New life for an old 340 (stock stroke)

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nm9stheham said:
Stroking always raises CR, all else being equal. Just looking at that tabulation of number on the SCAT website shows static CR's between 10 and 11. With a small cam like that, the dynamic CR may well work out too high.

Running some numbers quickly for that crank and piston setup.
  • That kit with the ICON 741 pistons (which I think are what they are using)
  • Typical J heads, not milled
  • .039" thick head gaskets
Works out to a static CR of around 9.5, with a standard height block . Not as bad as I feared. Those pistons do not stick up out of the heads like stock hi-po 340 pistons did, so the lower piston height helps the keep the CR from rising.

Dynamic CR accounts for the cam size and ought to stay at or below 8.0 or so for iron heads to be able to stay away from detonation on premium pump fuel. A smaller Lunati Voodoo cam would be a 10200702, at 265 advertised intake duration, and .475 lift. Pretty easy to work with. dynamic CR would work out around 7.9-8.0. So that is as small as you would want to go on the cam. A very nice, torquey street engine at that; you would want to approach the tune-up carefully; I assume you are in CA near to sea level...yes???

And the nice thing about keeping the CR up is that you can go with a bigger cam and not hurt your low RPM torque.

BTW, with the heads you mention, you're not going to be stressing a stock cast crank, IMHO. They just are not going to flow the air.
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Well with the kit it comes with a forged steel crank. And I will be running the 701 version of that lunati cam you mentioned. The heads have the 1.88 not the 2.02 valves . Thank you for the info cause they really helps been trying to run the numbers on it and this will be my first reputable v8 build I'll do. The stock crank stroke was I believe a 3.31 and ill be going to a 3.58 so trying to keep compressing below 11 honestly cause I still want to be able to just cruise it. I wanted to go with the kit and I havent picked out a intake of carb yet. I live about 1 hour from the ocean so yes. Thanks again this is why I love fabo everyone helps one another out I'm still fairly new to fabo but this has helped me on a lot of things cause now I am getting into more aggressive builds rather than my usual restoration that my father and I do.
 
OK, well that 701 cam's duration is short enough that the dynamic CR will be pushing 8:1, and with that 91 octane you have out there, will probably be prone to detonate. So that is why I looked at the 702 as the smallest cam to use. With good 'area under the curve, those cams have the potential to pack more mixture in, and that adds to the likelihood to detonate. Open chamber heads, no quench gap, and iron head material also push towards that condition. So proceed with caution; I'd personally step up to to the 702 and get a few more hundred RPM's on the top end and get a bit more detonation margin. The low RPM torque will still be quite good.

If you are using that kit with that 701 cam, then some steps ought to be taken to lower static CR a tad. If you use the standard Felpro head gaskets which are .051" thick then it keeps the DCR a hair below 8. Seems workable to me. You just need to be careful and not use not quite as much total ignition advance that is used for lower compression engines, and bring it in slowly vs RPM's. An AFR meter might be a good thing for your setup. Good luck with it!
 
nm9stheham said:
OK, well that 701 cam's duration is short enough that the dynamic CR will be pushing 8:1, and with that 91 octane you have out there, will probably be prone to detonate. So that is why I looked at the 702 as the smallest cam to use. With good 'area under the curve, those cams have the potential to pack more mixture in, and that adds to the likelihood to detonate. Open chamber heads, no quench gap, and iron head material also push towards that condition. So proceed with caution; I'd personally step up to to the 702 and get a few more hundred RPM's on the top end and get a bit more detonation margin. The low RPM torque will still be quite good.

If you are using that kit with that 701 cam, then some steps ought to be taken to lower static CR a tad. If you use the standard Felpro head gaskets which are .051" thick then it keeps the DCR a hair below 8. Seems workable to me. You just need to be careful and not use not quite as much total ignition advance that is used for lower compression engines, and bring it in slowly vs RPM's. An AFR meter might be a good thing for your setup. Good luck with it!
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So with that cam you think it would be the safer route and with that scat kit what would be the best route then you think if I may ask? Or maybe stock grind can? What do you think of this cam with that combo of the the engine?
COMP Cams 20-309-4
 
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Keep in mind that you can get an engine with ANY of the cams mentioned so far to detonate if you are not paying attention to tuning... and can happen with larger cams too. So, if you are keeping DCR up to make the low RPM torque as best as you can (appropriate for a spunky driver/cruiser IMHO), it is more a matter of working with that fact and being aware of the care that is needed. I personally would not sacrifice low RPM torque out of fear; it's manageable where this is, IMHO.

