Just like Leigh mentioned, cam timing is critical and I am not talking about specs from the cam manufacturing, but rather the install.

Most cams come right out of the box with 4* Adv built in. That's what the customer wants after spending his / her hard earned money, instant gratification / instant torque.

The fact that you have no low-end grunt leads me to believe there could be an issue with the cam timing. Nothing will kill low-end torque more or faster than retarded cam timing. Even a few degrees later, moves the power band to a much higher RPM range. In laymans terms, retarded cam timing screams at higher RPM, but has no or little low end torque.

Crane says your cam should kick-in at almost Off-Idle, at 1600. So having said all this, my question is, when was the timing chain set installed and was it installed straight up like it should be?
A couple degrees of slack in the chain will match some of the conditions that you are dealing with.

 

Running 1.6 ratio rockers is NOT helping the situation. It effectively makes the duration longer on the cam.

The overlap on that cam is 54*. If you're at sea level then 9.5 CR would do the job. If above 2500 ft then 10:1 would be ok. 10:1 at sea level would make this a strong cam choice with the 1.6 rockers.

Do you still have your 1.5 rockers from stock config? If so I would run those.
There could be other issues, but my money is on too little CR.
Pistons may be located too far down the bore at TDC. Some compression height pistons place them .020" farther in the bore.
Advertised 64cc's may actually be larger than 64cc's further reducing CR. Head gasket too thick? Further CR reduction and quench reduction.

If this is an automatic then 2000 is the recommended minimum stall for this cam. 2500 is likely much better.

 

Ignition timing curve sounds Great. OK
But static CR sounds a little low.
Idle vac of 13.5 also sounds a little low, even for that cam. My BB has a lil bigger cam and idles at 15.
A CR in the 9-9.5 range is lower than what I came up with quickly, but it sounds like you ran the numbers. It is not optimum.
That could drop your DCR below 8, even mid 7s with that cam, and that's definately not optimum.

If you just used a standard chain and installed it normally, the cam is installed 4 degrees advanced because that is the way it is ground.
If you used a degree wheel and dial indicator, and took that 4 degrees out by really installing it straight up, that is a whole different issue.

To me, idle vac of 13 seems low, and low rpm TQ seems low, both of which could be caused by low DCR and/or retarded cam timing.
I would "run the numbers"

These Wallace Racing calculators are very good:
The Compression one you really need to know your gasket and deck height tho. (If you have never decked your block someone could give you an estimate of what a non-decked block normally runs). Jeff always decks the blocks and sets them to .010 or zero. depending on gasket and CR and piston rock. So I guess they start at .020 or so?
http://www.wallaceracing.com/cr_test2.php
Then you can punch in your cam specs here and get your IVC number.
http://www.wallaceracing.com/cam-deg-calc.php
I ran your cam and got 60 degrees or 64 degrees depending if it is really 4 advanced (as ground) or straight up.
This one will give you your DCR, target is 8.0-8.5. Below that it really gets "soft" quickly.
http://www.wallaceracing.com/dynamic-cr.php
I ran the DCR for your 9.3 CR ( at both one at 60 and 64 IVC) and got 7.5 to 7.7 DCR. It could be much higher. That could be why it feels soft.
If you check the cranking compression I will bet it is pretty low.

Low buck solutions:

1. thinner head gasket.
2. advance cam to 4 or even 6 degrees. (Degree wheel and dial indicator).
3. Smaller cam (214 ish)
4. I see no need for 1.6 rockers, they may actually hurt you a little here. They change the IVC point some. They should add 5-7 HP, but at 6000 rpm.

You do not have a lot of first gear, and that is very expensive to change, so you need the low rpm TQ.

Only statement of yours that made no sense to me was "advancing timing in earlier than 3000 made it run much worse"
Anybody have any ideas on that one?

 

Took her to a car show today. runs very well if accelerating lightly to med. nail it hard and it runs, for lack of a better description, "Choppy" , gets up to about 2,900, clears up and takes off like a shower of ****.
checked speed in first gear at 3K RPM. about 27-28 miles an hour.
I am going to pull heads. putting in shim type (.015) head gasket, going to replace stock rams horns with 2 1/2 inch ones. No long tube headers, sorry guys. and replace the performer RPM duel plane with a med rise single plane. To help with my EFI. And I am also thinking hard about replacing the rockers. going back to 1.5 . If all of the above doesn't clear it up. then I will look at pulling the oil pan, timer cover and replace the almost new timing chain and gears with a set that I can advance the cam timing with. One step at a time. just the parts will take me 2 months or more to round up. I am still looking for good advice in the meantime.

