more would be possible with a set of triples, but i guess he aint talking about 1.75 SUs

Any feeback would be apreciated

[warrenm]

3x 1 3/4" carbs can potentially flow 624cfm. If I get a chance tomorrow I'll run the numbers.

[salamiman]

Would appreciate that.

I have read the carbies will support around 200 cfm each, but what figures have actually been produced on a 202 with a decent 9 port head & cam, say to max 7000 RPM with them.

Most have gone 2'', but im not chasing 300HP.

Would just like to know what real world figures members have got, using HS6 1 3/4 SUs, or am I wasting my time with 1 3/4 triples trying to chase 250+ HP with them & maybe i need to look at other options?

[I'm a Red Motor fiend]

You already have a set of 1 3/4" inch ready to go obviously?

[Bruiser]

The bloke I referred to before was talking about
200 rear wheel hp -
What would you call that at the flywheel?
Is the drivetrain loss 30% or so?
Even 20% would give you 250
30% works out to 285
I suspect he tried every trick in the book
and modified the bejesus out of them though

Pretty good if true

[salamiman]

Yes Adam carbs on a working red 202 in my LJ, but have come across a virgin blue motor Block with crank & rods to play with. , just trying to keep costs down.

 

Bruiser, sounds like 250 could be the limit with them then.

 

You would think 600 CFM could support more power?

 

it would be interesting to hear of anyone else's experiences?

[Bruiser]

Not sure the 600cfm total can be considered in holley terms,
Something to do with one 200cfm carb being shared
between 2 cylinders in that holden shared port arrangement.
All cylinders pulling on a single carb vs only 2 per su
It's been discussed here in the engine forum at length
..somewhere
I think the result was to use less cfm flow than you'd think
modern flatslide carbs like mikunis were brought up.
Probably easier to wait for the guys who have tried 1 3/4,
and 2" back to back to educate us both

[Bruiser]

Just watched the video, 263 hp with a 390 holley?
Triples should at least equal that??

[grumpy xu1]

If you look at the piston speed, you will need decent rods & rod bolts. So it holds together. At 7000 rpm, i reckon that you're going to be on the limit of a basic crank balance ect & carburetion, but 250 should be doable with a good cylinder head & cam to suit the head.

[salamiman]

Well Lets Say Constant 6500rpm changes and redline 7000!(spoke to HSD in Melb for head work on my old yella 6000 head)

 

The red in it now was put together in 1985 & it still has no probs reving to 6k(and this car sat idle from 1992 til 2019) but its leaking a fair bit of oil, so time to pull it out for a refresh or the blue motor build!!!!!!

 

Bruiser, great minds think alike, I reckon the triples should perform better than the holley as well???

[warrenm]

That 624cfm is [email protected]", can't remember if the 600 Holley is measured at 1.5" or 3".

[I'm a Red Motor fiend]

The triples will perform better otherwise we would all run Holleys (yuck)
Head, cam, compression, pipes, ignition and 250 should be had.

[salamiman]

Thats what im Hoping for 250 plus if possible.

 

Talking about holleys below.

 

http://www.gmh-toran...carby/?p=878142

 

4bbls measured at 1.5. 

[salamiman]

Thanks Warren, if you can make 260hp with the 390cfm holley, I cant see why you shouldnt get a little more with 624cfm from triple 1 3/4 SUs.

Hopefully we might get some feedback from someone that had a bit more experience using those carbies.

[Bruiser]

Heehee warren looks like a wizard with these things, redmotorfiend
has been through all this too, bet he knows most of the ins and outs too
While you've got their attention, i reckon dream up some questions and
get to asking 'em

[salamiman]

I better stop there then bruiser B4 i embarass myself anymore.

 

Just love these little engines & want to make sure the package I put together 35 yrs after the last one. is going to do the little six justice.

 

Thought some of the fellas might have had dyno figures over the yrs of where 1 3/4 finish & whether the investment or search would be validated in HP to chase a 2'' option.

 

This thing will be driven on the street.

 

Any help or guidance would be appeciated.

