I have a worked over 350 which I am looking at fitting to my avatar roadster for Kalahari Desert Speedweek this year. My engine guys (I don't know very much about this side of things) are recommending a single plane manifold and 750cfm carb (looking at around 500hp+) The existing camelhump heads have been ported at some point and measure 51mm x 31mm. Initially they were suggesting a Victor Junior, but I am wondering about port matching etc - will the bigger ports cause issues if we run the manifold out the box? My thoughts are that the Super Victor might be a better call as the port size is a better match. Reading on them I see mention of raised port and standard port. It seems that the casting numbers should tell me which heads I have, but if they have been opened up as much as they seem to have been, how will I really be able to tell which one to go for? Am I missing something here? (I don't have pics of the heads/ports right now but can get if that helps.... Since I am half a world away I don't want to order the wrong parts (and can't really afford to buy twice anyway)
Where your ports are now is anyone's guess, but, if the heads started out as standard production (e.g. not Bowtie/GM Performance), from a production car, they have(had) standard ports. Larger ports and runners favor sustained high RPM operation, at the expense of low-end torque. You will need to evaluate how you are going to use this vehicle. Realistically, what will the average operational RPM be? A few extra horsepower at 7500RPM will not be of much use if the torque curve craters at the bottom-end. Also, if these are/were production heads, the ports, even ported will be in no way as large as those of an aftermarket head, which the Victor series is aimed at.
Thanks for the reply. You asked a couple of questions that I've been knocking around in my head: Right now the car runs a 307 (with 305 heads, Performer manifold and a 600 Holley) and that really is more than enough grunt given how light it is. The thinking with the 350 is to fit it for our Speedweek and see where we can get to. The car ran about 130mph last year, and felt really stable (lots of guys seem to struggle with that at the event) which is what got me thinking. I know that things can change quite quickly as speed goes up, but I am planning some aero and other mods. In theory I think 150mph will be a cinch with more power, and 175 seems possible. I will need to find some higher speed rated tyres that aren't too wide (and that I can afford) otherwise the whole idea goes out the window. With current gearing, I should see 165mph in fourth gear, around to 200 in top at around 6500rpm (without factoring in slippage/traction issues) Back to the 350: I only plan to run it for this event, and then either sell it or build another car for it (it will eat the Getrag 'box and/or Borg Warner M75 diff that I am running if I tried to use it on the street, especially if we do it as a high revving set up). I am not overly concerned about low end torque given the weight of the car and this once off application. I guess I need to know how much power I am realistically going to need, rather than just trying to squeeze out as much as possible - if a dual plane setup will still give me enough? How much more (roughly) is the single plane going to give at the top? It would make sense to go that route and have something more street-able in another vehicle afterwards.....
You can get where you want to go installing no more than a stock Q-Jet and cast-iron intake off a mid '70's 350... And I wouldn't worry about port miss-match. Now all this said, if you are actually able to turn 7,500 rpm, then you probably will have a decently sized solid lifter cam with matching valve springs along with headers, (or at the least 2.5" dia. ram-horn cast-iron exhaust manifolds with straight down dumps.. Therefore an old Holley 30-36 true hi-rise or an old Weiand 8016 Stealth intake along with a tuned 3310-2 vacuum secondary Holley carb. will run great. You can get this stuff off ebay if you want.. Don't forget that if you want power, then get your compression up to match the cam IF you can get good gasoline!!! Our old L-48 350SS engines were stock at 10.25 to 1 and probably actually at 10 to 1 CR so start from there.. At least mine in my bought new '67 SS/RS Camaro was.. pdq67 PS., and if you are serious about 7,500 rpm, then 2 things! A forged rotating assembly and if it is a stick transmission, a "blow-out" proof bell housing to protect your feet!!
