sutphen 30

what dyno do you use?

SB

We (the dyno owner and I) pulled a million hr one out of a boat and threw it on the dyno before putting it in an old crust crew cab 86 Chevy Dually. Wanted to see if it needed help or was fine to throw in the truck. Made right at 330hp. 334 if I remember correctly. Land and Sea engine dyno like I believe you have Bob.

Didn't check anything (carb, timing, ignition) and etc .....so BobL's testing is right in line. This motor we checked was very well used ! Thus why being pulled.

Edit in: engine tested with 2" primary 3 1/2 collector Schoenfield headers. No mufflers.

95NovaSpyder

I have a question about exhausts on these motors - per above posts the stock Mercury exhaust is very restricted, but under another thread here - someone stated "not to waste money on exhaust upgrades - for very little return". reason I ask is - I am new to performance boating and have a 1992 Nova with a Mark IV 454 - 365hp MAG - all stock (except carb) low hours. I was going to do exhaust this spring (has stock manifolds and thru-hull) - and then next winter HCI on stock bottom end. Even if it doesn't do much performance increase on stock - I think reducing some weight has a benefit (IMO). Thanks and I have been searching through this site for 6 months - finally joined.

apollard

On a stock engine, changing the exhaust will not make much difference - do, if leaving it stock or near stock, don't bother IMO. The reason to change exhaust is for future changes, not to help the stock engine. That is why you see folks advising getting a good exhaust and then upgrading components. BTW, depending on your ultimate HP goals, the 496 stock exhaust is a good one, with individual runners of a decent size and a good riser. Raylar has posted on here some easy changes that can make them a good choice for above 500 hp. Stock he says they are limited to about 500 hp. And they are usually easy to find in the swap shop cheap (I paid $400 shipped for very low hours manifolds and risers).

TomZ

Great question being your first post!

Regarding the exhaust, well, it kind of depends. Raylar had a good thread going about performance levels with the dufferent exhaust designs:

http://www.offshoreonly.com/forums/g...rformance.html

From the thread:

From Ray@Raylar:

I thought I might chime in here to kind of even out the questions of horsepower and torque gains from exhaust upgrades on 496's. First, keep in mind that for any motor to gain horsepower or torque it must basically get more efficient. Obviously any things changed on a motor that increase the volumetric efficiency can increase power. There are basically three types of marine exhaust manifolds,

1. The tradtional old mercruiser log manofolds that came on the 350 thru 502 carburated and MPI motors from 60's thru mid 90's. these manifolds because of their log (all exhaust ports dump close to the head into a long square chamber and then exit a back end up thru a small vertical riser entrance) are very innefficient, heavy (iron) and were poor at letting the motor develop hp and torque.

2. The aftermarket and new Mercury (Gil) short runner, center riser manifolds. These are aluminum units like Eddie,, Revolution Imco, Gil, CMI E-tops and 496 Merc., etc. they all have similar short runners 8" - 10" that merge into center riser openings and definitly flow better than the old log type most boaters have been use to. They will definitly make more power and torque than the old log manifolds.

3. The tubular stainless and special cast units with long 18" to 24" semi-equal length with good merge collectors, like CMI, IMCO Super Powerflo, Stellings, Eichert Bassett, Dana, etc. will generally flow exhaust more efficiently than either of the two other types.

The real question here is the 496 engine. The stock 496 Merc (GIL) aluminum manifolds (type 2) are really pretty good units when compared to other (type 2) manifolds. Their individual runners and merge into the stainless steel round big radius risers with merge collectors can do a very good job of helping the 496 develop its great torque and good power. ESPECIALLY WHEN THEY ARE GIVEN EVER SO SLIGHT MODIFICATONS! If you were to take the turbulator plates alone out of the 496HO and dyno the motor you will see about a 15HP increase alone! So if you compare certain aftermarket manifolds (not type 3 tube headers) you will in most cases see no significant power increases from stock 496 manifolds.
If you are looking for more Bling, polish or paint the Mercury 496 manifolds, polish the stainless risers and you have some good look'in aluminum manifolds that work well and you will save yourself about $1500 minimum.
If your 496 is stock and you choose to step up to a good (type 3) header system you will probably see about 25-40HP net increase over the stock exhaust manifolds and risers with the "turbulators" removed, depending on your boats riser to transom configuration and muffler use if applicable.

Trust me when I say that Raylar has probably made more dyno pulls on stock and modified 496's with many combinations of exhaust than probably anybody in the industry short of GM and I have the dyno sheets to prove it! We have made over 525HP on a normally aspirated 496 with stock Mercury 496 exhaust manifolds (turbulators removed and manifold riser openings lightly ported.) This is about the limit, normally aspirated, for these stock manifolds.

If your plans are to go above 525HP with a 496 either normally aspirated or supercharged 496, then invest in a good set of (type 3) real headers or manifolds, you won't get there without them.
I am not trying to endorse or critisize any aftermarket exhaust manufacturers here, I am just trying to get the real world results of their use on stock 496's where I have my expertise.
Remember engines increase power from increased breathing and efficent use of fuel. The 496's need to breathe better on the intake side to make more power above 450HP and this will only come from improvements in heads, cams and intake manifolds, supercharger or turbo charger addtions . You are not going to get a 475HP from a stock 496 from just installing any set of headers and especially not from a set of $2000 manifolds. If you do, let me know how you did it.

Just some real world facts!

Best Regards,

Ray @ Raylar

-----

Regarding what's been said in this thread, the exhaust on the 420 was a good upgrade from the normal Merc log manifolds. They had individual cast runners that dumped into a long sweeping, dry-joint riser that flowed much better than the cast iron Merc stuff. Maybe worth a couple miles per hour. More important is the fact that this exhaust was necessary to protect the engine from water reversion, and this is why exhaust upgrades are usually mention as one of the first things to do in the process. Spending $4k on a set of tubular headers won't net any huge returns, but the $1800 manifold system will set you up to safely upgrade other areas.

I hope that's helped.

-Tom

TomZ

What he said!

I'm using these manifolds on my blown 454 project. I will probably upgrade to headers next year, but for now they'll work well (my risers will be extended). I got mine from the Swap Shop, used but with a brand new manifold for $350 shipped a couple years ago. The 496 setup is made by Gil for Mercruiser/Mercury.

TomZ

More on exhaust... I don't know if anyone has covered this before, but in my mind it's worth mentioning.

My buddy Wayne (oso'er Hollowpoint) has a set of Stainless Marine manifolds on the blown 454s in the Bullet. Huge manifolds (but very lightweight) that have 4.5" OD stainless risers. Really nice looking from the outside. Anyway, we were taking them off to do some powder-coating, and I thought I'd have a look at the manifolds to compare them to my 496 Gil/Mercs: VERY DIFFERENT, and not so much in a good way. Granted these are older manifolds, but there isn't really too much to them: the runners (if you can call them that) are maybe 2-inches in length, and they open into a large cavity that then exits out the top through a 4-inch opening then out into the riser. Not much difference in design over the original Merc center-riser logs... just HUGE inside with a very large opening. Needless to say, I was surprised! I thought they would have had runners connecting into a common chamber. Does it work simply because the chamber inside is so big? I would think that scavenging via exhaust pulse would be non-existent. Anyway, something interesting to think on... don't want to derail the conversation too much.

bobl

It's a Land & Sea 13" dual rotor that I can run on prop shaft or on an engine stand.