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I run slightly higher compression and cranking pressure than this. Aluminium heads. On the street.
With the correct timing curve, absolutely no issues whatsoever.
Nothing at all to concern yourself with.
You are fine OP.
I know people who have pushed it further, but then the tuning gets incredibly important.
The late IVC of 62* of the moderate overlap cam, is enabling you to run high compression of 10.1 CR
It's a lot like an Atkinson Cycle engine, where they run up to 12:1 CR on the street.
The OP has a 20% compression stroke reduction, 2.99" vs 3.75" due to the IVC.
Atkinson cycle can push that to 30%.
They just do it with much less overlap as well.
The compression / expansion ratio greatly helps engine efficiency. link
Why do you think those darn Civics get such incredible MPG?
They are Atkinson cycle engines.
You are fine OP.
I know people who have pushed it further, but then the tuning gets incredibly important.
The late IVC of 62* of the moderate overlap cam, is enabling you to run high compression of 10.1 CR
It's a lot like an Atkinson Cycle engine, where they run up to 12:1 CR on the street.
The OP has a 20% compression stroke reduction, 2.99" vs 3.75" due to the IVC.
Atkinson cycle can push that to 30%.
They just do it with much less overlap as well.
The compression / expansion ratio greatly helps engine efficiency. link
Why do you think those darn Civics get such incredible MPG?
They are Atkinson cycle engines.
I think there may be some confusion about this DCR calculation. As wth any mathematical formula, garbage in garbage out....it has to be apples with apples.....i.e. if you are going to enter the degrees of the advertised duration (normally measured at 0.006 inch of lift opening, to 0.006 closing) for the calculation, you will have a bigger number of total degrees. With this cam, it is 268 total degree from when the valve reaches 0.006 off the seat, till it reaches 0.006 from closing. If you measure the duration in degrees from when the valve reaches 0.050 off the seat the whole way around till it is 0.050 inch back on the seat, it is 220 degrees. The cam opens and closes the valves base on the angles built into the cam and the cam card tells you when the intake valve closes.....but its based on how many degrees after the measured starting point at 0.006 valve lift.....or 0.050 inch lift. If you start the degree measurement at 0.006 lift.....you will have bigger numbers than if you wait to start the degree measurement at 0.050.....and why 268 advertised duration is only 220 degrees at 0.050 inch lift. The IVC degree does not change......but its a measurement based on the starting point. You can enter either the degrees at advertised or at 0.050 into the calculation, as long as you enter the corect IVC number, into the calcuation,....and the DCR will be the same. The cam manufacturers can provide one or both of these IVC numbers, but you have to use the right one in the calculation.
Now....Leigh stated that the 62 degree IVC is a "late" closing point, which I would say is slightly misleading, because in fact, compared to most longer duration cams people use, it is actually an EARLY intake valve closing point.. If people are accustomed to talking about IVC numbers when measured at the starting point of 0.050 inch, and they hear the number 62 ABDC, then it sounds VERY late, but its not. My IVC degree when measured at the starting point of 0.050 inch lift is 38 ABDC. If you don't keep the apples with applies, 62 sounds like that valve is open way longer past ABDC. As a point of reference, the Isky Cam I had in the previous engine had an IVC close at 71 degrees from starting point of 0.006 lift and 47 degrees from starting point of 0.050 inch lift. That cam had 10 degrees MORE overlap. So.....my new 220/224 cam has an EARLIER intake valve closing point. Measured at 0.050 inch...my new cam is IVC is 38......the Isky cam was 47.... NINE degrees later. And that cam bleed off MORE pressure.....because it was designed with more overlap...to produce more HP at higher RPM.
The entire subject of building torque has been something I have been familar with going back to the Harley cams I chose, and I learned from cam guys in that world that the sooner you close that intake valve, the more torque you build. The only reason for more cam overlap is the known and proven efficiencies you get at high RPM because of the energy of the fuel / air mixture...packing the cylinder with more air,..which is ONLY because of the high RPM. But if you don't push the engine to those high RPM numbers....you are bleeding off cylinder pressure unnecessarily,....and a result, you lose torque at low RPM. HP is a calculation that includes the measured torque AND RPM. And sure,....its a bigger number, but only at the high end of the RPM range. HOWEVER, with that kind of cam....you lowered the torque part of the calculation because you bleed off pressure.. You gain at the top because of cylinder efficiences, but lose at bottom because of less torque produced. When you limit RPM like I do.....that overlap, i.e. bleeding off cylinder pressure,...you lose torque, and is a negative. The cam I chose for my Harley along time ago was a cam with an IVC closing point that occurred sooner ABDC than the factory cam,.......and it produces more torque at lower RPM than the factory cam. And yes.....HP at high RPM was probably less, which is irrelevant to me and how I operate the bike.
