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#Post#: 440--------------------------------------------------
Trumpet selection & induction lengths for 8 & 16v big bl
ock engines.
By: JMR Date: October 2, 2012, 3:25 pm
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I was working through some options earlier to ensure a customer
had the right trumpet length for his 16v Corrado and figured an
article based on the popular variations for 8 & 16v carb & ITB
conversions would be a help...and I found some common ground
whilst armed with a tape measure!...read on.
To start with, some basics ...
8v...
Head port length...valve seat to manifold face...100mm
DCOE type inlet manifold...83mm
Misab plate (carb to manifold gasket/seal)...5mm
DCOE / DHLA sidedraught carb...118mm
For those without a calculator to hand the above adds up to
306mm. A good starting point for "total" induction length for
open type engines...i.e carbs or T/B's rather than std type
plenums is 320mm from the trumpet tip to the valve seat. Now
it's not quite an exact measurement as the distance through the
head port and the manifold will vary going through the turns &
around both the long roof side & short floor side of the
head...so I've come to the above figures by measuring the long &
short turns and averaging them out, then comparing them with a
measurement through the middle of the ports & manifold.
So based on the above, we need a trumpet for 8v engines of
around 14mm to start with. Well it's quite handy then that the
shortest current trumpet that Weber can supply is 16mm!
I've had good result's in the past with 40mm trumpets on 45
DCOE's, giving a total of 346mm on 1800 hillclimb
engine's....making 172hp @ 7,200, and when changed to 60mm
trumpets the owner reported back a noticable performance
improvement on track as expected, though we did'nt get to
re-check it on the dyno.
On my own hillclimb engine I've always used 60mm trumpets on my
48's, giving a total length of 366mm. The old longer for low end
and shorter for top end doesn't always ring true as my engine,
and others I've done since with similar lengths make peak power
between 7,500 & 8000...so dont lack top end with longer intake
lengths in 8v form. When I'm next on the dyno and time permits,
I'll try a few different lengths and see how it rocks the power
curve, but for now the above guide will get you in the ballpark.
And for the 16v brigade...
Head port, valve seat to manifold face...96mm
JMR DCOE inlet manifold...75mm
Misab plate/gasket...5mm
DCOE/DHLA carb...118mm
So we have a starting point not a million miles off the 8v in
terms of the head port and overall length. I factored the head
and carb length into the equation when I speced our manifold a
couple of years ago, along with installation room & common
available trumpets.
With the above, our starting point is 294mm, so to get to our
320mm overall length we need a 26mm trumpet. Weber have been
good to us again with the availability of...a 26mm trumpet!
A popular trumpet that many used sidedraught's come with is
40mm, so giving us a total of 334mm. I've seen 175hp on this
length on 1800 16v's with a fast road ported head & 276 cams. To
get to the total length we've found to work on the 8v in high
spec form we need a trumpet of around 72mm. Weber are good to us
again with a 75mm trumpet, though the common size in the older
steel trumpet is 60mm...giving 354mm total length.
And finally...for now...DTH ITB's.
Head...96mm
DTH Jenvey...112mm
Common trumpet...120mm
So a total starting point of 328mm. I've recently seen just shy
of 250hp @8300 with 167ib/ft of torque from this length on a
rally spec ABF, so it obviously works ok to a point, but maybe
an improvement can be had with more length...time & the dyno
will tell. Jenvey do a 150mm trumpet which would bring us up to
358mm total length. I would suggest at that length tho that DTH
bodies wont enable sufficient under bonnet clearance, so DCOE
style bodies on a more conventional manifold would allow for the
extra length extended into the front panel.
Well that should get you all thinking, and give anyone new to
carbs or T/B's some starting choice....dont be affraid to ask
tho for specific applications...we're here to help.
#Post#: 441--------------------------------------------------
Re: Trumpet selection & induction lengths for 8 & 16v bi
g block engines.
By: Stooza Date: October 3, 2012, 6:52 am
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This is great info.. Make it a sticky!!! Cheers Jason
#Post#: 452--------------------------------------------------
Re: Trumpet selection & induction lengths for 8 & 16v bi
g block engines.
By: JMR Date: October 4, 2012, 4:21 am
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Yr welcome... ;D It ain't going anywhere baby!...lol
Im looking forward to some experimenting on the dyno...we have a
project or two to get ready for next year... ::) so will be
juggling trumpets then. ;)
#Post#: 464--------------------------------------------------
Re: Trumpet selection & induction lengths for 8 & 16v bi
g block engines.
By: dumma Date: October 5, 2012, 11:05 am
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Not sure if you've seen these;
HTML http://www.emeraldm3d.com/emerald-adjustable-length-intake.html
Not sure if these will make life any easier with those tests on
the dyno? Seem to remember claims of very small affects on flow
during the tests, then selecting the appropreate 'normal'
trumpet afterwards.