That Comp cam does not change things hardly at all versus the 702. Intake closing angles are the same, as are the difference between advertised vs .050" lift durations.
 
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To a degree yes because it doesn’t allow the engine to lug or chug if that makes sense. Overall, the whole package has to be balanced first. It starts with the engine.
 
Guess I better get this on the dyno in order to un-hijack the thread. I leaned on a buddy and scrounged an oil filter plate and stub (I hate calling it a nipple). These parts are $40 each at the dealership here. It's currently full of oil and pushrods are cut to length and made-which I may have gotten ahead of myself. I made ball-cup pushrods using a 273 set of adjustable rockers to check length-but am now considering the PRW-PQX stainless roller rockers which require ball-ball pushrods. Still I think the roller tip is a pro that outweighs the cons. Will have the rockers/pushrods next week. J.Rob
 
As long as the rocker is well made, I don’t really see a “CON” to them. Price is a draw back that is long forgotten years down the road when it still performs without flaw. Light weight is a plus.
 
rumblefish360 said:
As long as the rocker is well made, I don’t really see a “CON” to them. Price is a draw back that is long forgotten years down the road when it still performs without flaw. Light weight is a plus.
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The PRW's are less than the Crane iron's I was planning by about $50. J.Rob
 
I'm happy to report that the engine is alive and well. Had the chance to dyno it this evening. Broke the cam in and proceeded to put 15 pulls on it mainly testing carbs and spacers. Found some interesting things with this combo. First surprise was the fact that it liked 32 degrees total timing best. It did not like 34 or 30. Thirty-two was the majic number. All testing was performed on Ultramar 91 and I am really impressed with this fuel. The engine started and shut off perfectly with my go to locked out Lean burn distributor--it even smelled abnormally good. Next post will contain more info. J.Rob

340ondyno.jpg
 
Let me say that I am relieved and super happy with the results. No smoke, no leaks, no bad noises and pretty good power exceeding my expectations. A 650 cfm carb with an 1" HVH four hole tapered spacer was THE perfect package. I tried a 750 XP and it lost almost 20 tq @ the start of the test compared to the 650 with about a 2 HP advantage at the peak. Manifold vacuum was 9" at 1000-1050 rpm. Hot idle oil pressure and I mean hot after repeated pulls to 6900-7000 rpm was 30 psi with a nice and steady trend to 60-70 psi in the upper rpm's. Valve lash was great as in did not move after my initial cold settings. The only thing I didn't do yet is a cranking compression test--but I will. J.Rob

340dynosheet.jpg
 
Thanks as always RAMM! When you say this 'liked' a certain timing, what characteristic is optimized with the 'best' timing?
 
So here's what is kind of stunning really--check the spread from peak torque to peak HP. A typical build will be 1300 RPM between, A pretty good engine will be 1500 RPM, an above average build will be 1700 RPM. Yes the engine has VERY good throttle response and as an added bonus I took exactly 22 litres of fuel in to dyno with and brought exactly 10 litres home and put it in the wife's car. I find that kind of remarkable considering the break-in time alone usually consumes about half of that under the steady state , moderate load 2000-2500 rpms for 15-20 mins conditions. I suppose the small cubes and 650 carb really are the players here. I find this graph displays the spread amazingly well if not starkly. Oh and the PAC-1908 dual spring may be my new fave short install height spring for now. J.Rob

