# Another 400 Ready For the Dyno - Guess the Numbers...



## lars (Sep 28, 2004)

I just finished up a 1976 400 for a customer, and I'm getting it ready to take to the dyno to get some “real” numbers…

This smogger 400 was the pinnacle of American performance embarrassment, putting out less than 200 horsepower. Actual compression ratio was right at 7.25:1 (actual measured – this is less than what was advertised).

The owner wanted the engine to look very stock, yet get the performance into the Ram Air IV range. He also wanted to run all accessories, including air, using the stock 1976 brackets and mounting points.

After running some calculations, it was realized that the best compression that could be obtained using the stock heads, milling them max amount, decking the block, running thin head gaskets, and flat top pistons would be 8.7:1 – and then still have the crappy small-valve heads. This simply isn’t enough compression for a “real” camshaft.

I found a set of GTO “670” heads (1967 400 large-valve) for $100, and did a nice multi-angle valve job with a set of Manley Race-Series necked, polished stainless valves. Without any milling on the heads other than a .006” skim cut to assure flatness, these heads, with the stock block deck and stock thickness gaskets, produce an actual comp ratio on a .030-over 400 block of 10.08:1 – just about perfect for a big-cammed engine on premium pump gas.

Since the ’67 heads don’t have the accessory holes in the same locations as the mid-70’s heads, and they’re missing several of the accessory bracket mounting holes, the heads were modified to install accessory mounting hole pads to accept the ’76 alternator lower pivot bolt and the A/C lower attach bracket.

I’ve installed a custom hydraulic roller cam in it that I’ve had very good luck with in the past – it’s very comparable to a RA-IV, but with a little more lift. I also run a 106 intake centerline for great performance up here at Denver’s altitude. Intake is an Edelbrock Performer, which has a relatively stock appearance and will allow use of the stock air cleaner and Ram Air system. This intake is better than the horrible smogger EGR ’76 intake, but it’s a little limiting for this engine.

The owner intends to install the 2.5” aftermarket Ram Air cast exhaust manifolds, but I can’t use these on my test run stand or on the dyno, so I run some old 3-tube headers for test purposes: The 3-tubes duplicate almost exactly the flow performance of the Ram Air 2.5” manifolds, so the test data will be good with these “cheap” headers.

Photos show the engine mounted up on my test run stand – this is not the dyno. My run stand does initial running of the engine to verify no leaks, to set the timing, and to do preliminary carb adjustments. This assures that the engine is actually ready for the dyno with no dyno time wasted for basic setup or leak fixing.

My camera does a weird color shift on many colors: The engine appears blue in the photos – it’s not. The engine is actually the correct aqua metallic that was used on ’76-’79 Pontiac engines, so don’t call “foul” on the “wrong” engine color – the color is really an exact match to the ’76 correct original.

I’d be interested in hearing you guys here on the Forum take a few guesses on what the power, torque, and rpm numbers will be: I’ll be testing the engine with the stock, re-jetted Q-Jet along with a back-to-back run against a Holley 750 vacuum secondary (light spring) carb. I’ll optimize both carbs to the same correct WOT A/F ratio. With that said, give me some guesses on HP and Torque number @rpm for the Q-Jet and the Holley… I’d be curious to see the anticipated numbers – I have my own numbers already in mind…

Here are the pics:

This one shows the passenger side of the engine with the ’76 A/C bracket bolted up to the “670” heads with new accessory provisions added to the side of the head. I’m leaving the compressor and the other brackets off until after the dyno run just in case I have to pop the valve cover off.











Engine on the crude run stand. Quite effective for initial engine checkout, though. Wideband A/F plugged into the collector gives initial indication for carb idle and no-load jetting/setup.











The color in the photo is not a good representation of the actual color on the engine – the real color is aqua. I run the alternator on the engine during testing just to be able to turn the waterpump – since the alternator is not charging, it’s not sucking any power – it’s just acting as an idler.