[I'm a Red Motor fiend]

Have you had your headwork done yet or thought about cam selection?
To get 260+ HP out of the 1 3/4", it's going to have to be a well built engine and fairly high strung.
If your willing to go to that extent and if money is not a huge issue start hunting for some 2".
They will basically be bolt on extra horsepower for the combo you will end up with trying to wring the 1 3/4"s necks.

[Bruiser]

He's right there, looks like 250 hp is approaching the limit of
the 1 3/4's capabilities.
Adam, do the 2" carbs behave much different in the low end and midrange
or are they just a gain up top?
Using a set of 2", could 250 hp be achieved with less cam
i.e not such a highly strung stinker?
Not quite as many revs?

[salamiman]

Awesome question Bruiser.

 

The 1 3/4 & old 70/30 watson in the car ATM, behaves quite well on the street & to be honest since giving the old girl some xtra spark & paying attention to to the advance curve it runs far better than it did back in the day, and its fun to drive(makes me smile, but no idea of HP, a guess of 180@ flywheel)

 

So knowing how the 2'' behaves in the higher HP six, would be nice, do they help it behave better at lower RPMs as well?

 

 Adam,

Thanks for your help,

 

I have a M22 box & 3.08 diff which i will fitt, so around 2750 RPM @ 100Kmh, so your right, no good having a cam that doesnt come on to 3000!

 

Head is an old HC 173 Yella bathurst 6000(HSD in melb have quoted to bring it up to 250-300 HP flow rates).

 

No cam chosen yet but,

 

HSD Have mentioned a Crow XU1 cam to get the HP mentioned, had a bit of a check & it seems those grinds are hydraulic.

 

I was thinking more solid cam, as I was going for yella terra adjutable joined roller rockers, to get away from the hyd setup.

 

Any suggestions, would be appreciated.

 

So if i was going to spend some Xtra dollars on 2" carbies would I be better to go down the HSR path??, or is that too much of a race option?

[Bruiser]

My head flows 190, and I currently have very close to
the smaller lj xu1 cam, 226° bigger lift, though
And a 4 barrel too
Dynoed 140 at the wheels years ago
Maybe a bit more now, if my "improvements" have worked at all.
The bigger xu1 cam is still only 240°.
I don't think it would get it to 250hp.
Phone clive cams or tighe about it, they'll set you straight.

The hsr thing has been discussed in here at length, too.
There is a feller who has done it
Try the site search here and put in mikuni, hsr or flatslide
and see what comes up

[salamiman]

Thanks Bruiser.

 

Ill give those blokes a call, solid seems to be the way to go now(read Oldjohnno's invaluable pages any times, excellent information)

Never had any probs with hyd, but rarely took my old motor past 6000.

 

Thought pattern originally was, If HSD in Melb would build the head, he could match cam choice to headwork, or is that not how its done?

 

Had read a bit about the HSR thing & thought it may be a tad easier to get a hold of & cheaper(was thinking I might also get away the old LYNX manifold as they talk 38-42 mm HSRs & hoped they might fit on it with some work)

 

I think 2'' SUs and a manifold are gunna be hard to find today?

 

Or just build the engine with better carbs in mind, use what ive got & see how it goes?

[Bruiser]

Yes, that is how it's done
Get head done and get the flow figures, and choose cam to suit.
Those guys have been around a long time, probably nearly seen it all
Big name in heads, and I'm sure their heads are top notch.
But they're not called head and CAM stud development.
I generally collect as many opinions as possible and compare whole lot
anyway. Try the cam experts and see what they say.
If you want to achieve 250hp, find out whats involved,
and how easy it will be to live with, etcetera
It's a reasonable jump from what you have now
if it still suits you then, stick with the plan and go for it.
Personally, I'm not sure as radical as a 250hp engine needs to be
would suit me and the way I want to use my car.
Loads of engine builders are pretty generous with their time and
could help you spec the whole motor out.
Seems to be plenty of guys around here who could do this too

Bruce

[salamiman]

Virtual Cheers to All, thanks for your help.

Appreciated!