Looking for a 409 engine bonnet-compatibility?

[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!

[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