Close up showing the new lower alternator mounting bolt point in the “670” head: This point does not exist in the stock “670” heads, but must be used to allow use of the ’76 alternator bracket.











Yup, I altered and forever destroyed a real set of GTO 670 heads. They only made a quarter million of the heads, so shoot me.


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## facn8me (Jul 30, 2011)

370 hp and 420 tq


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## the65gto (Oct 9, 2008)

Thanks Lars for letting us see this project. My guess 421 HP (funny number) @ 5200, 476 LB torque @ 3800 (corrected for sea level) )


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## BearGFR (Aug 25, 2008)

Cam specs?

Bear


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## Koppster (Jul 27, 2008)

Lars...where are you located?


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## lars (Sep 28, 2004)

BearGFR said:


> Cam specs?
> Bear


My own spec design that I've developed with my contacts at CompCams - top secret stuff: I've spent 30 years and a pile of junk cams coming up with this setup that actually works well: I have a bunch of crap cams that I'll sell real cheap.. As noted, it's similar to RA-IV specs with more lift on an aggressive roller profile and a 106 intake centerline.



Koppster said:


> Lars...where are you located?


In Denver, but that's irrelevant since dyno data is corrected for sea level.

Good guesses above - I think they're in the ballpark, especially facn8me... an engine with RA-IV performance, passing emissions in a '76 4-speed car should be a real kick to drive.

Lars


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## Instg8ter (Sep 28, 2010)

385 HP, 458 TQ ....thanks for the tuning worksheets Lars.....:cheers

What kind of roller cam would you spec out for a 471 stroker for a mainly street build, looking to get in the mid to high 400's with the HP, will be running 2700 stall to a 3:55 chevy 12 bolt rear end


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## BearGFR (Aug 25, 2008)

Ok I'll play 

Lessee... 450 HP @ 5500, 450 lb. ft @ 4800

Bear


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## Jimmy The Greek (Aug 31, 2011)

Is it like the Price Is Right. Closest score without going over wins. I guess 425 HP @ 5400, 482tq @ 5100. And remember to spay and nueter your pets!!!!


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## lars (Sep 28, 2004)

Hmmm.. everyone is really high on their torque rpm. I'm betting torque will peg out at or below 3500 and that the Q-Jet will kick the Holley's butt for torque and power under 3500.


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## ALKYGTO (Mar 29, 2010)

190 @ 4800 rpm. Torque: 240 ft/lbs @ 3200 rpm. :lol:

Nice looking motor. Any pics of the heads?


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## lars (Sep 28, 2004)

So here's what I'm doing just for fun:

I'm taking each of your hp @ rpm and torque @ rpm guesses and plotting a hp/torque curve that results from the data points you're guessing. Since there is a relationship between hp and torque, the 2 numbers you've given me actually gives me 4 data points to work with, and the curves have to pass thorugh your guess number points. Once I get them plotted, I'll post your resulting "dyno curves."

Right now, Jimmy the Greek has numbers that are not achievable, so guess one more time, Jimmy: If you have 482 ft/lbs torque at 5100 rpm, you end up with 468 horsepower peak at 5100 instead of your guessed 425 horse max. You either have to lower the torque guess or drop the 482 anticipated torque down at or below 4600 rpm...

The others have numbers that will produce interesting curves... I'll post them up once compiled and we'll see how they compare to the actuals.

Lars


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## geeteeohguy (Feb 2, 2008)

Neat stuff. You're a better man than I, Lars, getting a 670-headed .030 over 400 to run on premium pump gas. I've never been able to without severe pinging. It'll be interesting to see the outcome....a big improvement, for sure. Good luck with he dyno and install. My guess: 390HP at 5200 rpm and 475 foot pounds at 3400.


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## lars (Sep 28, 2004)

Is there a way to upload or paste a .pdf file into a post...?


