Fast Road 2.5 engine build advice & opinions

[Callan Hyde]

Hi all, ive got a triumph 2000 estate which is undergoing some very major surgery at the current point in time. Originally a 2.0 auto, im planning on building it into a 2.5 Manual OD.

Ive built several engines before but they are not my area of expertise so thought i would speak to those in the know about what I can expect to make from a 2.5 with the following work done. This is the current plan for the car, may differ in practice.

2.5 block shaved to remove recess and up comp rate

Tr250 head shaved to bring comp rate to normal figures and a bit more to further up comp rate.

0.60" bore, match weighted pistons and rods. 

Newman PH2 cam

Hoping to lighten flywheel a little

6-3-1 extractor manifold

Ported head and long manifold for HS6 carbs provisionally, plans to go to efi in the long run.

Megajolt distributorless ignition.

Im aiming to get a solid 150bhp out the car on carbs when i put it on the road with hs6 carbs and standard exhaust etc. By the time its done im hoping to be up at 170.

If those who have experience with engine builds like this could chip in itd be great. As far as i can tell those numbers should be realistic seeing the work done. Ive no experience building triumph 6 engines so any advice on snags i may encounter would be much appreciated. 

The gearbox ive got to run it through is a J type OD saloon box which as far as I can tell should handle the extra juice okay. Ive got the choice of the 2.0 auto diff  or the manual OD, undecided which one to try first.

Im expecting I may encounter issues with the UJ joints as well as the anti rattle straps flexing excessively under load, these will be nailed out in practice. 

Thanks to all those who may comment. 

 

Pic attached is the car in its current state, obviously not ready for the road quite yet lol Welding isnt the best in places but it works, car was fit for nothing other than the scrapyard when i started.

[Batch]

Hi Callan

I can certainly recommend that you lighten the flywheel, you can take about half the weight off. I have a 4kg one on my TR6 and it certainly spins up much faster and I don't seem to be suffering from lumpy tick over that some report.

Similarly I recommend that you think about CV driveshafts, not cheap but well worth the investment and easily capable of handling your predicted BHPs.

Dave

[Tim Bancroft]

The 'long' manifold may be an issue (strut tower), use the 2500S HS6 inlet manifold. You will be surprised how good a set of SU HS6 can be...throttle linkage can be an issue though. Difficult to get a decent filter in the gap between the carbs and the strut tower.

Bastruk in Germany do a lightened flywheel, otherwise talk to Chris Witor.

I agree with Dave in the last message, CV shafts are well worth it. I have Classic Driveline units in my 2.5 and yes, very good.

Think about a 123 distributor....some don't reckon them, I have had no issue with them.

Don't go mad on the compression ratio...

[Slimboyfat]

Beware the TR250 head has unique port spacing on the manifold side. You are limited to using the original Stromberg TR250 inlet manifold.

For that reason the TR250 manifold gasket is also unique to that head.

 

[Roger Keys]

As tim suggested, no downside to CV jonted drive shafts.

Im not sure why you think that there may be an issue with the anti vibration staps? Never had an issue on mine with similar power and more torque. The torque however did trash 4 diffs in short order.

[Callan Hyde]

On 04/11/2021 at 07:51, Slimboyfat said:

Beware the TR250 head has unique port spacing on the manifold side. You are limited to using the original Stromberg TR250 inlet manifold.

For that reason the TR250 manifold gasket is also unique to that head.

 

Ah, bugger. Thanks for the heads up, part of the reason I made this post so i can catch things like that before I get the head worked. Suppose ill have to use one of my other heads then. 

[Nick Jones]

Also be aware that if you deck the block enough to remove the fire-recesses, you’ll end up with some piston “pop-up”. Probably between 0.015 -0.020”, which is too much for comfort. So you’ll also need to deck the pistons. I did just this on the 2L engine now in my Vitesse which has 0.005” pop-up.

To get to the power figures you are naming will take some high quality head work, especially if you want it to play nicely with CD carbs which limits cam choice a bit.

I got just under 150bhp with my PI engine using the standard 308778 cam, TR6 cast manifold (down pipes are a difficult fabrication!) with Megasquirt controlling fuelling and sparks. Not a massive number but with >160lb/ft from 1800 - 5,200 it actually went rather well and 30+mpg even when “making progress” was good too.

Lightened flywheel and a good quality balancing job are huge benefits 
 

Nick

[Steve P]

Personal experience with my 2.5 Vitesse build:

Spec is...originally a PI  engine.

+20 bore,-10 crank grind,Vitesse flywheel with spigot added,nitrided crank,everything properly balanced and matched.Paddle clutch.

Modded oil pump.Head work and HS6 long inlet manifold flowed and matched (by GT).HS6 Short pot carbs.

Mike the Pipe 6-3-1 into custom made exhaust from the manifold back by Mat Simpson.(Ex BTCC)

TR5 Cam,Compression 10:1,standard 6 dizzy at present but i have a mappable 123 USB version to go in.

Saloon box with J type o/d and 3.27 diff.Custom prop with 100mm flanges.

