Looking for a 409 engine bonnet-compatibility?

[pasini s]

Hello all,
I have put my 1966 409 back on the Road after the disastrous flood that hit my country in May and my Cars, too. She works passably well but now Im looking for bonnet to modify to create some outlets for the heat that made the V8 stall in this year's scorching heat. The question Is, does the bonnet from a 410 or 408 fit my 409? So i can look around a bit more easily. Thanks!
Stefano

[dwomby]

So sorry to hear of your flood damage.

I too have very high engine compartment temperatures and have wondered about putting louvres in the bonnet but do not want to spoil the appearance. Looking at photos of an Aston Martin DB5 being restored, it seems to have louvres in the front wheel wells. Might that help?

Good luck with your search.

David

[pasini s]

Hello, I don't think that It would help, as we have the large 'cavities' on both sides of the engine compartment and they are ducting fresh air into the cockpit, so engine fumes would get inside. I think that louvres, if neatly designed and executed, would not be too intrusive. I am looking for a spare hood to make some experiments without spoiling the original part. Thanks!

[Stefan]

Well I must say I've been tempted to have louvres cut into a lovely Bristol bonnet to release the scorching air that we generate in such large amounts.
And today's climate change makes this all the more critical.

I do remember as a plus side for all the spare heat emitted, that four of us parked in an icy layby one Winters day and were unable to proceed. However we waited 10 minutes and a generous patch thawed around the whole car ,enabling us to proceed gracefully on our way.

[Nick Challacombe]

Good day Stefano, I have a bonnet for a 407 which I have had for a while. I do not know if it is the same as a 409. Unfortunately the
spares handbooks do not mention body parts only items attached to them.
Sorry to hear that the floods affected you, cannot think of anything worse.
I hope this finds you both well. Nick

[pasini s]

Nice anecdote, Stefan😁 but nowadays we face a hotter climate and denser traffic in long immobile queues in the scorching sun, that's where my 409 showed that problem.
The late Martin Barnes once told me that the early V8 Bristol's up to the 411 suffered of serious overheating problems in Central London traffic due to a combination of so much heat generated and preserved in those massive V8 iron blocks and the very narrow engine bay...
Cheers
Stefano

[Roger Morrall]

Stefano

Sorry to hear of your problems. Here are some thoughts re bonnet compatibility and overheating in general

1) May I suggest contacting Dr Stefan Cembrowicz, the Chairman of the Bristol Owners Heritage Trust ,who played a significant part in the rescue of various body bucks when Bristol cars assets were sold during the final liquidation, with a view to discovering if he knows whether separate bucks were created for 407, 408, 409 and 410 or an existing buck modified. If for example an entirely new buck was created during this series comparability would probably be lost, but if there was only one buck that was modified (forward of the bonnet) compatibility seems likely.

2) Graeme Payne at the Classic Bristol Parts Company may also know know about compatibility even if he doesn’t actually have a second hand bonnet in stock. Bristol cars services tended not to throw anything away and anything potentially useful was salvaged and put aside

3) Some panel beating may still be necessary to ensure a good fit, that’s how it was done originally

4) It seems likely that most of the extraneous heat under the bonnet actually emanates from those horrible cast iron exhaust manifolds rather than the block itself. The former are tucked up right up under the cylinder heads and there is simply nowhere for the vast amount of heat they generate to go when you’re stuck in traffic, even though the block itself is still cooled by the radiator. I went for broke £’s wise when I owned PEU186F having had a lot of other trouble with them and went for SLJs magnificent tubular manifolds. I perceived (and these are only my perceptions, they’re not scientifically proven) a significant drop in under bonnet temperature alongside a worthwhile improvement in performance - it felt as though the engine had previously been stifled by the cast iron manifolds. It might well be possible to wrap SLJs manifolds with insulation as they are fitted which should further improve matters as far as temperatures are concerned.

5) if you still have the original Carter carburettor also be aware that the float needle valves wear and leak over time which results in the carburettor bowls overfilling, particularly when you’re idling in traffic, resulting in an over rich mixture and a stall. The hotter the air temperature the richer the mixture will be. Suspect this as a potential issue if the idle needle valves have to be screwed at all far in (from memory once I’d fixed this issue the I found to my surprise that the engine idled most happily about three turns out) or if there is a tendency to fail pick up cleanly from idle.