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## OrbitOrange (Jul 5, 2010)

curious as to the results


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## BearGFR (Aug 25, 2008)

lars said:


> Is there a way to upload or paste a .pdf file into a post...?


Yeah, go "advanced" mode and use the paperclip button to save it as an attachment. Some file types aren't allowed (like .xls) so you have to get creative. .doc types however are allowed, so if you bury an .xls as an imported object inside a .doc, for example.... 

Bear


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## lars (Sep 28, 2004)

So when I do that, you can't actually see the document in the post: It gives me a link in the post to click on to get the file open. I was hoping to post these graphs one above the other so they can be seen as you scroll through the post.... is that possible? I've seen people actually post their dyno chart graphs without a "click link" process...


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## jtwoods4 (Dec 22, 2011)

430 HP @ 5200, 465 lb. ft @ 5000


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## BearGFR (Aug 25, 2008)

lars said:


> So when I do that, you can't actually see the document in the post: It gives me a link in the post to click on to get the file open. I was hoping to post these graphs one above the other so they can be seen as you scroll through the post.... is that possible? I've seen people actually post their dyno chart graphs without a "click link" process...


To do that I think you have to get it as some sort of image file --- like a .jpg or .gif. that's reachable via a URL. Then you can include it in the body of a post with image tags that reference the URL. Like below, (only replacing the curly braces {} with square ones [] - otheriwse it'll try to interpret the code and you won't be able to see it in the rest of my post.)

{img}url of image file{/img}

Bear


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## Jimmy The Greek (Aug 31, 2011)

facn8me said:


> 370 hp and 420 tq





Jimmy The Greek said:


> Is it like the Price Is Right. Closest score without going over wins. I guess 425 HP @ 5400, 482tq @ 5100. And remember to spay and nueter your pets!!!!


OK. I will take a Mulligan on my first guess. I still hold out for 425 HP but lets get it in around 5200. Torque how about 430 @ 3900. Hope this guess plots out.


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## lars (Sep 28, 2004)

Jimmy The Greek said:


> OK. I will take a Mulligan on my first guess. I still hold out for 425 HP but lets get it in around 5200. Torque how about 430 @ 3900. Hope this guess plots out.


Jimmy -
Those numbers make a very nice graph that actually looks realistic - I think you could be close...

All the others graphs are plotted, too, and it's very interesting to see how your fantasy graphs look... I just gotta' figure out how to get them posted up now.



jtwoods4 said:


> 430 HP @ 5200, 465 lb. ft @ 5000


jt - Your numbers are the only ones that that don't work: 465 ft/lbs at 5000 produces 443 horsepower, so you have to either drop the torque guess or lower the rpm at which peak torque occurs. Shoot me a revised guess and I'll get you plotted out - I think these fantasy guess graphs will be alot of fun to compare to the actual numbers off the dyno - fun stuff!



facn8me said:


> 370 hp and 420 tq


I think you may be right in the ballpark with that guess. Care to guess rpm for each of those numbers so I can plot a graph with your name on it…?



geeteeohguy said:


> Neat stuff. You're a better man than I, Lars, getting a 670-headed .030 over 400 to run on premium pump gas. I've never been able to without severe pinging. It'll be interesting to see the outcome....a big improvement, for sure. Good luck with he dyno and install. My guess: 390HP at 5200 rpm and 475 foot pounds at 3400.


Geeteeohguy –
You bring up valid concerns on the compression and pinging issues. Here at 5,000 feet elevation I can get away with a little more compression than you sea level guys. I’ve been able to stay out of detonation using cast iron heads up to about 10.5:1, provided the ignition timing curve is properly set and the vacuum advance is carefully selected to avoid part-throttle detonation from over-advance. Using a cam with some good lift and overlap also helps . I’ll be able to tell if it’s detonating on the dyno: We run premium pump gas during all testing, so it will be a valid test.


