I've just finished running in my brand new Swaymar Marine V8 (www.swaymarmarine.co.uk) and I 'd like to share the experience.
This engine was built by David Martin (formerley of Aston Martin) in Horsham and was installed in my boat late last year.
The engine, which turns out about 500hp is simply sublime.

I have never come accross a marine engine with so much torque across the rev range. My boat is 27.5 ft in length and weighs about 2500kg, and with this engine it is doing 30mph at 2700rpm. The top speed will be well into the 50's.

The engine is an absolute gem and I would recommend David highly to anyone thinking of re-powering a V8 boat.
The icing on the cake is that it costs about half what a Mercruiser EFI500 would have cost, and I know that it is far better built with very high quality components and by a real craftsman.

Well done Swaymar!
I am happy to help discuss the experience with anyone thinking of doing the same.

Mariah 275


Fitted the Stainless Exhaust Manifolds to my 5 Litre Mercruiser and they are superb.

Easy to fit, much lighter, so feels like a performance increase, although I think the Engine Is producing more Power as David at Swaymar supplied me with the correct size head gaskets for the 5 litre engine.

Engine bay is now easier to work on, looks much nicer and no more Dry Riser Issues.

Had a fab summer and was easily over 50MPH in my Maxum.

Mike - Cornwall


Have recently taken delivery of a new 5.7l Chevy engine from Swaymar and am in the process of working how to get it into my new build boat project.
The engine is beautiful to look at and has been built to a very high standard. David Martin has been very helpful in guiding me (a relative novice) with tips on how things should be done, and equipment required to mate with the engine. He is always up for a chat and very willing to help. I opted for the wiring package as well and now just have to sort out the wiring off the engine to be able to plug it in (good wiring diagram supplied!)

Ian Reed


Just wanted to report on the new manifolds. While a slight bit louder at certain rpm I am very pleased with the results, smoother running, cooler running (manifolds running at least 10-15 degrees cooler, as does engine bay), much improved engine response from what appear to be better breathing exhausts.

J.W. from Sheffield


After solving a series of boat system gremlins the engine has now done 30 hours since rebuild.

It now pulls 4.5 – 4.6k revs on a 24” 4 blade prop (from Andy). It pulled 4.8 – 4.9k on the original 22” prop. No cavitation problems. I am thinking of going to a 25” considering the cam’s 4.3K peak power and the very strong mid range pull.

As for fuel consumption in less than ideal conditions it consistently shows 45 ltrs / hr @ 3K, 30 knts, was 50. Max has increased from 102 to 115 on the same un altered Rochester carb.

Max speed shows a consistent 3 knt gain from 46 to 49, present max 50.1.

I am currently waiting for the wind to drop and some flat water to collect more reliable data.

Will let you know the outcome.

-- Additional --
Hi David, I hope you are well. My engine has now passed 60 hours and is currently propelling my 2.5 ton Scarab at 51.5 knots @ 4500 rpm on a 3 blade Mirage 25 inch pitch prop. The 2 way slack water test on GPS also indicated 72 ltrs / hr @ 40 knts, originally 80 ltrs / hr. This is 3 ltr / hr improvement over the 24P Bravo One 4 blade. Now thinking of trying a 26 inch pitch up from 22P on the original spec Magnum 454 engine. The boat pushes up on the plane effortlessly and will accelerate hard up to 48 knots reaching maximum speed within a minute or two thereafter. Ignition is via MSD spark box + MSD Blaster coil. Oil consumption remains minimal with the oil still clean after 50+ hours. After reading articles by your friend D.V. I am thinking of adding a Plasma ignition booster. The fun continues....... Regards,



Great company, product and service. Can highly recommend.

Nick Bailey

Just a short note to thank you for all the work you did on my new engine.
The boat is running well and the engine looks amazing in the engine bay.
I've enclosed some photos of the engine when it arrived, installed in boat and a photo of us recently on Loch Lomond.
Very best regards,

Andrew Meek.

I found Swaymar via their Web page about 18 months ago, and made an enquiry in respect of the Hi-Tec Stainless Steel Manifolds and Risers they supply. I spoke with David Martin, who is quite easily one of the most knowledgeable marine engineers I think I have ever had dealings with. He just inspires you with confidence and I should hav had my first 502 MPI Mag rebuilt by him in the first place.

He Priced up my engine but I thought I could get it cheaper so passed on Swaymar the first time around - to my cost !!

After I explained to David what had happened to my supposed "rebuilt by another" 502 he was very helpful, and listened to my story and came back to me with a spec for a brand new big block motor, with high torque cam, closed cooling system, air gap manifold, carb and the stainless steel manifolds and risers and everything else that goes with a high performance motor. The spec was fantastic so I bit the bullet and ordered one.

From the off David was in constant contact, explaining the process and progress on the building the motor. A month ago the Motor arrived, with around 500hp, and has been in the process of being put into my Wellcraft Nova III. Even the Mercruiser appointed dealer, who put the motor in the boat, commented on the quality engineering and the " Crisp Note" of the engine.

The higher torque lower down the rev range means I've swapped from a 4 blade stainless 24 inch pitch to a 4 blade 26 inch pitch.

The engine is now in and I can't wait to actually get it out on the water to try it out.

Can't recommend David and Swaymar enough !!

Darren Le Couvey

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