As I understand it....
The goal with an exhaust is not to get the biggest diameter pipes, as the
honda in the next lane with the exhaust you can drive your spitfire into
might suggest. True, too small produces restrictions. But too large
damages the flow of the exhaust. Ideally, the force of the previous puff
of exhaust travelling through the pipe helps scavenge and suck the next puff
out of the chamber when the exhaust valve opens. Removes a little pressure
off the piston during it's exhaust stroke. Too large a diameter both slows
(by losing momentum), and weakens that scavenging power b/c the puff is a)
taking up a greater area in the pipe, and b) not flowing as straight as it
should. Rather, the air is curling around and winds up being pushed out by
the next puff of exhaust until it too loses it's momentum. The Vizard book
on porting heads explains this much better (which is why he wrote the book,
and not me ;) )
Also, as I understand it, the exhaust puffing of 2 cylinders leaves too
large a time in between puffs to effectively scavenge the next puff. It
needs to be relatively close to the head to be effective. THat's why most
V8's usually limit themselves to dual exhaust. So even if you reduce the
size of the dual exhaust pipes, your still not as optimized as with a
cirrectly size single pipe with free flow exhaust.
I'm sure the more knowledgable on the list will correct me in the areas I'm
mistaken, or too vague.
Michael
-----Original Message-----
From: dt gebhard [mailto:kimkell@decaturnet.com]
Sent: Thursday, November 30, 2000 10:04 AM
To: Terry Thompson; spitfires@autox.team.net
Subject: Re: Engine Rebuild
snip> As an immediate suggestion, dump the dual exhaust,
> that's costing you
> power.
Please explain why this is true...
Dave Gebhard
1977 Spit building power on a budget!!!!!!
----- Original Message -----
From: "Terry Thompson" <epharisto@yahoo.com>
To: <spitfires@autox.team.net>
Sent: Thursday, November 30, 2000 9:43 AM
Subject: Re: Engine Rebuild
>
> I don't know about 10,000 hp out of a single over head
> cam four cylinder with about 100 cubic inches of
> displacement, but I'd have to agree with every other
> comment Nolan made.
>
> There's so many options and combinations of parts now
> for spitfire blocks, it's difficult to say what is the
> best set-up. I've been beating my head against a wall
> trying to decide.
>
> Most people choose to work with what they have and
> what is proven by using the Triumph Competition Prep
> Manuals. You'd use existing blocks, heads and cranks
> that are machined for balance, weight reduction and
> flow. And upgrade to over-sized pistons (TR6), sport
> cam, and higher flow carbs.
>
> But if you want to spend some deneiro, there are
> forged and aluminum pistons ($500), chrome-moly
> connecting rods ($700), billet cranks ($3k), titanium
> valves ($400), quad carb setups ($1k) or electronic
> ignition systems ($2k), superchargers ($2k) and
> six-hundred dollar roller-rockers that will work on a
> spitfire engine. And you can spend some good money on
> ceramic coatings (especially if you start coating
> everything including timing chains and roller rockers
> etc.)
>
> First: try and set a limit to what you are willing to
> spend. Then look at all of the options that are out
> there, and decide which ones will fit within your
> budget. (make sure you figure in some buffer for
> incidentals like hardware gaskets etc.)
>
> Then take the list of items that you think will work,
> and ask someone like Mike Lewis of Protius or Ted
> Schumacher of TSI if it's a good plan to put those
> pieces together. Some things are sort of common
> sense...like buying a $2000 super charger and using it
> on a ZS carb and stock cam...probably not the best use
> of your $2000.
>
> You can easily surpass $10,000.00 on parts and
> services alone if you add it all up.
>
> In the least you should have the block and head
> hot-tanked and magnafluxed. And consider shotpeening
> on cylinder walls. Machining the engine as described
> in the competition prep manual is not the cheapest
> thing but does improve upon an already proven engine
> design.
>
> Companies like PAECO will sell you a stage 1,2,3,4
> engine but the stage 1's (pretty stock except for a
> hotter road cam and head porting as well as balancing)
> start around $3,000. The stage 2s are around $5,000
> and the 3's and 4's they don't list because it depends
> on what performance components you choose. The above
> prices also required your old engine as a trade in.
>
> Now for other problems. Let's say you've gone ahead
> and spent $10,000 on your engine and it's built
> producing close to 200 horses. I'd like to start a $1
> pool and see who can guess how long it will take
> before you tear the differential or transmission out
> of your car when you excellerate too fast.
>
> The triumph components are well made, but even the
> works spitfires with their estimated 100 hp, had
> modified TR4 tranny components for more beefiness. In
> the least, such an engine will probably go through
> U-joints at an alarming rate and torsion on other
> components like your drive-shaft and half axles will
> take it's toll. Not to mention that such an engine
> requires lots of care and upkeep beyond that of a
> stock TR. Constant adjustments to roller rockers and
> valves are gaurenteed.
>
> I'm not trying to discourage you. Just that there's a
> whole lot to think about, and no one out there has yet
> been able to say "this is the best combination". I'm
> still (after 4 months) mulling over my twenty thousand
> dollar list of options to decide which items I'm
> willing to take a chance on and which I'm going to
> red-line to bring the whole concept into budget.
>
> I'm actually shooting for a HP range but it's
> difficult to tell what sort of affect/effect (?) these
> parts will have to boost hp. If it's marginal (Eh,
> you'll get another 5 horses out of that $3,000.00
> part) then off list it goes. Especially since everyone
> you talk to has a different opinion about what is good
> hp value for the dollar.
>
> But then the greatest fear is spending several
> thousands of dollars on engine components, then
> getting it bench dyno-tested and instead of your 57
> bhp, you get a 59 hp. Or what is probably even worse
> and more likely, you over-shoot your optimal HP goal
> and your having to crawl everywhere so you don't tear
> out your drive-train. Then there's always the
> possibility that someone didn't torque something right
> and you throw a $250 forged piston head through your
> $2000 ported, polished, titanium valved, ceramic
> coated head (and your recently painted bonnet to
> boot).
>
> -Terry
> "Oh...Those are speed holes. They make the car go
> faster" - Homer Simpson
>
> --- Nolan Penney <npenney@erols.com> wrote:
> >
> > There's an old saying "speed costs money, how fast
> > can you afford to
> > go?" It's as valid today, with you, as it was then.
> > If you've got the
> > money, you can get 10,000 horsepower out of that
> > engine. Gonna cost you
> > upwards of half to a full million dollars, but it
> > can be done. I say
> > that to point out the folly of your question. You
> > need to put some
> > parameters in it. What kind of money do you want to
> > spend? What kind
> > of performance do you want? What about life
> > expectency? These things
> > all sway the modifications. After all, nitros and
> > 40psi of boost are
> > great power increasers, but life expectency is
> > rather short.
> >
> > As far as every trick in the book, pick up every
> > engine book ever
> > written, and study them. Then, you will no most of
> > the tricks in the
> > book for squeezing power out of your engine. And as
> > soon as you've done
> > that, know you're out of date immediately, because
> > in the time it took
> > you to read these words, at least 60 new tricks have
> > been discovered or
> > improved on.
> >
> > As an immediate suggestion, dump the dual exhaust,
> > that's costing you
> > power. Then do some serious tuning (how did you
> > select the needles?
> > what is your advance curve? etc)
>
>
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