Carbs, Cams or 904?

[em_dot]

If you dont have bores in like new shape the 865 kit is not a good idea in the first place.

That just seems like a no brainer to me, and yet it needs to be said.

On a less related note I just compared the total price of a 904 kit with all the goodies with a small block Chevy crate engine. You get a lot of motor (350 ci) for $5K. Unfortunately, I sold the Corvette years ago...

 

[SCBonneville]

That just seems like a no brainer to me, and yet it needs to be said.

On a less related note I just compared the total price of a 904 kit with all the goodies with a small block Chevy crate engine. You get a lot of motor (350 ci) for $5K. Unfortunately, I sold the Corvette years ago...

The Nikasil lining that Triumph uses is among the best in the industry...

I started with a 790 engine and bought a set of 865 cylinders that had ~5k miles on them... they still had the initial swirl marks in the bores. I bought and installed a set of Wiseco 10.5 to 1 pistons. The "secret" is to properly set the ring gap to the bores...

I now have a higher compression 865 engine with 790 cams on stock heads/valves running rejeted CVK's and pods through Staintune reverse cones... It makes mid 70's HP and low 50's lb. ft. of torque for a total outlay of less than a twelve hunded dollars and that was with my "dealer wrench" doing the engine build and the two of us taking the "old" motor out of the Bonnie and installing the "new" one...

I'm VERY pleased with the results... I gave me everything I was looking for performance wise... ESPECIALLY when the cost is figured in... I am happy with the performance level and am "done" with engine mods on this Bonnie...

The "old" Bonnie engine will most likely be built a bit differently as the project Bonnie it is going into will have a bit different design brief... I will most likely go with the TPUSA 865 performance kit and will do some mild head work while the engine is apart...

 

[SCBonneville]

Which one do you reckon I should do first? (it's an '05 Thrux, preds, K&N pods.) I'm going either 39mm FCRs or 813/T-Bike cams or the 904 bore kit. I can only afford one of these mods at this time.

Decisions decisions decisions!

Thanks for any advice guys,
Pete

If I had to do the upgrades in stages... Here's the route that I would go:

I would upgrade the cams (easily installed without cracking the engine and the 865 cams really suck...) and get you ignitor reprogrammed by Pieman.... Those two mods, along with an aibox carve/pod filter install and installing free breathing exhaust will give you a pretty fair upgrade in performance... Probably the biggest performance boost per dollar that you'll find...

Then, if you're set on carb upgrades... do that...

Save the piston upgrade or big bore kit and head work for a single tear down/rebuild session...

Just my two cents worth...

 

[Texas94fs]

if I Had To Do The Upgrades In Stages... Here's The Route That I Would Go:

I Would Upgrade The Cams (easily Installed Without Cracking The Engine And The 865 Cams Really Suck...) And Get You Ignitor Reprogrammed By Pieman.... Those Two Mods, Along With An Aibox Carve/pod Filter Install And Installing Free Breathing Exhaust Will Give You A Pretty Fair Upgrade In Performance... Probably The Biggest Performance Boost Per Dollar That You'll Find...

Then, If You're Set On Carb Upgrades... Do That...

Save The Piston Upgrade Or Big Bore Kit And Head Work For A Single Tear Down/rebuild Session...

Just My Two Cents Worth...

This.

 

[mikenva]

That just seems like a no brainer to me, and yet it needs to be said.

On a less related note I just compared the total price of a 904 kit with all the goodies with a small block Chevy crate engine. You get a lot of motor (350 ci) for $5K. Unfortunately, I sold the Corvette years ago...

yea and just becausethey look good dont mean there still round and stright the coating is tuff stuff but the castings are not that good they can move around with time.

 

[mikenva]

Comp.ratio and bigger cc both make more torque on these motors if they have enough air flow and the right pipes.Now max hp works something like this.
Lets say we have a 790 with a stock head flat slide carbs 813 cams good pipes .lets say it makes its max hp at 8500 rpm .It will make less torque then a 865 motor with the same head,cams carbs and pipes but the max hp will be very close because the 865 might have a max hp rpm of lets say 8200.Then we build a 904 with the same carbs cams head and pipes it will make more torque but max hp will come at a lower rpm.Hp will still be close.Now we do the same test with a built head max torque dont change much but max rpm hp goes up so does hp with size.You can really see this when you get in the real big bore stroker kits.some have 1100 and 1200 motors with lots of torque but dont have enough head or cam to make any more hp then say a 988 motor.
A few years ago a 100hp bonnie was a dream untill tpusa and fast freddy came up with heads and cams up to the job.Now carlos can sell you one.I havent had mine tuned righ and dynoed yet but so far I have seen 106hp and 76ft/lbs.I think I have it close to right now with the 2ino2 system we will see soon.