[dwomby]

Originally Posted by pasini s

....................... so much heat generated and preserved in those massive V8 iron blocks and the very narrow engine bay...
Cheers
Stefano

I have always thought Bristol should have changed the engine bay side sheet metal instead of sitting those V8s in the narrow space designed for the Bristol engine. Did they eventually do that on the later cars?

David

[Kevin H]

Before cutting a bonnet to create louvres I would suggest improving the engine cooling system. The original configuration of electric fans (or a single fan on the 409) mounted six inches in front the radiator, albeit in a cowling, seems inefficient by modern standards.

I would suggest replacing the original radiator with a thicker, higher performance radiator and mounting modern fan or fans directly onto the front AND rear of the radiator - with the rear fans designed to pull rather than push air. This will both improve engine cooling and get more air flowing through the engine bay. Obviously removing the original cowling and fan (or twin fans on the later V8s).

[DODD]

I read these postings with interest. I have considered, all be it briefly on occasions, about installing louvred vents in the bonnet of my 410 but for obvious aesthetic reasons I couldn’t and wouldn’t bring my self to disfigure the looks of that long elegant bonnet.

In my opinion the size of the engine bay in a 410 is just about suitable for a straight six but Bristol managed to shoehorn a V8 inside and yes, it looks and is very impressive. Those of you who do maintenance on your car will know how fiddly it is just to change the spark plugs!

David is absolutely correct in his posting, whereby he notes that Bristol should have changed the side sheets in the engine bay. Let’s be fair, the 410 wasn’t the first model to house a V8. I am sure with a little thought it could have been designed more user friendly to take into consideration the trapped hot air in the engine bay.

When I stand back and look at the bonnet of my 410 on a sunny day, I can see a slight bloom in the centre where the finish on the paintwork has changed. This is due purely to the heat from the engine bay not being able to escape once the car has stopped and the engine turned off.

For a long time I have been going to replace the radiator on my car. My car has always had a tendency to get very hot in standing traffic, necessitating the use of the override switch for the cooling fan before the thermostat cuts in and turns it on.

This has very recently come to the forefront of my projects on the car. I have recently installed an independent ATF oil cooler, this has left the existing oil cooler in my radiator defunct.
I currently have a new radiator on order with a slightly thicker core. Additionally, I have purchased a new very high performance 16” cooling fan (the largest and most powerful I could find) and fitted it to my existing radiator while waiting for the new one.

I agree with almost everything Kevin noted in his posting, except having a fan on both the front and rear of the radiator. I had a brief discussion regarding this very point when talking with a specialist cooling fam manufacturer, asking his advice. Unfortunately, they no longer fabricate for the aftermarket sales but nevertheless he shared his knowledge. Basically, having a fan on both sides can give other issues insofar as they must operate at exactly the same speed at all times, the blades must also be the same and positioning has to be considered very carefully and that’s before taking into consideration any voltage irregularities between the fans. All in all he advised me against it; apparently, in cooling fan design for cars, Amps are King.

None of this solves the problem of heat build up in the engine bay once the car stops and the engine is turned off. Unless you fit a thermostatically controlled override switch to the fan, which personally, I wouldn’t do.

As an afterthought, If the bonnets on the 407,8,9 and 10’s are all the same, it might be worth considering having a batch of fibreglass units with louvres manufactured!

Brian

[Kevin H]

Brian,

The reason I suggested putting a fan on the rear of the radiator to pull air through, is because I have done that on my 411.

I'd had air conditioning installed in the 411 and once the radiator had a condenser placed in front of it, the cooling system as no longer sufficient. The original A/C installers had bodged the job so as part of a much larger project the A/C installation was re-done and I was persuaded into replacing the radiator and reconfiguring the cooling system. We removed the original fans and cowling and installed the new radiator forward of the original position, with two modern electric fans sandwiched between the condenser and the radiator. Unfortunately this was still borderline in terms of cooling on a 30+ degree day, sat in traffic. So we added a large electric fan to the rear of the radiator; this dramatically improved the cooling, so even on the hottest days the engine will not overheat.

As far as I am aware there was no consideration given to the speed of the front and rear fans, but it definitely works.

