Power vs. Fuel economy

Don · Postby **Don** » 03 Jul 2009 18:01

I am pulling the eninge and trans out of my TR7 to replace the clutch. While the engine is out, this is a good time to think about engine upgrades. Of course I want more power, but at the same time, I don't want to seriously degrade my fuel economy.

These are the options I am considering:
1) just add a header and leave well enough alone.
2) Header + street cam.
3) Header, street cam, port the head.
4) Header, street cam, port the head + high compression pistons.
5) All of the above + Webber carbs.

I know many of you have modified your engines. Was the increase in power worth the cost? What happened to your fuel economy? How was drivability affected? Any suggestions or comments on this topic would be appreciated.

Thanks.

Don

TR7 spider, '48 Willys jeep and (hopefully a TR8 soon!)

FI Spyder · Postby **FI Spyder** » 03 Jul 2009 18:32

Personally I would:

Tuned header (4-2-1 for usable mid range power), street cam, 9.25 to 1 pistons, K&N filter.

This let's the engine breath and rev higher more freely.

Not sure of porting the head for street use. I've read the rough casting surface helps mix air/fuel mixture better for better fuel economy. Bare in mind many race/power improvements are at the expense of fuel economy as this is not as much a factor at the track. Just trim the intake and exhaust gaskets to match openings.

As far as the Zenith/SU/Weber argument I always get the impression it depends more on the familiarity of the person tuning the carbs than actual advantage of one over another. Some one on this forum mentioned someone who races on Zenith carbs which is considered at the bottom of the totem pole so I have my suspicions whether well tuned carbs would make that much difference for street use (considering cost) or whether people are just arguing how many angels can dance on the head of a pin.

TR7 Spider - 1978 Spifire - 1976 Spitfire - 1988 Tercel 4X4 - Kali on Integra - 1991 Integra

jclay (RIP 2018) · Postby **jclay (RIP 2018)** » 03 Jul 2009 19:00

Get a pocket port done on the head.

If you want fuel economy, DON'T use the downdraft Webers. With just the DDWs, no other mods, I only get 19 MPG

jclay

[url="http://web.mac.com/jclaythompson/iWeb/Site/Welcome.html"]My Triumph Site[/url], [url="http://web.mac.com/jclaythompson/iWeb/Technical/Intro.html"]Technical Stuff[/url], [url="http://homepage.mac.com/WebObjects/FileSharing.woa/53/wo/HJMTK8gsojtwKleP.1/0.2.1.2.26.31.97.0.35.0.1.1.1?user=jclaythompson&fpath=Triumph_Articles&templatefn=FileSharing4.html"]Download Page[/url]

Beans · Postby **Beans** » 03 Jul 2009 22:55

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by FI Spyder

... As far as the Zenith/SU/Weber argument ...<hr height="1" noshade id="quote"></blockquote id="quote">
The Zenith-Stromberg carb has only con's, fragile diaphragm and not very much choice in needles. So not very tunable.

SU or side draught Weber/Dell Orto/Solex are much more tunable and reliable.
If properly set up and with the same engine spec a side draught carb should give slightly better milage over the SU. On the other hand the SU gives better low down torque.

What ever you do, make sure you know what you are doing or know someone reliable who does [:p]

<center>

1981 TR7 FHC Sprint (better known as 't Kreng)
1980 TR7 DHC (my first car currently being restored)
In parts a 1980 TR7 PI DHC, 1981 TR7 DHC, 1981 TR7 FHC
http://tr7beans.blogspot.com/</center>

Hasbeen · Postby **Hasbeen** » 04 Jul 2009 01:20

Don, the people who know in Oz reckon the zeniths will give just as
much power as the SUs. They also say that webbers will give more
performance, but no where as much as they should, given their fuel
consumption.

I stick to SUs for their simplicity, & because I started mucking
with them in the early 60s, so know them a bit.

Efficient air filters, & good headers will give a fair boost in
power, & get rid of the air pump, & exhaust rebreathing while you
are at that area. Cleaning any dags out of the porting is
worthwhile, but full porting only does much if you want to rev the
thing hard.

However we got some of the low com 7s, & they all say, with the
experience of both, that the most important thing for power is
compression. High com pistons is the best way, but the blokes who
competed in 2.0L 7s, before everyone went V8, used to shave the
heads a long way, without trouble. They were running up to 10.7 to
1, with good results, in rallying & track work.

I find my 9.7 to 1 compression, 2.0L will run on 93 octane unleaded
OK, but wants 95, to be happy. It performs really well between 2,300
& 4,000 RPM with good filters, exhaust, & a very mild cam. The
filters & exhaust improved the smoothness & power, right down to
1,800 RPM.