 

[Aussie_T100]

I've been wondering if the extra 39cc and a tad more comp would make that much difference. Then I found Aussiebiker's posts in the sticky dyno thread at rat.net...

http://www.triumphrat.net/twins-technical-talk/97729-twins-dyno-results-thread-5.html#post1540235

It seems that is does!

Based on his results you would have to think 5ft/lbs is within the realms of possibility on a highly modified engine at least. That's either an exceptional motor or a "happy" dyno though. It's not a perfect comparison because it's an EFI 270 engine and he started with 10.3 to 1 comp @ 865 and went to 11.6 to 1 comp with the 904 whereas the TPUSA 865 kit is 10.8 to 1 and the TPUSA 904 kit is 11.5 to 1. He did see a 4.5ft'lbs increase in torque though and it's probably the best comparison we will find.

I'm still of the opinion that a 904 kit is not worth the extra cost over an 865 high performance kit unless you are going to do head work & FCR's as well. The complications added for us Aussies with customs duty, GST & brokerage fees being payable on any import over AU$1,000 probably has a big bearing on that opinion though. The same problem applies to importing a TPUSA modified cylinder head as well and finding a local with experience in modifying these heads is difficult, all of which makes building a high HP Triumph engine in Australia very very expensive.

 

[Pete R]

I'm still of the opinion that a 904 kit is not worth the extra cost over an 865 high performance kit unless you are going to do head work & FCR's as well. The complications added for us Aussies with customs duty, GST & brokerage fees being payable on any import over AU$1,000 probably has a big bearing on that opinion though. The same problem applies to importing a TPUSA modified cylinder head as well and finding a local with experience in modifying these heads is difficult, all of which makes building a high HP Triumph engine in Australia very very expensive.

I hear you there mate!

However we have some excellent engineers and machinists down here with performance pedigrees stretching from their beginnings during WWII all the way the to Formula One engine development and construction. Until the advent of the WWW it was these blokes we turned to.
I can remember a young Mick Doohan at the first Australian round of the World Superbike Championship in the mid/late 80's. He rode a locally prepared bike and lapped everyone but second place. The head work on that bike was done 1500 metres from where I work.

I'll do a Lindsay Buckingham and go my own way. I'll give some of these old local guys a call. See what happens!

Thanks for the advice guys,
Pete

 

[Phil-1100]

I have just had a head ported, flows just in the 300cfm range with large valves. Here In South Oz

 

[mikenva]

I am sure there are lots of good head men all over the world .Its more a mater of finding one that will do the many hrs of flow and dyno testing to learn what works best on these motors .There are so few of these motors compared to other motors not to many want to spend the money and time to get the best out of them.TPUSA has been there and done that.There heads and cams are second to none.

 

[mikenva]

Based on his results you would have to think 5ft/lbs is within the realms of possibility on a highly modified engine at least. That's either an exceptional motor or a "happy" dyno though. It's not a perfect comparison because it's an EFI 270 engine and he started with 10.3 to 1 comp @ 865 and went to 11.6 to 1 comp with the 904 whereas the TPUSA 865 kit is 10.8 to 1 and the TPUSA 904 kit is 11.5 to 1. He did see a 4.5ft'lbs increase in torque though and it's probably the best comparison we will find.

I'm still of the opinion that a 904 kit is not worth the extra cost over an 865 high performance kit unless you are going to do head work & FCR's as well. The complications added for us Aussies with customs duty, GST & brokerage fees being payable on any import over AU$1,000 probably has a big bearing on that opinion though. The same problem applies to importing a TPUSA modified cylinder head as well and finding a local with experience in modifying these heads is difficult, all of which makes building a high HP Triumph engine in Australia very very expensive.

look at post #25 of that dyno tread that was my 904 with a procom box the bike pulled even better that after going to a pieman box.That tpusa 904 had just a run of the mill 2mm os valve head 813 cams 42mm flat slides and d&d 2into1 pipes.84.67hp and 63.89ft/lbs sae hp the bike that was running to lean allso.

