Powerboat Forums at SpeedWake banner
1 - 12 of 12 Posts

·
Registered
Joined
·
175 Posts
Discussion Starter · #1 ·
In the quest for more power (437 on the dyno wasn't enough), I have decided to once again up the cam in my 383. I currently have an Comp XM276HR which is a 224/230 112°LSA hydraulic roller. I idle at 750 rpm in gear and have no reversion issues. Compression is at 10:1 and I have 5.7" rods. Exhaust is Kodiak manifolds with IMCO short risers turning down into an S pipe for below swim exit. The tips split the waterline. I plan to build a new jacketed S pipe with the water mixing with exhaust a couple inches before the tip. The drop with the S is about 18". I want to hear from other enthusiasts out there with small blocks on how big a cam you have and what brand / type of exhaust. If you can go even further and note your overlap, that would be nice as well. I would like to venture into the 236/242 with a 110LSA but we will see.

Here are mine:
XM276HR 276 282 224 230 .503 .510 112° 55° overlap
 

·
Registered
Joined
·
1,757 Posts
My cam is over 600 lift with a 110 center line.But the heads are tricked out.The exhaust is dry to the tips.My advice is call a pro with all your info and desires.No sense guessing,pita to change cams and you could go backwards if the flow is wrong.Call RMBUILDER,great guy and knows his stuff.He has helped quite a few people on this site.BTW,I ran the same cam as yours with 1.6 rockers in my 383 last year.Check your fuel pick up in the tank,make sure it will carry the volume of fuel you need and your water separator.Mine were too small for what I ran.Luckily I didn't lean anything out and burn it up.Hump changed his and picked up 3 mph.
 

·
383 Mouse Powered 80.5GPS
Joined
·
682 Posts
I also ran that same XM276HR in last years 355ci. I ran 1.6R on the intake and made it a 226/230 .537/.511 112+2. Ran really good. 10-1 static.
I had Glenwood manifolds and FastGlass short risers. Had reversion in the center runners. Welded 16" extensions onto the risers and problem fixed.

Currently have a 385ci with 6" rods, AFR 190 heads, 10.1-1 static. I also had Bob Madera "RMBuilder" design me a custom hyd roller and its awesome. This cam was meant for a 383 based engine with good heads and exhaust. It's a 234/240 .580/.568 112+4 Peaks at 5700 and holds to 6000rpms. Violent midrange from 4500+. 68.5* overlap degreed in at 108 ICL

Currently have GLM manifolds and stainless FastGlass long risers dry into the tips. Cookin and I have the same setup. No reversion.

I also agree with cookin. Call and talk to Bob Madera about marine cam selection. He's simply the man. Wonderful guy to talk to and will explain everything.

Let us know if you need his ##..
 

·
Registered
Joined
·
175 Posts
Discussion Starter · #4 ·
Yeah, I know I'm going to have to talk to RM. I'm doing this for two reasons. I'm shoring up my stance on the bigger cam and potential consequenses, and providing a resource for anybody else that may be dabbling with moding a smallblock. It would be nice if there was some information with reguards to stock manifolds and cam selection as well. Then someone would realize that by making another mod, there reversion problems wold go away. More or less, I've see similar threads for big blocks, but scr*w big blocks. I like beating up on big blocks with my little small block microboat, and I want to help anyone else doing the same. :D
 

·
Registered
Joined
·
175 Posts
Discussion Starter · #5 ·
BTW, is there any prudence to my jacketed S pipe helping combat reversion, since gravity is helping pull the water down. Or is the sucking back going to be that strong that the water falling down will easily enough come back up?
 

·
Registered
Joined
·
19,039 Posts
ACrooks69 said:
BTW, is there any prudence to my jacketed S pipe helping combat reversion, since gravity is helping pull the water down.
Yes.

Same effect with the newer Gill HP500 risers that rise higher and thus drop further then their previous version that didn't rise, and thus fall, that far.

Gravity is a big factor and thus can greatly help.
 

·
Registered
Joined
·
175 Posts
Discussion Starter · #7 ·
Cool. Ryan, I want a bigger cam than the one you have then. :D Or at least ground on a 109 or 110LSA.
 

·
Registered
Joined
·
19,039 Posts
:laugher: :laugher:
Just go for it then, how about on a 106 installed at 102 ICL. :laugher: :laugher:

I know you know, but just to make sure, I didn't say the S pipe would stop all chance of reversion. :laugher: :laugher:

BTW: the inner pipe thing that Cookin and Ryan and Myself have done will help things too.
 

·
Registered
Joined
·
175 Posts
Discussion Starter · #9 ·
That's what I talking about with the S pipe. I'm going to section some stainless tubing to replace my current arraingment with a 3 or 3.5 in inner to slip in the exhaust of the riser and a 4 in to jacket the exhausr pipe, then it will come together at the water line before exiting the transom.
 

·
Registered
Joined
·
19,039 Posts
Yup - you got it. I'm wondering if slash cutting the inner will help even further vs straight cut that I believe the 3 of us have. Slash cut will give the water at top of inner a chance to fall down with less chance going back into the inner ????

I think a lot of exhausts would not be as prone to water reversion or would revert less if the inner wasn't bent/blended to outside pipe as most ss pipe riser systems do.

= is outer pipe
- is inner pipe

=============================

------------------------


------------------

=============================
 

·
Registered
Joined
·
19,039 Posts
Standard SS tube riser set-up that blends inner to outer where the water coming out of space inbetween them can easily be pulled right back into the inner.


=========================/==========
---------------------------------------------/



---------------------------------------------\
=========================\==========


vs better way that I showed above in Post #10

===================================

-----------------------------------


----------------------------

===================================
 

·
Registered
Joined
·
175 Posts
Discussion Starter · #12 ·
Good idea and I agree. I will take that into account when I make the pipe.
 
1 - 12 of 12 Posts
Top