We also did away with the original Otter switch for the electric fans, which I believe the 409 also has, and replaced it with a modern variable thermostat which can be set to turn the fans on a little earlier that the original 98 degrees C. We also fitted a separate ATF cooler.

If I was a 409 owner with a borderline cooling system, I'd probably start by just mounting a slim electric fan directly of the rear of the radiator and see what difference it makes. It's a relatively small cost in the scheme of things. You might need to install a relay to power the new fan, triggered from the original fan power feed.

[pasini s]

Hello all,

thanks for your suggestions, all of them very helpful, but I'd like to point out that after I did fit a new set of electric fans behind the newly recored radiator and an electronically controlled thermostat, I never had any problem with the engine temperature. It remained well under control anytime, even during last week's hot queues. My problem is the engine bay heat that makes the carburettor boil and, as a consequence, the engine stalls.

The opening of some louvres on the hood would surely help lower the engine bay temperature, as no obvious exit was provided for this heat. The fact is that all the heat produced in the combustion chambers of the iron-block 318 is enclosed in a nearly completely sealed 'box' that is the 409's engine bay and this heat cannot escape at all.

I'm sure that Roger is right in suggesting to remove those heavy cast-iron manifolds to put in some tubular manifolds would make a significant improvement, but the cost and modifications would be a bit too much for my taste; apart from that, I think that as the manifolds do not produce that heat, they just transmit it, it would not probably cure my problem completely.

My idea of buying a spare 409 hood would be to make some experiments; I'm sure that I could solve the problem with some judiciously studied louvres but I need to try.

Thanks again for your help,

Stefano

[dwomby]

Originally Posted by pasini s

Hello, I don't think that It would help, as we have the large 'cavities' on both sides of the engine compartment and they are ducting fresh air into the cockpit, so engine fumes would get inside. ...................

Just to clarify, Stefano, I did not mean the neat openings that Astons have between the front wheel and the A pillar. That would be very tough for us given the compartments Bristol is famous for! I meant further forward in the actual wheel well. See the photos.

I am away from my car until mid-September. So I cannot check if air could pass from that area of the wheel well into the cabin.

David

[Philip]

Biggest source of radiant heat by far will be the exhaust, so I’d look at ceramic coating or wrapping the manifolds (at least). Make the cooling system as efficient as you can (modern radiator, shrouded electric puller fans, high-flow water pump etc), carb spacer, good oil cooler, heat shielding/sleeving fuel lines, reflective bonnet insulation, maybe even removing the bonnet seal etc.

[Kevin H]

Stefano,
Are you sure your problem is not a fuel supply volume and/or pressure issue, and/or perhaps the wrong carburettor?

I have a 450 cu inch engine in my 411 which I am sure puts out just as much heat as your 318 engine, and I have driven it on 30+ degree days without a problem. My engine bay is very similar if not identical to the 409 and I don't have bonnet louvres, in fact my bonnet is insulated.



Best regards,
Kevin

[AndrewA]

If it helps the bonnet on my 410 is 165 cms down the long edge 107.5 cms across the top edge (nearest the windscreen) and 85 cms at the front.
Got me thinking as well and found these chaps
https://sportscarmetalworks.com/bonnet-louvres/
The links at the bottom of the page are interesting (well I thought so - from Jag forums - sorry).

I appreciate you weren't necessarily seeking advice but I'd try a mix of everyone else's suggestions before you break out the tin snips. So if it was me, phenolic block for carb (if none already), then if no difference remove sealing strip between bonnet and car to let air out (though increased risk of pongs in car).

As I suspect your issue maybe carb related and fixable you could try initiating the problem i.e. driving it around on a hot day then pull over and let it idle for ages this time with the bonnet open slightly and see if it cures your hot start problem.

A bit as per Kevin, I was recently stuck for an hour and a half on the motorway on a very hot day and was reluctant to turn the engine off in case it failed to restart. I'd let it idle for 45 minutes much to the understandable annoyance of other road users and in the end I gave in and turned it off and had no problems restarting. Mine's still on the cast iron manifolds and the only mods I've made are the phenolic spacer on the carb and it's got a new 500cfm Edelbrock on it.