Hey Bear:
If I send you a .pdf of your graph, could you see if you can get it to post so it can be viewed right on the post without having to click on a link? Then, tell me how you did it and I'll post the all the graphs for some fun viewing.

The motor is ready for the dyno, but I just had some surgery done to my neck. As soon as I heal up a little (about 2 weeks) I'll get the dyno runs done and we'll see what we end up with. I'll post the dyno results and photos under a new thread so everyone can see that the testing has been done.


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## Jimmy The Greek (Aug 31, 2011)

lars said:


> Jimmy -
> Those numbers make a very nice graph that actually looks realistic - I think you could be close...
> 
> Cool .....to get those results I can say: 1) I plugged all variables into a program i developed in conjection with top NASA engineers. 2) My extensive expertise building engines allowed me to make a reasonable estimate. 3) I kinda pulled it of my you know what cause those numbers sound like a really nice engine. Seeing how I don't know any of you personally I am going with the NASA option.:rofl:
> ...


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## lars (Sep 28, 2004)

Okay - the bets are on the table and all plotted out... So here are the dyno guesses plotted out based on a “reasonable guess-curve” from the torque and power points you guys guessed – some interesting graphs and numbers:

First one up is AlkyGTO. Alky guessed 240 ft/lbs @ 3200 rpm and peak power of 190 hp @ 4800. I sure hope his numbers are low, but they do make a very pretty and reasonable graph:









Bear’s guess was 450 torque at 4800 and 450 hp @ 5500. This produces a very steep and “peaky” power curve which would be great for a drag car:









Geeteeohguy came in at 475 torque at 3400 and 390hp at 5200 rpm. This produces a torque curve that drops off fast, but gives a nice smooth rising power curve up to the peak power number:









Jimmy revised his numbers a little and ended up with a nice, flat torque curve peaking at 430 @ 3900 and slowly dropping off to produce peak power of 425hp @ 5400 rpm. A power curve like this would really put you back in the seat as the rpm came up:









The65GTO is predicting 476 torque at 3800 and peak power coming in with 421 hp @ 5200 rpm. This kind of torque in a 4-speed car will certainly fry a set of rear tires off the rims:









Lastly, here’s my guess… I think the torque curve will be fairly flat, and that the cam will sacrifice some torque for higher rpm power, in spite of the stock cast iron heads. I’m saying 400 ft/lbs at 4000 rpm, and peak power of 386 at 5600:









facn8me just submitted a guess that plots out awfully nice: Guess (post below) is 420 ft/lbs at 3600 and 370 horsepower at 5200. The way this one plots out, and the numbers guessed, just may have this one as the "money-guess." If I were to bet on a curve, I think facn8me just might be in the running...:













Now let’s see what the real numbers show during testing!!


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## Jimmy The Greek (Aug 31, 2011)

This is a great thread. I can't wait to see who has the best guess. The excitement is unbearable........... :willy::willy::willy:

And the winner of the 2012 Tin Indian Award for Best Guess of Engine Performance goes to????????????????????


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## facn8me (Jul 30, 2011)

370 at 5200 and 420 at 3600ish


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## lars (Sep 28, 2004)

Just plotted you out and posted your curve with the ones above - check it out...


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## facn8me (Jul 30, 2011)

lars said:


> Just plotted you out and posted your curve with the ones above - check it out...


And yet we are still waiting on actual numbers...


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## lars (Sep 28, 2004)

I just got out of neck & spinal surgery Monday afternoon, so it's going to be about 2 weeks until I can load an engine on a dyno and be able to load & drive a truck. What's with the sarcasm on that...?


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## facn8me (Jul 30, 2011)

I had no idea you had surgery, I hope all is well. Don't wish surgery on anyone. We have to go to San fransico monday morning to specialist for my wife. And sorry it was just a joke.


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## jetstang (Nov 5, 2008)

Lars, what did you have done? I just had spinal fusion between 6 and 7 last Wed, crazy, just found out friday prior. I'm doing great now, but cant lift for 3 months. What'd they say to you?