Hasbeen

Marko · Postby **Marko** » 04 Jul 2009 02:20

carbs and fuel economy usualy dont go in the same sentence.

most of the time due to the bad adjustment and bad maintanance.

with FI you can have your cake and eat it too. that is an EFI car will save fuel on low engine load much more than the carb's are capable , and still feed the ponyes when needed.

its all about how much money are you willing to spend. that is when will the investment in fuel eficiency bring back profit.

best upgrade will be to get a 16v head.

you can work your ass off in intake and exhaust pressure wave tuning, reducing mass of everyting, porting , diffrent cam ,

and you have only one intake valve and it is huge , that is it limits your revs and it limits your intake flow.

you cant get more air+fuel in than that intake valve alows , you can invest in any tuning part but that is the choke point, so some serious HP is impossible to get. that is with a N/A engine [:o)]

nadg63 · Postby **nadg63** » 04 Jul 2009 06:41

Want economy buy something sad like a Prius!

john 215 · Postby **john 215** » 04 Jul 2009 07:12

Hi Don,
SOD ECONOMY STICK A DIRTY GREAT BIG V8 IN HER [:p] SOMETHING THAT SUCKS THE WILD LIFE OUT OF THE HEDGE ROWS [}:)] YOU WILL NOT REGRET IT [8D]
Cheers John

LIVE LIFE A QUARTER OF A MILE AT A TIME!
1979 3.5 FHC(STATUS PENDING!!)

1982 2.0 DHC NOW A 4.6,ON THE ROAD NOW KICKING AR5E !!!!

Spectatohead · Postby **Spectatohead** » 04 Jul 2009 09:00

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by john 215

Hi Don,
SOD ECONOMY STICK A DIRTY GREAT BIG V8 IN HER [:p] SOMETHING THAT SUCKS THE WILD LIFE OUT OF THE HEDGE ROWS [}:)] YOU WILL NOT REGRET IT [8D]
Cheers John
<hr height="1" noshade id="quote"></blockquote id="quote">
You, sir, are a total motorhead. I could not have said it better myself.[:D]

Jim, with the pitifully small 3.5 liter TR8
The larger wildlife is still safe.

'80 TR8
'97 Maxima 5spd

trv8 · Postby **trv8** » 04 Jul 2009 09:38

Nice big dirty thumping V8 = smiles per gallon [:D][}:)]

Beans · Postby **Beans** » 04 Jul 2009 13:00

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by john 215

...SOMETHING THAT SUCKS THE WILD LIFE OUT OF THE HEDGE ROWS ...<hr height="1" noshade id="quote"></blockquote id="quote">
You won't need a V8 for that, just put some nice open Weber DCOE's on [:D]

1981 TR7 FHC Sprint (better known as 't Kreng)
1980 TR7 DHC (my first car currently being restored)
In parts a 1980 TR7 PI DHC, 1981 TR7 DHC, 1981 TR7 FHC
http://tr7beans.blogspot.com/</center>

Don · Postby **Don** » 04 Jul 2009 16:27

OK, Thanks for the info. Everyone seems to agree that porting is really not neccessary. I have 175 SU carbs and it sound like the SU's can be made to work well. I was already planning on a Header, de-smoging and a K&N air filter.

Now some questions:

FI Spyder - Does 93 octane burn ok at 9.5:1? What has happened to your Km/Liter (mpg for us in states)?

jclay - What is a pocket port?

Hasbeen - How does one know how far the head can be shaved? I like this idea because it does not require diving into the bottem end of the motor which was just redone 20K miles ago, and is a low budget option.

Marko - I love the idea of a 16V head, but these are impossible to find in the 'states, and if you do, they are very expensive. Can you suggest an after-market FI?

John 215 - Yes, the V8 would be fun. I'm hoping to purchase a TR8 soon (I'ved got something in the works). I want to keep the Spyder semi-original for show purposes.

paul w · Postby **paul w** » 04 Jul 2009 17:05

You cannot beat displacement!The 4.6 v8 in 'godzilla'put out 260 bhp
at the fly wheel,so if i 'drive it like i stole it',i get 11 to the
gallon!! But,there is ssooo much torque-like a Scania truck.Drive it
at 2000 to 2500 rpm(can pull in 5th at 15mph up to illegal easy)and
i can get 35 to the gallon if i drive it like a granny.And the sound-
did they mention the roar?Like a drug,gotta get another fix.....

See ya',Paul.

MCNX BFF · Postby **MCNX BFF** » 04 Jul 2009 17:25

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Don

... I want to keep the Spyder semi-original for show purposes.

<hr height="1" noshade id="quote"></blockquote id="quote">

 Whew! As I was reading this thread, I thought this WAS about your Spider. Personally, I am glad you are hoping to keep it as stock as possible. Don't get me wrong; I am not a purist, per se. If (or when?! Knock on wood!) my car's engine takes a dive, I would love to have something with a little more "umph" put in under the bonnet! [;)] For now, it will remain as is. 

----MH-----

Underdog · Postby **Underdog** » 04 Jul 2009 18:02

9.5 has always worked for me on 93 pump fuel. With an alloy head you can get another point or 10.5

Pocket port...this is when you blend the bowl area directly under the valve. Emphasis is usually on the short side radius. This is done on street engines to increase volumetric effecency. Idea is to smooth out the flow where it makes the sharp turn and create sort of a venturi effect. You can get a really nice job when done in conjunction with larger valves. The larger dia seats provide more material to work with in the bowl area. The runners are usually left alone except to clean up casting flash. It's been shown that too large of runners actually hurt because of the slower air velocity. It really is a science in itself...interesting stuff and labor intensive to get a good job.

72 MGB BRG
80 TR8 Persian Aqua
If women don't find you handsome, they should at least find you handy.

Anonymous

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