With so many issues going on with the dyno, I wouldn’t trust any of it. I’d dyno it elsewhere before changing anything

Dude, I have never read anyone calling you an idiot!! Don't be so hard on yourself!! I for one, really appreciate what you do and give to the community!

Richard Holdner recently had a similar issue with a SBF. He lost 50 ft./lbs. from previous pulls and couldn't figure out why. Turns out the collectors on the headers were way shorter and causing it! Put on the headers with longer collectors they used before and BAM! torque returned to where it was.

Haven't even watched the whole video and already appreciate you and your work

Enjoyed the video, and good luck sorting things out. Thanks for sharing

Hey eric, in my engine world - more flow and and area rarely makes more power - OR torque. We work on really advanced 4 valve heads that produce hug power per CI or CC, and really good torque as well. The rev really high, a 4 inch bore engine will limiter at 11500 or 12000 for lower hour engines ( in our world - a 11500 engine will last 100 hours of extreme hard run time). It's frustrating but finding what the engines want is not achievable fo rme on the flow bench. We just dyno our ideas and see now - coupled with baseline flow testing to confirm our measured areas match up to flow rates. Our 80mm bore engines (about half displacement) rev to 15000, last 20 hours, and make even more power per cc but not the torque per cc. I think ultimately heads get to a point were at extremely high delta p's seen in running condition they just want to be taller/straighter rather than more area. Most often we fill floors up - but oddly enough some heads need epoxy in the roof too. Point is - after a certain point, it's not about flow we can measure but about flow quality. WE also see that bigger ports like smaller cams, smaller ports bigger (relatively to one another). Contrary to what the magazine car world says. And we run extremely "advanced" inlet cam timing considering the rpm and cam sizes. Almost always as much advance as we can get in the cam until piston to valve. I think a really informative test moving forward for you will be getting to try diff heads on the dyno back to back to back...with various MCSA and such.

I would swap the camshaft keep the duration the same but have it ground with the same 103 lobe separation that the old camshaft was ground on I'm pretty sure that would help bring the torque back and pull the power down to a lower RPM for that duration. Between those great heads and the 108 lobe separation that it has now it's probably what's making the engine Carry further up the RPM range

Glad you figured it out. Was thinking it may have been the wider LSA, but the fact that it was the dyno must have been a HUGE relief!

Sometimes we plan on a certain result and the engine does want it wants! I understand you missed the target rpm you wanted. It'll be if he try a dyno once it's installed in the truck and see how it does then. Thank you for your time and all your information you freely share! Ive learned way more being able to better understand head flow, velocities and coefficients/ effects on power. You'll get it figured out thats one thing I know from watching you! Take you time and relax, you got this!

Excellent opportunity to learn something. You're gonna come out on the other side of this more knowledgeable than before, and thanks to the miracle of youtube we all can benefit from this experience.

And I enjoy your videos and the tips. I have a Pro street 73 Plymouth Duster that went low 9 seconds in the quarter mile with just a 100 shot of nos. Andy helped me build a 421 cubic inch small block from a 340 block and a set of brodex B1 ba heads.

Many years back I built a 383ci engine.11.1 compression. I had built 2” headers with 4” collectors with 5’ extensions. On the Dino torque was way down. I slid in 4” x 4’ spiral baffles from a radiant tube heater. Picked up 50ftlb instantly. My hunch is a combination of the Dino possibly being off and header collector length are playing a big part in your results.

Hi Eric. In my experience the bigger the problem, the more simple the answer. Because you have overlooked it so many times. That said, you said you checked the cam timing, but you only mentioned the intake lobe. I personally always check the exhaust lobe as well. I have had custom cams supplied to me where they have not ground what I asked for, because they thought they knew better. I've had a few arguments with cam grinders, they even supplied a cam card that said I was supplied what I asked for. I had a motor back firing at 6000rpm through the carby, eventually I rectified it by changing the headers, it was a wave tuning issue/reversion issue. That said, I would suggest carefully looking at the cam, intake and exhaust, adding some collector length. The fact that the power keeps climbing might suggest that the exhaust side is not working as designed. We are of course assuming that the dyno numbers are actually in the ball park. With all of the sensor issues there would appear to be some justification for doubt. Good luck with this challenge, but please go back to basics first. Regards Greg.

