Have a new SPX intake. Going on my stage 2 headed 470. Any idea how much hp difference there might be between an as cast intake versus gasket matched ports? Going on a flat tappet (290-08HL) 10.57 to 1 street motor. I’m only talking about matching the intake openings to the gasket, not a fully ported flowed version like Wilson manifolds do for the Roadkill guys. Heads are cnc ported.
It would depend on the size difference between the as cast intake exit, and the cnc ported head entry. I can tell you this: A while back I was doing a dyno on a 500HP 470... we first testing and tuned with an out of the box performer, and then went to a ported cast iron, with the top cut out.. the ported cast iron was worth 5HP over the out of the box performer.. while we were testing with the iron, I had my porting guy port match the performer.. no more than a resize to just a touch smaller than the head entry, blended up about an inch into the manifold. When we were done with the Iron intake, we put the now port matched Performer back on, and I was surprised to see it pick up 15 HP over the non ported numbers for that intake, and 10 HP over the ported Iron. WE then took the intake off again, and cut the center divider down in a mill about half inch from the carb base, and then put a nice rounded finish on that divider.. that mod traded 10 ft lbs at peak, for 10 HP at peak.. So we picked up 25 HP with a couple simple intake mods. I usually recommend that work for the typical GS hot rod build, for a heavy car like a Riv or something, I would rather have the torque than the HP, so I usually leave the divider alone in that application. Also like leaving the divider alonet if your running a 2.93 gear and a big converter in your GS.. JW
Here’s the Dyno sheet for the iron head stage 2 untouched as cast with a out of the box QJ SPX 950 black diamond quick fuel carburetor. 78 jets all four corners. Only 28° timing. Unfortunately we lost the cam hydraulic 246/264 on a 113 lope center.
Thanks for the info. Ill do some work on the intake, stay slightly small than the ports of the heads.
"lost the cam" Dang I feel better about using a 20+ year old cam with matching lifters that I have on the shelf than a new one now days;( https://racingsynthetics.shopamsoil.com/
Little bit black magic here with intake port matching Some believe and have proven that a ledge around the perimeter of the transition...shears fuel...and acts as a bell mouth if you will like a formula one runner..in principal Very popular in bbc world to run a rect port intake on an oval port head.....its been proven time and time again to pick up power on those engines..and actual feel different Not much air along the port walls so...Joe Sherman wrote a nice article years ago about his findings on the subject....he said he wouldn't worry about port matching again...as it just wasnt necessary....i myself am of the the big volume pushed into a smaller opening will speed up flow
It can and it can’t. If there’s a bottleneck in front of it,I wouldn’t bother. The most restrictive area will dictate the air flow.
Wasn’t just the Cam’s fault the engine was originally run for a very short period of time in 2014 and there was an issue with the bypass valve was sticking in the oil pump housing. The engine sat on the stand till September 2021. I should have taken the intake off and put some new cam lube on the lobes.
That's funny I've seen several dynos of mid 600hp motors loose 20+hp and tq but swapping to a rect port intake on oval heads. Now mercruiser did make a production motor that used the rect port intake found on the 454 and 502 mag mpi's on small peanut port heads.......was rated the same hp as the carb motor........it was the only bbc efi intake they had......