 

get a degree wheel or timing tape for the balancer and a 35 buck harbor freight dial indicator and base. while heads are off verify true tdc and degree the cam so you know where it is installed at. never change nuthin until you know what you are removing.

 

Hmmm. yes ...efi issues...you may be on to something there!

I was assuming the AFR was perfect.... being electronic. and all....BUT... I have heard stories of some issues with certain EFI units in combination with dual plane manifolds. If the EFI reads manifold vac from only one vac port.... on a dual plane that means it is only reading 4 cylinders...and the pulses in the dual plane mean the other side AFRs can vary. OTOH certain people says this is an invalid theory, while others swear a single plane cured their car. So who to believe? In your case the pulsing would be strongest at low rpm and WOT and that is where your symptoms are. I am assuming you have a throttle body style EFI with one oxygen sensor.

I am converting a friends car to EFI right now and am concerned about the same issue.

But I have almost no idea on how to prove the theory. Maybe compare plugs? 4 different than the others? Move the O2 sensor to the other side? Temporarily install a large one hole spacer? Try and figure out where the MAP sensor reads vac? Any way to monitor AFR from two O2 sensors while driving for test purposes? You could even just mill down the divider in your dual plane manifold since you do not need it's effects. (Kinda drastic tho).

I would investigate this much more before pulling the heads.

Low DCR / compression should run "soft" at both part throttle and WOT (at low rpm) without the significant change that you have mentioned at WOT.

 

If this were a carb I'd say it's running rich at WOT. Your symptoms describe too much fuel then @ 2900 it can finally handle the extra and burn it.

 

I get 9.55 static compression with your inferences to what you have for heads, pistons and gasket. If you go with a steel .015 shim and get the quench down to .040 total you will get your compression up to 10.11 and then you have more cam choices. Something that has around .500 to .520 lift will give you some fun performance with the headers and other upgrades you said you have. I like the comp cams extreme energy cams. They have enough duration to sound good and still give you really high dynamic compression. I've had my 327 set up with a bit more compression and a similar cam but with 1.6 rockers. I couldnt keep the tires hooked up off the line but still was able to lay down 108mph in the 1/4 mile. My best time was 13 flat but couldnt continue because i didnt have a helmet with me. Each lap my time got lower but anything in the 12's requires a helmet at that dragway. It was a great street engine and was a blast to drive. I'm running a mellow big block now

 

My last combo was similar, l48 with 64cc Brodix IK 180, 268HE cam, 1.6 roller rockers, TH350 w/3.08 gears, edelbrock 600cfm. It was close to 9:1 compression, and was pretty soggy under 2500RPM. I don't think less quench or more compression is going to help you much. I would look at the XE262 or even the XE256 and drop the torque curve a little. I know I wish I'd gone smaller for street use.

I

 

The only way he's going to know what his true CR is, is to cc the heads. We don't know that 64cc advertised is 64cc measured. In an as cast head it probably is not.
I also have not seen any reference to the CH of the pistons yet or the volume of the piston tops either. These are also big players in the CR equation. Not enough information to determine what the CR is on this engine.

 

Engine Masters just did an episode a month back that showed that compression makes power. They used 2 motors identically built by Bositick racing engines in Yuma Z. https://www.facebook.com/bostickracingengines/

They were made identical except for the cams. Both used Comp Cams thumper Hydraulic roller cams with solid roller lifters. They swapped the top end so there was no difference with the intake or carb. the cam specs wer227 intake duration/ 241 exhaust duration both at .050 lift on 107 lsa. Thye didnt provide the cam number or lift but you can look it up if you care. The 9.7:1 motor made 440 ft/lbs and 445 hp. The 11.25:1 motor made 440ft/lbs and 454 hp. I believe both were initially on 91 octane but they messed with timing and octane later in the episode for testing sake, but at this phase you can see the difference.

I would get the proper qwenchand find an appropriate cam for your setup. You should call com cams and tell them your setup and your esires and they will give you options. Its better than asking us unless there is a cam design engineeer here

 

Not sure about how much 1.6 rockers increase duration.
I have heard some say it adds 3*.
I did some research that said 1.5*

The 1.6 rockers made the engine run cooler and moved the sweet spot up 200 rpm.
I'm happy w/results!

 

you can find the factory specs and divide by 1.5 then multiply by 1.6 to get the new lift. You may be able to find a calculator to get the duration. I added 1.6 rockers and loved how it performed.

