Hey everybody. I took my engine to the dyno this week to iron out a few little issues and did some full power runs while I was there. The specs are in the sig. Let me know what you think. I was a little dissapointed.

390 HP
426 ft/lb

It's breaking up on the top end to the point that the HP curve just drops right off. I didn't notice it before so maybe there's more in it. Not sure what was causing it. I really think the lifters are suspect.

All of the work done previously was completed at Dyno Serve in Ackerson Lake Michigan. **** (The owner) and I have been at this for some time and hope to complete it soon. Your help is greatly appreciated.

 

That is pretty high compression. You must be running race gas. What is the duration of the camshaft?

 

Do you have a dyno sheet or graph if not what rpm did it start to die. What kind of springs are you running and the installed seat/open pressure. If that cam is a Comp extreme cam then you might be floating the valves. those cams need good springs to stay out of valve float.

 

390 rwhp, divided by 0.78, to correct for your 700R-4 and axle, gives 500 crank HP, which sounds about right.

 

1989GTATransAm - Actually with the overlap on the cam and the aluminum heads I can get away with running 93 pump gas. That's what all the testing has been done with and we have had no pinging at all. I was impressed as well. The cam is a Comp XR270HR dur. 270 - 276.


Big Dog Chevy - It started falling off at about 5,800 and the cam is spec'd tp 6,500 although I'd never take it up there. The springs are the 986 springs Comp recommends for the cam. I believe they are 110 lbs on the seat.


Atilla the Fun - Unfortunately Atilla that at the crank. This was done on an engine dyno. I assume you think there's something left in there is you think 500 crank HP sounds right. I believe the cam is holding me back but it's a street car so drivability is my number one concern. That and not breaking up at 5,800 as the car does see some track time.

 

Did you degree the cam?

 

Yes sir. Degreed and installed straight up.

 

What is the timing set at? What did you try while on the dyno?
Also what size headers were used during they dyno?

 

The problem is your valve springs, trust me on this. The cam is on the small side but you should be making more power than that and should be able to pull 6500rpms with that set up. For example: a 10 to 1 355, vortec heads modded for .540 lift and 2.02/1.60 valves, Comp cams hr 12-422-8, performer intake with the divider cut down 1.5", beehives set for 138lbs seat and 370lbs open, 1 5/8 short tube headers, 2.5 inch dual exhaust, 650 holley and a 1 inch spacer. On a chassis dyno the car laid down 364hp at 6037 rpm and 398lbs trq at 4317 rpm that's about 435-445hp at the fly. Yours should be there or better with better valve springs. Look at your dyno graph if there is a sharp drop off or jagged spikes on the top end that's a sign of valve float.

 

bluegassz - The timing is set at 15 initial and 35 total with distributor advance. We tried going for more initial (20*) to take care of a slight off-idle bog but the motor seemed to like the 15/35 setup. We went all the way out to 40 total without pinging but power fell off slightly. We were there to mainly address the off-idle bog issue and only really started to look at the drop-off at the end of the session so we didn't try to address it formally.

The headers were 1-3/4 primaries with 3-1/2 collectors. I run Hooker long tubes and cut-outs in the car.


Big Dog Chevy - Valve float was the first thing we suspected when we saw the sharp drop-off. What confuses (angers) me is the fact that these are the springs that Comp says to use for the cam. They have less than 1,000 miles on them, and were never abused (over-revved). Before we went to the dyno we tried to identify the bog issues in the shop on our engine stand (non-dyno. No brake) We even went so far as to purchase a spring rate testing tool and found that all the springs were in perfect shape. I cannot understand why I would be experiencing valve float with my setup. What do you think?

 

"3-1/2 collectors"

How did you arrive at 3 1/2" collectors. Do you think that they might be too big? Maybe something around 3" would work better?

"It's breaking up on the top end to the point that the HP curve just drops right off"

Could be valves, could be ignition. If indeed they are 110# on the seat that will not get it done. I like to see something in the 140 to 150 neighborhood. If beehives you can get away with a little less.

