|
Originally Posted by bobl
(Post 3030530)
These heads have the heart shaped combustion chambers. I've built and dynod several engines very similar to this. HP is around 450 at 5500 rpm(but I don't run quite as large a cam) They will detonate with very much timing. Because of the chamber design, combustion occurs much faster, thus requiring less lead time for ignition. This information has been documented many times. Pull the timing back and give it a try. BTW I own Full Throttle Marine and build marine engines for a living(so you know my background).
Good info. |
fixx
Originally Posted by Ghostrider
(Post 3030248)
I definately have the Vortec heads (10141279...96-up...oval..CLOSED.."Vortec 7400", 100cc chambers) Technically speaking, now 105cc.
I had them openened slightly to allow better flow and I had the oval ports matched to the Felpro gaskets. I then bought the RPM Air-Gap manifold (PN 7561 - Oval Ports) and had it CNC Flowed and port matched as well. .I had the heads resurfaced / shaved 0.020" to 55Ra which will also help with the comp ratio. The combination of head chamber size and my pistons allow for about 10.5:1 Comp. They run the standard valve size (2.065" I & 1.72" E) with the large oval ports and a better exhaust port profile (which Merlin and Dart use on their heads now too.) Reason you don't see many marine engines with them (IMO) us that too many people think that all oval ports are too small and they 'must' run Rect ports to make any power in a boat! Truth is, the Vortec heads flow better than all the other ovals and the exhaust port profile makes them a far more efficient head! Only downfall is I'd like a set of 2.19" intake and 1.88" exhaust Iconel valves in there to open them up! I'm interested to learn more about the 'fast burn heads' thoughts though from Bobl. I hadn't heard that before and it is well worth considering. So if I set the timing to 8 deg initial withthe 20 deg curve (for 28 total) and give that a go it should be safer? Or will it possibly make more power? Cheers all. Good discussion! |
Originally Posted by bobl
(Post 3030530)
These heads have the heart shaped combustion chambers. I've built and dynod several engines very similar to this. HP is around 450 at 5500 rpm(but I don't run quite as large a cam) They will detonate with very much timing. Because of the chamber design, combustion occurs much faster, thus requiring less lead time for ignition. This information has been documented many times. Pull the timing back and give it a try. BTW I own Full Throttle Marine and build marine engines for a living(so you know my background).
This engine was bascially put together to run about 500hp using the bits I had (block, crank and heads.) I thought the heads seemed like a good idea and figured I'd build the remainder of the combo to best suit them by maximising combustion through comp ratio and smoothing out the ports on the intake and manifold. I think the valves are a limiter to anything much more. I did as was advised with the bowls and chamferred the edges and the tip of the heart to limit edge glow and hot spots, I went with a finer Ra on the surface to help seal the increased comp. I have a Crane 741 cam I was planning on testing but I think now that these heads won't allow it to perform well enough! Time to look for decent set of Big Valve heads? I'd love to find a set of big oval ports so with big valves already in them so I can keep my current intake combo! Are the 088s the best? Thanks again all. Funny how a Carb discussion invariably leads back to the root cause of most issues: Timing and Flow! |
yes, the intake ports on the 781' 049 are much larger than heads you are running...I have a pair of 781's we ran on a mild race engine...
|
The 781/049 have the same 230 cc intake runners as the L29 Vortec heads. These are not the peanut port heads.
Originally Posted by ezstriper
(Post 3031009)
yes, the intake ports on the 781' 049 are much larger than heads you are running...I have a pair of 781's we ran on a mild race engine...
|
Originally Posted by Ghostrider
(Post 3030738)
Thanks for that mate, that clears up that issue I'd say.
This engine was bascially put together to run about 500hp using the bits I had (block, crank and heads.) I thought the heads seemed like a good idea and figured I'd build the remainder of the combo to best suit them by maximising combustion through comp ratio and smoothing out the ports on the intake and manifold. I think the valves are a limiter to anything much more. I did as was advised with the bowls and chamferred the edges and the tip of the heart to limit edge glow and hot spots, I went with a finer Ra on the surface to help seal the increased comp. I have a Crane 741 cam I was planning on testing but I think now that these heads won't allow it to perform well enough! Time to look for decent set of Big Valve heads? I'd love to find a set of big oval ports so with big valves already in them so I can keep my current intake combo! Are the 088s the best? Thanks again all. Funny how a Carb discussion invariably leads back to the root cause of most issues: Timing and Flow! |
probably something like the 731 cam would work well don't you think.
|
Just looked up the specs on the existing cam. It is 236/244 @ .050 and 110 LSA. That is not a good marine cam. Something similar to the crane 731 is what you want. Around 226/234 duration and 112 LSA. This would be the largest cam I'd put in that engine. That cam will make peak power around 5600-5700 RPM. Just my opinion of course. Good luck.
|
hay ghostrider did you try a 23mirage prop ?????? that prop i beleave your boat will run 72 to 74 at 5300. .4900 is not going to do it:eek:
|
I put the Crower cam is as it was what I could find. I had trouble finding a decent 731 as Crane had gone while I was looking. I found a used one (ebay) but it's a bit pitted / grooved and I'm not keen to use it. I'm running an Eagle crank and GM dimple rods so i'm confident with the bottom end.
I've just found these heads on Ebay in Havasu but he won't ship overseas. Can I ship them to someone on here and they can forward them to me? I'll cover all the costs. EBay Big Valve BBC Ovals |
Fixx
Originally Posted by Ghostrider
(Post 3031477)
I put the Crower cam is as it was what I could find. I had trouble finding a decent 731 as Crane had gone while I was looking. I found a used one (ebay) but it's a bit pitted / grooved and I'm not keen to use it. I'm running an Eagle crank and GM dimple rods so i'm confident with the bottom end.
I've just found these heads on Ebay in Havasu but he won't ship overseas. Can I ship them to someone on here and they can forward them to me? I'll cover all the costs. EBay Big Valve BBC Ovals i have a set of 088 heads ill let go if interested.. |
ghostrideryou say your motor about 500ponys ,if so your boat should run about 70mph . put a 23 pitch prop on your boat and you will be runnig low 70 . . hay i built a454 with 365hp mag motor over 500hp on my boat they all told me i be in the 80 mark :bsflag: i run 66.7 mph gps 70 on dream speedo . now i had a 540dart block dart pro i heads .dart single plane intake comp cam and now i am runnig over 80mph ....11 just my testing is you need big cubes and tq and ponys so the bottom line for you is put that 23mirage prop on and see wt speed you get . low 70 is pretty good for your set up . try posted your boat and ask wt speed others are getting out of there boat??????
|
I always went back to the 23p Mirage on my 89 Challenger with a mild built 454. I tried numerous props however always went back to the 23. The rpm's in my boat were around 5500 to 5600. The cam was a tad more than the 454/420hp cam.
|
| All times are GMT -5. The time now is 10:05 AM. |
Copyright © 2026 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.