View Full Version : Glenwood headers on X-18

Rob Birch
12-21-2012, 04:24 PM
Because I am sprucing up the old small block 350 I have been cruising the performance forums for information as well as scanning exhaust systems. My boat came with aluminum glenwood headers (not logs) and from what I have read they appear to be performance manifolds. Can anyone enlighten me on these as it am unable to find them on other Donzi (pics... anyway). I do know that the original motor was a Ford and at some point in the 80's (before I bought it in 1990) the engine was swapped for a small block 350.

Rob Birch
12-21-2012, 04:36 PM
correction..... the Glenwood manifolds are round log style with the 3 inch opening facing the stern of the boat.

12-21-2012, 07:57 PM
Glenwood manifolds have been around for decades and are very good "Old School" performance style aluminum manifolds.

Many old boat racers of various class, & type, boats have used them over the years in the decades past. They have been on the market for a very long time.

Holman-Moody used very similar style manifolds & aft snail style risers on all their original OEM Ford V-8 engines that were originally installed by Donzi in the 60s & 70s.
Perhapps Glenwood made these original Holman-Moody manifolds also ?
Not really sure if this was the case but they appear to be almost identical ?

Many vintage & antique boat restorers use the Glenwood logs & risers when it's time to replace their older original Holman-Moody units to keep the original vintage style H-M look of the boat's engine & keep it period correct looking.

The Glenwood manifolds & riser elbows fit very well in the "Classic" series 16,18, & 22 Donzi boat's engine compartments if you don't wish to use more modern style center riser, or custom built Stainless Steel marine headers.

Don't use these, or any other aluminum manifolds, if you boat much in saltwater however as they will quickly corrode away very rapidly and will soon self destrust,

12-21-2012, 09:58 PM
Hi Rob Birch, the log style exhausts work well for low performance engines, but are not so hot once you start to make more power. They offer no runner separation, so the exhaust pulses work more towards hurting the flow of gasses out, and they really hinder the heat from leaving the exhaust valves in the back of the engine, which even with good valves will shorten their lives.
Your best bet would be to get a modern set of center riser manifolds that use an aluminium body and stainless steel riser/tail pipe. I wouldn't worry to much about using a modern aluminium exhaust in salt water, they're designed to fail and leak outside of the engine long before the fail and leak into the engine. I use Stainless Marine's version, and even with a nuclear type overheat when they were fairly new, they've been on three different engines over eight years and still look great and show no signs of going bad.

12-21-2012, 10:05 PM
Just wanted to add that I went with the stainless marine manifolds when I switched from a ford motor to chevy. The ford had log style exhaust, and kept killing the exhaust valves in the back cylinders.

12-22-2012, 12:09 AM
Glenwood makes both the large 3" outlet round style log manifolds as well as the smaller square log manifold style.
The smaller square style are fairly restrictive as compared to the larger 3" outlet diameter round style units.

As long as you keep your engine horsepower in a reasonable range of 225-300 max horsepower range they should be OK .

If you are building much more horsepower than this range you need to really consider the bigger runner, and more costly Hi-performance center riser; or custom header tube style units as Maddad suggests.

There are many photos of the Glenwood, & Holman-Moody manifolds on older Donzi "Classics" to be found.
There are a number of photos on this site that show the original Holman-Moody aluminum manifolds~~~you just need to search this site a bit for them.

12-22-2012, 09:59 AM
a stainless marine exhaust and cross over cooling system was added to this 350 in a 72 cigarette. the weight savings was dramatic ( you won't see as much as the logs are alum the logs on this 350 were cast iron but we also lost a water pump and all it's plumbing) they let the motor breathe and the performance gain was easy to see. they look good too.

got a hull number on your X


12-22-2012, 03:26 PM
Spending BIG money on a Hi-performance Stainless Steel exotic exhaust system as shown above on a basically stock moderate horsepower marine engine will yield very little, if any, real horsepower & speed gains.
It would be mostly for show and would be a waste of money on an otherwise basically "stock" engine.,

To get the most out of such an exhaust system the engine must have better High-Flowing cylinder heads with bigger intake & exhaust valves installed, along with a more aggressive marine camshaft, better pistons, better intake manifold & carb, and possibly new high-performance ratio rocker arms etc.
A supercharger ,or turbo-supercharger would also be very worthwhile.

In short you would also have to build a new High-Performance & Higher Horsepower marine engine to get any real worthwhile results out of these exotic, & very Costly, stainless steel marine exhaust systems.