I feel your pain, have had similar experience eventually traced to turbulence entering the chamber smooth that out and the power came back, you've probably looked at that one already just thought id pass on my experience. an old guy who used to build Formula one engines said to me never doubt the dyno that is a big mistake. thanks for all the videos.

From what I've experienced, with almost 50 years in, I think you're frustrated to the point of having scattered thoughts, I call it. Back off of it for a day or two, put it out of your mind, then return with a fresh mind. You're already chasing what I would naturally go to, which is the cam. Sometimes, engines throw you a pretty big curve, relative to what you know works. It usually only takes a slight difference in a single thing, to wake that particular engine up. You have infinite more resources at your disposal than I have ever had, and I know you will find it. Thanks for sharing this, this is where everyone learns. Keep it up, it will work itself out. I hope you will continue to share your experiences with us.

I ruined a good intake messing around on the floor of it . Lessons hard school . Getting recipes to be perfact & duplicate is like heart surgery's. Cool & Clever vidio 🥂🏁🥂🏁

Thanks for sharing your knowledge.

Ive been around people engine wise since the 80s, your very very good at what you do ,make no mistake

Lowered air speed would decrease cyl pressure which would reduce torque. Higher RPM increases air speed then in comes the power. The 3 most important things for power production is, air speed, air speed and air speed.

I remember a few years back a local shop that was doing all my machine work was upgrading their customers 418sbc. I can't remember if the engine had a Dart 230 or Brodix 230 but one of the "upgrades" was going to be the brand new AFR245. They fly cut the pistons for some additional P to V so probably lost a little compression (comb chamber volume before/aft?) and changed the rockers taking the cam from around .680" lift to around .725". In doing that they inadvertently added more duration therefore bleeding off even more compression.. On their dyno the engine previously made just over 650hp with the old combo and around 530tq. They spanked that poor engine silly for days and could only get 660hp out of it and lost a whack load of torque. I even lent them a set of 1-7/8x2x3-1/2" sprint car headers with 2 feet of collectors on them. In the end they swapped the AFR245 for an AFR227 and the engine made 685hp and 565tq. Good luck. I hope you get it sorted out. Love the content!

It's mostly the intake and headers, but you stated everything in this video. You have your answers. It's that the overall combination now hits just right to make it scream. It was being held back before to maximize TQ, and now it's not.

I build a little 355 engine I called Summit Racing and they told me to put a 465 lift cam in it with 224 intake 224 exhaust I did what they told me to do Andy engine would fly it was fast as hell I went with 10.8 compression ratio that was enough for the street your truck would jump sideways the people at Summit Racing know what they're talkin about but I like the video man keep up the good work

Good luck and you will figure it out and keep us posted on progress

Another great video Eric. I got faith in you, you'll figure it out. Without a doubt the dyno is off, as well as the camshaft. I don't know your full head flow and valve sizes, or your rocker ratio. I'm not sure how you figured .750 of intake and .690 of exhaust. Based off what you showed I calculated this: The cam has a lift of .590 (intake) and .656 (exhaust) with a 1.6 rocker. 648HP 7100rpm and 539TQ at 5500rpm. I guessed the rocker arm ratio. Just for fun, I'd do a leak down test to see if something could be going on with the rings.

Eric, try those heads on a larger displacement sbc. You are getting big block, big cubic inch flow numbers from your mods which is what you would want for a full race engine. That 406 would pull like a freight train on the top end!

you are very knowledgeable, it's definitely a fluke, like many others say, i would test on different dyno, then i would try carbs, intake, an different cam, 2 of my friends picked up about .8 tenths from carburetor manufacture imperfections.

