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 Post subject: cam selection
 Post Posted: Sat Jun 05, 2010 7:23 pm 
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Location: queensland, australia
hi , i am after some help with cam choice. 428 sbc,,dragon slayer crank , six inch rod oliver with stroker clearance ,12.5 ,1 cr, ported afr 220 old style with 2.1 and 1.6 valve flow around the 300 at 600 and chasing a bit more. .super victor with 950 aed, 17/8 four into ones. 3200lb car with three speed 4.1 gear, 5000 rpm convertor my plan is to work on a gear change point of 7500 rpm .ideally a little cylinder bleed of would be good so it can run on our pump fuel here in australia , 98 octane or a bit more . im thinkin around 280 @50 and 690 ish lift area, i am also curious if the oliver stroker rod will clear a full size cam bilet or a 930 base has to be used . thanks in advance all suggestions appreciated .


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 Post subject: Re: cam selection
 Post Posted: Sat Jun 05, 2010 9:19 pm 
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I've built two 4 inch stroke SBCs and both required a small base circle roller cam. If you've got a raised cam block then you might be able to run a standard cam. One of my engines is a pump gas 434 that is about 10.5 compression and the other is now a 434 that is 15.2 to 1 on methanol. There is a considerable amount of work in the pan rail area on a GM BowTie block to clear the 6 inch Eagle H beam rods with L19 bolts that I used on the 15.2 engine. I also had to cut the inside of the rods for additional cam clearence. The low compression one has a set of Carrillo stroker rods in it and it is a stock GM 4 bolt grenade block with aftermarket billet steel caps. That engine has been together now since 1991 or so in one form or another.

The low compression engine has Brodix Track 1 heads with a mild port job that were never flowed. That one runs a Comp Cams roller 268/272 @ .050 with .660 lift using a 1.5 rocker. I've run it with both single Dominators and also dual 750s on both methanol and gas with little if any performance difference in the two. It will pretty much fall on it's face above 7200RPM but I have turned it 7700 on quarter mile passes. That engine ran low 10s @ 130 something in a 3500 lb street legal door car.

The high compression engine has Dart 18* fully CNC ported heads that flow up around 370 or so. That one is running a Bullet Cam roller which is 276/290 @ .050 with .736/.752 list using 1.6 shaft rockers. It pulls hard up through about 76/7800 RPM on a good day and pulls a 2450lb full chassis Camaro in the low 5.50s @ over 130MPH in the eight mile. I've run that one with both a single Dominator and dual 750s on both gas and methanol with the fastest time to date being a 5.51 in the eight mile earlier this year on the two "out of the box" twin 750 HPs that I have running 112 octane race gas, which is $9.50 a gallon here in the "states".

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 Post subject: Re: cam selection
 Post Posted: Sat Jun 05, 2010 9:30 pm 
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Location: queensland, australia
i made a mistake in my calc it is 418 ci , 3875 stroke .4.145 bore


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 Post subject: Re: cam selection
 Post Posted: Sat Jun 05, 2010 10:24 pm 
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I do think that Rick360 built one near that CID using 23* heads so he may have more info for you.

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 Post subject: Re: cam selection
 Post Posted: Sat Jun 05, 2010 10:36 pm 
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GiDay, that size engine pulling 7500 will out pull the 300 cfm head flow. The heads will be the choke on the motor. You have suggested a big cam duration and thats to try to get the limited heads to work better for the cylinder. But if it comes together in the air flow department and actually gets good cylinder fill then the 98 RON fuel is not going to cut it.
The engine will most likely be detonation limited with that comp ratio. (The timing wont be optimised) So if your a street legal car then your best option is to go smaller in the cam with less lift at the valve. That way the timing can be better and the heads wont choke back up at the pushrod pinch and fuel seperation wont result. Fuel seperation from too high air speed in the port will kill the motor, it will wash the bores and make it very hard to avoid detonation that comes from lean areas due to the seperation and lack of mixing etc. I think its likely that engine combo would work better on a 750 carby rather than the one you have. Certainly a 750 would be a safer carby option to start with.
Personally I'd lower the compression ratio and then it would make life a lot easier.