 

Those were the dyno headers. My car has 3" collectors. It will have very little if any affect on what I was seeing on the dyno.

 

I agree but after 5500rpm the springs are going to bnce the valves with only 110 on the seat with a heavy hyd rllr lifter. 110 is ok for a little hyd flat tappet cam but not hyd rllr. Just try it some better springs.

 

I run the xr282hr-12 and it calls for the comp 986 or 987 springs. I run about 137lbs seat pressure and have cranked it to 6500 without any problems.

My cam has a 2000-5800 rpm range, so it shift around 6100. So you may need to shim the springs. Also check the push rod length. The valves might not be opening enough.

Oh yeah, my specs are in my sig.

 

I was going by memory about the seat pressure. I looked it up:
* Outside diameter: 1.430 in. * Inside diameter: .697 in. * Seat load: 120 lbs. at 1.750 in. * Open load: 280 lbs. at 1.250 in. * Coil bind: 1.150 in. * Rate: 296 lbs.

After reading bluegasssz's comment though I'm thinking I'm fine with the springs I have but what does everyone else think? If i remember correctly, I'm shimmed as well. I'm not with the car so I'll have to verify that tomorrow.

 

Define what you mean by "straight up". That term means different things to different people.

Another thing to consider is lifter pump up. Once the lifters pump up, the springs can no longer control the valves and power drops like a stone. If you can, grab a copy of the current issue of Hot Rod and read up on a way to address that.

Hope this helps.

Jake

West Point ROCKS!

 

Straight up = 0 degrees advanced, 0 degrees retarted.

I'm not sure how to address the question of lifter pump-up. We were experiencing lower oil pressure than usual on the engine dyno so if anything I'd say we had less pump-up than in the past when the engine ran correctly. Although I have never had it on an engine dyno so I cannot be sure if the drop-off in power was there before but it exibited no symptoms like it was. It used to run like a champ and all of the sudden stopped.

 

Did you measure the load on the springs with the shims?

I am running the stock AFR190 springs with shims. I check with comp and they recommended the 986 or 987, so I used shims to bring the seat load up to the lbs that was needed.

 

I did not measure the load with the shims. So what you're saying is that the recommended springs are insufficient and require shims? Could this be a bad set of springs that fatigued very quickly? Like I said, this build and the way the motor was used in my opinion is very mild. I have a hard time believing the springs can't keep up. If I were to simply replace the springs what would you suggest? The next step up from comp?

 

[quote=DNSTA;4249144]I was going by memory about the seat pressure. I looked it up:
* Outside diameter: 1.430 in. * Inside diameter: .697 in. * Seat load: 120 lbs. at 1.750 in. * Open load: 280 lbs. at 1.250 in. * Coil bind: 1.150 in. * Rate: 296 lbs.

Not enough to control the hyd rollers up top. Seat should start off around 138-145lbs and open 360-380lbs brand new. Reason because as the springs get broken in they will loose 5-10% of there force. Just look at what the other guys are running and how high they make power. Those springs are ok for a light weight LS motor valvetrain. I'm going to try to scan two dyno sheets of the same car, one with weak springs and one with the right springs. On the track the car FELT the same but on the dyno it was a 50hp diff @ 6000rpm. All it took was 15lbs more on the springs and we were running 123lbs on the seat and 330lbs open before the change.

 

Big Dog Chevy - I would love to see the dyno sheets if you are able to post them. It would make my decision very easy.

I'm still confused why Comp would recommend these springs if they are so off the mark. The cam is specifically designed as a conversion roller cam so they know it's going in an old small block and not an LS style motor.

One thing I forgot to mention that may help in the diagnosis. After completing full power pulls, a very distinct, loud tapping like misadjusted rocker arms could be heard during deceleration. It lasted for about 2 seconds and then quieted right down.

 

That tapping sound might be the lifters. During the pulls they might be pumping up or bleeding off and when you decel they might be readjusting the lash. Or your rocker arms. With valve float you can damage springs, rocker arms, valves and pushrods. What was your oil pressure at idle and wot?