Eric. I've been modifying high performance multi valve heads for race and rally for forty years. Although you are being hard on yourself, you have actually discovered the sweet spot. For an engine curve to not "turn over" and continue revving with more power like that means the system itself is perfect. It's just the numbers don't suit you. Somewhere along the line, a part of the inlet tract (manifold runners?) are too large (or flowing more no matter what size- could be the shapes?) and the whole thing needs choking down up to the throat. As an upside, I bet that engine will sound glorious in a circuit race car.

As with all of your videos, I appreciate all of your efforts to share your knowledge and experiences. I can see how this is a head scratcher. My first thought was cam timing and lobe separation. Further in through watching this, I more and more question the dyno accuracy. I would try another dyno, and if that done fix it, I would try a different intake and then change the cam if the intake don't make much difference. Tighten lobe separation. I'm curious and look forward to a follow up as to what happens with this engine and issue you ran into. I've never seen a cam that size make power that high.

Keep on and you'll figure it ,we're with ya!

Hey Eric, great information on the video! I seriously doubt it was anything you did. That engine should have hit it out of the park. I think something could have been wrong with the dyno. You said the air hat sensor was questionable. Did he run a known motor on it recently with no known issues? My suggestion would be after Cecil gets it installed to run it on a chassis dyno. If your torque and hp are down similarly across the board, I would suspect some clearance or something in the bottom end is too tight. If you end up making 500 ft lbs or more on the chassis dyno, you found your problem. Keep up the great work, you're an awesome dude!!!

Just a suggestion, do a leak down test. Check the percentages. Your idea of advancing the cam. Header extensions. Change manifold. Great content. Nice horse power, says heads Are working. The camshaft is conservative. Thank you, EM.

That thing is a monster ! It just keeps giving ! And giving !

Eric, Nothing to be ashamed about. I would advance cam timing 4 to 6 degrees. Intake port volume may be too large & could require some epoxy filling. This is why you dyno. Great first attempt. You'll get it. Terry

You're a badass engine builder, but you can win 'em all!

He will be driving his pick up Quarter mile @ a time. Going to the Grocery store.

I second what others said about collector extensions. But if you really want to have an accurate test, you've gotta run the headers you're gonna run in the chassis. What engine masters found with collector extension is you basically have resonant tubes behind the headers up until you hit a muffler. For open headers drag racing you'd want a particular length collector extension for optimum torque.

Man u got so many beautiful parts....

That seems like the Cam is much bigger than a 248 @ .050 on a 108 for it to make peak at 7900...

We had similar issue with my TFS R-Series (from TEA 356cfm@700 lift intake 282@700 exhaust) headed 13:1 430W on E-85🌽: 1st cam had to much split duration; it was LSM 55MM 282/296 @.50 768/768 net lift. #Lunati signature series crank, Oliver speedway series rods, diamond pistons. We thought the motor would flirt with 800 horse and it only made 705/559 tq. My engine builder said "F it" and we spec'd another cam. Ended going with a comp 271/281@ .753/753 net lift. The smaller cam made 716/592 hp/tq and made a lot more lower end tq too. The 1st cam from LSM was a custom ground that was heavily nitrous spec'd but because duratiin split was 14* degrees it was bleeding off cylinder press and losing power NA. Sinve the motor will spend most of its life NA - the 2nd cam split duration was only 10* degrees. We still think a motor like that shoulda made mid 700s power and lower 600s tq, but the only thing we can think if is it has a heavy ring pack, so there's rotational friction holding it back. Checkout my channel for both dyno videos: 430W dyno pt 1 & 2. 📷📸📽🏁🎬🔥

Intake plenum volume has a treshold, where it stops pulling new air through the carb, and only feeding the cylinders with the mist that lingers in the plenum. You should've taken it to the 9000, just to see how it reacts. Second thing is the lobe separation/exhaust valve timing. When you are running high octane fuel, it burns slowly and if the exhaust valve opens before the fuel has done it's job, the power output goes down. This is backed by the smaller header, so when there's more back pressure in the exhaust, it makes more power, keeping the combustion inside the chamber. One quick fix is bigger lash on the exhaust valve, another is faster burning fuel. but both of these won't help on the plenum volume. If you have a spacer on the intake, take it off and try again.

