David Jenkins
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| posted on 24/8/05 at 09:11 AM |
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Disappointing session on the rolling road
I took my car to a rolling road yesterday - and found that I had the jets pretty much right, and that the engine's only producing about 85 HP.
engine = 1660cc X-flow, GT head.
carb = Weber 32/36 DGV
cam = Kent BCF2
electronic ignition dizzy
free-flow exhaust
With this setup I had expected a bit more (or am I over-optimistic?)
After fiddling around with the carb the tuner decided that the primary choke was rich, while the second was correct. If he adjusted the mixture on
the primary the mixture went lean when the secondary opened, so I lost power. The only gain to be made was to advance the ignition a bit - which gave
me an extra 1 HP!
He was wondering if the cam was a bit too hot for an engine that's barely modified - but I had been assured by the Kent techie that it would
work OK on my setup (but he would say that, wouldn't he!).
The only thing that was obviously limiting my power was the fact that I'd set my rev limiter to 6000 rpm, when the cam is rated from 2000 -
6500rpm. the soft cut-out was also coming in at 5800 - 5900, which spoilt the top end power. I wasn't sure what the max revs is for a
standard-ish x-flow - can anyone tell me? The tuner suggested a hard cut-off at 6200rpm would give a noticeable bit of extra power.
Finally, can anyone suggest a not-too-expensive way of actually using the cam's power range? I don't really want to change the cam as
that's a total PITA on a x-flow, and I don't want to go to the expense of a pair of DCOEs just at the moment.
All suggestions gratefully received!
rgds,
David
P.S. The car still feels good and fast on the road, though!
[Edited on 24/8/05 by David Jenkins]
[Edited on 25/8/05 by David Jenkins]
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JoelP
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| posted on 24/8/05 at 09:16 AM |
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mine is a 1640 crossflow, with a similar sort of cam, the only difference being that mines on twin 40s. It read 112bhp on the rollers last week, so im
guessing that 85 is quite poor - can twin 40s really make nearly 30bhp difference?!
However, rollers are relative - its possible that his set is reading too low. The guy at boggs brothers said he could make his say anything (something
about the settings? not sure how though).
mine only revs to about 5500.
[Edited on 24/8/05 by JoelP]
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MikeR
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| posted on 24/8/05 at 09:44 AM |
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is 85 at the wheel or flywheel?
With the usually quoted "20%" transmission losses you're 85 goes up to just over a 100. At the end of the day, despite the fact we
all want to quote mega numbers, the number is irrelevent, its the improvement that matters.
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Surrey Dave
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| posted on 24/8/05 at 10:28 AM |
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There's alot of interesting power figures quoted!!! , a Lotus Elan twin cam only had 105bhp I believe , but they where quick.
I think Formula Fords with the basically standard cleverly blueprinted crossflow engine made around 100bhp, I drove one once , surprisingly
fast........
The Caterham sprint had about 125bhp ,with Webers, Kent cam, they are fast cars..........
You could change to Webers but you may lose lower/mid range,and gain some at the top end.......
You could put bike carbs on and gain driveability right through the range + top end and economy.......
You could get a really professionally ported head, I reckon thats where most of the gains could be found , but thats likely to be quite
expensive......
[Edited on 24/8/05 by Surrey Dave]
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scoobyis2cool
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| posted on 24/8/05 at 10:36 AM |
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Do you have a printout from the session? Would be interested in seeing it if you have.
Pete
It's not that I'm lazy, it's that I just don't care...
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Peter Cowley
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| posted on 24/8/05 at 10:40 AM |
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Mine is a 1660cc with piper 3cfy cam (mild road), gt spec head, twin 40 dellortos, lightened flywheel, freeflow exhaust, non vac aldon dizzy and high
comp pistons.
Mine was setup at protec in preston and was producing 85bhp at 4000rpm (not run-in the engine fully yet), he said it would produce 120-125 at full
rpm.
Certainly goes well !