 

I put your combo in my dyno sim just to see, IF you are running 11.9 to 1 CR the sim says 470 hp @ 6000rpm 490lbs trq @ 4300 rpm subtract 5% for human error and you have about 447hp.

 

I know for a fact that I'm running the stated compression. Typically we see around 20psi at out 750rpm idle and about 60psi during the run. A few times on the dyno after we got hot (200*) we saw the pressure drop to around 10psi at the 750rpm idle. We though this was a little too low and changed the oil from a 10w-30 to a 15w-40. It helped a little but we are going to drop the pan and inspect/replace the oil pump while we're there.

 

That's what I suspected you meant, but that isn't straight up. That term, "Straight Up" is often misunderstood so don't feel like the Lone Ranger.

Merely because an off-set bushing or a crankshaft Woodruff key isn't used doesn't mean the cam is installed "Straight up". Straight up is when the intake installed centerline angle (ICA) has the same numerical value as the Lobe Seperation Angle (LSA). So when your cam is ground on, say, 112 LSA and you degree it and find the installed centerline angle is also 112, that's straight up. If your degreeing results show 108, the cam is four degrees advanced and 116 means four degrees retarded, etc.

However, since most cams are ground with some amount of advance (many times four degrees), simply aligning the dots doesn't put the cam in the straight up position.

When lifter pump up occurs, the valves float, (not seating as they should) and because of that, power drops like a stone. When, for example, the intake valve is held open much of the mixture simply exits through the opening on the compression stroke.

In order for power to continue to be made, especially at higher RPMs, the lifter must follow the lobe profile and not get tossed. More spring pressure can help with that, but that strains the lifter and, over time, shortens its life. Another way to extend the rpm range is to increase the lifter preload.setting. There are other ways, too, most having to do with making the valve train more rigid and/or lighter. Hence the move to lighter valves and titanium retainers, etc.

Due to their design characteristics, HR lifters often experience some degree of pump up/valve toss right where your engine's power is dropping off. However, some guys move to SR lifters on their HR cams. To me, the jury's still out on whether this is a good idea, but a lot of guys do it with great results.

The main reason some say NOT to do it has to do with the difference in the cam's ramps being too aggressive on a HR cam. Not being gentle enough to slowly take up the lash. Those that have great results resort to just using a tighter lash setting.

Jake

West Point ROCKS!

 

Got a graph!!!

 

That motor should be able to make peak hp way past 5300 rpm. It looks like they have a good buffer on the dyno graph print out which makes it look smooth. From what I see you still have more hp to gain with more rpm and better valve control.

 

I tend to agree. The next question I have then is regarding spring selection. If I currently am running the 986's which Comop suggests, what, in your opinion, would be the logical step up in springs knowing that the dimensions (physicaly) need to remain the same to allow use on my current heads?

 

Need to know the spring installed height on the heads.

 

Installed height = 1.800.... which leads us to a problem.

According to Comp, installing the springs at 1.750" gives me a seat pressure of 132lbs and an open pressure of 293 lbs, close to where everyone says I should be. The numbers I stated before were just the springs themselves, not at installed height.

Actually after going back I see Big Dog Chevy was saying 360-380lbs open which seems like a lot to me. What is the trade-off of valve control vs. valvetrain longevity using such a powerful spring?

What springs do you suggest?

 

Big Dog Chevy, please scan those dyno sheets of the two pulls with different springs if you get a chance. Thnaks!

 

Thats why I shimed my stock AFR springs to have 137 lbs at 1.750".
This could be your problem.

I myself would go with a larger cam like the xr294hr or the xr300hr to take advantage of the heads.

Like this http://www.summitracing.com/parts/CCA-12-433-8/
or this http://www.summitracing.com/parts/CCA-12-443-8/

maybe even this http://www.summitracing.com/parts/CCA-12-444-8/


Depends on how much street/strip time you plan on.

 

bluegrassz - the 5lbs of seat pressure makes that much difference?

I elected go with this cam after months of research into power vs. streetability. I think I've found the perfect balance if the valvetrain was in order. A 750rpm idle and over 400hp is good enough for me.

