The lines on the lower part is the afr.
The rockers was the full roller self guided kind. The tips were beat up from the springs not being able to control the valves at high rpm.
The reason for looking at the springs was the lack of top end hp and rpm from the dyno while I was tunning the car (the dyno guy said the cam was too small). The car ran fine and you could not tell that anything was wrong while driving it. While data logging during the tune before I saw anything wrong, we were getting some knock counts between 5000-5700rpm. And after trying to tune it out didn't work that's when I thought it had to be in the motor. You won't know your springs are bad unless they were good at first and you saw the performance of the car drop. We would have been chasing ghosts and changing out parts for nothing if it wasn't for that dyno graph. That motor made 350 to the rear with a smaller cam than yours and those type of dynos read a lil low so somthings not right.

 

Ok, thanks for the clarification. I agree something is not right and I hope to have the springs tested this weekend. Hopefully the springs will test bad enough to be obvious as I don't want to spend another $350 to take the engine back to the motor dyno just to see if i fixed anything. Man, this sucks so bad. I'm never going to get me car back.

 

Keep your head up, it's somethng small that you over looked, that's why it's hard to pin point. I've been there many times but for me it always works out in the end. $350 for a motor dyno, Damn! You could have put the motor back in and do a car dyno for $100 bucks an hour. Man I hope those springs are the problem.

 

Actually the shop where I do all my work, DynoServe, is a chassis dyno shop but I'd hate to put the motor back in the car only to find there's still a problem and doing a chassis to engine dyno pull certainly isn't apples to apples.

So I went to the shop this weekend with the intention of testing the springs and moving forward but ended up going down a completely different (horrible) path. I'm not sure if I mentioned it before but on the engine dyno we saw lower than expected oil pressure. Last week while contemplating the spring issue we decided to take the oil pump off and inspect it. We found some pretty serious scoring, enough to cause a drop in pressure, and decided to replace it.

Before we buttoned up the bottom end we decided to pop a few main and rod caps and see how the bearings looked. (The engine has less than 1,000 miles on it) To my dismay the main bearings and the crank itself are shot!!! I'll post pictures as soon as I get them emailed to me. I have no idea how this happened but I suspect a line boar issue as the rod bearings looked far better, almost as good as you would expect save the slight damage from the crank material in the oil.

So it's off to the machine shop to have the block cleaned and the crank turned (hopefully). It's just one thing after another. Unfortunately I doubt this had anything to do with the problem I started out to address. It's just another issue to spend money on before I get it running.

Thoughts? Ideas? Donations?

 

WOW! That lil motor is givin you fits. Well what I would do after you get the crank turned is take that motor down and put it back together and note all the specs. Go over that thing with a fine tooth comb. And if it still isn't right then I'd sell it and start over. Just my 2 cents.

 

That's pretty much where I'm at. We took the heads apart as well and measured the installed height of the springs. They were right of course. We are definitely going to go through everything with an eye to detail when we put it back together.

I'm sure it will run fine after we pretty much build it from the ground up again I'm just still a little worried that the cause of the power drop may still be there as we will be using the same parts. The springs being the 950's really make me believe they are not the problem but we're taking them to the machine shop to have them tested anyway.

If it weren't for my ridiculously high compression I'd build it into a 383... NOT!

 

When you looked at the springs what was the lbs for the installed height? Also if you are going to use the heads again have them flowed to see what kind of numbers you have. Around here it only cost $50 bucks to have a set flowed. Are you sur the carb is ok? (just had to ask) 390 hp is low for a H/C 11.9 to 1 350.

 

if there is even a possiblility those valves are floating they arent floating much or it might be lifter pump up

heres an idea... once the engine is back together make a pull or two and compair against the previous runs....

THEN decrease lifter preload to ALMOST NOTHING will get rid of any pump up that could be causing the valves to hang open


now for the really important question... how are you sure you arent detonating a quick guestimate

ENTER YOUR DATACALCULATED DATACylinder Head Volume (cc)Cylinder Head Vol
(cubic in.)03.965Piston Head Volume (cc)Piston Head Vol
(cubic in.)-0.671Gasket Thickness (in.)Swept Volume
(cubic in.)44.610Gasket Bore (in.)T.D.C. Volume
(cubic in.)04.089Cylinder Bore Diameter (in.)Gasket Volume
(cubic in.)00.462Deck Clearance (in.)
Note: Neg. nubmer above deck, Pos. number below deckDeck Volume
(cubic in.)00.333Stroke (in.)STATIC COMPRESSION RATIO11.910
OPTIONAL DATARod Length (in.)Adjusted Stroke (in.)02.790 Intake Closing Point (degrees)
ABDC @ 0.050 lift plus 15 degrees DYNAMIC EFFECTIVE COMPRESSION RATIO09.747


would say way to high for pump gas or at least ragged edge territory

or is your math different

 

