Do hotter cams sound different, or is something wrong...?

[moppit]

I'm slowly getting my new 3.5 engine with eddy 500 running better and better. Just changed jets to 86 primary, 67-55 and 83 secondaries. Previously I had set it way too lean.

The car runs much quicker with great throttle response. I've been manually advancing timing after short drives to good effect but no pinking as of yet. What is odd though is the engine sounds a bit like a subaru or VW beetle. Weirdly offset beat. I have sidepipes from each bank. It never used to sound like this with the old engine.

Old engine had a piper 270, but my old sidepipes were lacking in any kind of back pressure as all the wadding had come out. It was much louder before but did not sound offbeat.

Would my new Typhoon cam sound different? Is a new silencer likely to affect this? It sounds almost like my cylinder order is different but I've checked the wiring and all is ok. removing each plug lead in turn results in a reduction in idle so I'm thinking electrics ok? any thoughts? Maybe more work to do on the jetting (plan to fit a AFR meter in due course).

[sidecar]

I'm slowly getting my new 3.5 engine with eddy 500 running better and better. Just changed jets to 86 primary, 67-55 and 83 secondaries. Previously I had set it way too lean.

The car runs much quicker with great throttle response. I've been manually advancing timing after short drives to good effect but no pinking as of yet. What is odd though is the engine sounds a bit like a subaru or VW beetle. Weirdly offset beat. I have sidepipes from each bank. It never used to sound like this with the old engine.

Old engine had a piper 270, but my old sidepipes were lacking in any kind of back pressure as all the wadding had come out. It was much louder before but did not sound offbeat.

Would my new Typhoon cam sound different? Is a new silencer likely to affect this? It sounds almost like my cylinder order is different but I've checked the wiring and all is ok. removing each plug lead in turn results in a reduction in idle so I'm thinking electrics ok? any thoughts? Maybe more work to do on the jetting (plan to fit a AFR meter in due course).

You may well get on 'odd sound' with sidepipes, my Cob has them and it is due to the firing order and the fact that the two sets of pipes are not linked. I just live with it!

With regards to timing please don't fall into the old trap of advancing the ignition to the point of pinking then backing it off a fraction. This method of finding the optimum ignition timing figure is crap! I have banged on about this before now on this forum but in short any engine will produce peak torque at any given RPM when the peak cylinder pressure arrives in the combustion chamber when the crank is between 14-20 degrees ATDC. Now in order to arrive at this situation the charge must be lit several degrees BTDC. Now with some engines you may never get the peak cylinder pressure high enough to cause the mixture to detonate, on some engines you might be able to run the engine into detonation when the peak cylinder pressure is at say 4 degrees ATDC. Would you then back off the timing say 4 degrees which stops the detonation and then think that you are running the best timing figures? Really you would still be running the timing too advanced!

I ran a 3.5 with a Typhoon cam a long time ago, you need to be careful as you are starting to get into the area where you could have a mis-match of components, on my engine the cam would allow the engine to rev to 7k and it would buzz round to this figure in the lower gears in the blink of an eye, the problem was that the pistons, conrods and valve train had not been modified/replaced in order to cope with this sort of rev range. Also with the Typhoon you are getting to the stage where the valve guides 'may' need machining and the pistons 'may' need eye browse cut into them. If you do not want the check this stuff out then you need to avoid cams that are in this 'danger' area! It is not hard to check this stuff but it does take a LONG time to build an engine when you have to mess about doing this. You need a few 'special' tools like weak checker springs, adjustable checker pushrods, solid lifters, etc.

Another thing to consider is whether your heads flow well enough to make use of the Typhoon cam, I'm not saying that they are or aren't, just putting the question out there!

With regards to the 86 jets, did you get hold of them 'outside' of the kit? I did not think that you got them in the kit as they are the standard jets that the carb leaves the factory with.

[moppit]

In reverse order....

For the 86 jet I just put that back in (I think it came with that)

The engine build was by Paul Bristow (Paul's place in Shedfield, Hampshire - specialist V8 engine builder) a couple of years ago. Paul is no longer around in the area so I don't know the history but I do have the receipt that shows pocketed pistons etc. This is not something I have randomly put together. I think Paul was a well respected chap and knew what he was doing. I bought the finished engine off a chap in the NG owners club who had originally commissioned the build (£5k). The engine was in a part finished rolling chassis that never saw action so had not been used other than a bench test.

Timing - I started by setting it with a strobe to around 6 degrees and marked the dizzy up. I felt this was not enough and have been gradually advancing things on a sort of trial and error basis, so guilty as charged! What is the optimum method? I'm running a mallory unilite electronic dizzy.

I do like the sound (happy to live with it - it certainly draws attention from passers by!!) but it's just bugging me that perhaps it's not running as smoothly as it should.

