Well here is the deal on KT's 298...
Some good news some bad.
Good news is that it seems to run fine with a couple of exceptions.
Intake manifold is not much more than a door stop and the heads while good maybe
for a short rod 355 are not anything like they need to be with a long rod
298..Way too big so ended up soft on torque, unfortunately you need torque to
make HP. Started with what seemed sensible and only had 360 ft lbs and 520 hp..
pretty sad no matter how you look at it. But it ran fine with no problems other
than the cylinder to cylinder fuel distribution was less than ideal but no real
bad.
Played with the jetting and timing a couple of pulls but little to be had there.
The carb was rated at 725 CFM and the CFM according to the dyno was 770.. Well
that would lead you to believe that the manifold pressure was over 1.5" Hg... so
switch the bores and boosters to a 825 carb setup and jetted accordingly..
That was good for 377 Ft lbs and 540 hp.. Not good but better..
Played with some carb spacers..
that got 393 and 564 hp.. Not good but all it has without a redesign or the
heads.
Did try a smaller set of headers and moving the cam around..
The headers were showing some promise but they would never fit in the car and
did have to have enough header for the nitrous pulls which the smaller ones may
of had but maybe not. So we filled that away for another day with smaller heads
and a proper manifold.
So we had an engine that makes ft lbs in the 390's to low 400's and hp in the
560's
not a race day piece but what it has.
Things different from last time out and reported #'s in the 590's for hp and
390's for torque.
The cam is shorter much shorter Cam is a 268/272 at 0.050 with about 700 lift.
Down from 280's at 0.050 and a little more lift.
Pistons have a little less compression and are a lot thicker/heavier also did
away with the 'gas ports' in them.
Reasoning goes like this. With the old combo the pistons expired after a couple
of runs on nitrous, so we backed it down to take a try at making full runs under
power.
We backed the cam down for 2 reasons, the first was to hope to make a little
more torque but the heads and manifold combo was not going to let that happen no
matter what we did. The second was a little more subtle in my mind. We have had
problems with mixture distribution moving around with changes in rpm most
notably the higher you rev it the more they move around. Old cam wanted to run
at 8800 new cam is happy at 8000 to 8200.. peak torque is the same but is over
1000 rpm lower as well so it ought to drive away from the line and get up to
speed quicker earlier on the course.
The last thing to consider is how the power is measured. The last trip to the
dyno with this engine the corrected #'s did not make any sense to me as when i
used the published correction factor and the uncorrected power they were off by
a considerable amount. I took the trouble then to call the manufacturer of the
dyno and ask about this. They said that they apply the weather correction to the
'frictional hp' well that is merely a calculated # and not measured so it will
lead to artificially high power readings.
The reality of it all. The engine makes within a few hp one way or the other
this time around and nothing short of new heads and intake are ever going to
change any of it. The only other way might be to run a 'low deck' block and
shorter rods but that is not going to be any cheaper either.
So now it is off to the nitrous wars..
We had 2 basic choices, run a plate system or foggers both were available and
installed.
I went with the foggers for 1 reason only and some reservation as well. The fuel
distribution was less than optimal so that made the foggers look good, but we
really only need about 150 hp and the lowest setting that was published on the
fogger was 250 hp an the plate system could be jetted down to 50 hp that made
the plate look good..
I went with the fogger because i had no faith that the plate would put equal
amounts of nitrous in each cylinder. They had a jet package listed at 250 hp but
we had some smaller untested jets.
We set up the nitrous to come on at 7000 rpm and ran it to 8500 at both 600 rpm
per second and 300 rpm per second. Initially had -10 degrees timing on the
nitrous Depending on bottle pressure we had from 775 to 805 hp and around 540 ft
lbs of torque. Well it liked the nitrous and we got a lot more power than was
expected. With the jets we put in I expected about 730 hp and 500 ft lbs... I
comes on smooth over a 500 rpm range almost a non event to be honest as it
probably takes a while to fill that big intake manifold and settle out. Ended up
with -8 degrees 900 lbs bottle pressure and 794 hp and 535 ft lbs on 2 pulls
that were very consistent.
What did we learn from all this....
Engines are combinations and parts are good parts when they fit the application
and have no value at all individually.
Is nitrous the 'hot setup' well maybe..... But this is going to be a point and
shoot sort of thing. Drive it up to the mile of interest and pull the trigger..
Can you tune up a bad combination and make it a good one. No you can't and I
never thought you could anyway. Can you make it a better one? maybe a little bit
but you can not make it right with carbs, spacers and jets..
As a side note we did learn that with KT's intake manifold if you rejet the carb
by 2 jet#s you end up with 2 cylinders going cold and 2 others going very hot..
not good at all...Plugs to watch 6,7,8...
Things to do..
smaller heads or 406 engine to put them on..
Intake manifold.. lose it..
EFI and / or nitro/alky.. probably a better combo to run fuel classes
End of the day what does this all mean...
We got what we could out of it and if we keep an eye on it it ought to be fine,
don't drive it with the nitrous on for the whole course, just when you need it..
Will it set a record? who knows? it has power enough and when it came off the
dyno the leak down was 2 to 3 % the plugs look right and the ports are nice and
clean. There was almost nothing in the scavenge filters so if it does break
there was no damage from it's visit to the dyno.
Tune up specs....
timing 34 degrees
Compression ratio 12.5/1
cam 268/272 700 lift
carb 825 cfm BG Demon
6.5 lbs fuel pressure
#90 jets best power 13.5 air fuel ratio
#95 jest best torque ( picked up the bottom end some..)13.0 a/f on the bottom
12.2 on top
Headers 2" stepped to 2.250 about 30" long way too big collectors
fuel C-16
nitrous jets 0.024
fuel jets 0.022
7 lbs fuel pressure (nitrous)
900 lbs nitrous pressure
-8 degrees timing on nitrous.
Dave Dahlgren
/// unsubscribe/change address requests to majordomo@autox.team.net or try
/// http://www.team.net/mailman/listinfo
/// Archives at http://www.team.net/archive/land-speed
|