 

[hankmarx]

106hp and 76ft/lbs.
:worthy:
:cheer:
:headbang2:

 

[Pete R]

look at post #25 of that dyno tread that was my 904 with a procom box the bike pulled even better that after going to a pieman box.That tpusa 904 had just a run of the mill 2mm os valve head 813 cams 42mm flat slides and d&d 2into1 pipes.84.67hp and 63.89ft/lbs sae hp the bike that was running to lean allso.

:huh: Run of the mill 2mm os valve head? 42mm flatslides?

Aussiebikerdave's bike had stock CV carbs, stock valves and stock ignitor box. Comparisons with your bike or your results in this instance are pointless mate.

Anyway you missed the point - which was to show the increase in power and torque from just going that extra 39cc to a 904 kit. The results were really good for less than 5% increase in capacity (and a bit more comp)

 

[mikenva]

WELL i have to agree with aussie t100 I think that guys dyno numbers are alittle to good.
I was just showing you mine to see what a 904 with average stuff we do to them can do.Besides that anyone that would go to all the money and work to build a 904 would be nuts to run stock cv carbs.A 2mm os head is not that wild on this side of the pond theres alot of them .The head i have now makes that one look like a toy .

 

[mikenva]

:huh: Run Of The Mill 2mm Os Valve Head? 42mm Flatslides?

Aussiebikerdave's Bike Had Stock Cv Carbs, Stock Valves And Stock Ignitor Box. Comparisons With Your Bike Or Your Results In This Instance Are Pointless Mate.

Anyway You Missed The Point - Which Was To Show The Increase In Power And Torque From Just Going That Extra 39cc To A 904 Kit. The Results Were Really Good For Less Than 5% Increase In Capacity (and A Bit More Comp)

Looking Closer Thats Not A Cv Carb Bike Thats A Efi

 

[Pete R]

Sincere apologies, EFI it is. Other points still stand - I think we know quite well what the results of the average stuff you do to them does.

We were trying to compare apples to apples and establish the effect of one mod and one mod only.

 

[mikenva]

Well thats a hard thing to do .One mod afects the other .You need to set what your looking for as far as pwer then you can deside what you need .Stock these bikes dont have enough air flow ,just going bigger with out fixing the air flow wont get you much just alittle more torque and a lower rpm max hp.
In the case of a stock 865 carbs, airbox ,cams and pipes hold you back the most after that you need to get inside the motor.Then the price goes up from there.But you will need the first 4 things to see any good gains from what you do inside the motor if you get those 4 right first you can go as big as you want inside the motor.

 

[Pete R]

Well thats a hard thing to do .One mod afects the other .You need to set what your looking for as far as pwer then you can deside what you need .Stock these bikes dont have enough air flow ,just going bigger with out fixing the air flow wont get you much just alittle more torque and a lower rpm max hp.
In the case of a stock 865 carbs, airbox ,cams and pipes hold you back the most after that you need to get inside the motor.Then the price goes up from there.But you will need the first 4 things to see any good gains from what you do inside the motor if you get those 4 right first you can go as big as you want inside the motor.

yeah I understand that Mike, it's all a dynamic thing.

But that example I gave of Dave's scrambler was good I think because he had a dyno readout before the 904 kit and one straight after the 904 kit - with no other changes. I didn't think the extra 39cc and a bit of comp would do that much (don't think Dave did either!). I realise that doing the 904 by itself (without the other changes Dave had made) may not have had the same result - but it's still a good example I think...and the only one I could find of before and after 904 graphs

BTW thanks for the wall thickness measurement. :up: Much appreciated!

.118"... not much there is there? You'd reckon that under 3mm would be pretty weak...doesn't leave much room for punching them out either

hmmm...

 

[1087]

yeah I understand that Mike, it's all a dynamic thing.

But that example I gave of Dave's scrambler was good I think because he had a dyno readout before the 904 kit and one straight after the 904 kit - with no other changes. I didn't think the extra 39cc and a bit of comp would do that much (don't think Dave did either!). I realise that doing the 904 by itself (without the other changes Dave had made) may not have had the same result - but it's still a good example I think...and the only one I could find of before and after 904 graphs

BTW thanks for the wall thickness measurement. :up: Much appreciated!

.118"... not much there is there? You'd reckon that under 3mm would be pretty weak...doesn't leave much room for punching them out either

hmmm...

Dave 904 is in race trim ( high CR, cams, head, racing fuel, high end tuning, not your everyday street 904.

 

[Pete R]

To quote Dave -

"modified Arrow 2:1, airbox removal kit, TB cams and head work (port&polish and 1mm shave)"