Big Dog - Thanks for sticking with me on this. It's good to have someone to bounce ideas off of. The 950's have an installed height of 1.900 which is what mine were at. At that height the spec is 133lbs on the seat and 332lbs open. The flow numbers I have been using for my calculations and assumptions are the advertised numbers for the heads I've read on lots of independent sites. I did a LOT of research before getting these heads. I'll see if I can get access to a flow bench to put that question to rest.

The carb is top notch. We've had 3 other carbs on there with no difference in performance although we did not run any other carb during the dyno test.

SpitotRs305 - Why do you feel that valve float is not the issue? I ask because you seem to be the only one in the discussion that feels that way. Interesting bit of info though. When we were trying to address the off-idle bog that started this whole journey we found that reducing the preload, to the point that the valve train was unacceptably loud, almost completely eliminated the bog and made the engine run better. Does this point to bad springs or maybe excessive lifter pump-up?

Almost forgot. The compression ratio was painstakingly calculated and is accurate. We can say without a shadow of a doubt that we are not experiencing any knock. This has been proven both electronically with the use of an MSD knock sensor and digital readout and physically with our frequent teardowns of the engine and complete lack of any signs of detonation internally. No issues there.

 

it isnt that i dont believe it could be a problem... it is just that people have run that cam with the 986 and 987 springs and have been fine now you are running a retro setup and have chosen springs with higher seat pressure and higher open pressure

because of that and the fact that there are other things than valve float that could be causing your problem i would look else where before worrying about springs

what do you have your plugs gapped to? what are they made of? you could be experiencing spark blowout real high cylinder pressures/ large plug gap? try decreasing it by .010 or bring it down to .035 and see

how much preload were you running on the lifters anyway... only stock needs the 1/2 turn should be running like 1/8-1/4 turn tops to prevent lifter pump up... and i am not sure how you would be able to tie lifter preload changes improving a bog, to bad springs but i would say not it points to the valves being hung open due to lifter preload... now you keep talking about and off idle bog what kind of RPMs are you talking about? as you couldnt blame valve float for anything under say 4k RPMs not with those springs

 

The off-idle bog was just that. From my 750 rpm idle if you smashed the throttle wide open you'd get a hesitation, a slight backfire, and sometimes a complete stall. It was drivable but completely worthless for racing and it wasn't right. Defiantly not spring related. I like your 1/8 -1/4 preload thoughts but I'm curious why I've never read/heard that before and why neither one of the professionals I had work on my engine used anything but 1/2 a turn. When we tried 1/4 it was loud enough to think any high rpm run would damage something.

 

I have one question. Why are you running domed pistons and so much compression with that cam? I was actually considering installing that same cam with a compression ratio only in the low 9's or so on my engine. I would think that 10:1 or so would be enough to get the job done. Domed pistons also really hurt the combustion speed as they impede the flame front. IMHO, you would be better off using flat tops instead. Any loss in power from less compression would be easily made up by the increase in combustion speed and reduced timing for peak torque. I would say a good set of flat tops with the appropriate ammount of quench would do a better job overall. I've been messing with my new engine (goodwrench short block w/ trickflow 195's, Isky 221/221 .465/.465 cam with a 108 LSA), and the engine only needs around 30 degrees of total timing with a CR of 9.3:1. Any more than that and it slows the engine down and heats up the heads. JMO, but running domes with the newer head designs is basically going backwards as you defeat the purpose of the small, high swirl combustion chamber.

 

Thats a lot of timing for so much compression. I would say that if the engine actually needs that much, than its good justification to go with different pistons to rework the CC. The more timing needed, the more power you have to expend compressing the burning mixture.

 

dimented24x7 - We too have discussed the domed pistons and flame front speed but concluded that the power made from the high compression would be greater if it could be kept under control. As we are running pump gas with no problems I would have to say that it is under control.

