Picking out a cam...risers worth it?
 

Hey guys,

I'm doing a new engine build after some bad luck with my engines. We are working on picking a cam and looks like Bob Madera has a design in mind with the stock exhaust. That said, I was talking to my engine builder and he thinks there's a little bit left on the table with a bigger cam in my 383s if I were to buy a pair of risers. I told him to go ahead this morning but wanting to make sure this is the right call if anyone has experience with it. I know headers would be the way to go, but I can't swing $4500. I can do $1600 for some 4" aluminum risers.

Any thoughts?

Again check with Bob M, he is the man that knows what he is talking about.

Wannabe

spending 800 for better risers that only fit stock merc manifolds is a waste of 800. stay with a cam that'll work with stock manifolds till you have enough for a real exhaust. you will get no noticable improvement in performance over stock manifolds. and the stock manifolds run out of breath at around 350 hp.

Lightning are more like $2900 as long as you don't need stainless on the outers.

You will need manifolds and risers or headers to see any noticeable gains.
The only risers that fit stock Merc manifolds are some by Imco and I doubt they will allow you run hardly anymore cam anyway.

The others are right about the Imco/Hardin performance risers for stock/GLM manifolds will not let you run more cam without welding on inner extensions to prevent reversion. They do flow better than stock though and are advertised at 10 hp. Not enough to feel or see on the GPS.

As most know I'm running the alum GLM manifolds, Hardin performance risers with 20" dry extensions on my 383. This setup per Bob M should make 475hp and runs low 80 GPS @ 6200 rpms. Would a $2500 SM or EMI long riser setup gain speed vs my poor mans hp exhaust I don't know.

I do know that a member here years ago dyno'd his 383 with a Stainless Marine manifold short risers vs GLM manifolds and Imco stock performance risers. The GLM setup was within 7 hp peak vs the SM setup.

Im curious how stock manifolds run out of breath at 350 hp when stock mercs are rated higher?

You have a cam guy that is recommended by many on this site. I have no personal experience so I can't comment...but he is raved about on here by many. Take his advice if you want him to help you and set up the motor the way he says to. Once you invite others into the equation it is a recipe for disaster...just my opinion

What stock SBC merc sterndrive was rated over 350hp. The old 377 blue scorpion had CMI headers, the 6.2 is 320hp and the 5.7 mag is 300hp. I will say that when my old Searay had the original 5.7 in it with a 260H comp cam, Edelbrock perf, and roller rockers, I picked up 2 mph when I installed the Kodiaks (EMI) with the stainless risers. So that did make a difference, but unless you are going to be pushing over 450hp at the motor, headers are not worth it, but premium manifolds are. If you are going under 400hp the GLMs are more than adequate for the job.

Here is my Kodiak vs dyno header test.
http://img34.imageshack.us/img34/1372/61y2.jpg

Uploaded with ImageShack.us

I agree completely. When it comes to building an engine you can get 10000000000000 (exaggerated) opinions. Listen to the one person you trust and go with them through the entire project. That way if there is an issue you have followed their recommendations to the letter. If you waiver then they might be less inclined to stand behind their work if there's an issue.

Bob M def knows his stuff for what works in the marine world. The little bit you might be leaving on the table to be able to have trouble free boating is worth it 10x over in my honest opinion.

Scorpion 377's have stock manifolds

That motor was 377hp in a bobtail configuration and rated at 350hp for stern drive wasn't it. And I was wrong about the CMI's, they came on the 383 scorpion.

Headers were optional on the 383 scorpion. 400 hp w/o, 425 hp with. I have the pdf from Mercury stating this.

was referring to mer bbc

Don't know what a bobtail is..... Please tell more ... I don't get much info on these motors

A bobtail motor pkg is one you would see in something like a ski boat with a transmission attached to it..

Ahh .... Thanks..... I have never seen a blue 377 setup like that

Lucked out and found out I actually have GLM manifolds! Pretty great surprise. Ditching the captain's call. So we decided to pick up the risers and we had Bob grind us a couple cams. Hopefully I'll have some good dyno information to post here soon!

I have not either or have i seen any ones with cmi exhaust besides Mr x's 28 scorp he had but then again i think he installed them when he worked at donzi..

the bobtails are usually the black scorpion engines..the one with the flame cover instead of the blue cover..