Thanks for the reply - The motor already has 7009P 11:1 pistons, BRC knife-edge ally 6.2 rods, Sig Erson R278/1 13.5 lift cam, and 11-89 Crane rev kit with full roller 1.5 ratio rockers (I'm quoting as details were sent to me - hope they make sense).... Quadrajet would be great but good ones seem really hard to come by....so right now I'm looking at a 750cfm Holley Crank is cast though - so I'm thinking more like 6500rpm? Does this make the single plane idea redundant? Scatter shield is on my list of things to do - I plan to fab one from 5mm plate, will that be sufficient?
All production chev heads are std (non raised port) some chev racing bow tie heads can be raised port but never were on a production car and are pretty rare to stumble on. There a many after market heads that are way superior to the double bump heads. A honest 500hp from a 350 with double bump heads is about the max and for racing your way farther ahead building around a pair of after market heads... 23, 18 or 15 degree heads are all available in various port volumes and styles. Most can be ordered CNC ported and assembled. Remember the the HP required to push ur car from 130 to 150mph is way less than the jump from 150 to the 175mph you mentioned. As in all racing its all about how fat your wallet is.
At 11 to 1 CR, the old Isky Z-27 or their Z-30 solid lifter cam will do nicely. They are "old-school", but will still get the job done, imho.. Just install Isky's recommended valve springs. pdq67
I agree with Otto, starting with some aftermarket heads will be money ahead in the end. More power and less trouble trying to get it all working. Unless your current heads are done and just running as-is, the money to rebuild them is near what aftermarket heads would be, and then you have heads that can support much higher potential power levels.
7,000 rpm is possible with a cast crank if things are properly balanced and setup during the build. I would not be afraid to run the Victor Jr with your heads and current specs as given to us, radius all the internal junctions and open the head end of the runners up a bit. going from a smaller runner to a larger port will increase port velocity that will not hurt you one bit at higher RPM. You don't have a lot of lift on your camshaft if computes to about .530 in inches hopefully your duration is long enough to compensate for the lower lift. I would want to run a carb in the 800 cfm range if I could personally. That is something that you are not going to get with a Q-jet and they are not a performance carb anyway. If you find an Carter AFB for a larger displacement GM mill that will put you into the 800 CFM range or a bigger Holley if simplicity is what you are after. Anyway those are my thoughts just off the top of my head.
Thanks for all the feedback guys - much appreciated! I understand that the heads are probably the weak link right now, but I think I'll stick with them (for this year at least) and just try to get the most out of them that we can. The whole set-up was in a Camaro, with a Performer manifold (I don't know what carb was on it) and though I never got to drive it my buddy who did said it was 'really strong'....so it is at least partially proven. I just got a great deal on a new 770cfm Holley, so I think we'll run that. I can borrow a single plane manifold for Speedweek so will probably just go with that for now. It'll be interesting to do some back to back runs swapping it out with the dual plane... One more question - I'm told I need a fluid dampner. Price on what I am told is 'OE' is more than double the price of one from Speedway. Is the extra $ justified?
With due respect, I think sweeping statements like this are a bit dangerous. Here's some interesting reading on the subject of torsional dampers, including some technical input from a guy that works for Fluidampr: http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=2863084 Sorry to get off topic.
Yeah, that's not biased info.... I have seen 7 broken cranks, due to Fluidampers. I am speaking from experience. Two of them were mine. The failure mode is well-known. There are SAE articles on it.
LOL it is always better to take the advice of the vendor over the end user. I would say no on the speedway damper but you better get a second opinion on it. I think that in general Speedway sells an inferior product but there was bad blood between speedy bill and my family. If it were me I would go with the Gimps advice here. Hit up summit racing and if you let them know about your endeavor they may even cut you a brake. ATI does build an excellent damper by the way.
If there is something you can't get or someone is unwilling to ship to you let one of us know we can get it worked out somehow.
Thanks for the offer - we do have a number of shops over here importing parts and I'll go with that route first. Great to know there are other options if I don't come right!
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