That said some tasteful louvres could look cool and I like the idea of having a summer and winter bonnet!

Good luck

[Roger Morrall]

Stefano.

Andrews comment in the previous post puts me in mind of another potential cause of your under bonnet temperature problems.

He mentions a phenolic block. This is often recommended with a view to isolating the carburettor from the inlet manifold - which raises another question. Why should the inlet manifold get particularly hot in the first place?

Sure, it’s in the centre of the block, but the block itself will not exceed about 105 Celsius which is not particularly hot at all. So why should the Chrysler original equipment manifold get any hotter than that? The answer lies, perhaps, in the exhaust transfer ports that Chryslers introduced with a view to attaining a rapid warmup, and alleviating the Los Angeles smogs. These transfer ports run across inside the inlet manifold between the left-hand and the right-hand exhaust ports with a view to warming the manifold on a cold start. They were originally brought into play by a rather crude flap in the left hand exhaust manifold driven by a bimetallic coil. This closed when “cold" and opened when "hot"

It seems rather unlikely that this bimetallic coil and the flap has survived on your car to cause the inlet manifold to be over heated, but I have heard that some have survived. If it hasn’t the transfer ports will still remain if your car retains its original inlet manifold and gaskets and will continue to heat the manifold to some degree. The heating will be exacerbated eg by an imbalance in silencer back pressure or, indeed, some blasted bambino inserting a potato up one of the exhausts, emulating said flap, whilst idling in Italian traffic

It might be worth checking on the surface temperature of the inlet manifold in various circumstances - these simple stick on temperature recording strips might prove invaluable. https://temperature-indicators.co.uk...vel-indicators. (I’m sure there will be an Italian equivalent)

Should you perceive that the inlet manifold is getting unduly hot (and that the original equipment flap and bimetallic arrangement is not to blame) I understand modified inlet manifold gaskets may be available that simply omit the holes for the transfer ports and thereby block them off, if not I’m sure this would not be beyond the scope of an Italian engineer.

Worth thinking about perhaps and certainly a lot cheaper than SLJs magnificent tubular manifolds?

[DODD]

Roger’s posting above reminds me of issues I had with my 410, as per one of my previous posts of June 25th 2021.

I had what I thought was a blown cylinder head gasket; unfortunately, on further investigation it turned out to be a crack in the cylinder head between two chambers.

As noted previously, the bimetallic coil which controlled the flap within the exhaust manifold had seized. The result was that an excessive amount of exhaust gases were diverted across the inlet manifold to the opposite exhaust. This also in my opinion was the cause of my exhaust manifold developing hairline cracks.

Additionally, whether related or not (I think it was related), the small metal plate which sits on the inside of the inlet manifold had accumulated large amounts of carbon buildup between the plate and the metal casting; in fact it was a solid block!

As a result of the above issues, I completely removed the flap in the exhaust manifold to alleviate future problems.

Additionally, Roger noted in the same thread that when he fitted the SLJ swept exhausts system, a small aperture maybe/was required in the wheel arch. I imagine that this aperture would also help disperse some of the heat buildup from under the bonnet. This is something I will seriously consider doing on my 410 this autumn; if anyone else has created vents in a similar position, I would be interested in their views.

Brian

[dwomby]

Originally Posted by DODD

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Additionally, Roger noted in the same thread that when he fitted the SLJ swept exhausts system, a small aperture maybe/was required in the wheel arch. I imagine that this aperture would also help disperse some of the heat buildup from under the bonnet. This is something I will seriously consider doing on my 410 this autumn; if anyone else has created vents in a similar position, I would be interested in their views.

Brian

Thanks, Brian. I have been wondering about the possible benefit of venting into the wheel arches to let hot air out of the engine compartment. I hope to investigate the possibility when I get my 408 back on the road (hopefully in a month or two ).

David

[AndrewA]

Roger/Brian, I'd forgotten about the carbon under the metal plate and the bimetallic coil/ flap - when I took the top end of engine apart my inlet manifold was cracked and even the second hand one I got from SLJ had a lot of carbon under that plate. It took 6 cans of Mr Muscle aerosol oven cleaner, a powerful jet washer, assorted tooth brushes and bottle brushes to get it all clean again!
Logic would say it's all related, creating a hot spot under the carb.