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The LS build thread started out with a smaller exh lobe than intake,even though the .050" are the same. I've seen this mistake several times and been a while since I called them out because of people getting crazy over bringing this up while they can't see/won't see/won't look it up duration #'s past .050".
When people pick an intake lobe from one family and and exhaust lobe from another, things like this happen. He stuck a potato in the exhaust........Maybe e should talk about this on another thread or that one...I don't know......I don't want to get in an argument over it. :) So yeh, picking lobes this way adding more .050" duration than what one would think, is needed before even adding head characteristic/ compression and etc into the equation. :) =================================== Back to the OP :) I 'm struggling to get a jist of what he really wants.
Originally Posted by MTScott
(Post 4685781)
What I'm considering, is an upgrade to AFR 265 heads.
Reasons: * I think the runner volume on these heads is way out of line. It would only make sense if I ran this engine to 7K rpm, and it rarely runs above 5K, 5200 at most. * Despite about 20% less volume, AFR 265s flow better than the 990s = win across the board. I would think much better midrange with the increase in port velocity * Weight: this should shave about 70lbs of the stern. * 112cc combustion chamber should bump compression slightly. I don't expect a huge return from this, but every little bit counts. Likely an upgrade to stainless/aluminum exh manifolds as well while doing this, saving another 70 lbs or so off the stern. so there is like 5K of stuff. None of this will happen for a year, but I need to start planning/saving now. Currently an EFI conversion is under way. This is a family boat on a big lake, so cruising performance is important, and we may do some skiing/wakeboarding now and then. Before I switched to a 17P 4 blade prop this thing would barely get out of the hole. Going flat out all day long is not a priority - it'll run near 50 now if i want to, that's all I need. A cam upgrade is possible as well, but I'm not quite sure what should be run with these heads yet. Perhaps something that is similar to the cam that is in the carbed 400s/425s |
Originally Posted by SB
(Post 4686108)
The LS build thread started out with a smaller exh lobe than intake,even though the .050" are the same. I've seen this mistake several times and been a while since I called them out because of people getting crazy over bringing this up while they can't see/won't see/won't look it up duration #'s past .050".
When people pick an intake lobe from one family and and exhaust lobe from another, things like this happen. He stuck a potato in the exhaust........Maybe e should talk about this on another thread or that one...I don't know......I don't want to get in an argument over it. :) . |
Originally Posted by MILD THUNDER
(Post 4686099)
What exhaust are you planning on running on this build?
https://www.cpperformance.com/p-1443...ndard-kit.aspx But I'm not hard set on anything. While the above might not be the wildest setup, the goal here is to make the best running engine in the designed RPM range. Also, I would guess I'm not far from needing replacements anyway. |
Originally Posted by Griff
(Post 4686058)
You would be better off and money ahead to find a good low hour take out 502-540ci engine, especially if the engine you have has never been rebuilt.
This motor is original, with about 400 hrs on it now. The original owner didn't use it much. We put about 50 hours a year on it our short season (Montana). It still runs fine. |
Originally Posted by SB
(Post 4686104)
I do not like the stock cam performance wise, but it will last seemingly forever since it's ramps/lobes are so easy on the rest of the valvetrain.
... the OP, if you are staying hyd flat tappet, Crane has several marine cams that do real well. Some have even come stock in the higher hp black motors. Not saying these are the only choices...just mentioning them. Crane Part#132561 Grind # H-228/312-2S-14 T1.2 Duration at .004” : 298, 306 Duration at .050”: 228, 236 Lift with 1.7 rocker: .530”, .551” LSA 114LSA ICL 109 ATDC , ECL 119 BTDC As far as swapping a powerplant, I guess that's an option too, but it seems a shame to waste this the forged internal shortblock. I guess my main interest in the AFR 265 heads, is they just seem superior (on paper at least) for this application (an engine designed to rev to 5200 rpms). |
Id skip the stainless marines, and go with the Diamond Performance manifolds. Similar cost, but its like comparing a shorty header vs a long tube. Long tubes will make more torque.
The smaller afr heads are a good option. Theres also good options from brodix, trick flow, dart, etc in the smaller runner variety. Dont get too caught up in the smaller is better game. It can be as detrimental as the "bigger is better" issue we all learned years ago. In the car world, big cams and heads can hurt big time, esp in heavy cars that are tall geared. Street Car engines spend tons of time between idle and 2500rpm. Boats, spend most of their time at 3000 and up. Point being, is sometimes something that might net morr response and efficiency cruising down the road at 1600rpm, might hurt ya in the 3500 and up range. The stock heads, although a rather large volume, did produce some big torque in many applications. Truth is, they suffer more at high rpm, from a lack of flow. Point being, if you took a 454, and swapped the stock rect out for a good flowing cnc head with less port volume, youll likely see a slight increase in low end torque, but a large increase in upper rpm HP. I think the lack of flow hurts them more than the port volume. |
Originally Posted by MTScott
(Post 4686176)
I'm not really sure where to find an powerplant like that, nor how much it costs.
This motor is original, with about 400 hrs on it now. The original owner didn't use it much. We put about 50 hours a year on it our short season (Montana). It still runs fine. |
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