So, I never heard about the Atkinson theory......but what I do understand is that closing the intake valve SOONER is better for producing torque. When Leigh called the IVC a "late" closing cam, I think that can mislead some people, including myself at first, but its a relative term....late verus early. I think the point is, it closes AFTER bottom dead center (ABDC)......so I thnk that is why it is called "late". Some would say it should close right at bottom dead center, and ask why would you want it still OPEN as the piston starts up on the compression stroke?? I am sure there is an answer, I don't know enough about it to explain why, but most cams in our SBC engines close the intake valve AFTER BDC. However, my cam IVC is EARLIER than a longer duration cam, not later, .......and a cam with an earlier IVC number is better for production of torque. When you close the intake valve sooner you are trapping the combustion pressure into the cylinder instead of bleeding that pressure off by delaying the intake valve closing point on the combustion stroke. When you bleed it off, you lower the pressure. And its that pressure that pushes that piston down on the power stroke,....and the more pressure....more torque. Before anyone chimes in.....I know, an engine produces more HP at higher RPM. RPM is a calculation. This is about best torque within my operating RPM range of idle to 4000 RPM.
Back to the DCR calculation......if you use the bigger advertised duration of 268 in the formula,......but you enter the 38 degree IVC point (which is the 0.050 inch lift number)., like OMF did....yes, you will have a plus 9.4 DCR, and that makes sense because now you are closing the IVC WAY early, increasing the cylinder pressure,....and exceeding the recommended 8.0-8.5 DCR number. Conversely, if you were to enter the 0.050 inch duration of 220 degrees into the calcuator, but use the 62 IVC number (which is the 0.006 inch number), the DCR would be extremely low. Both are incorrect if you want to know the actual DCR. You have to use a formula that is based on either the advertised duration....or the duration measured at 0.050. Can’t mix up the numbers and get correct results.
Last edited by Torqued Off; 04-26-2024 at 09:58 AM.
4.125 bores have very little meat between the bores. Why would anyone with any common sense use a 4.200 bore gasket which is even thinner? Then to "ZERO" deck and subject the already stressed gasket by having to use thicker head gaskets for some quench. Very poor planning. 4.125 gaskets are availiable.
As for the value of calculating the Dynamic Compression Ratio.....I have read lots of posts on lots of forums, and there are many people who believe that DCR is irrlevant. Many times, very experienced people....and "experts" believe it is an irrelevant number. I agree that there is alot more to engine design and how it will perform than a DCR number. But.....I think its real value is in ensuring detonation resistance. Its a number that can be calculated that includes many factors, including static compression ratio, cam timing (IVC point the key), ignition timing, squish, piston design, planned RPM operating range, fuel octane used, etc. Given the industry standard determined of 8.0-8.5 DCR that is safe to prevent detonation,.....I think it has a value.
Ultimately, it all makes sense, at least to me. DCR is more about defining what is the pressure within the cylinder? There is a pressure that is too high, and will cause detonation. Calculating DCR allows you to engineer the pressure, by choosing the cam, combined with the combustion chamber and piston volumes, which create the static compression ratio. The cubic inch of the engine is part of the calculation. I think its a useful measurement.
What is interesting to me about this engine, versus the previous Mark Jones engine is that the DCR is NOT that much different. And thus, its likely the torque, and feel, of the car may not be much different. That engine was larger cubic inch, had more cam overlap, made more HP than my new engine will. It had higher static compression, and thus the overlap had less penalty to the production of torque and why the DCR is similar.. I accept all of this to be true, and intentionally made choices. Some may be compromises if defined simply by power output. This new engine is going to be more mild in many ways, it certainly will produce less total HP. It has less displacement 400 versus 408, it has a cam with much less duration and less overlap...which will change the torque curve to increase torque at lower RPM.at the sacrifice of top end HP. But it also has a superior combustion chamber wtih better piston head design, better squish / quench. I believe the RPM intake manifold is going to be a better choice for street operations than the RPM Air Gap, because the air / fuel ratio will be better. This, as well as the increased idle vacuum I will have, is going to make the fuel air mixture better, and easier to tune. Overall.....the engine is less intense.
