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ClimberTom

V8 Carb tuning/snorkle/intakes

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Slowly but surely I'm getting the truck back up to par.

One thing that has been slightly frustrating since i've had it is that its a bit lacking in power so this is the next thing to tackle.

First thing on my mind is the air intaks - She's got twin snorkles (around 2.5" ID) but they aren't plumbed in, theyre more for show (currently). They also get a bit battered by trees and bushes in the nice narrow Devon lanes I drive. So any thoughts on improvements in them? I'm thinking lowering them (as I've started in the photo of the passenger side one) and a safari type top to them that I can get tucked inside the boundary of the roll cage for a bit more protection.

Next down the line is the air box (or lack of) a previous owner fitted a nice lumpy survo assist to the clutch which take up most of the space the air box would fit. in exchange for the air box I have two lovely small K&Ns on the carbs which are clearly restricting air intake. Thoughts on improvements here? An original air box wont fit but what sort of size would a custom box need to be to get the most of out of it? Has anyone done similar? Fitting an air box would also allow the  snorkels to be plumbed in...

Or any other throughts on air intakes? At the very least will be new filters on the carbs if I can't make any progress with the snorkels/air box ideas. I have wondered about some form of scoop on the bonnet to help get cleaner/fresher air to the filters but I wonder if that will also allow too much moisture to them as well in rain/off road. It has got a fibregalss/composite bonnet.

Next on my list is to check the timing and get that set - Check TDC against the timeing marks then check/adjust the timing to get as much advance as possible without pinking?

Finally is the carbs themselves - the dark art of balancing them. I've done a lot of reading and research but if anyone has any pointers on this I'd be very greatful!

I have already fitted new (correct) spark plugs, new flame traps, new oils, filters etc.

Have I overlooked anything? Or should I be looking at things in a different order?

Is it worth looking at the exhaust too? It has tubular headers then is starnard from the 2-1 'Y' piece back.

Some pitures to hopefully show what I have to work around with snorkels and air boxes:

IMG_20190309_112933 (1024x768).jpg

IMG_20190309_113244 (768x1024).jpg

IMG_20190309_113304 (768x1024).jpg

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Your low power is more likely just the age + tune of the engine, if the truck is an original V8 it'll be quite de-tuned compared to Range Rover lumps.

The air filters suck but are unlikely to be causing you issues until high RPM anyway. I run 200TDi air filters on my 4.6's as they're compact-ish and should flow more than enough. I don't think you need worry about the snorkels, a single 2.5" would be fine unless you're screaming round on the rev limiter - petrol engines don't breathe much unless the throttle's wide open.

Other factors could include gearing - are you running big tyres with original transfer gears or ???

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Big tyres, cage, rock sliders and lots of other heavy stuff.... ;)
A 3.5 will never be a fire breather, especially on carbs.

 

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Yes, she's on bigger tyres (and I presume standard gearing) so that's not helping the situation.

A mechanic friend (and land rover nut) who did the MOT recently agreed that it is partly down to tyre size/lift/etc/generally not being a spritley engine. But he did also agree that even considering the above, there are still improvements to be made. That and it's my opertunity to tinker and learn...

I'm not too worried about the snorkels as I know they'll cause a restiction. My bigger issue with them is the battering they get so wanting to get them a bit more tucked into the cage to protect them (and give me a little more clearance above).

Has anyone fitted or know of a smaller air box that might fit in the gap I've got left to stop the filters sucking up so much engine bay muck which is my bigger hang up. Its either that or I just look to replace the cones like for like and try to keep them clean.

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3 minutes ago, ClimberTom said:

Has anyone fitted or know of a smaller air box that might fit in the gap I've got left

I already suggested 200TDi airbox - failing that, a panel filter from something like a TD5 or P38 might be tuckable somewhere.

Are you asking about engine mods or what - because with an unknown old V8 there could be no lobes left on the cam and a load of slack in the timing chain so unless the basic engine is in good nick you're only turd polishing if you start trying to improve the other stuff.

And I say again - your snorkels won't cause a restriction 99% of the time as airflow is related to throttle times RPM, if you're worried then spend £10 on a vac gauge and plumb it into the snorkel to see how much vacuum is being developed due to restriction at the engine end.

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Sorry, I miss understood that the 200tdi box was smaller.

I also may not have been very clerar that I'm fairly new to Land Rovers and more so to petrol (carbed) engines. So really I'm looking for anything obvious that I've missed or can look into.

Clearly stripping the engine and doing a complete rebuild will be the only way to get it to a known state that is in top spec. Until something major forces that though it's not really an option. I'm happy with the truck I just want to make sure it's running as well as it can for it's sake and for getting the best I reasonabley can out of it.

Hence I'm looking at things like timing, carb balancing and a more efficiant way of getting the air in rather than through a pair of clogged air filers.

