static and dynamic compression and pump gas

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Intake close of typical .006 256 degree cam 110-112 lca is close
interesting how a much bigger cam with 107 LCA works out
I do not see it building sufficient around town cylinder pressure
 
Wyrmrider said:
Intake close of typical .006 256 degree cam 110-112 lca is close
interesting how a much bigger cam with 107 LCA works out
I do not see it building sufficient around town cylinder pressure
Click to expand...
In post #9, the OP said no street/ all race. He is probably not too worried about around town.
 
oh right race only
then why a motherthumper and it's comp not crane
291 intake not a problem but 311 20 degrees more on the exhaust with those heads and open headers?
you need extra exhaust on stock low flow exhaust heads but not on his
if you own the cam give it a shot
post up your cranking compression
comps diagram says intake closes 69 ABDC as Aj motes above
but exhaust opens 82 BBDC open way early for a long rod motor going to cost some power
lot of overlap, not a lot of dynamic compression for a race car- what say you AJ
let's see how it works
 
Wyrmrider said:
oh right race only
then why a motherthumper and it's comp not crane
291 intake not a problem but 311 20 degrees more on the exhaust with those heads and open headers?
you need extra exhaust on stock low flow exhaust heads but not on his
if you own the cam give it a shot
post up your cranking compression
comps diagram says intake closes 69 ABDC as Aj motes above
but exhaust opens 82 BBDC open way early for a long rod motor going to cost some power
lot of overlap, not a lot of dynamic compression for a race car- what say you AJ
let's see how it works
Click to expand...
the lower the budget, the bigger the compromise's, reason for this thread is for me to learn how big a compromise it is...to learn how to better plan these compromises! in a perfect world id be useing aluminum heads and 4 inch stroke and have a cam ground specific to my build but where im at is far from a perfect world!
 
I'm trying my hardest to be polite here;
The advertised intake duration on that cam is over two cams sizes bigger than it needs to be, for a 235 cam@.050 cam .And the advertised exhaust duration is over 3 sizes bigger than it needs to be for that 235*.
And like you said and I paraphrase;the exhaust is all messed up . When you get down to it, it's just a 235 cam with attitude, hard to tune, won't make any more power than a proper 235 cam,drinks gas, and did I mention hard to tune, and soft even up to 3500 in this combo. It will make good power once it gets on the cam, but will go over the top and crash pretty early, so the right trap gear will be critical. And, without cylinder pressure, it will be kindof gutless until it gets on the cam, so IMO the 2800 will be the first thing to get replaced. Then possibly/probably gears.
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>I had a 292/292/108 in my 367 @11.3Scr, with a 4-speed, and I think Mopar rates those at 248@.050. These two cams have some similar valve events. My power didn't really get going until 5000rpm and was done early. And the low rpm was the deal-breaker. It mighta made a good race car engine, but was horrible as a streeter.I got rid of that cam just as fast as I could.
>I think a guy with a lot of tuning experience could make this 291/311/107 work in a small stroker,with aluminum heads, and lots of cylinder pressure;but I wouldn't dream of putting it in my 367,even at 11.3Sr.
>The thing is, if you build your engine around this cam, and you don't like it, you're kindof screwed; and if you don't build your engine around it you're still kindof screwed.
And another thing, if you tune your chassis for this cam and you decide to rip that cam outta there, you got a lotta money tied up in the chassis, that may not work so good with the next cam.
>I think it really is too much for a 318, there is just no good way to make enough cylinder pressure in a 318. And IMO it's just too much for most 318 owners..... unless we have deep enough pockets to start over for the next season.
But I'll tell ya, it will have a great idle sound, after you finally figure out how to get it to idle at 750. But it won't like that 2800 that's for sure. This cam was made to sound like a race motor, and the rest was detuned for street use. For a race only car, that sounds "badazz", it should have a "badazz cam". AS much as I disliked that 292/108 on the street, it would be a great race-cam, just not in a 318.Still trying to be polite.
>>Bottom line is this,a low compression, race-only 318,needs a solid-lifter fast-rate hi-lift cam, on a tight LCA. And as always;with matching TC and gears. Or, if you set up right, you can use a hydro with hi-quality hydro-lifters, and a minimum lifter preload.
I would just get a proper cam, to match the components Op already has. It will be almost maintenance-free, durable, cheaper to build, and way more fun. The cost of a proper cam is waaay less than a bigger TC.
Let's see how it works? Not on my time,lol.
I tried that 292 on my time, I know what Op is up against. I retimed it twice, tried three intakes, and four carbs. And hey, I had 11.3Scr!! That was a long summer
 
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DWB did you ever say exactly what heads you have and what mods if any
and a measured mechanical compression ratio
 
Wyrmrider said:
DWB did you ever say exactly what heads you have and what mods if any
and a measured mechanical compression ratio
Click to expand...
10.3 compression, not picked heads yet! really just trying to learn how cam effects dynamic compression. need more cubes for cam i got seem to be my lesson here! X heads or 308s ported if i add the cubes, smaller roller cam if i dont.
 
dirty white boy said:
10.3 compression, not picked heads yet! really just trying to learn how cam effects dynamic compression. need more cubes for cam i got seem to be my lesson here! X heads or 308s ported if i add the cubes, smaller roller cam if i dont.
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RUN ALUM. HEADS !! 10.3 AINT SQUAT.
 