My point is,....some may say that the fact I have a very similar DCR as the Mark Jones build,....means that all I did with making this engine more mild was to lose top end power, and gained nothing at the bottom. Given the predictable change in the torque curve, I would disagree, but its possible that engine raised the torque curve higher and balanced all that out??
But my way of looking at this is that I have built a more mild, less intense engine, that is going to perform equal to, or better, than that engine......within the operating range I drive the car. That is a win win to me. Then of course.....the real gain / win is going to be an engine without all the documented problems of the two previous engine builds....hopefully... and only.time will tell.
I missed that earlier on. Good point. Very thin head gasket between bores. Hummm.
As per cam and DCR. sounds like your cam spec's are similar to what I'm running on my 350. With 1.6-1 rockers I'm just a tad over .5 lift. Mine pulls hard from 2 Grand up. No pinging, no problems.
I think your 8.26 DCR is just fine.
I have seen people push that much higher, but it does require very careful tuning, and does not always work as well, or better, and can be worse if you go too far.
That was my point.
I agree with your Torque and cam timing analysis. Based on my engine builders vast experience, and his many conversations with me. His engines out-performed others hundreds of times. There are naysayers out there for any and every topic. Once you have decided, don't worry about them. I go with the scientific method: Once a hypothesis/opinion has been proven to be correct by hard evidence, it becomes a (proven) Theory. One can still take shots at it, but you have to prove your point with hard data. Until then, it stands.
I am sorry I brought up the Atkinson cycle, it was just to show that the car mfgrs do some pretty strange things with cam timing these days. Variable cams and computers bring up more options, and can make tuning both difficult, and easy at the same time. But none of that really applies to old school SBCs. It doesn't really apply. My mistake in bringing it up. I do not intend to confuse anyone.
I got the engine painted yesterday. I used this Eastwood Ceramic paint with 4:1 Activator, Chevy Orange. It claims to be able to be brushed on,...so I tried that. First coat was terrible, barely covered the block. They also claim it can be painted directly onto case without primer....but I think primer may have helped some,...but the paint is just plain thin in terms of opaqueness. So.....I finished off the masking and sprayed it with my small cup gun. They say you may need to thin it 10% with urethane reducer, but my small gun sprayed it fine. It still took almost four medium spray coats, 20 minutes in between each coat, over the brushed first coat. And, frankly, there are still places on sharp edges that you can see through it. I did have one place, just in front of fuel pump mount that fish-eyed. I had wiped the entire block with Dawn dish soap, followed by Acetone....and it seemed clean, but I guess this area was still contaminated with oil, etc.
The good thing is that its a very thick, shiny, durable and resistant surface, even where it fish-eyed. I may sand that area and brush coat it again. The area is not that visible,....but with me,....its a thing. We'lll see. The pictures below were taken about 15 hours after it was sprayed, and its dry......but looks wet.
Would I recommend this Eastwood Ceramic paint? Well....its a great coating, but I think it sucks how transparent it is. Its possible if you started with primer it would have been better, but I doubt it. The paint is just too thin. I think its definitely a better looking and more durable fuel resistant coating than Duplicolor spray can, but certainly takes more work. I think its a slightly darker orange than the Duplicolor Orange.
Last edited by Torqued Off; 04-27-2024 at 12:21 PM.
One thing I keep noticing is the crank balancing holes. I can't see all the throws, But when you recieve a Scat forged crankshaft it has a wired on tag that directly states the maximum number of holes per throw. What happens is flat rate balancing man gets paid on number of jobs completed. like getting paid 50 hours and only working 40 hours. It is less time consuming to just drill three holes in one throw than to jig it up and do it correctly across the several crank throws.
I don't know if you went with 350 main or the larger 400 main journal size and I don't know what your from Scat crank tag said.
Did some checking on things today,.....and took some pictures. There AFR heads are a work of art,....I like just looking at them. I checked that the oil drain paths at each end have no blockage going into the block...they fit pretty nicely. All the pushrod holes and bolt holes all line up perfectly. The casting quality is awesome. And the CNC machining is well done and smooth.....not as smooth as the RACE versions, but good enough for me.