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 Post subject: Re: cam selection
 Post Posted: Sun Jun 06, 2010 12:41 am 
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Location: queensland, australia
hi shrinker, these heads and cam , manifold etc came of my 383 at nearly 13.1 we raced on ms 109 and knocked back timing for a little street use and used 98 . it made 610hp peak , average of about 590 and 490 ft/lb the engine had a good twelve yrs until it had a crank failure recently hence the new capacity. The 950 aed is a cnc carb that we back to backed on the engine dyno and the track with a bolaws 750 on the oldengine . The 950 made more peak hp with the bolaws a little sharper in the earler rpm, we ended up having to go beyond bolaws jetting recomendation which was why we ended up with the 950.This old car combo went 10.34 @130 at 3300lb on radials full exhaust with the 950.afr were in the 12 -13 range if i remember correctly. i do realise the heads are small for a big cube engine and they r presently at the porter to see if we can scrounge just a bit more flow.. i believe maybe we can get a littlemore flow with the valve size we have ????? If i went smaller in the cam and duration i am going to see increased cylinder pressure which would increase detonation wouldnt i I ?? if i was to lower the comp a bit what sort of reduction am i going to see any estimate ??and wht comp would you suggest. thanks alll info is a help


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 Post subject: Re: cam selection
 Post Posted: Sun Jun 06, 2010 2:52 am 
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If you go less duration with a wider lobe seperation angle you will close the intake at the same place but have less cylinder fill . wider LSA will also get you more vacuum so your brakes will work.
What Im suggesting is to also consider the valve lift, If you have the valve curtain area as the pinch its less of a problem fuel wise than having the pinch back up in the port. What I'm pointing out to you is that you cant use your comparison of the old 383 engine and its performance on street fuel and just say it will be OK with 418 cubes or whatever it ends up as. I have seen engines go absolutely backwards by just increasing 6 cubes with a rebore. One engine went from 900hp down to 840hp with increase from 406 to 412 cubes. That took a lot of work to get back right. So this subject is not easy and simple. I picked up another engine by going from 434 cubes down to 416 with a destroke.

See 600 hp is about right for 300 CFM heads or around that flow on a 383 but your bigger cubes alters all that. It will exceed the porting and that's bad for turbulence. I'm not saying it wont work I'm just saying you wont get all that you could. What different people expect from an engine and what they think is excellent varies quite a lot.

I would only go to 11.5 comp as a safe bet. Its not really something that you can hang a number onto, although everyone does. You have to analyse the combustion of an engine with a gas bench to figure out why its does what it does. 12.5 might be fine, you have run more before so your going to have to factor that into thinking as well. But be aware that turbulence causes fuel seperation and once the fuel seperates in the flow through the port your going to get rich and lean areas in the chamber and that means it limits the compression you can run. It only takes one lean area to detonate and you have damaged an engine, it doesn't matter what the overall AFR of the cylinder is as an average it just matters where the fuel is distributed, one error and your history.
Seperation is when the fuel predominantly goes out one side of the port/valve and it also does it in big blobs not a fine spray like it should be. If the 418 cubes pushes it over the point of no return then you will be sorry about the compression. It's easier to gain compression later on with a head shave but its harder to get it lower, costs a lot more to do that.


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 Post subject: Re: cam selection
 Post Posted: Sun Jun 06, 2010 4:03 am 
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Location: queensland, australia
thanks shrinker , one of the problems i have is these heads have been compromised by angle miling with my last combo and now have small chambers . I wish i could afford a new set of 235 afr for it but its a fairly big change with pipes and rockers.I have been doing some piston suggestions and have come from the first suggestion of puting the piston 10 down the hole to zero deck and a 10 cc valve relief to get compression down . i was told that putting the piston down the bore can lead to bad quench and detonation . i have worked on 41 thou (felpro) head gasket . It is possible i go to a cometic of a slightly thicker composition ?? I probably should of just gone 3750 again with the 4145 bore but its now to late .i am hoping to maybe find another ten or so cfm in the heads . I ideally want to se about 650 horsepower so im not wantin to squeeze it ultra hard . i have not confirmed the pistons yet because they want cam specs so i have a little room to move . I am going with diamond pistons .


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 Post subject: Re: cam selection
 Post Posted: Sun Jun 06, 2010 4:54 am 
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If you can, go to a custom piston with the dish in the piston as a mirror image of the chamber. Then set the piston to zero deck so that the squish works right. Having a dish mirror gets you the most valve clearance possible for whatever compression ration your running. Ding it that way doesn't inhibit piston to valve and also create flow cone formation issues. It gets the flat area of the piston that the valve interferes with as far away as possible. Its good to do it that way from a inside the chamber point of view and that means stroking it is a good thing, but you have to consider the porting flow as well. So angle milling the heads to get small chambers is a good thing it means you have to create the compression by dishing rather than bumping. Bumping restricts spark formation etc all sorts of stuff.


