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8 & 10 cyl Bristol cars Type 407 onwards - restoration, repair, maintenance etc

Tubular exhaust manifold for 411 S5

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Old 15-12-21, 12:15 PM
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Default Tubular exhaust manifold for 411 S5

Hello,

as I am currently completely reworking the Chrysler 400 engine on my car, I wonder if there is anyone who has fitted tubular exhaust manifolds to his 411.
I know that there a multitude of designs available for this engine in the USA but I fear that it is very difficult to find the space for these in the narrow Bristol body.
So question is: Has anybody done this? What brand of manifold was used?

Rgerads

Thomas
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Old 15-12-21, 01:35 PM
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Thomas I may not be able to help but I am interested in what you plan with the motor. I have a 411 mk2 with a 383 in it and a 412 with the 400 like your mk5. The 383 although largely stock ( manifold , mild cam and standard cast iron exhaust ), it has enormous power and will rev happily to 6500rpm. On the other hand the 412 with tubular manifold and alloy inlet has ample initial pull but runs out of punch over 3500 rpm.

I am told the 400 motors can be made to go very quickly with different pistons cam and alloy heads. It might well be that you put your money into that area rather than new exhaust manifold.

I believe the system on the 412 was a custom built set and are not entirely satisfactory because they are to close to the spark plug leads and also as the engine mounts sag and you turn to full lock they touch the steering shaft.

As I said I am interested in what your plans are as I intend to do something to get the 412 going quicker.
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Old 15-12-21, 02:54 PM
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Thomas, why do you want to fit tubular exhaust manifolds to a 411?

Peter, the Chrysler 400 CID engines were fitted with "smog" heads to comply with new emission standards (they didn't breathe well) and the engine had very low compression ratio.

You could get an immediate improvement by fitting earlier (pre smog) "906" casting heads as used on the 383 - these are indistinguishable from the heads on your 412.

People often get them ported and polished and increase the valve size, but that all adds to the cost to the point where you could just get some after market alloy heads (which will look different).

There is a lot more you can do to increase the performance of these engines such as changing pistons and cam shaft.

You may need to get hardened valve seats in the 906 heads.

Just google "mopar 906 heads"
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Old 15-12-21, 04:27 PM
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Peter,

I am not au fait with the 400 engine but may I suggest you contact Spencer Lane Jones who do offer very impressive tubular exhaust systems for the V8s. See https://www.spencer-lj.com/services/...evelopment.htm. They’re not cheap. My experience (on a 410, but I understand they also cover the 411) is that one significantly improved the breathing and responsiveness on a car that was already well up to the mark. I speak only as a satisfied customer.

The other advantage that I perceived over the ghastly original cast manifolds is that the exhaust heat is no longer concentrated right up under the heads and the engine bay runs cooler. This might be further enhanced by wrapping insulation around the individual pipes - there is a win-win here as there is a further potential gain in performance to be had if the engine can ingest reasonably cool air, which is pretty uncommon stuff under most V8 Bristol bonnets!
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Old 15-12-21, 04:29 PM
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Ok, I understand I was very unprecise with the expression „reworking the engine“..

What will be done is:

- Forged pistons
- New connecting rods with floating wrist pins
- Aluminium heads with larger valves (much easier to get in Europe than 906 heads)
- Roller camshaft with max 240 deg duration that will give maximum low end torque
- Weiand inlet manifold
- Quickfuel 650cfm carb
- raise compression to 10 - 10,5

My expectations/hopes are to get around 350 DIN hp from this setup and a much better gas mileage than with the choked original 400.

As the original manifold has the mechanism for the inlet manifold warming ( which is a nice thing when starting from cold, but terrible when you have a warm engine). The warming flap has either to be discarded and plugged or better flowing manifolds could be installed.

Regards

Thomas
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Old 15-12-21, 09:50 PM
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Sounds to me you are on the right track. Can I suggest that you dont hot it up too much or you loose the charm of a quite smooth motor after all they are touring cars. The alloy heads are the way to go less weight and much less heat.
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Old 16-12-21, 05:17 AM
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Thomas,
Be careful which forged pistons you buy. I have JE forged pistons in my 411 and they are very noisy, especially when cold - it sounds like a diesel engine!


Kevin
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Old 16-12-21, 05:31 PM
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Hi, Thomas. Please pardon me if I echo Peter's words of caution. It's your car and you must do it the way you like but my car has a 360 with a performance camshaft. It's ok when up to speed but idling and at low speed it sounds like a US muscle car and not at all in keeping with the refinement I'd expect from a Bristol.

David
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Old 17-12-21, 11:25 AM
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HI David,

I am totally with you. My aim is to improve the 400 engine, which was really not a very good piece of engineering, compared to his predecessors, because of the US emission restrictions.

I will use a camshaft with a duration which should be close to the original cam but with all the benefits of modern camlobe technology. My aim is to have the engine as smooth as possible but with improved low end torque and fuel efficiency.

Regards

Thomas

Quote:
Originally Posted by dwomby View Post
Hi, Thomas. Please pardon me if I echo Peter's words of caution. It's your car and you must do it the way you like but my car has a 360 with a performance camshaft. It's ok when up to speed but idling and at low speed it sounds like a US muscle car and not at all in keeping with the refinement I'd expect from a Bristol.

David
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Old 17-12-21, 11:33 AM
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Hi Kevin,

I talked about this with my Chrysler guru yesterday. He told me that JE sells forged pistons with several different alloys, each needing its specific piston/cylinder clearance. You might have a problem that the clearance used on your engine does not match the piston used. I know this sounds like a bit smart-alecky, but I only wantet to share this information with you.

Regards

Thomas


Quote:
Originally Posted by Kevin H View Post
Thomas,
Be careful which forged pistons you buy. I have JE forged pistons in my 411 and they are very noisy, especially when cold - it sounds like a diesel engine!


Kevin
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Old 17-12-21, 11:14 PM
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Quote:
Originally Posted by Thomas591 View Post
Hi Kevin,

I talked about this with my Chrysler guru yesterday. He told me that JE sells forged pistons with several different alloys, each needing its specific piston/cylinder clearance. You might have a problem that the clearance used on your engine does not match the piston used. I know this sounds like a bit smart-alecky, but I only wantet to share this information with you.

Regards

Thomas

Thanks for this Thomas. I am very unhappy with the guy who rebuilt my engine. He did a number of questionable things and it is quite possible that he made a mistake with the piston specs. In fact I think he saw me as an ideal opportunity to experiment with engine mods that he had wanted to try out at someone else's cost. I regret agreeing to the modifications and wish I had only sanctioned a less ambitious rebuild.

That said, from memory the compression figure for each cylinder were good. When I have some time I will list the piston and ring specs along with the rebore specs and perhaps you could ask your Chrysler guru for his opinon. It is something I would like to resolve when I can find the time.

Regards,
Kevin
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