TWO rocker arm stud holes penetrate the intake ports, just barely,...so I am determined to seal those up well to prevent the leaks I had previously. I am considering sealing it off at the bottom of the thread hole with high temp something, and then Hylomar on the threads.
I also am pondering how I want to deal with the exhaust crossover. When I used the RPM Air Gap, there were no decisions, because they are blocked by design. The AFR 195 STREET heads have a very small 3/8 inch diameter hole, and the inlet is located in ONE exhaust port un the head, just downstream of the exhaust valve in the port. These holes are much smaller than the large factory SBC crossovers, and therefore are going to flow much less volume of heated air.
The AFR 6900 head gasket includes the hole to allow the crossover, the Felpro 1205 does not. So, I can pick open or closed. As I discussed previously in the thread, I am using the RPM NON-Air Gap manifold because I actually DO want some manifold heat, because as I explained, my research shows that the fuel / air mixture is improved with some level of heat.to better atomize the fuel, and reduce an un-atomized fuel droplet filled mixture washing the cylinder walls, mostly on startup and warmup. Having the oil valley heating the underside of the non-Air Gap manifold is probably enough, but the exhaust crossove adds more heat just under the floor of the intake manifold. The question is.....how much is enough,...how much is too much??. Its an unknown..at least to me. I called Jeremy at AFR, and he said the small crossover in their heads is minimal, and he said either way is fine, neither is that much different. I know aluminum intake will retain heat well,.....so I may just go with 1205 Felpros, blocking the crossover...although I do question whether over time does the exhaust heat burn through the gasket???. Ultimately,....I don't think it makes much difference...i.e.splitting hairs. I think the choice between the two gaskets is going to be more abouit the fit and seal,...than worrying about this exhaust crossover.
INTAKE PORT EXHAUST PORT
EXHAUST CROSSOVER HOLE on INTAKE MANIFOLD SIDE
EXHAUST CROSSOVER INLET JUST PAST THE EXHAUST VALVE IN PORT
OIL DRAIN PATH AT END OF HEAD.....LOOKS LIKE ITS BLOCKED, BUT ITS THE IMAGE.....ITS WIDE OPEN
Last edited by Torqued Off; 04-27-2024 at 05:37 PM.
Could you please take a picture of the drain back area on each end? The used to need contouring down to the drain to keep from pudling oil up against the springs and valve seals?
On my heads I just tapped the crossover hole and installed a plug. I didn't want any crossover heating at all. I also did a little grinding work to aid in the oil drainback.
Just wondering. If you are buying all new components and using very little off the old engine, Why did you not let CNC Motorsports complete the engine build? I'm sure they have a dyno and can break the engine in for you.
Just wondering. If you are buying all new components and using very little off the old engine, Why did you not let CNC Motorsports complete the engine build? I'm sure they have a dyno and can break the engine in for you.
I explained that in Post #24 - I don't trust anyone.
Yes, I know I "trusted" them to build a short block.....but I also explained my rationale for that in my previous posts, and not repeating it here.
As for the engine break-in and tuning...I will do it in the car, where it matters. And as for knowing meaningless HP/torque numbers out of a dyno, I just don't care.
Last edited by Torqued Off; 04-28-2024 at 06:40 AM.
As a Harley rider. Let me explain my point of view on this.
Ever notice how really good your Harley runs on a very cool autumn day? Your out there freezing your butt off in Oct. - Nov. It's really a crisp day. And your bike is running its absolute best. Ya know what I'm talking about??
I lived in Northern Wisconsin most of my life before moving to paradise. Those end of the season rides when I was more than frozen, the Harley purred and pulled better than ever. The Hog loved that cool dense air. Just loved it. Atomisation be damned! These old school pushrod engines love that cool, dense air.
Chevy V8's and Harley Big Twins are so similar in so many ways it's not funny.
My humble opinion is, block off that exhaust crossover completely. Your thoughts on Atomisation are flawed. Think of your Harley on a cool Autumn day.
04-25-2024, 07:15 AM
Then to "ZERO" deck and subject the already stressed gasket by having to use thicker head gaskets for some quench. Very poor planning. 4.125 gaskets are availiable.