Others I am sure will chime in with their own opinions based on proven experience & true results.

12-22-2012, 04:12 PM

as maddad has said the logs are hard on the back of the motor. the stainless marine system is far from exotic and is a moderately priced high performance exhaust system. In your other posts you said you are tweaking up to around 300 hp as you tweak you'll find that a good exhaust is needed to keep your investment intact.

true bolting on a new exhaust is not going to give you a magic boost in performance unless the old system was extremely restrictive or heavy but it is the type of investment that let's you further tweak the motor. your existing setup being alum. is not heavy.
It is worth it as it is the foundation for making more power. In an AQ Volvo boat a jump from 260 to 300 hp is not really going to be that noticible but once you get to 350 hp or so you'll notice the difference.

on the motor i pictured the weight savings with loosing the chris craft iron risers and all the iron plumbing we lost around 225-250 lbs it also let the lt1 motor breathe we picked up about 4 mph true real world numbers gps'd . that boat was a 19 cig and was a heavy 20 foot boat it had a 350hp 350 motor on a non trim volvo 270 it went from a 53-54 mph to a 57-58 mph boat with no motor work just the new risers and the crossover.
Again i feel mainly due to the weight savings but adding them let the owner have other work done that would not be able to be done without an exhaust upgrade.

I am sure there are other stainless marine type systems out there that some guys here might recomend that are high performance but not total custom cmi and stellings.

would like to see some pics of your X pics are always good

good luck on the project

12-23-2012, 09:54 AM

one thing that is in your favor is the motor has been switched to a chevy, marine hi-po parts for a chevy are far more economical than the ford and are readily available.

here are a few choices from CP shopping around can always save a few bucks, again i can only speak for the quality of the Stainless Marine system it ran for 8 yrs without a glitch



here you can see the difference between an off the shelf hi-po system and a true custom built sytem in the price tag, CMI have been known to have issues with leaking and reversion in certain applications


HGE know nothing about them




IMCO entry level performance


as you can see there are many choices for exhaust that will be more hi-po than the logs without being exotic for around 2500 and under of course you can drop way more

Rob Birch
12-27-2012, 01:34 PM
Thanks Mattyboy. I hope to get the serial number of my X to you soon. Tt is at the marina now getting the engine work done. I will look for some digital photos somewhere and hopefully can post them as well.

Rob Birch
01-03-2013, 09:33 AM
Hi Mattyboy,

the serial number of my x (DMR181040774-X)

What can you tell me about this boat?

Rob M
01-03-2013, 10:32 AM
"the serial number of my x (DMR181040774-X)"

DMR = Donzi Marine
18 = Hull length 18'
104 = Hull # 104
07 = July month of production
74 = 1974 year of production
X = X 18 deck style

01-03-2013, 11:10 AM
ok yes as Rob said it is hull 104 out of 171 built

original setup for 104

started july 29th 1974 invoiced aug 21st 1974

white and lettuce green, 300 hp Chris craft chevy 350ci volvo 270 outdrive sold in hollywood fla.

send me your email and also your serial numbers for the motor and the drive


Rob Birch
01-03-2013, 02:16 PM
Thanks Rob,

Hey Mattyboy,

I tried your email but it kicked back. Anyway the engine and 270 were replaced in 1990 due to severe deterioration from salt water. The hull is still original and the upholstry is very multi colored to match the hull. There was a set of trumpet horns on the deck that were very old when I got the boat in 1990 and I replaced them with new ones. (I have to find pics). There was a brass plate on the dash the said "especially built for Robert Steven Finklestein" .... if I remember correctly. I had a new one made in 1990 that says "especially rebuilt for Robert Ballard Birch LOL.
I found out how many X's were built but in your estimation how many are still around?

01-03-2013, 02:22 PM
sorry fixed the email link

yes that would be the original owner Finkelstein

pm or email me your email addy and I'll get you on the Lake George Donzi Classic Club mailing list

01-03-2013, 02:29 PM
there are quite a few of the x 18 left i would say 50-75% still survive maybe even more

01-11-2013, 07:54 AM
any updates or pics of the x 18

Rob Birch
01-16-2013, 04:18 PM
Alas not yet Mattyboy. I went to the Marina today and the engine is out and they are painting the engine bay etc... so the X is really not in prime condition for photos.\
You mentioned a guy (Marina) that has a ton of Volvo 270 & 280 parts kicking around.... can you tell me again because I want a reliable source for the trim motor and control unit?

01-16-2013, 04:22 PM
I think his name is herbert