some compromises work some dont!! studied all this more and got better data as some was off! so with what i learned an applied to my limitations, few changes and ideas applied. so take my 85 318 roller cam block and bore it for 3.97 silv-0-lite 1278 pistons with a ch of 1.658 leaves .029 to shave off the deck for 0 deck height with a 6.123 rod and a 3.58 crank for 354.5 ci! for good quench a .039 head gasket on a EQ magnum combustion chamber of 59cc's works out to 11.3 static compression with effective stroke of 2.66 and dynamic compression of 8.65:1 a cranking pressure of 176.73:1 and a V/P of 140 with cam installed a 69 degrees at an altitude of 822 ft! hate giving up the LA shaft rockers but figuring $$$ vs flow i cant see it any other way! gonna work the heads simmiler to IMM's in this HR artical Make Big Power With Your Magnum 5.9L Mopar With These Heads! - Hot Rod Network and with a eye towerds IMM's Build Your Own 455HP Pump-Gas Magnum V8 For Around $4,000! - Hot Rod Network and Build A 500HP Capable 360 Magnum Short-Block On The Cheap! - Hot Rod Network gonna be 5.5 ci less than a 360 .030 difference in the bore, same stroke! the 36 extra cubes and lil over 1/4 inch more stroke .27 should pull the power band down some in rpms yes a 4 inch stroke would bring it down more but a head to feed that 4 inch not in my budget! doubt ill have as good results as IMM if it makes 400 id be right proud!! still gonna be a high rpm motor but should have more lower end than a 318....dwb
 
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thay iron heads might havta add lil sunoco blue to pump 92, can always dran a couple gallions outta my dirt late model! gotta build it first but thats the plan couple class's at piedmont dragway i can run it in is the plan!
 
dirty white boy said:
thay iron heads might havta add lil sunoco blue to pump 92, can always dran a couple gallions outta my dirt late model! gotta build it first but thats the plan couple class's at piedmont dragway i can run it in is the plan!
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At 177/140 and iron; if you can keep it from detonating, she'll be a ripper, hang on tight.
 
Good homework, DWB! I like it when folks get to going through this info. And I like your project overall.

IMHO, your DCR is gonna require better than pump fuel with the iron heads. I have run 8.3 on iron heads with quench and had to limit ignition timing carefully. If you really end up a 8.6, then be very careful.

Just some thoughts, in no particular order:
  • Any reason to not go with Edelbrock AL heads? Better detonation resistance and the cost has come down.
  • Do the EQ Magnums have 59 cc chambers or 62 cc? I thought it was 62 cc's....IMHO, you'd be a bit better off with 62 cc's. With 62 cc's, I come up with SCR = 11.2 and DCR at 8.45 with an ICA of 69.
  • You can always retard the cam a bit to help. But the fuel change may do the trick.
  • Ya know, you can get the EQ's machined for the LA rockers.....
  • With pushing the DCR up so much, those cast pistons are gonna be living on the edge.... Hypers or forged are better for surviving detonation. But I guess you are working with the stroke issue and getting anything off-the-shelf is gonna be a challenge.
  • For pure drag race, high DCR is gonna make your traction headaches bigger. But you'll have a wider torque range and so should be able to make the top end better with lower rear gearing with just 3 gears. That should be interesting; do you run 1/8 or 1/4 mile? OK, I see... 1/8 mile... so the extended top end speed may not as much benefit.
  • Pins are floating for those pistons, in case you had not noticed.
  • I am questioning if you are going to get adequate piston-to-valve clearance with those no-eyebrow, flat top pistons at zero deck.
  • Something like the Silvolite 1438 might work for eyebrows if you can find some bushings to go in to the rods and use the smaller pins (press fit). What rods are you using?
 
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other than money just never run any aluminum heads. im not sure see some say 59 and others sware 62 so figured it at 59 thinking if higher it be safer, dont really know what a target DCR is, just that i was needing to bring it up some. knew EQ's came with LA intake bolt arrangement but never herd of EQ shaft mount rockers id be interested in them!! a couple cc of chamber and valve notches bring it back down to SC of 10.6:1 and DC of 8:1 with CP of 159.28 VP of 124. silvolite 1438 307 chevy pistons will work with lil less bore 3.935 max, very doable!! its all bout the compromises....DWB
 
Here ya go.... also available with 1.92" valves at a lower cost. But if you are racing, that seems like going in the wrong direction.

Hughes Engines

AL heads? The Edelbrocks are available now for $200 more for a pair versus than the 2.02" Indy X heads. If you are pushing the DCR envelope, it seems like a no-brainer to me to have the extra detonation resistance. But I am no expert on the porting work that you may be considering.

As for the pistons.....
  • Put eyebrows in the ones you chose. Might be the easiest way to go. Not sure how thick the domes are on those.....
  • If you are using the stock rods, then you might be able to press in some Eagle B930 bushings after turning them down to press fit into the rods... then hone the bushing for a press fit of the .927" pins. I am thinking of doing this for another stroker design.
  • Or, buy 6.125" long Chevy rods for 2.100" journals and turn the crank for the smaller bearings.... you can even offset grind it to get a 3.60+" stroke and less decking on the block. The press versus floating pin matter may still need to be resolved, depending on how the rods are set up.
The above type of mods seems to be the order of the day when you are doing non-standard strokes on 318's/273's.
 
dirty white boy said:
would a well tuned small block with 10.37 static compression with good quench, and 7.89 dynamic compression and cranking pressure of 159.1 run on good pump gas? AJ/FormS how 7.89 dynamic gonna work with 2800ish stall in a 904 with 4:10 gears and 28 inch tire?
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Yes. But an 8.4 dynamic would be 91 material.
I run a dynamic of 8.86 on 91

Advance the cam 4 degrees and that should about do it...otherwise you can run 89 on that 7.89 or even 87 without vac advance.
 
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