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As fridge says,  with an old V8 you're wasting your time if the cam lobes are worn and the timing chain is stretched.  V8s get through both at reasonably low mileages- not a huge job to check and replace and can restore a lot of missing power.  Even a low compression 3.5 should feel pretty pokey in a 90, snorkel or not.

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Do a compression check, and pull the rocker covers to measure valve lift, that will give you some idea of what state it is in.

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So the cheap/free stuff first - checking stuff costs nothing, as Bowie suggests, and then you know where you stand. If the truck feels flatter than it used to it's likely there's some fault or something out of tune so find & fix that 1st.

Aside from properly servicing and sorting out the carbs & ignition (use genuine ignition parts, NGK plugs) there's not much you're going to gain without getting the spanners out - anything you tweak up will either be masking some underlying problem like a bald cam, or be so marginal as to be not worth the effort.

The V8 is a very simple old hector - a full or even partial top end rebuild is dead easy and not very expensive. A cam is dirt cheap - V8 Tuner supply the full kit with standard parts 3.9 EFi one in a kit for £200, a set of gaskets, some nuts & bolts and if you're feeling flush a duplex timing chain kit. Heads can stay on, just the front cover & inlet manifold to remove. The RV8's will soldier on as if nothing's wrong with no lobes left on the cam.

 

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I agree: compression-test first - you need to be seeing at least 170PSI on all cylinders. Anything less means you've got piston-ring or valve-leakage issues [or you're running a sad low-compression V8 which will never perform].

Then a valve-lift check. Old Rover V8s trash their camshaft-lobes because from the 1990s general engine-oils removed the 'high-pressure' oil-additives - traditionally based on Zinc Dithiophosphate - or "ZDDP" - because leakage/burning of this into the combustion-chambers really messed-up catalytic converters. An old RV8 run on post-1995 oils is guranteed to show pitting/erosion of the camshaft lobes; I've seen a few where the lobes were so badly eroded that they only gave 0.2 inch of valve-lift!

Also - if it's an irregulary-driven vehicle - check the distributor. The grease on the spindle can harden to the point where it traps the centrifugal-advance weights in the fully-retarded position. The result being an engine that is horribly-numb above about 3200RPM.

A healthy 3.5 RV8 should really start to sing at 3500 and happily go on to 5500 before the fun starts to tail-off.

"If in doubt, change-down" - you can never over-rev a healthy RV8. Shell V-power fuel works just fine in a TVR Chimaera with 10.5:1 compression pistons....

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1 hour ago, Tanuki said:

Shell V-power fuel works just fine in a TVR Chimaera with 10.5:1 compression pistons....

Higher octane fuel won't help a distributored vehicle as you'd have to adjust the timing to see any benefit - only EFI systems with knock sensors (4.0 / 4.6) would benefit.

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1 hour ago, FridgeFreezer said:

Higher octane fuel won't help a distributored vehicle as you'd have to adjust the timing to see any benefit - only EFI systems with knock sensors (4.0 / 4.6) would benefit.

A friend has a late-1970s 10.5:1 P6  (specced to take 101-0ctane 5*) with distributor/SUs and timed as standard with the original 101-octane-curve distributor (OK, it's got bronze valve-guides and stainless valves) he runs it on Shell V-power and on his European drives he's happy to run at full-throttle/5400RPM down to the Adriatic and back to see his girlfriend every other weekend.

The carbed LR/RR V8s were crippled in order to take poverty-grade fuel. We don't have to put up with this in the UK.

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Great stuff, thanks.

I was probably a little quick and didn't quite consider what I was writing to begin with but now I think we're getting there.

Yes, free/cheap things first. In reality at some point I do have a complete rebuild on my mind, but for the time being I can't really afford that in time or money terms... Am I better to wait out and do a complete rebuild or would doing the top end first then the bottom end later make much sense to spread the time. That said I'm thinking that top end should be do able in situe but a full reuild will  be an engine out job?

So added to my orginal list of checking the timing and balancing the carbs is to check/clean the distributor; check the valve lift and do a compression test.

Hopefully that should give me a picture of what condition the engine is actually in and be the first steps to getting everything running as it should be.

Sorry for the completely bone question, but when you say measure the valve lift, how do you go about that? I've just had a trawl through the workshop manual that I have but there's nothing that I can see in there other than it stating what the lift should be. I'm sure this is an obvious one so appologies in advance!

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Depends how big you're going on the rebuild really - a lot of people would just drop a 3.9 or 4.0 or even 4.6 in from a running donor rather than spend the money fettling an old 3.5, but it's all swings & roundabouts - not to mention cold hard cash!

You can spend a few hundred or a few thousand on a rebuild, really depends on your goals.