[sidecar]

This is not something I have randomly put together.


Timing - I started by setting it with a strobe to around 6 degrees and marked the dizzy up. I felt this was not enough and have been gradually advancing things on a sort of trial and error basis, so guilty as charged! What is the optimum method? I'm running a mallory unilite electronic dizzy.

Please don't think that I was implying that you had randomly put the engine together, that certainly was not my intension in my last post.

Really there are two ways that you can set the all in timing figure up...

1. You can run the engine on a rolling road and measure the BHP with various amounts of timing dialled in. You could then spend even more time trying to find the optimum figures or other RPM's you can then try and dial in the figures by messing about with bob weight springs! (You might be able to a rough idea if you spent a whole day on a drag strip but then again other factors come into play here)

2. The second way is just to take someone's word for it and assuming that you trust that person you will probably be within a degree or two of what your actual engine needs. You will be within a couple of BHP of the potential total output of your engine. Des Hamills book list's the all in figures for the popular sizes of RV8.

I have been meaning to go for option 1 but currently I am running option 2. In other words I have just read as much as possible on this subject and googled for info as well. The RV8 with an open wedge chamber has been around for years, the 'ball park' timing figures for the various engine sizes are well know. A normally tuned 3.5 that is not running a stupid CR or 'funny' fuel will need about 34-36 degrees advance, all in at around 2750-3000 RPM.

The idle timing figure is something that you can find by messing around with the engine, it is a little tricky but you can do it. Set the RPM fairly low then advance the timing 2 degree from a starting point of say 8 degrees, you will hear that the RPM rises, let say it rises 20RPM. Then advance the timing another 2 degrees, the RPM may rise another 20. At some point the rate at which the RPM rises will drop, there still will be a rise in RPM but it won't be as high, this plateau is usually around 2 degrees wide. Basically this is where you want to set the idle timing. I have found that it is around 12-14 degrees on the 3.5 engines that I've worked on. My 4.6 runs at around 18 from memory. Many things can have an effect on what this figure will end being and I'm sure that the cam duration will be the main one!

The other thing is that the Eddy 500 vac port really does not work well with the Lucas dizzy, it may well not work too well with your dizzy, if you use a vac system you may well have to run less advance on idle and the RPM that the all in figures arrives at may have to be set higher.

I wrote this lot ages ago, its worth a read...

http://how-to-build-a-pilgrim-sumo.wiki ... by-members

The bit I wrote is titled "Setting up a standard Lucas RV8 ignition system for maximum performance"

BTW, I now run a programmable MSD system with a MAP sensor, the difference between it and the modified Lucas system was 'shocking' LOL

[sidecar]

Just noticed that you are running 83 secondaries, I think that the smaller engines need bigger WOT jets because they pull very little vacuum on WOT.

The spreadsheet that I PM'd you does not really have many setting pertaining to the 3.5 engine but from memory the standard 95 jet is not a bad starting point and may well be the jet that you need.

Mind you this does all depend on how good the air flow is into your carb!

[moppit]

Thanks!

Will have a play with the 95 jet and see how that changes things.

Your link is a good read. How are you setting max advance? Did you play around with the springs in the dizzy or bend the tabs? My dizzy is different but found a good guide online http://documents.holley.com/mallory_ins ... _29014.pdf

I found a guide on adjusting the timing using a vacuum gauge (which I have) - have you tried it this way before?

see last post here
http://www.britishcarforum.com/bcf/arch ... 28394.html

[DEVONMAN]

I bow down to sidecar's knowledge on this subject but I'd just like to add that a richer mixture burns quicker than a lean mixture so if you adjust the jets in the carb then you need to play around with the ignition timing again.

[sidecar]

Thanks!

Will have a play with the 95 jet and see how that changes things.

Your link is a good read. How are you setting max advance? Did you play around with the springs in the dizzy or bend the tabs? My dizzy is different but found a good guide online http://documents.holley.com/mallory_ins ... _29014.pdf

I found a guide on adjusting the timing using a vacuum gauge (which I have) - have you tried it this way before?

see last post here
http://www.britishcarforum.com/bcf/arch ... 28394.html

Setting the max advance was easy because you just twist the dizzy then rev the engine whilst pointing a strobe at the damper. The problem is when the max advance is setup and you then find that the idle advance is no good. You are then into the relms of modifying the dizzy either by filing or by making bob-weight stoppers. This was all in my past as it is all done via my MSD system. My dizzy is locked out, it has no bob weight advance built in at all, nor does my dizzy have a vac advance as that is controlled by my MAP sensor.

With regards to the Lucas dizzy vac system and an Eddy 500 carb I was limited with what I could do, the basic problem was that when the vac system was connected to the timed port the engine would kick back just as the throttle was cracked open whilst accelerating out of a bend, the kick back was due to the vac canister adding too much timing to the advance that the bob weights had already added.