Just think of the knowledge this situation will give you when you figure it out. No matter if it’s simple or complex you’ll laugh about it later and I would say write it down lol but you’ll never forget it .great work

I don’t think it’s one thing! I would try the old cam just to eliminate some variables. I wouldn’t be suprised If the torque is better (but still down from before). It would be really interesting to see where it noses over with that one (If you see what I mean). Still have huge respect for you! Keep up the good work 👍. Johan Lindstrom/LRE Sweden 🇸🇪

That's some impressive HP for that duration cam. I'm thinking the intake is on the big side. Maybe tighter lobe separation. But I am wondering about the dyno calculation of torque .of course I'm guessing

I’m guessing that the dyno is not exactly correct and the headers are hurting more than we really expect them to. But my explanation for the power loss is the intake manifold. Large intake manifold will definitely kill torque and make big rpm’s up top!!! JMO. Great video.

Just wondering. Have you ever measured the air speeds in a intake manifold bolted to a head on your flow bench? I haven't seen anyone do it yet.

I feel your frustration, I invested way too much time just getting all the blue printing aircraft quality right. Seemingly everything fought me. Though it turned out blessedly well. I'm wondering about your dyno personally. But I think 570 torque would be maximum expectation but I'm not sure. your 50 away. As for the peak hp above the 355 is just bizarre. It would keep me up at night. I'd have to spend some money to someone like kaase identify the situation. Thus might keep me up at night. There should be a way to scale reset dyno for torque and power easily.

Most of it is the cam I think. Those comp K lobes are very aggressive and great until they send the valvetrain crazy and lose control. Plus now your also hurting torque by closing the intake valve later.

David Vizard did a piece on dynoes w/blown engines w/some pretty interesting intel!

What was the Length of the Dyno Header's Collector? What type of Carb Spacer, Open or Tapered Four Hole such as the HVH SS4150/4500-1.5A? Did you try advancing the Cam to see if it liked it? How about seeing if it liked 1.6:1 Intake and/or Exhaust Rockers?

I wonder how much a difference a dual plane intake would make. My guess is the air speed has peaked, but because of the intake design it can still keep ingesting more air at high rpms. Or maybe lower the rocker arm ratio so there is less lift. Might help low lift air speed, but these are just ideas. Can't say I know any more than Eric about what is happening. Still a good engine though.

I doubt it one single thing. Majority of it is likely in the camshaft. What’s the dynamic compression with both camshafts?

Are the heads too big for the camshaft engine combo?

It seems you`ve built an open wheeled circle track motor, more compression, more cam shaft and crank it to 8500+ and that pump would scream. I hosed myself like this about 25yrs ago with a superlate model asphalt motor. I replaced an 034 bowtie casting 207cc intake runner with a 220 RHS head, with a solid roller instead of a solid flat tappet that was in the 034 head. Lost maybe 60ft/lbs of torque and only gained 18hp, it was sleepy under 5500 and reached max hp at 7700rpm. Respectfully I believe the loss of torque was the cylinders weren`t being filled, so I had the intake valves increased to 2.050 on the bowtie heads (new rule change) and bowls blended, kept the solid roller and that was what we needed. Got back 90lbs torque (+30 net) and about 60 hp (48Hp net). For what it`s worth my friend, good luck and don`t beat yourself up too much.