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Good info from Soren here, look for the video:

 

Just to be clear, in the YouTube video you'll see that the pushrods are marked with white marker. They are designed to rotate with the tappets, the rotation of which is caused by the cam lobes being ground slightly tapered. This causes contact on one side of the tappet more heavily than the other and round it goes as its lifted. A worn lobe will contact evenly across the face and won't rotate the tappet.

If you want to measure the lift, it's probably more important to check that it's even between the valves rather than an absolute value. Camshaft data might show you what you should be expecting for as a value, though. In any case, Soren's method is quick and easy. 

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Thanks, that video makes it look nice and simple. And yes, I get what you mean that valves opening relatively evenly to one another is better than necisserily opening to the book value. As is the importance of them rotating evenly accros the bank to show that the cams are worn evenly and not overly worn.

 

On a slight tangent, does anyone have any diagrams (or photos) of where the breather and vaccum pipes should go in the original state? I ganed my truck with a few alterations (as you can see in the original picture) I have replaced the nicely perishing rubber hoses with silicone ones but I wonder if I fit a new air box, should I consider modifying the breather and vauum hoses back towards where they would have come from originaly?

The only thing that you can't see in the picture is the small filter at the back of the engine block in the centre but just aft of and lower than the valley (which any pointers on it's purpose would be nice?)

My current understanding is: The vacuum survos for the break (and in my case clutch as well) are connected to the block (in the valley just forward of the carbs). Presumably this port connects to the intake manifold to cause a vacuum from after the carbs? This then assists the actuation of breaks and clutch.

The crank case breathers (one on top each rocker cover) connect to the carbs via flame traps. This port is also on the intake side to cause a small vacuum to help evacuate gasses from the crank case to avoid the crank case becoming pressurised?

Finally there is a small vacuum line from one carb (passenger side towards the centre of the engine) that goes to the vacuum advance on the distributor. This causes the ignition to advance slightly as the carbs take in more air due to the increase in vacuum in this line?

Finally there is the unknown small filter mentioned above at the rear of the block...

Have I missunderstood anything there or have I missed something obvious (or anyone spotted something that is not in the right place or should be improved upon?)?

 

Cheers again!

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17 minutes ago, ClimberTom said:

The only thing that you can't see in the picture is the small filter at the back of the engine block in the centre but just aft of and lower than the valley (which any pointers on it's purpose would be nice?)

No idea on this, could you get a pic? 

18 minutes ago, ClimberTom said:

My current understanding is: The vacuum survos for the break (and in my case clutch as well) are connected to the block (in the valley just forward of the carbs). Presumably this port connects to the intake manifold to cause a vacuum from after the carbs? This then assists the actuation of breaks and clutch.

Yep, that's it. 

18 minutes ago, ClimberTom said:

The crank case breathers (one on top each rocker cover) connect to the carbs via flame traps. This port is also on the intake side to cause a small vacuum to help evacuate gasses from the crank case to avoid the crank case becoming pressurised?

Been a while since I played with SU's, but I'm pretty sure that's right. 

18 minutes ago, ClimberTom said:

Finally there is a small vacuum line from one carb (passenger side towards the centre of the engine) that goes to the vacuum advance on the distributor. This causes the ignition to advance slightly as the carbs take in more air due to the increase in vacuum in this line?

Not quite. The connection should be just after the throttle plate (manifold side), and advances the timing under vacuum - light load. Full load timing is defined by the mechanical advance controlled by the spring biased centrifugal weights alone. There have been a fair few setups with a "ported" vacuum connection, which places the pickup just ahead of the throttle plate, so at idle you get no vacuum advance, but as the plate opens it passes the hole and shows it vacuum as normal. Ported connection is a very crude emissions cheat designed to hit some misguided regs of the period. 

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Posted (edited)

Thanks for that, very helpful! And yes, the hose to the vaccum advance is in the right position externally to come from the manifold side of the carb so that's cleared that one up for me.

I can get a pic but it will be a couple of weeks I think unless I can find something shoing it else where, I'll see what I can find!

Edit: After more searching it sounds like it is the fresh air intake to the crank case (From another  thread on here) Which sounds like it's right to have a small filter on it but if I do fit an air box then it should go to that (or tee into the hose to the carbs)?

 

Edited by ClimberTom
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Morning all.

Another quick question regarding carbs and balancing them - If setting them up with a vacuum gauge, where would you fit the gauge line? As opposed to one of the Gunson type balancers that go over the filter inlet.

Am I right in thinking it should go on where the line to the flame trap>rocker cover connects? Or is it elsewhere?

 

Thanks all

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The breather connection may not produce enough vacuum to read, but it's worth a go. 

I often do a quick check by cupping my hands over both intakes, leaving gaps I can vary with my thumbs. You'll soon get a feel for which is sucking more air in; I've found it's proven to be fairly accurate against the Gunson flow meter. Another quick cheat I use is to simply look at the gap under the pistons. If one is higher than the other, I know its way out of whack. 

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