RR session when run in made 172 BHP,can`t remember the torque figure,i have the printout somewhere.

Drives great with bags of grunt and torque at low revs,over 30 to the gallon on a run easily.

I only run on it Shell V power which is getting expensive but for the mileage it does no bother.

I use Valvoline VR 1 oil,always holds good pressure.

No knowledge of saloons but mine ate a driveshaft in Cornwall on the 2012 RBRR,CV`d it after that.  

Still great after 20`000 miles since built.

Steve

[JohnD]

ByI'm sure that you can get the figures you want from your 2.5L engine.

The flywheel was MUCH heavier in the saloon than even in the TR6, let alone the 2L applications.  From memory, 27kgs (or was that lbs?), And halving that wil do no harm.   But take weight off the rim, not at the hub. Or find a 2L 'wheel to start with.

I think that skimming the block to remove the recess is a mistake, as long as you fit the correct gasket.    The compression ring works well.   'Decking' the block by skimming isn't a useful way to raise compression, unless you also equalise the piston heights by machining their faces to ensure that not only are the chamber's the same size, but they rise into the chamber the same height.  This can allow 'piston popup' which can be a last resort way to raise compression.

6-3-1 good choice, but ensure the primaries are the same length.  Mine are 17"

Good luck!

John

Edited November 6, 2021 by JohnD

[Guppy916]

Almost the same as mine 

Edited April 12, 2022 by Guppy916

[Guppy916]

I run triple 40's 

[1147cc]

Id suggest the Mikuni HSR45 carbs over the EFI and SUs

[Gt6s]

On 12/04/2022 at 17:41, 1147cc said:

Id suggest the Mikuni HSR45 carbs over the EFI and SUs

Dissagree, EFI is far more tunable (no compromises) carburetors in thier very nature have compromises. You can even do a workaround to be able to use the massively oversized PI throttle bodies (Creative unconventional low speed mapping) Never mind the WONDERFULL 3D ignition management.

Edited April 14, 2022 by Gt6s

[RobPearce]

31 minutes ago, Gt6s said:

Dissagree, EFI is far more tunable (no compromises)

Yep, absolutely. If you can engineer your intake properly (which may not be easy) and have access to a rolling road for proper mapping, then EFI will beat any carb setup. But carbs are a lot easier for ordinary joes to bolt on.

[Gt6s]

Not that difficult 

[Nick Jones]

ON a saloon you can base your EFI on the PI throttle bodies and all the parts exist to make it fit.  Or engineer your own.

Newman PH2 will be ok with a plenum type and single throttle body.  Wilder than that and you'll get a better result from individual ones, though the factory PI ones are a bit big for easy mapping and the factory linkage is just nasty.

Nick

[1147cc]

K.I.S.S.

[Spitfire6]

On 12/04/2022 at 17:41, 1147cc said:

Id suggest the Mikuni HSR45 carbs over the EFI and SUs

Hi,

Free to have opinion.
Why do you say this? How many HSR45's are you suggesting & with what manifold?

Cheers,
Iain.

[1147cc]

Ive installed about 8 sets of HSRs and they are awesome.

Just use the stock manifold with 2 of them.

[Gt6s]

On 14/04/2022 at 17:28, Nick Jones said:

 PI ones are a bit big for easy mapping and the factory linkage is just nasty.

True EASY not a word I would use for it, But it can be done completly sucessfully with creative unconventional mapping. eg fueling for 70Mph at 1%  throttle. My ECU had to be tricked to map at 0% 1% 3% for example. As for the linkage Yes they are garbage. I found that ball jointed adyustable rods make a HUGE difference

[Nick Jones]

50 minutes ago, 1147cc said:

I've installed about 8 sets of HSRs and they are awesome.

Just use the stock manifold with 2 of them.

Ok..... nice and simple for sure.  Looks good. This is using new, genuine Mikunis?  From what I can see they are the thick end of £ 500 each, which is more than I spent on my first EFI project including ECU.  Chinese ones more like £ 120 each but may not be worth having.

There must be some kind of adapter also - is that some kind of rubber neck to bolt flange like this?

Nick

[1147cc]

you dont need the whole bike kit; just the bodys I pay about 300 USD for each one; rubber mounts about $30

still cheaper than a new set of HS6s

[Nick Jones]

The cheapest I can find the carbs only in Europe is on a Dutch Harley site @ €465 each + adapter + tax + shipping. Things like this are often significantly cheaper in the US, so it might be possible to source there though shipping and VAT take the shine off.

If I were going the CD carb route in the UK I’d hunt down a pair of the later HIF6 /HIF44 (big improvement on HS) IMO and rebuild those. I do also know a couple of people using Stromberg CD175s with excellent results. They can still be found quite cheaply as people remove them from ex-USA TR6 /TR250s and they aren’t very popular.

[Gt6s]

14 hours ago, Nick Jones said:

£ 500 each, which is more than I spent on my first EFI project including ECU

Mine came in at £750 with a brand name ECU. Granted that was back in 2002. Edit JEASSSUS That's 20 years ago !

Edited April 16, 2022 by Gt6s