I don't think that 35* of total timing is excessive. In fact I think it's optimal for a street car. We don't have any issues with heat either.

Did you have a chance to look at the graphs Bog Dog and I posted? What did you think? Springs, heads, something completely different?

 

35* timing is not that much. And I've ran dome pistons in the past, yeah you have to use more spark advance but you can still make some good power. That dyno graph I posted, that car has domes and 72cc chambers on a iron head and it made the most overall hp with 38* timing (pump gas no knock). I'm tuning it again now and will have some new dyno numbers to show you guys you can make some good hp/trq with a small cam.

 

How much large an offset in degrees did you have to use install the cam "straight up"? I think comps profiles are not necessarily symetrical, so depending on how you degreed it, it could have moved the actual centerline to some other location. It sort of looks like the cam may be too advanced. This may not be the correct method, but I usually just install mine with the recommended timing set with no changes to the cam timing. After all, its the cam grinders responsibility to ensure that the lobes are ground properly, so no additional changes should be needed unless you purposefully want to change the cam timing.

 

True, in the grand scheme of things 35 degrees is not excessive. But, it indicates that the combustion process is taking longer than a similar chamber with a flat top. Domed pistons is teh old method of doing things IMHO. Newer engine designs feature chamber designs that optimize swirl and reduce the surface area to volume ratio of the chamber. This means that the chamber is closer to a hemispherical shape. This results in the flame needing to traverse a shorter distance. The advantage is that there is less work lost and lower octane fuels can be run.

Ive run several different sets of heads, and the old 72 CC heads where the worst from a knock and timing standpoint. They required ~36-38 degrees to make peak timing, and where prone to detonation on regular even with a CR of ~8.2:1. The vortecs and similar heads require much less timing. In my experience, anything over 32 degrees begins to reduce power output. I also experimented with running lean AFRs and high loads. On my 350 with a low CR of around 9.1:1, I ran the engine for short periods of time at increasing loads on 87 octane to see how it would react. Believe it or not, at full load, the vortecs would stay out of detonation for a short period of time when running lean at 20:1 AFR. The engine would pretty much just idle as it made no power, but it proved that the increased swirl really helps reduce detonation. If it was held there, eventually knock counts and audible pinging would result from the chamber heating up, but its still impressive none the less.

 

Another consideration with high compression is that its decreasing marginal returns. I attached a graph showing the theoretical max efficiency vs. CR. From a theoretical standpoint, after about 10:1, the increase in efficiency is small with increasing compression. Obviously with something like a diesel with a CR of 16:1 or more, the increase really does help the cycle efficiency. But on a gas engine, the increase in CR may not = more power. It may be a wash, or result in less power than a similar lower CR setup with a chamber that results in faster combustion. One of the major advancements over the years has been in the chamber designs. A good example is the LS1 engines. Those make great power without needing to run high octane fuels. With faster combustion, theres less time for the fuel to autoignite. Not criticizing running high CR, just offering some food for thought.

 

I agree with you 100% on that. But most people don't start off with a built motor they work with what they have. If I started that build up from scratch I would have went with flat tops and 58cc chambers to get the cr and propr quench but he already had the motor in and he didn't want me to pull it out or spend alot of money so I worked with what I had. I knew the setup wasn't optimal that's why I focused more on swirl and port speed when I was porting the heads. With DNSTAs setup maybe his cam is advanced I don't know. What I do know is he should be making more power than what he made and that's more power than that Camaro's motor that I posted.

 

Ok. I misunderstood your comment. I was under the impression that it was built that way, as opposed to being modded after the fact.

I definitely agree that he should be making more power with the engine as-is. The torque curve peaks real early for the cam thats in there. Would expect the peak to be around the 3000 RPM range or so. Would you agree?

 

Yeah, I was thinking the same thing somthing like 4000+. That might be an indicator to his 5300 rpm hp peak. On street motors like that one hp and trq peaks most of the time are 1400-1700 rpm from each other (on a car dyno that is) motor dyno may be diff i don't know. The camaro made it's peak trq at 4400-4600rpm.

 

The motor is off to the machine shop to have the block cleaned, the crank cut, and the bearing replaced. We're having the springs tested as well so we'll know for sure what pressure we're getting. We can add shims to bring it up as we're in no danger of coil bind. Pistons and rings look great. Cylinder walls still have cross-hatching so we're good there. No component is bad except the crank. How do you destroy a crank in ~1,000 miles?