 

I'm working on it. I have the first one and I'm looking fo the second one. The springs you have and the installed height are not matched right with your cam. Comps 977 or Cranes 99893 would work well and last long when properly set up on your heads. You should then be able to make HP till your cams limits if everything else is ok.
The reason I said 360-380lbs NEW is because after the springs are broken in they WILL loose about 5-10% of there force. If you setup your springs at 120lbs on the seat new then I bet they are a little less than that now. You must measure the springs lbs at your installed height and your valves max lift height to make sure they are setup right. If you have the retro tie bar lifters then they need more sping lbs because they are heavier than the stock ones which are also heavy too.

 

Yeah, but your install height isnt 1.750, so your not even getting the 132 lbs.
There will be more difference than just 5 lbs. Add that and depending on the lifter preload and the difference could be quite a bit.


On the cam, Im just looking at max potiental. It all depends on what you consider streetable. Im running the xr282hr in a stock bore/piston/rod/crank
L98. Now in a 383, this cam would be somewhat tame, but still make some good power. With my stock bore 350, It acts as a little more radical.

I think my xr282hr is just fine for the street. I even thought about adding 1.6 rr's to up the lift to .544 and .554 in the future.

For now, you can test your springs at the 1.750 install height and see what you have. You can always add another shim to bring up the lbs. They that and see what you get with the motor.

 

I'm going to get out to the motor on Saturday and see what I can accomplish. Big Dog, will the springs you recommended (The 977's) fit the same spring pockets as the 986's?

 

Yes, they are 1.460" and the ones you have are 1.430".

 

I didn't read much between your reply to me and the bottom, except to examine your dyno graph, but first I think your cam is smaller than I guessed, so now I expect you should be around 450 crank HP. You have valvespring issues from 5500 rpm to about 6700 rpm. More spring pressure will only make things worse. Because of the load on your lifters. If your cam is on a 110 lobe sep, then get a 276/282 on a 112. That'll keep your driveability where it is. Keep your rockers to 1.50:1 or 1.52:1, stay away from 1.60:1, because you have to multiply your spring pressure by your rocker ratio to know the load on your lifters. You want less, not more. A set of COMP's 26981 (not 26918) springs, unless you go for the XFI lobes, then run 26915s with some "plus fifty" locks. and AFR's Hydra-Rev kit. 1.75" headers, a Mufflex 3.5" exhaust, ( a single 3" won't be enough ) And you should be around 475 crank HP. You should try to get your static compression to 10.5:1 if it's currently less than that. If you're running valves .100" longer than stock, those will have to go. You don't need them anyway, and they screw up your valvetrain geometry, even if you did adjust your pushrod length for proper sweep of the rocker tip across the valve.

 

Whow, Lots of information there. Thanks Atilla. Where to begin...

I also expected around 450hp at the crank which I'm quite a bit off only making 390hp. The cam is not the problem. I do not need to switch my cam or change any of its characteristics to gain HP, only fix the top end power issue. I'll refrain from calling it a valve float issue at this point because I do not have any proof of that other than the graph I posted.

I'm sure 1.6 rockers are not causing my problem as many other people run them. It may not make it better but it's not the cause. I understand the reasoning around it and agree with you but.. The springs are suspect, that is correct. I certainly DO NOT need a hydra-rev kit. This is a street car that turns to 6,000 and by everyone's accounts is a pretty mild build. I agree.

The numbers in question were produced on an engine dyno. Therefore, the exhaust was not/is not an issue. It had 1.75" primaries into a 3.5" collector and then tubes going outside. It was not a factor in the graph you saw. My car has a single 3" and cutouts. Also, plenty of exhaust for the power I'm making. Again, street car. I don't need an exotic 3.5" system.

My static compression is far above 10.5. As my sig states it's 11.9 which is another reason I should be making more power than I did.

The general consensus is valve springs but I recently discovered after looking at some invoices that the springs I currently have are not 986's but are actually 950's which put my seat and open pressure right where some of the other posters said it should be!

Do I still have a spring problem or is something else amiss? Let me know if you need any more info to hazard a guess.

