tri-y headers and smaller exhaust system

[cjperformance]

Hey Tony, still a stout streeter even with chambers youre not keen on.
Hope you dont mind me throwing 2c in on the pipes,, at that hp on that tri,y style (im assuming commodore/torana?) On the 1st set of pipes I'll put the primaries at 'just' on the big side for the hp ,, the secondaries at pretty dam spot on, the choke and collector and in 'assuming' 2.5" 3" were OD's? But even so for that pipe architecture pretty spot on for the hp. So all working pretty well really.

Then the 2nd set that obviously affected the engine combo,,, primarys same 'just' big, secondary pipes too big and even though a nice lookin choke/collector the velocity loss from the secondarys dont allow the choke/coll to operate properly.

So why did it like lash? Even with the 1st set of pipes, ,,, same 'quantity' of exhaust gas (+ a little more as the hp picked up some) to pass in a smaller time frame due to reduced effective duration = higher gas velocity allbeit for a shorter time but allows the 'just' big primaries to operate with a stronger pulse/signal and from there the sec, choke and collector just work that bit better too. So your lash call and thoughts on an alternative cam would be spot on.

I would guess that with the 2nd set of pipes and seeing that a choke does not like a velocity lacking pipe ahead of it, a crutch that may have helped would be to try a straight 3"collector which on that pipe design would leave the secondary merge as the choke point. This would make the pipes as a whole less sensetive to the larger secondaries and probably would kill a little tq earlier on but not hurt the hp as much.

Feel free to discuss or correct anything I have said here based on your tests/experience,, everything i have learned on pipe sizing and this style of tri-y (ford stuff in particular but as you know the pipe architecture is not all that different brand to brand on these types of tri-ys )has been based around a mixture of drag race with open and full system, street with full system , comparing my results with others , fixing/improving on other peoples setups that I have had to work on, making a lot of mistakes and having to work out how to fix them!!- but learning a bunch along the way and being willing to hear as many opinions and experiences as possible and retesting to achieve my own opinion. So im always happy to be corrected where required.

[zums]

More fuel to the fire, did some testing today with a couple of sets of tri y pipes & left with results contrary to what everyone in the room was betting on, including me.

Motor was a 383 Holden street & occasional strip.
Pump fuel (our 98, equivalent to US 93), solid flat cam, 268/272 on 109 centres, in on 105icl, lift around .630/.610 with 1.65 rockers.
12:1 comp, 850 carb.
This motor wore alloy heads rather than the ported iron I favour for this sort of build, roughly 300/208cfm at lift used & a chamber I did not like (soft & shallow).
Made 500lb @ 6100, 570hp @ 6300 as a baseline.
Baseline headers were 1.75/2/2.5 choke, 3" collector tri y.
Then we tried 1.75/2.25/2.5 choke, 3" collector - much nicer choke & collector.
It lost power bad, 10lb & 10hp before 5500rpm & dropping hard with rpm, aborted run at 5500, it was nose diving & down from the hit at 4500.
Faffed around for 2x more aborted runs & only dropped more power.
Put the crappy looking pipes back on and it mirrored the last run with them.
So it didn't like more header, which begged the question is it over exhausting?
So, despite the consensus in the room saying it was a waste of time I took exhaust lash from .018 to .024".
It picked up from the hit too 1000rpm past peak, 7lb & 5hp.
We finished up at 507lb at 5100, 575hp at 6300, holding 560hp to 7100.

I was right to dislike the chambers, it was timing insensitive, 28/30/32 deg, very little change - a good chamber will see significant loss 2 deg either side of the sweet spot, this did not.

If I was to grind another cam for it I'd take out 4 deg ex duration & .020" of lift, bump compression to 12.3 or so & I think it could make 590hp.

The second set of headers have over a 1.5" area change, cant see them running good on anything that isnt really taxing the 1.75 primary
Tom

[KnightEngines]

The motor the 2nd set of pipes were for was Mondo's 355, flat tappet, iron head methanol engine, 620hp @ 7400rpm from memory.
It begs the question would that 355 also prefer the smaller pipes?

Owning a dyno, having a bunch of spare time to mess with stuff & the $ to play would be very informative.
Unfortunately I'm not blessed with any of the above, so I have to be content with gleaning as much learnings from every dyno session as possible!

[blown265]

This has been a very interesting thread, as I've been considering new primary pipes for a 1.7hp/ci supercharged 273ci I6. (and thanks to all who've contributed their real world findings, and apologies in advance for a potential hickjack).

The current exhaust is:
3into1 1.6" X 36" primaries,
2into1 2.5" X 18" 'collectors',
and then a short 3inch single system open to atmosphere behind the front wheel.