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 Post subject: Re: cam selection
 Post Posted: Sun Jun 06, 2010 6:04 am 
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As for the cam I would err on the conservative side. I think 280 is too big, that sort of duration is for higher revs than what your aiming, if its going in a road car then you want torque and response from cruising around with light load and RPM's. If you just cruise around then it has to be snappy, it will blow off more dudes that way than having a few more top end ponies. So the smaller carby option if you have one is worth a try. A correctly setup 750 will power 650hp on a 420 cuber with a moderate 260 to maybe 265 cam with power spread etc. Once you start going over 270 you start to lose drive-ability in lower range RPM's. Most of the gains of your engine will be in the carby tuning, its going to be very critical to get a good tuner on the case. It will be easier to get a reasonable transition circuit and emulsion package for the 750. I hate those 950's, so far the amount of work to get a 950 right is not economical for customers compared to fitting a 750 and selling the 950 to some turkey. For the power your after a 750 is fine.
If you have an old school 750 and not a HP one, your already near the finish line, the HP's delivered to OZ are a long way off on some engines. Though I will admit that one combo in particular is perfect for the USA calibration HP 750.
Your 950 might make more mumbo but you would probably get a longer lasting engine with a 750. The additional air speed of a 750 barrel size creates more gassing of the fuel in the inlet tract at high RPM and that is what you might need to do to overcome seperation. Its all a balance of ways to do it. Once the fuel is gassed it cant seperate its only liquid flows that cause issues.


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 Post subject: Re: cam selection
 Post Posted: Tue Jun 08, 2010 12:40 am 
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I've never tried (or liked) long duration cams to kill cylinder pressure to prevent detonation. It should reduce low rpm knock but will hurt full throttle power and probably not reduce knock at full throttle racing conditions at racing rpm. You could back off timing and may get by with driving it around as long as you put better fuel in when racing it. Part throttle, low rpm knock is not as dangerous as full throttle knock. Converter stall & gear can make a big difference in load the engine sees when driving around town.

I'd ask your cyl head guy if he could open up the chambers more. Dished pistons would be better. A 280@.050 cam will make it a slug unless you have a lot of converter and gear.

My 414ci has flat tops (2 valve relief) with ??cc (don't remember) heads that made the final compression ~ 10.75 and my cam is 261º@.050 (drag race only) with 5700 stall (not enough) and have been running straight 92octane unleaded pump gas. 36º timing. I have run up to 12.5:1 compression 355's on 100LL aviation fuel, so your 98 octane may not be too far off.

Rick


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 Post subject: Re: cam selection
 Post Posted: Tue Jun 08, 2010 1:45 am 
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Location: queensland, australia
hi again, since my last post i have taken the cyl heads to the porter and 1) open the chamber to suit the larger bore size, increasing my available chamber it also will unshroud the valve a bit more , these heads have a 2.1 valve and originally were 2.08 and havent really been modified to much to take advantage of it . ,2) some more porting which he is confident of finding another 10-15 cfm .He did however point out that i shouldnt be to critical of the overall flow but the airsped etc. I have also redone my estimate on cr to about 11.5.1 now and i know that i can get away with pump fuel for driving and probably ms104 for racing. The 280@50 camshaaft was the one from my 383 and believe it or not wasnt a slug 4.1 gears and a tight convertor. 1.4 in the sixty with full exhaust street car however it could of been a bit snappier.The old combo was good for 1.6hp /cube and i am hoping for around the same with the extra cubes. I am now not going to run so much duration and probably somthing around that 260 mark im thinking. The old engine had a 250/260 @50 at one stage and i must say it was a lot more street friendlier .I would like to see around the 650 comfortable hp ???On the piston front depending on chamber final size on how much relief but im thinking around -18 /20 so not a huge amount . Rick what sort of lift did your cam have and how much hp /tq did it have ??


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 Post subject: Re: cam selection
 Post Posted: Tue Jun 08, 2010 9:17 am 
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Here is a link to the dyno info on that Rick360 engine.

viewtopic.php?f=5&t=6673

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 Post subject: Re: cam selection
 Post Posted: Tue Jun 08, 2010 6:17 pm 
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Location: queensland, australia
Thanks ken for the link , it was most helpful. I would be hapy if i can be somewhere close to ricks combo. It will make a nice street/strip combo .


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 Post subject: Re: cam selection
 Post Posted: Wed Jul 21, 2010 3:01 am 
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Location: queensland, australia
Hi again , the build is still dragging along . I have settled on 12.1 comp with a 56 cc chamber . I have had the heads and manifold ported and i am told a good amount more power . i have a camshaft suggestion and would like any comments .Its a competition cams roller the part cs2234/2208r110 small base circle 930 , 276,284 @50 703 lift with 1.55 rocker ,110 lobe center ,4 /7 swap and tight lash design i asked for a shift point around 74/500 rpm . The head porter has been around doing race heads for over twenty five yrs and is confident we will have enough cyl head to support the 417 ci. Hope for some ideas thanks in advance.


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