 
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NS Dev
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| posted on 24/8/05 at 10:44 AM |
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sounds like it might be an at the wheels figure possibly.
The 32-36 weber should be good for plenty more than that. we had a 2 ltr pinto making 130hp on one so the carb isn't the major restriction.
What porting has been done to the head? The GT head is not particularly good in stock form, and usually non-gt heads are used as a basis for
modifications (If I am right in thinking the gT one is the one with little chambers in it instead of being flat?)
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Peter Cowley
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| posted on 24/8/05 at 10:54 AM |
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The gt/MEXICO HEAD HAS GOT SLIGHTLY LARGER VALVES THAN THE STD HEAD AS WELL (ACCORDING TO THE BURTONS BROCHURE ANYWAY !).
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NS Dev
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| posted on 24/8/05 at 11:00 AM |
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ahhh, didn't know that.
I am a know nowt when it comes to crossflows, but I was regurgitating something I remember being told by a "good" engine builder about not
using gt heads as a modifying basis, but that was on an engine where the valves would have been replaced with larger as a matter of course anyway.
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Surrey Dave
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| posted on 24/8/05 at 11:12 AM |
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Was the Kent cam fitted with standard cam wheel/timing postion or setup with offset dowels / vernier wheel?
For some annoying reason when they reprofile a cam they dont/cant grind it in the same position, so the full open point they quote needs to be checked
with a degree wheel, as it can be quite a few degrees out.
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Surrey Dave
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| posted on 24/8/05 at 11:31 AM |
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Here's a link to an interesting Crossflow Tuning article:
http://www.pumaracing.co.uk/cflow.htm
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britishtrident
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| posted on 24/8/05 at 11:34 AM |
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It might be worth checking
(1) The float level height is correct
(2) Fuel pump through put
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zxrlocost
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| posted on 24/8/05 at 11:37 AM |
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mate unless youve had your engine totally rebuilt and serviced etc
I wouldnt be to dissapointed..
perhaps with a bit of setting up and the right advice you could get 95+
I had a rover 216 gti twin cam rolling roaded the once and that came out at 126bhp at the wheels was only over 100bhp..
and that is a very technically advanced engine still.. the civic version pumps out 150bhp form the 1.6 same engine with VTEC...
HTH
chris
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Locost82
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| posted on 24/8/05 at 01:04 PM |
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Locost racers usually produce around 85-90 at the flywheel, but as was said before, there's a lot of rubbish spoken when it comes to power
output. Some roilling roads get a better figure by doing the power runs in 3rd gear. A recent Locost racer sold claimed to have 105 at the flywheel,
which the owner genuinely believed, my 85 was faster than that!
If your 85 is as fast as somebody else's 105 then it doesn't matter one bit. Rolling roads are there to get the best from your set-up.
How important is it to have a screaming engine? If it's important, get ready to spend £1500+ getting it ported, balanced, carb'd etc
etc.
Mine revs to 7000 (7300 if I forget to change up!), but power drops off rapidly after 6300 anyway with my 1300GT set-up.
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britishtrident
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| posted on 24/8/05 at 05:45 PM |
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quote:
Originally posted by Locost82
Some roilling roads get a better figure by doing the power runs in 3rd gear.
?
Last time I looked power = 2*pi*n*t
I
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MikeR
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| posted on 24/8/05 at 05:54 PM |
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I believe its to do with the losses when you do the coast down. It makes the final figure look better.
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David Jenkins
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| posted on 24/8/05 at 06:14 PM |
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Replying in no particular order...
I used the standard cam peg to locate the chainwheel - but when I checked afterwards it was very close to ideal.
I would have been happy if it was BHP at the wheels - but the man told me it was the calculated flywheel figure. It doesn't say so on the
print-out though.
Everything in the carb is set correctly - float, etc.
If I was confident about max revs with a x-flow I'd take it a bit higher - but I can't get any authoritive statement on what max revs are
safe with a standard x-flow. I don't mind if it rattles the valve springs more than it should - just that I don't want to break anything!