As a bonus, they don't look difficult to make either - I could
get some nice, thin guage stainless tube from work if required.
:)
#Post#: 469--------------------------------------------------
Re: Trumpet selection & induction lengths for 8 & 16v bi
g block engines.
By: mitlom Date: October 6, 2012, 4:49 am
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[quote author=dumma link=topic=76.msg464#msg464 date=1349453117]
Not sure if you've seen these;
HTML http://www.emeraldm3d.com/emerald-adjustable-length-intake.html
Not sure if these will make life any easier with those tests on
the dyno? Seem to remember claims of very small affects on flow
during the tests, then selecting the appropreate 'normal'
trumpet afterwards.
As a bonus, they don't look difficult to make either - I could
get some nice, thin guage stainless tube from work if required.
:)
[/quote]
I sent Jason the same link 1/2 a yr or so ago....but he's
getting old and been to bed a few times since :D
#Post#: 480--------------------------------------------------
Re: Trumpet selection & induction lengths for 8 & 16v bi
g block engines.
By: Tonyb Date: October 7, 2012, 7:50 am
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This is an interesting thread. I've acquired an engine from the
'dark side' that appears to have too many valves however as it's
out of a single seater circuit racer it should be reasonably
lively and it's dry sump (so might nick that for the 8v).
I'm not sure what I'm going to do with it yet but it probably
not going to replace the 8v, as that goes well enough, might put
in in the caddy van I have here for track days and keep it as a
spare backup engine for the 8v while it is out of the car. The
guy the engine is coming from tells me that while it had more
power on paper than the 8v it replaced (230bhp) it was never
quicker as it just didn't have enough low down power, and there
is the interest for me.
I know a guy who runs a 16v Golf in the midlands championship
and he went to an 8 injector set up to find a better power
spread as he found the 16v wanting over the 8v he had before.
I'm just thinking that to get a decent power spread you need a
longer induction system, that seems to be the norm. People seem
to use direct to head set ups and I believe that suits high end
power rather than low end power. On an engine that is well known
for poor low end power it would seem to me that the induction
length needs to be longer than would traditionally used.
Obviously you need to fit things under bonnets for road cars so
DTH systems help in this respect and practicality is more
important for the road but for racing that sort of becomes
secondary to performance.
On my engine I'm thinking to run a long primary length up to the
throttles and then shorter trumpets and keep the overall length
on the longer side. I'm also considering whether to use 8
injectors, 4 at the head and 4 up at the trumpets. Is there
performance to be gained. I know the guy who uses 8 injectors
said there was a useful gain in low end power.
I'm also thinking that the problem with the low end grunt must
be to do with the exhaust valve being vertical so I'm thinking
that may be there needs to be some clever chamber or port trick
to get the exhaust gases out at low velocities or maybe bigger
exhaust valves than you would normally go for, as opposed to
just sticking in bigger inlets that you would normally go for.
I know the Spiess 8v head I had was fitted with 36mm exhaust
valves and 41mm inlets (not the norm) and those engines were
well known for being very torquey which is why Spiess ran then
until 1991 in F3! I know they were air restricted but all of the
other porting was what you would expect on a very well developed
race head and they flow as well as anything else out there, I'm
sure Jason will confirm that as he's had that one on the flow
bench.
Anyway something there to discuss!
#Post#: 527--------------------------------------------------
Re: Trumpet selection & induction lengths for 8 & 16v bi
g block engines.
By: JMR Date: October 18, 2012, 2:40 pm
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Keep forgetting this...
Id start with around the 360mm mark for induction. We did a 16v
recently with that kind of length at it didn't lack top
end...peak power was up over 8k...low end power and overall
torque was poor tho...the full spec is currently unknown until i
pull it apart so not really a fair showing.
Getting the stuff out is a lot easier than getting it in...an 8v
has verand wetical valves too and we don't lack torque!
The best I've seen to date in terms of 16v torque is 167ibft.
.with good low end grunt...so they don't need to lack low end.
#Post#: 916--------------------------------------------------
Re: Trumpet selection & induction lengths for 8 & 16v bi
g block engines.
By: Smudge Date: September 10, 2013, 2:09 pm
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A very useful and interesting thread, when I made my 16v ITB
setup I ran an inlet track length of around 355mm this was
chosen after some research. I found these pictures interesting
recently when carrying out more research on the subject.
[IMG]
HTML http://i64.photobucket.com/albums/h199/the_smudger/999a374ca0feaea1abeb1d72f9b9fb18.jpg[/img]
[IMG]
HTML http://i64.photobucket.com/albums/h199/the_smudger/52c5bc632e099845e17954ef3611b72b.jpg[/img]
I have recently manufactured my own plenum and went for a 360mm
inlet track after discussing with Jason.
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