Exhaust valve seats question - lost power!

[nosman]

Hi,

I have an old rover v8 in my capri, i never changed the valve seats when i rebuilt the motor around 18 years ago, now i know there is controversay regarding the hardness of the seats, but a friend of mine said his burned out slowly and the car just got slower and slower.

the heads are SD1, and ive run on regular unleaded as it doesnt seem to like high octane, when it was first tuned it made around 220bhp at the wheels, today on (different) rollers she made 190bhp at the fly, which is quite a loss, the car doesnt feel as crisp and its running very hot all the time even without the thermostat in.

The compression test results were close to what tey always were, but oil in the plug hole makes no improvement, its alwasy used lots of oil, and is still basically the same, but does anyone think the valve seats could be to blame, or would we guess it needs new cam/followers/gears again maybe or just a general refresh?

The point is, if its not likely to be the valve seats, i may as well sell it on and put the cash into a small block ford i have in the garage to finish that off (although then the bulkhead has to be cut back so id rather not!)

any help gratefully recieved, but, and i kno this may sound rude, i arent after internet hearsay! so if anyone has had a similar experience id appreciate the help!!!

Thanks Doug

[bigaldart]

Its unlikely to be the valve seats, personally I would look at the cam. Timing chain slack won't help either. Lots cheaper to put a cam kit in it rather than have new seats fitted.

Alan

[SuperV8]

Just curious, what mods has it had to make 220 at the wheels? That's doing well for a 3.5.

Was that rolling road someone you trust? Maybe the 220 was exaggerated? If it's running too hot that could cause loss of power.

If the compression tests results haven't changed then that would tell me the valve seats are fine.

Tom.

[5000SE]

Just curious, what mods has it had to make 220 at the wheels? That's doing well for a 3.5.
Was that rolling road someone you trust? Maybe the 220 was exaggerated? If it's running too hot that could cause loss of power.
If the compression tests results haven't changed then that would tell me the valve seats are fine.
Tom.

220 is HUGE at the wheels for a 3.5 - it takes quite a serious 3.5 to make 220 at the flywheel.

I had a big throttle single plenum 4.6 with stage III heads and all the works from inlet to exhaust which made something like 305 flywheel and 230 wheels (if memory serves).

What's the build/heads/cam/inlet system?

If your compression readings are close to what they always were, there's not likely to be anything wrong with the valves - perhaps just a wildly ambitious initial dyno reading?

[nosman]

The comps are close, 5 to 10 psi down maximum, although its hard to get sensible readings as the starter is at best tired, so instead of saensible rpm it turns over at around 6-10 rpm!

The spec is

3.5
20 thou overbore
9.75:1 compression ratio
arp bolts/studs throughout
steel timing gears (standard style chain)
sd1 oil pump/tadpole relief valve
viper typhoon cam
rhoads lifters
tlr 50 springs, with shortened guides
polished lifter gallery
stock manifold (intake) with pent roof removed, opened internally to make a common plenum with ported entries to the intake, welded on weber 2 barrel adapter plate and a 32/36 dgav(variable secondaies) and a K&N filter
heads were a little bit special, they came with the sd1 engine, but when they were stock, i compared them to another set i bought and the ports were much larger (before any porting), so i dont know what was special about them, as they were both stock sd1 heads
I ported the heads myself, paying special attention to the valve throats around the guides etc
the dizzy is mechanical advance only and is an opus(less) running static advance of 6 degrees btdc
tubular exhaust manifolds of small bore, with free flow exhausts again made by me
probably other stuff, i cant remeber its been built years!

i always figured the initial figures were atad optimistic, but not 80bhp optimistic!

it was always rapid, its on a manula 4 speed trans and an open 4ha diff, so trans loss is minimal, both run on ep80 oil

[nosman]

Just curious, what mods has it had to make 220 at the wheels? That's doing well for a 3.5.

Was that rolling road someone you trust? Maybe the 220 was exaggerated? If it's running too hot that could cause loss of power.

If the compression tests results haven't changed then that would tell me the valve seats are fine.

Tom.

its only recently started to run hot as the power is dropping off, maybe its just the cam timing is getting retarded if the chain is stretching, i know too much ignition timing is a sod for overcooking the motor, but the ignition seems about right timing wise, so i would assume if the cam was retarded, ipso facto the dizzy would be too!

the rolling road guy is very renowned, and was always very impressed with how the car went, but i wouldnt lik to name him for fear of damaging his reputation!

when the engine was stock, (still SD1, 9.35:1) with a new hurricane cam and new stock lifters and stock su's etc, made around 120 at the wheels on his rollers, which after what real steel claim and the motor should put out, seems about right id say

[ChrisJC]

You could take the rover covers off, and by using a DTI, check that the valve lift and timings are all in spec.

Chris.

[5000SE]

Just curious, what mods has it had to make 220 at the wheels? That's doing well for a 3.5.

Was that rolling road someone you trust? Maybe the 220 was exaggerated? If it's running too hot that could cause loss of power.

If the compression tests results haven't changed then that would tell me the valve seats are fine.