I also sub to Broader Performance , Well done Summit. You just got a new customer

Eric, 1st I would test another dyno. If it duplicates or is close to the same results then I’d look at the cam lobes. Is the cam lobe design ( low shock) bleeding off to much cylinder pressure down low hurting the torque but carrying out up top to make good power beyond 7500rpm? Just a thought. 🤷🏻‍♂️

My buddy brought his blown big block Chevy to the dyno, the first run it made 400 horsepower. After almost puking they went over the motor, found nothing wrong mechanically, pulled the plugs and they all looked weird, so they changed the plugs and picked up 300 horsepower with no other changes, sometimes it’s the simple things that you overlook that make the most difference. After that the dominator carb wouldn’t work and after a few pulls they called it quits

Sound s to me you have a cam that makes power above your usable RPM range? Amd a merge collector with a 2.500 " cross section would work way better than a 3.5" straight?

Erik. What size the carb.I would look at changing carb.from what I saw of the early BSFC was lean.i have run 1,000 cfm pro systems carb on similar cid engines and made 600 trq around 5100.also used 1 7/8 primary 3 1/2 collector.on a quick note did you see if it had a dead cylinder,I have had that happen and it had me itching my head.the engine didn't sound like had any misfire .found it had a closed strap on the plug

Man I was just typing out a comment that the cam should be checked and then you go into the details of having it checked. I've got a set of your dragon slayers from 2016 going on my 427 with a Jones 254/256 solid roller an planning on dynoing it before installing in the car.

It sounds like you have 20-30 degrees more cam duration than what you thought.

To much cylinder head. Need more compression. Your one of the best cylinder head specialist around.

Thinking about my previous comment, I think i would install the original cam and dyno again, i think this would also showcase your porting skills and make an awesome comparison.

Port volosity issues ? Maybe the exhaust port is to big so it's lost the scavenging effect it would explain the tq loss and way the peak power has moved so high in the rpm range because the scavenging doesn't start working again until the engine is reving like a jet the sudden torque jump could be the point the scavenging effect is starting to work

Have you run this combo on a good computer program? I've had excellent results with Engine Analyzer Pro. Otherwize might advance the cam, reduce diameter of collector.

Much obliged sir for the insight. Whats the Bore & Stroke.

Hi Eric, brave video sir. What did you do to the ex port? Try a manifold with way less volume, and l dont get the small cam durations. Colin Lloyd, Headsense Engines Heads,, Aust

Did you measure cranking compression? Can you measure cylinder pressure?

What was the cranking compression at?

I had a similar thing happen to me and it was the camshaft, it was not ground anywhere close to what the card said in other words right card, wrong camshaft. . I replaced the camshaft and it fixed it. Not saying this is what your problem is but it does sound very similar although not very common. Question: did you experiment with headers and/collectors at all?

What's the intake center line and what is the quinch ?

Did you have an 18 inch collector extension on the headers? 108 degree lobe center on a 7800 rpm engine is kind of tight.

When you degreed the cam to get true valve timing you have to load it with the valve pressure I have seen up to 4 degrees with single point tension belt drives and 1.5 on the jesel according to spring pressure

Ask yourself, "what's really changed" compared to your other builds? For starters I would try a different dyno, 2nd I would suspect a camshaft issue if the dyno is eliminated.

Well thats why we back up and try again. All the building on paper we do and sometimes it just doesn't work out like we planned. You're good at what you do so put your boots on and get back to it.

I understand how you feel. Especially since the customer is family. I don't get why it's peaking so high though. Also, could the 1 3/4 inch headers be worth another 20-30 lb ft with a better collector? I wonder if reducing the exhaust duration and lift would help the combo, overall.

Do you have any pushr050 shorter the valve will come off the seat quicker would be a good experiment

Any thought of the inertia ratio setting on the dyno being wrong ?

Spring Pressure too much ? Intake valve too big ? runner volume too large (loss of velocity) ?

I watched it all. This is real life. This actually fun with all your data to go back and be a detective. My thoughts are lobe separation and that 4500 manifold combo not playing well together. That compression needs the libe separation to use scavenging to get flow going and just 4 ish degrees is taking it away, I think the manifold with a 4150 might not be distributing air to feed each cylinder with low (ish) compression and the fifth cycle not starting up flow. So lobe separation and +8 degrees is cause and manifold amplifies it. My bet is old cam would be happier in the truck.