I was considering increasing the primary pipe size to 1.75", all else remaining the same, working on the theory that the 1.6 inch primary may be maxed out. Has anyone increased primary size at this moderate power level and seen HP gains? The Pipemax version I have is ancient, and doesn't appear to model this setup well. From this thread, it would appear not worth the near $1000 for the larger pipe.

Thanks
Paul

[cjperformance]

Paul, I dont know your exh port csa or valve size but going on hp i say what you have up to the collector is fine. But id like to see the collector to atmosphere at 3.5" (talking OD's) ,, maybe just step it up right after the last merge , so you go from about 3" out to 3.5 for the rest of the final collector length.
( on a side note,, if it were not blown but same hp id say go 2-3-1 @ 1.625" - 2" - 3.5" simply to keep the 1st merge at a smaller csa to keep the pipes responsive and go a smaller choke prior to collector.)

I like the sound of this combo. Drag only i take it?
Cheers,

[blown265]

G'day Craig

This one is my personal car- 99% street. I did race it in the early 90s NA, but it hasn't seen a track in years!
Thanks for the recommendations- changing the final pipe to 3.5" isn't a problem, so I'll change that before the next dyno session in July.

The cylinder head is traditional 265- ported factory iron with 1.96/1.6 valves, and flows 250cfm @ 28". With this head, the CSAs were kept tight, with metal only taken from the usual areas, and a focus made on clean shape within the limits of the factory casting.

My concern/question was mainly around the cost vs gain of the larger primary. As Tony mentioned above, a dyno, money, and time is something I'm short on,, but would be very cool to have for these types of quantative tests.

Thanks again
Paul

[cjperformance]

Would be a dream job to live on the dyno and track just testing stuff and getting paid ! I wish , lol.

Cost per hp on changing you're entire header is probably not worth an assured gain , if you were to do it id suggest 6,3,1 but i be hard pressed to predict a worthy gain there on a blown combo.
But, sometimes change even at a loss is all knowledge gained, but im not going to tell someone else to spend anything unless i really could see a justified reasonable gain!!
(Yesterday I test drove a 304ci edelbrock headed straight gas "' 350 to 400hp "" engine that the builder talked the customer out of 11K for , not to mention the"" 2800 ""converter that actually runs to 1600 that was needed to ""make the combo work"" for another $1000! - the owner has worn it, the builder/s have gotten away with it,, thankfully i have some lpg experience so at least i get to fix it and get another customer out of it but man, how does a builder justify that !? Whinge over, lol.)

Try the 3.5 collector out ,, i assume this is just a track collector and you bolt up a full system for the street?
If there is a notable gain(or a loss) then a look at the rest of the pipes may be worthwhile. Do you have a pic of the pipes in question?
And sorry to Steve for the hijack but i dont think he will mind too much? I hope.
Cheers

[blown265]

Thanks Craig- yep, a full time 'job' testing my various performance changes would be unthinkably great.

The exhaust has an electric 3" cutout/dump pipe immediately after the last merge (a Flowmaster 2.5"/3" Y pipe), and then a single mandrel 3" over diff exhaust system, which with the Magnaflow muffler is deep but not overly loud. (the open bypass is not!). The headers are off the shelf Pacemaker 'Tuned Length' 1 5/8. The primary length and diameter are very close to Pipemaxs recommendation for a strong NA combo, but I'm not sure how close they are/should be for the blown motor. All exhaust* lengths, bypass and full, are as close as possible/practicle to Pipemax, but again, for a NA setup. (*primary, collector, and tailpipe)

The 6-3-1 custom header you mentioned is interesting (as opposed to the current 6-2-1) . Which cylinders would you pair? Firing order is 153624, with 1&6 2&5 and 3&4 in the same plane. The Pacemaker 6-2-1 have 1&2&3 and 4&5&6 combined.

Cheers, and cheers also to Steve for his thread!
Paul
PS, This car also runs on dedicated LPG (propane for our overseas members)- and the Gas Research system is tuned alongside a Tech Edge Wide Band. Ignition is programmable MSD.

[cjperformance]

6,3,1 always pair in complete alternate firing pattern.
So most typical 6's at 153624 go 1,6 - 2,5 - 3,4 , wide spacing between firing cylinders also allow you to run pipe diameters at the minimum.

Is this engine in a Val? Charger, centura? Should be fun on the street and reasonably cheap to run on the street.

[MELWAY]

More fuel to the fire, did some testing today with a couple of sets of tri y pipes & left with results contrary to what everyone in the room was betting on, including me.