Tom.

its only recently started to run hot as the power is dropping off, maybe its just the cam timing is getting retarded if the chain is stretching, i know too much ignition timing is a sod for overcooking the motor, but the ignition seems about right timing wise, so i would assume if the cam was retarded, ipso facto the dizzy would be too!

the rolling road guy is very renowned, and was always very impressed with how the car went, but i wouldnt lik to name him for fear of damaging his reputation!

when the engine was stock, (still SD1, 9.35:1) with a new hurricane cam and new stock lifters and stock su's etc, made around 120 at the wheels on his rollers, which after what real steel claim and the motor should put out, seems about right id say

That probably sounds about right at the wheels for a stock motor with hurricane cam if it was a healthy unit - those other mods don't make another 100 at the wheels.

There's nothing wrong with the build you list above, but it would be lucky to produce more power than a standard Vitesse injected unit, and I'd suggest 190 at the crank is about what it should be giving.

Please don't take this the wrong way but 220 at the wheels for that build is way out there in fantasy world, and whoever dynoed it should know, no matter what his reputation.

220 at the wheels means the best part of 300bhp at the flywheel - to get anywhere near that from a 3.5 you're talking a screaming full race engine and a hell of an expensively built one at that.
Even a 4.6 would need big valve heads, cam and modified fuel injection or quad carbs to get to that level - remember the standard 4.6 was only 225bhp @ flywheel, and 5.0 TVRs actually put out about 285-290bhp (they simply lied claiming 340), which would be about a 220 wheel figure.

[DaveEFI]

Hi,

I have an old rover v8 in my capri, i never changed the valve seats when i rebuilt the motor around 18 years ago, now i know there is controversay regarding the hardness of the seats, but a friend of mine said his burned out slowly and the car just got slower and slower.

the heads are SD1, and ive run on regular unleaded as it doesnt seem to like high octane, when it was first tuned it made around 220bhp at the wheels, today on (different) rollers she made 190bhp at the fly, which is quite a loss, the car doesnt feel as crisp and its running very hot all the time even without the thermostat in.

The compression test results were close to what tey always were, but oil in the plug hole makes no improvement, its alwasy used lots of oil, and is still basically the same, but does anyone think the valve seats could be to blame, or would we guess it needs new cam/followers/gears again maybe or just a general refresh?

The point is, if its not likely to be the valve seats, i may as well sell it on and put the cash into a small block ford i have in the garage to finish that off (although then the bulkhead has to be cut back so id rather not!)

any help gratefully recieved, but, and i kno this may sound rude, i arent after internet hearsay! so if anyone has had a similar experience id appreciate the help!!!

Thanks Doug

The valve seat hardness only applied to early engines - and even these are ok on unleaded. The SD1 ones are fine.

These engines don't use 'lots of oil' when in good nick, so something strange there. Is the crankcase breather system as per spec and in good condition? It should run at a slight vacuum - if it gets pressurized it will burn oil.

Compression tests while cranking only give a rough guide.

Most likely it's a worn cam. Even more so with aftermarket designs. They accelerate the valve train more quickly so increase the load/wear on the cam. Lift the manifold and have a look - it's usually pretty obvious as the cams don't all wear at the same rate.

[nosman]

well i always estimated it was more likely 220 - 230 at the crank, as real steel quote 252, but i didnt use their heads, or a holley carb.

it made 200 at the crank back in february, on motorscopes rollers in northallerton, the recent figures were at rstuning in leeds, both seemed feasable, however the car has just lost a lot of power, i can feel it

i have run with lots of different diff ratios/tyre combos over the years and the car used to love the high gearing, pulling hard against the taller ratios and actually returned better ET's, but its lost that hard bite it used to have, especially in the upper gears, i never had to shift down to overtake anything, when you stood on it, the old girl used to light up!

Now i dont know if having just sold a 600bhp GTR it doesnt feel as lively, but it always did, and it just doesnt have the oomph it did, regardless of what the rollers say!

i ran 15.22 at york, with 235x60x14 tyres and a 3.09:1 diff, against a best of 15.7 with the same tyres and the old 3.75:1 diff in the same casing!!

my previous best on nitrous was 13.6@ 112 mph, with a 75 sniff of gas (single hit) and major wheelspin! (all the way up in fact!)

now with good 60ft's, same gas, diff but larger tyres, that are a very similar rolling radius to the 235's, im getting 13.64 at 104mph and thats using the gas at the end of 1st gear!

so i dont know about power outputs, but i do know its not how it was and wont run cool, so as said my original gut feeling about the bump stick may bear out, so im guessing the next best thing is top pop the inlet off as i have a spare gasket somewhere anyhow!!

cant really use the DTI as the hydraulics will have bled down and wont give accurate readings, but i might be able to get it on the lobes themselves once the carb is off, or as said it may be glaringly obvious by sight!!

it would be nice fr a cheap fix save me building the 302 up until i have the time and money, as that will give me a good torque hike, but oh lord its heavy! and i cant afford alloy heads!!

[nosman]

sorry forgot the breathers, it doesnt have any valve seals, and the breathers are put to a catch tank, most rv8's are oily old birds in my experience, but when i say it uses a lot i mean compared to the saxo or gtr!

its not [quite] like a two stroke! ahem

[DaveEFI]

sorry forgot the breathers, it doesnt have any valve seals, and the breathers are put to a catch tank, most rv8's are oily old birds in my experience, but when i say it uses a lot i mean compared to the saxo or gtr!

its not [quite] like a two stroke! ahem

My 160,000 mile 3.5 does approx 3000 miles per litre.