It's not encouraging to compare my car with a Locost racer - I've got 360cc's more capacity, and a bigger carb!
The general comment that "if you're happy with the way it goes, why worry" is fair, though. It does go like stink, with a nice
health 'rasp' at full throttle!
Here's the Rolling Road Chart - it's a bit large for here!
rgds,
David
[Edited on 24/8/05 by David Jenkins]
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scoobyis2cool
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| posted on 24/8/05 at 06:36 PM |
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Looks like you've got a healthy spread of torque, so I shouldn't worry too much about the peak power. And as has been said, if it goes
like stink don't worry about it too much!
Pete
It's not that I'm lazy, it's that I just don't care...
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andylancaster3000
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| posted on 24/8/05 at 08:26 PM |
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A lot of the top rev's figures I have seen seem a little low. A previous race car of my fathers had a race 1300 x-flow in it which ran a
balanced standard crank and rods with slightly posher pistons. He saw 9000rpm from a missed gear once and it didn't bother it at all. Speaking
to Ned at the weekend, he was saying that his friend who races has even seen 10,000 from one, but I don't know what internals that had!
Andy
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Kieran
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| posted on 24/8/05 at 08:40 PM |
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I remember reading somewhere that the "correction" factor has a lot to do with making a dyno readout look good. Some firms alter this to
make the readings look better, horsepower sells engines, torque wins races etc.......
Kieran
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Marcus
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| posted on 25/8/05 at 08:26 PM |
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David,
That torque curve looks very similar to mine (piper 270 cam). This doesn't give much increase in power but a lovely torque spread.
I am a little surprised at the power figure considering a standard GT/Ghia crossflow gives 86bhp. I would expect in the region of 100.
Mine's a 1700 on the same carb with the aforementioned cam and a head ported by me producing 115 bhp (Noble rolling road).
Has the engine been built with the right head. As was mentioned earlier chambered heads need flat top pistons otherwise you get bugger all compression
ratio.
The cam timing may have been almost right, but a few degrees can make a hell of a difference. I used an offset dowel in mine to move the cam by just a
few degrees (can't remember how many!).
Marcus
Marcus
Because kits are for girls!!
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Volvorsport
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| posted on 25/8/05 at 09:32 PM |
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when my mk2 escort had a 1660 x fllow built by east lincs motor sport - it had an A2 cam and was reasonably quick it still only ran a single carb .
bear in mind the std xflow figure is 86 bhp at the flywheel i think the gt heads were slightly chambered , so would lower compression .
www.dbsmotorsport.co.uk
getting dirty under a bus
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MikeR
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| posted on 25/8/05 at 10:35 PM |
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GT head isn't chambered. A GT head has larger valves.
Basically the 'old' crossflow block had chambered head, small valves and flat top pistons. The 'new' crossflow block has flat
head, dished pistons.
If you have the GT head you get larger valves.
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Volvorsport
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| posted on 25/8/05 at 10:41 PM |
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it was 15 years ago - i was a fan of the engine - i got converted tho into something that didnt breakdown or not start in cold/damp weather
www.dbsmotorsport.co.uk
getting dirty under a bus
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David Jenkins
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| posted on 26/8/05 at 07:44 AM |
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It's a non-chambered flat-face head with big valves, and combustion chambers in the piston tops.
I've decided that it's not worth getting stressed about this - it does go very well, and I'm sure it's giving more power than
a std x-flow. I'm beginning to wonder whether the readings were at the wheel, not the calculated flywheel figure. As an example, I squealed my
tyres in 1st and 2nd when accelerating hard out of a slip road last week, and it'll reach 60 in around 6 seconds (or less) so it really
isn't a feeble engine!
I don't intend to throw too much more money at this engine, as it is 30 years old, after all! I'll continue to enjoy what I've got,
and save my pennies for a better engine in the future (Duratec?).
Cheers to all,
David
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