My MSD allows me to configure all of this, I carried out some tests using a vac gauge to determine the vac level whilst the car was cruising at about 50 mph, I then set the system up to add 14 degrees more advance at that vac level or higher but the extra timing decays very quickly if the vac reading drops below this level. The system is connected up to the timed port on my carb, as the throttle is cracked open the manifold vacuum may well be high enough to set the system off so that it adds the extra 14 degree BUT because it is connected to the timed port it does not get to 'see' the high vacuum at this 'transitional' state.

The other thing is that I've been thinking about totally changing the way that my timing works! If you assume that say at 1400 RPM with the throttle just cracked open timing needs to be say 20 degrees then this is a very different situation to when the throttle is on the floor at 1400 RPM, I think that the timing may need to actually retard from 20 degrees to say 10 degrees! Currently my system won't do this but it could if I used a non-timed vac port. You could also set an older dizzy/vac canister system up in a similar way again by using the non-timed vac port.

It was working on an old Mini that got me thinking about this, the vac canister was connected to a non-timed port on the SU carb. The tickover timing was only set to something like 6 degrees, the engine ticked over like a dog but as soon as the vac pipe was connected the timing rose to around 20 degrees and the engine had a nice steady tickover. If the throttle was booted the timing must have retarded back to the 6 degrees until the bob weights kicked in and started adding more advance.

[sidecar]

I bow down to sidecar's knowledge on this subject but I'd just like to add that a richer mixture burns quicker than a lean mixture so if you adjust the jets in the carb then you need to play around with the ignition timing again.

I guess the timing figured banded around the web and in books all assume that your mixture is within a 'normal' range. At WOT this would be around 12.5 to 12.8:1.

Just found this...

http://www.innovatemotorsports.com/resources/myths.php

[moppit]

This was all in my past as it is all done via my MSD system. My dizzy is locked out, it has no bob weight advance built in at all, nor does my dizzy have a vac advance as that is controlled by my MAP sensor.

Please do elaborate.. I'm intrigued! MSD system? Map sensor? is this for EFI or carb cars? If carb what would I need?

Apart from obvious easier setup what other benefits are there?

[sidecar]

This was all in my past as it is all done via my MSD system. My dizzy is locked out, it has no bob weight advance built in at all, nor does my dizzy have a vac advance as that is controlled by my MAP sensor.

Please do elaborate.. I'm intrigued! MSD system? Map sensor? is this for EFI or carb cars? If carb what would I need?

Apart from obvious easier setup what other benefits are there?

Blimey, the benfits of MSD, where do I start!

It is a multi spark ignition system, mine is the programable version so I can dial in any advance curve that I like, I can retard the ignition when my NOS system is running.

If you can stand listening two these to American Herberts watch this...


My system is mention at about 4:30 minutes into the clip.

Here is some gumph...
https://www.msdperformance.com/products ... parts/6530

A MAP sensor just measures Manifold Absolute Pressure (or vacuum) it converts this into a voltage that the MSD can read.

To sum up an MSD system, well put it this way, if you jumped into a lake then climbed out and immediately touched a HT lead on a car running an MSD system it would set your underpants on fire!

[DaveEFI]

I'm intrigued by the claims for this sort of ignition system. Has anyone ever done a comparison on a rolling road? I'm talking about the type of spark, rather than timing, of course.

[Ian Anderson]

Getting back to the original question.
The firing order should not change with a different cam.
With side pipes you are only listening to half the engine so you will hear an offbeat sound. But this should be the same as on your first cam.

I would suggest get the car started at night, turn off the lights and open the bonnet and see if you get cross arcing over the plug wires which in turn would cause an flat sound. It may be fine at idle but as revs rise the arcing may start so get revs up. Do not do this in a closed garage or you will gas yourself.

Also get an infra red thermometer and check that the temperature on each exhaust outlet is similar. It could show a duff cylinder not firing properly

Ian

[moppit]

Crikey! With a spark like that surely you would need plugs, leads (and underpants) made from 'unobtainium'?

[moppit]

Getting back to the original question.
The firing order should not change with a different cam.
With side pipes you are only listening to half the engine so you will hear an offbeat sound. But this should be the same as on your first cam.

I would suggest get the car started at night, turn off the lights and open the bonnet and see if you get cross arcing over the plug wires which in turn would cause an flat sound. It may be fine at idle but as revs rise the arcing may start so get revs up. Do not do this in a closed garage or you will gas yourself.

Also get an infra red thermometer and check that the temperature on each exhaust outlet is similar. It could show a duff cylinder not firing properly

Ian

Great idea , will need to do this soon before the nights get longer otherwise the neighbours will be peed off!