Motor was a 383 Holden street & occasional strip.
Pump fuel (our 98, equivalent to US 93), solid flat cam, 268/272 on 109 centres, in on 105icl, lift around .630/.610 with 1.65 rockers.
12:1 comp, 850 carb.
This motor wore alloy heads rather than the ported iron I favour for this sort of build, roughly 300/208cfm at lift used & a chamber I did not like (soft & shallow).
Made 500lb @ 6100, 570hp @ 6300 as a baseline.
Baseline headers were 1.75/2/2.5 choke, 3" collector tri y.
Then we tried 1.75/2.25/2.5 choke, 3" collector - much nicer choke & collector.
It lost power bad, 10lb & 10hp before 5500rpm & dropping hard with rpm, aborted run at 5500, it was nose diving & down from the hit at 4500.
Faffed around for 2x more aborted runs & only dropped more power.
Put the crappy looking pipes back on and it mirrored the last run with them.
So it didn't like more header, which begged the question is it over exhausting?
So, despite the consensus in the room saying it was a waste of time I took exhaust lash from .018 to .024".
It picked up from the hit too 1000rpm past peak, 7lb & 5hp.
We finished up at 507lb at 5100, 575hp at 6300, holding 560hp to 7100.

I was right to dislike the chambers, it was timing insensitive, 28/30/32 deg, very little change - a good chamber will see significant loss 2 deg either side of the sweet spot, this did not.

If I was to grind another cam for it I'd take out 4 deg ex duration & .020" of lift, bump compression to 12.3 or so & I think it could make 590hp.

Hi Tony
I built an engine almost identical to yours 402 Holden those shithouse come 590 heads same cam specs and comp
It was a dog and struggled to make 580
I bet if it had cast VNs it would make 30-40 more HP with less flowz

[KnightEngines]

You reckon it's the chamber killing the burn?
I'm not gonna throw them under a bus just yet, I can tell there is something to learn. I sunk the seats .040" after they'd already had another valve job from new, but in hindsight I think sinking them a solid .080" would be helpful, the height of the turns would allow it. Maybe run with a dish piston & mill the crap out of them to shrink that horrid chamber, get some quench into it & maybe speed the burn.
Wider lobe sep, less ex lift & more compression - even at 12:1 on pump swill it was showing SFA activity on the det meter with 32 deg timing, pretty sure you could pump 12.5:1 into it.
Maybe a coating on the chamber & piston crown to keep some heat in, it was just so cool in the chambers.

But then again we could just start with $150 iron heads rather than $3000 alloys that still need real $ spent. $3k buys a lot of grinder time & machine time.

[cjperformance]

I have a feelin that years a go I heard the C.O.M.E. heads and the YT heads were the same casting??
I could be well wrong and/or thinking of something else.

[MELWAY]

You reckon it's the chamber killing the burn?
I'm not gonna throw them under a bus just yet, I can tell there is something to learn. I sunk the seats .040" after they'd already had another valve job from new, but in hindsight I think sinking them a solid .080" would be helpful, the height of the turns would allow it. Maybe run with a dish piston & mill the crap out of them to shrink that horrid chamber, get some quench into it & maybe speed the burn.
Wider lobe sep, less ex lift & more compression - even at 12:1 on pump swill it was showing SFA activity on the det meter with 32 deg timing, pretty sure you could pump 12.5:1 into it.
Maybe a coating on the chamber & piston crown to keep some heat in, it was just so cool in the chambers.

But then again we could just start with $150 iron heads rather than $3000 alloys that still need real $ spent. $3k buys a lot of grinder time & machine time.

I think the chamber is the worst part. Prob need a welder to fix it. Also from memory the bowl was already too big and short turn was not nice
They lack burn speed and press recovery in a big way
First pull on the dyno you could hear/feel it didn’t want to fight the brake
I’m hand porting a set of YT-9 now and they are a much different casting. With a lot of material where you need it except the ex port

[KnightEngines]

Craig - pretty sure your thoughts on the headers are bang on!

James - could definitely fix the chambers with a tig, but that would be one hell of a job! Bowls were at something like 92% with the 2.02" valves they came with, I went straight to a 2.055" & was still at 90% or so, did no work in the bowls other than blend in the valve job, nothing there to shape! Same with chambers, had to leave them be, can't shape metal that doesn't exist.
I did reshape the turn for stability & opened up the pinch a tad, mostly just to try to make sense of that bowl.
Ex ports were real average with just a tidy up, had to do a decent amount of work there.

What block did you use on that 400 cube engine?
Was it also insensitive to timing?
The 383 was snappy on the throttle & pulled on the brake nice, it's a good engine, but is held back by slow burn.
It'll be a low 10 sec engine in the hq 4 door it's going in, 5000 converter & 4.3 gears.