340dynograph.jpg
 
nm9stheham said:
Thanks as always RAMM! When you say this 'liked' a certain timing, what characteristic is optimized with the 'best' timing?
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You're welcome. Well we can try 35-36 total which is what most small blocks like and do a dyno test and observe a 2-3 tq/hp loss. Then we dial back the timing to 29-30 total and observe the same trend. Then we dial exactly 32 back in and perform the same test and observe power come back like clockwork. Good question though because there is more to it than that . It is subjective though, I found the engine started better @ 32 and sounded better and idled better and was more responsive slightly jazzing the throttle etc.... Also when you roll in on the throttle at the start of the test and watch the TQ and whether it falls or climbs or stays rock steady tells you a lot as well. But that is hard to explain. J.Rob
 
skrews said:
IMO the wide LSA cam is helping spread the TQ and HP peaks too.
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Big time, that is why I tried this particular LSA. It idled awesome--Not choppy or hairy at all . My buddy who is no stranger to engines was surprised when I handed him the cam card. He guessed 236-238 @ .050" but clued in right away on the 113 LSA. More to LSA than most realize. As always SKREWS --spot on!. J.Rob
 
nm9stheham said:
And the fuel economy...
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No doubt and I can talk about this for quite some time. I have actual numbers concerning this in a real life carb'd muscle car situation. Would you believe 20.9 MPG with a 112 LSA cam (and superior power and mannners) vs. 18.9 MPG with a 110 LSA cam? Yes this was steady state HWY driving and expertly documented. I do not advocate tight LSA's for anything other than a true competition engine . As I also said a few years ago--Cubes DO NOT EAT DURATION--however this is not the thread for that discussion. J.Rob
 
RAMM said:
No doubt and I can talk about this for quite some time. I have actual numbers concerning this in a real life carb'd muscle car situation. Would you believe 20.9 MPG with a 112 LSA cam (and superior power and mannners) vs. 18.9 MPG with a 110 LSA cam? Yes this was steady state HWY driving and expertly documented. I do not advocate tight LSA's for anything other than a true competition engine . As I also said a few years ago--Cubes DO NOT EAT DURATION--however this is not the thread for that discussion. J.Rob
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Oh I can believe it.. .I lucked out 4+ decades ago in my first build and ended up with 114LSA cam with short durations... the Arab oil embargo caused a lot of cam change when fuel more than doubled overnight and you could only get 5-10 gallons per fill up max! That cam with the bigger breathing 351C parts like you have here made a flexible, wide RPM range engine... 19 mpg on the interstate, towed my rally car all over with it, and chased Porsche's and beat factory 440 GTX's time and again LOL. I really enjoy this type of design and these types of outcomes.

RAMM said:
You're welcome. Well we can try 35-36 total which is what most small blocks like and do a dyno test and observe a 2-3 tq/hp loss. Then we dial back the timing to 29-30 total and observe the same trend. Then we dial exactly 32 back in and perform the same test and observe power come back like clockwork. Good question though because there is more to it than that . It is subjective though, I found the engine started better @ 32 and sounded better and idled better and was more responsive slightly jazzing the throttle etc.... Also when you roll in on the throttle at the start of the test and watch the TQ and whether it falls or climbs or stays rock steady tells you a lot as well. But that is hard to explain. J.Rob
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I can believe it.. the combustion process is dynamically changing with even slight changes... sounds like optimizing around 'driveability' and throttle response.
 
Nice! Those mildly ported heads helped carry the mechanical cam a bit further than stock heads would by miles! I think the low amount of porting did a great job. How did it do under the posted test rpm? Is there an example around 3K done?

I know the small single plane doesn’t take so well that low.
Just wondering.
 
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I would be curious to see this based on a 360, I imagine an increase in low end torque up into the mid range. Nice build.
 
RAMM can you explain you comment on the rpm spread between peak torque and peak horsepower?
 
There are a few factors that broaden the power curve, the cam lsa, good average head flow numbers, Combo well matched w/induction n of course high VE like the carburetor only giving 2hp to the 750 points right to that...so it's parts and peices are obviously in harmony.
I think the overall output of this engine is what makes it more wow or striking to the reader here. Great job, it's almost 'just things overlooked by most people when putting a combo together'...'simplicity being one' and 'basic cam theory' another. There has been this train of either 110 "semi broad" or 108/106 "light switch power" for some time. People jump on many bandwagons and forget the basic idea in building.
RAMM can respond, his motor to know.
Thanks RAMM for sharing.
 
110lsa, off the shelf cam, dual plane manifold......2400rpm between peaks.

28057EFD-5DCC-4DDC-8B3D-19F584D61460.jpeg


115lsa....... 1700rpm between peaks

08B62B37-8E13-4CEE-AE51-99D7A49DAFDC.jpeg


Imo, there’s no magic in the lsa. It’s about the whole combo.
 
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