Hi Eric, What epoxy did you use on that intake manifold?

Iv never had any luck with cams in the mid 240s @.050 have you tryed a cam in the mid 250s i know it sounds wrong but iv had good luck there i like the isky stuff like 256/264 @050 on a 104 installed on 99 thats 5 advance make 770/595 torque

I always wondered how close them cam cards actually were on the boxes .

I think it cool that you want to make it right good man you will figure it out would like to hear what it was.

Did you try advancing the cam timing to even out the hp&tq some?

Eric, Every scientist has some bad days in the LAB.

I didn't think there was anything to make that much difference...until the intake change. I've seen big changes with them.

I think you are on the right path with going back to the original camshaft. The compression is a bit low. Were the valve seats ground? Lowering the compression even more? Maybe an angle mill on the heads to raise compression?

Did the cam move…? 7800rpm ? What was the cam installed at? What head again? What rocker ratio?

What ended up being the answer? I forgot but others mentioned Richard Holdener situation where 50 ft lb was "missing" and it was due to having no extensions after the collector.

It’s alright Eric, let’s see if we can diagnose this, so the first thing that caught my attention was the headers way to big for the displacement. Maybe 1 3/4 going to 1 7/8 would’ve been about right. Not sure if this cam was bought for this stage of the engine but 108* LSA, I’d probably go with 105-106. I’d almost question the performance of the dyno maybe something is wrong with it, besides some of the sensors. Are the rings broken in? The lash set correctly? A lot of times when things are changed from baseline, you got look back at what has changed and what’s the same. You’ll figure it out Eric your a smart dude!

Strange to be sure. Degree in the cam on a companion cylinder (6 probably) and on a back cylinder. Maybe the blank slipped while being made. Also, another dyno to back up results is pretty important to not go down the wrong path before you're too invested. I would also swing that cam timing both ways, you might be surprised at some cylinder fill harmonic or something. Lastly, if all that leads no where, I would change the cam on the dyno to a known one and eliminate 1 of the variables. Look at the bright side, maybe what you learn leads to a better 60 ft on your truck by finding torque down low without hurting top end! Good luck.

Back in the early 1970's I went to a hi-per auto mec. school. I was told there that "Nobody ever went faster by grinding the floor of a port." so maybe they were right, as I never have.

Is the cam the same from when it made 670 hp? If its the same cam did you change where the cam installed at ?

With your big head ports and valves sound like a Nascar cup engine, you need to get the port velocity up, for the lower rpm that you want to make power at. Come tonight to Richard Holdener podcast at 7pm Pacific and ask about your engine combination

It’s nice to watch a video about somebody telling the truth and know what he’s talking about at the same time 👍👍

my guess is intake modifications specificly runner length. might flow better, but maybe the modification messed with the pulse in the runner.

After that, do you have an intake that you know what it does? Did it return?

curious about the resolution was... I had done a 468 (14.5:1 NA on methanol) and was running different cams through the thing on a Gopower dyno.. One change was for an Erson cam they sent us to try. (was an incrementally larger cam on all numbers) . The first cold fire up and warmup tha thing sounded like a killer.. Engine was probably 25% snappier off load.. So first pull, the torque curve was off by over 100ftlbs.... so back to the dial indicator and degree wheel.. was right were it belonged, so... bumped it up 2º and it did not improve.. Really did not work on that cam any further.. As this was running in a drag boat, there was no room for the impaired torque curve.. I am used to trading torque for HP and vica versa but this cam was only a tiny bit larger but made a giant difference.. Probably should have worked on it more but like you, I was pretty unhappy on that session...

The heads try going back to them did it return?

I think the lobe separation angle has reduced the tourque number as you have widened the angle and taken cylinder pressure away.