 

Before you tear it apart, put in some good big tube headers. Don't use shorty headers as they aren't much better than the ramshorns. Then use either 2.5 inch or 3 inch exhaust. It will be like you uncorked a bottle. You should see a marked difference since the engine will be able to breathe. Then start messing with the wrench and maybe a cam. Since you know what it is and you want to upgrade, just do one thing at a time so you can see what each change effects your performance. If you do it all at once you won't really gain any extra knowledge. Plus one change at a time is less ecpensive

 

I think it sounds like now the focus here is on sub 3000 rpm performance. If the exhaust were an issue that should show up later in the rpm range. Closer to peak torque. The volume just isn’t sufficient below that to have a large effect on performance with a restrictive exhaust. Some scavenging may be lost with a poor exhaust.
op stated that above 2900 it took off.

kinda hard to say how much the EFI tuning may be affecting things as well.

 

I had EFI issues with a dual plane on my big block. IT was a mess. Nothing I did could help it out. I had an old tarantula style single plane on my 327 and the EFI loved it. It ran great.

 

I had my Fitech on a Performer RPM manifold for years and it worked well. I'm now running a Team G single plane (changed the whole top end chasing higher rpm hp), which also works well, and is also shorter than the Performer RPM, allowing a tall insulating gasket and a taller filter. Every setup is different, but both manifolds have worked well for me.

Sounds to me like you have a bit of a mismatched setup. I am a big believer in higher compression (ideally combined with tight quench for detonation resistance), particularly for bigger cams, it really helps fill in the low end and improves response greatly. Given how compromised you are in this area, assuming that you'll do the work yourself, and given your tight budget, I actually do think that it might be worth trying a thin shim gasket as a first step. I also think if changing cams then a hydraulic roller cam could fill in the low end without sacrificing top end, but it's not a low budget option.

 

I'll add all this to the story. first. tools like dial indicator and stand, Etc. I've had for over 40 years. I don't need to buy tools. second. I chose this cam on the recommendation of a friend who is running it in a very similar engine set-up. I am not certain it's too much cam. The MAP sensor is in the right side of the throttle body. The divider was machined out some time ago based on recommendation from Jebby on this forum. I will be putting in the shim type gaskets, I already purchased them. still trying to get new Exhaust manifolds and intake manifold. please keep in mind everything I have to bring over from the States ends up costing me 3 times what you guy's spend over there. So every 100 bucks is 300 bucks. So I have to shop extra carefully.
I am considering changing the rockers back to the stock 1.5 ratio ones. I put in the 1.6 rockers years ago when I still lived in the states. So no I don't have the original ones.
I agree that something in this combination of parts is just not right. But while the heads are off, I will change the exhaust manifolds and intake at the same time. Car has 2 1/2 inch chambered exhaust. exhaust has been on the car for 25 years and has always worked fine.
I will take the time to degree the cam when I have the heads off.
thanks for all the input so far.

 

If the CR is too low for this cam milling down the center divider would have made the low RPM situation worse. Removing the center divider is beneficial for mid to high RPM performance.

Once we can establish the CR of this engine then it will be possible to determine, or at least eliminate, the cause of some of the problems. Using the 1.5's is sort of a bandaid fix for the current situation assuming low CR and too much cam duration. If in the future you plan on remedying that then you shouldn't need them.

Dug up a thread started by me in 2012. It shows how to cc the piston in the bore. If your pistons look like those pictured then good quench is not possible.
https://www.corvetteforum.com/forums...mber-size.html

It is a similar process for the combustion chamber in the heads. You can even cc the intake runner if you want to. 185cc may actually be 190+cc. Makes a difference in the performance.

 

Milling the divider on an EFI setup does absolutely nothing to the throttle response on a dual plane manifold. There is no signal needed like a carb and that is the only reason the dual plane manifold exists.
The reason for the milling is a Sniper (like others) has the MAP only on one throttle bore.......on a dual plane there can be two distinct vacuum patterns from one side to the other, and this can trip up the mixture if one side needs more or less fuel than the other.....four runners are much longer and flow a lot less than the other four. In fact, the K5 Blazer with the Blueprint 355/385 came back for drivability and I installed a 1/2" spacer on it...problem went away......
If you look at NHRA Top Stock or Super Stock carbs on factory dual plane intakes....they are all stagger jetted side to side.....same type of thing. On the street the compromise is less, but MAP sensors are much more touchy than a carb booster.......
Hindsight 20/20.....given the hood clearance the guy has on that K5.....I would have put a 2975 Super Victor on it for runner length.....
I suspect a lot of problems coming up with Holley's Q-Jet Sniper....as the only reason to use one is to keep a stock manifold.....and all Q-Jet manifolds are dual plane......
I think someone told me that Holley has fixed or is going to fix this issue.......maybe I am dreaming.

Jebby