 

Man DNSTA, if you have the 950s and they ARE setup right then it could be anything that is causing the off numbers. I don't know what to tell you without going over you motor myself. Was your afr/timing ok. What about your carb, plugs and wires did you check them out. How about the dyno itself was that working ok? That motor is down on hp for the list of parts that you have, it's going to put down 310-325hp to the wheels.

 

Okay, if you're done buying parts, then the next step is tuning. Like with a dial-back (to zero) timing light, and plot your centrifugal advance in 500 rpm increments, from idle to 6000. Those heads should be getting you there, you're obviously getting the air to and from the heads, so the next concern is the valve job and bowls. Did you actually see the heads yourself with the valves out? If not, there could be ridges where the seats meet the bowls. that could make a 50 horse difference. Also, if you're having inaudible detonation, that could eat 50 ft-lbs at all rpm. What octane / booster were you running for the dyno results? If you bought the heads bare, did you install valves with 30-degree back cuts? That can be 30 HP on an engine like yours. And the dyno: what corrections were they using?

 

Big Dog - All the parts on the engine are new and what isn't has been gone over with a fine tooth comb. Carb is dialed in, A/F ratio perfect all the way through the run. Plugs and wires new and changed many times to see if they were the problem. I have no way of knowing if the dyno was working correctly other than the operator making sure everything was accurate. I'm at a complete loss here...

Atilla - The timing is perfect. We've been through setting it up at least 10 times with no real improvement seen. As for the heads, I don't remember what the bowls looked like when we installed the new springs last year. I know I'll get flamed for this next statement but.. I'd have to assume that's not the problem as these are very high quality heads which were bench tested before purchase and out-flowed the AFR's I was going to get.

Detonation is not the issue either. After we built the motor I drove it around for the first month with an MSD knock sensor and digital monitor Velcro’d to the dash. We were concerned with pump gas and the 11.9 compression. No sign of knock at all.

 

Got that dyno graph for you, I'll post it tonight.

 

There's no need at all to get new springs, just get a set of shims and shim them up about .060 to a little under 1.750". Its not rocket science. It'll cost you about $30 or less to fix your problem.

 

Hey said he found out the springs were comp 950s not 986s which are setup for a 1.80" seat height. If that's right then it might not be the springs.

 

Big Dog - Thanks for finding the graph and you're correct. They are the 950's which provide much better seat and open pressure than the 986's. I'm pulling the springs this week and testing them. I'll see what I'm really getting and determine if it's the springs once and for all.

Atilla - Please let me know what you though about what I said. If you feel the heads came from the factory in such poor shape I may be inclined to pull them and see what I've got..

 

You really never know unless you test them. Hopefully that will be the problem which can be fixed easily.


Oh the heads, I got a set of AFR 190's and the valve guides were way to tight from the factory. You could get the valves in some without some effort. We reworked the guides and played with the valve angles. We worked one chamber untill we got good results on the flowbench. We also worked the intake to match.

After that, I dont think I will ever run a head straight out of the box.

 

check the springs as installed on the head for seat pressure, you can measure the spring rate all you want, but the seat pressure may vary for each valve, put the weaekr springs on the tighter valves (less retainer to seat clearance) to minimize the amount of shims you need to use.

 

DNSTA, here's the graph. This was with a 52mm tbi edelbrock mpfi conversion manifold and small cam. The only changes was the springs and replacing the damaged rocker arms (tips were damage from the valve float). The car will pull to 6600rpm and still be less than 27 hp from the peak numbers. The car makes more power than this now.

 

Thank you Big Dog. The graphs are a little hard for me to understand but it may be because of the range. The curves are not the shape I was expecting to see but I understand the results which are clear. I assume you were using a stock style rocker arm and not roller rockers as you say the tips were damaged.

Was the reason you changed the springs in the first place because of the dyno results and the drop in/lack of power or were you addressing another issues and happened to realize that the new springs gave you a large boost in Hp?

I ask because nothing is wrong with my engine that you can tell without a graph, meaning that without seeing the issues on the graph from my dyno run, I would have already put the motor back in the car and been none the wiser.