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## lars (Sep 28, 2004)

facn8me said:


> I had no idea you had surgery, I hope all is well. Don't wish surgery on anyone. We have to go to San fransico monday morning to specialist for my wife. And sorry it was just a joke.


No problem - most of the enthusiast communities (Vette & GTO) were aware of my current issues, so I'm sorry I didn't make that clear here. I've been getting this engine ready for the dyno as much as possible before being somewhat incapacitated - I thought this little guessing game would be a fun excercise for everyone to participate a little and get involved before I'm able to get the engine loaded up and on the dyno: The engine is running on the test run stand, although the owner has yet to see and hear it run. I'm not healed up quite enough yet to risk pulling it off the run stand and loading it up for the dyno session, so don't assume I'm just leading you on with the promise of an upcoming dyno run...

I've had a C5-6 neck fusion once before, and I now managed to completely blow out C6-7 to the point that I lost functional use of my left arm and hand - rather crippling when you build and tune engines for people. The intent is to put this engine through an entire test profile to include a back-to-back Holley versus Q-Jet run - I run these dyno sessions hard, and I produce some good no-BS numbers and data that I enjoy sharing with fellow enthusiasts who are not as fortunate to be able to do this type of dyno testing on their own. The last small block Chevy I did went through no less than 27 different configuration pulls, and the results were published on the Corvette Action Center. This Pontiac will have exclusive coverage right here on the GTO Forum. I've also done dyno testing at Westech Performance Group for Hot Rod Magazine with then-Editor Matt King, so I have a pretty good background on running some good hard-core test profiles.

As with all my testing and articles, I'm more than glad to share info and tech data with true enthusiasts - contact me at any time for assistance and information.

Lars Grimsrud
"Tuning for Beer World Tour" Seminar Series
Tuned by Lars Corvettes - Denver


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## BearGFR (Aug 25, 2008)

:agree Music to mine ears ---- by the time all the bench racers and 3rd,4th, to nth party repeaters and retellers get done bloviating, it's a wonder that there's any atmosphere left to transmit facts through 

I'm a big fan of objective tests and real world results, and I really appreciate people who tell the truth.

Building a Pontiac is hard enough as it is, without having to figure out how to separate fact from folklore...

Hope your recovery is swift and complete. :cheers

Bear


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## Jimmy The Greek (Aug 31, 2011)

lars said:


> I've had a C5-6 neck fusion once before, and I now managed to completely blow out C6-7 to the point that I lost functional use of my left arm and hand - rather crippling when you build and tune engines for people.



Ouch- My college roommate (football tackle) had a rod inserted through, I think, 4-5-6-7 after a he tore up his neck on a tackle. Ended his football career. I don't think that upset him as much as the fact when he wanted to tip a bottle back to drain the those cools suds he had to arch his back at the waist to lean his head back to get the bottle to flow. It was damn near impossible for him to do sitting down and really dangerous to try standing up after a dozen or so beverages. But the important take away from this little story is not to give up. After 6 months of intense, almost nightly, "physically therapy," bottle after bottle, case after case, we .... oops ... I mean he overcame his handicap and was able to drain a bottle with only the slightest hitch in his tip. In fact, if you didn't know he had an issue, you would probably never be able to tell. I Know. I know. Its one of those Hallmark heart warming movie special scenarios that just brings tears to your eyes to know an Irishman and his suds would be together forever :cheers:cheer


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## lars (Sep 28, 2004)

BearGFR said:


> I'm a big fan of objective tests and real world results, and I really appreciate people who tell the truth.
> 
> Building a Pontiac is hard enough as it is, without having to figure out how to separate fact from folklore...
> 
> ...


I've been buidling and racing Pontiacs since the early 70's, and I'm old enough now that I really don't have to put up with bull and mythical stories... I run every engine I build on the dyno to get factual information both for the customer and for my files, so the infomation I have is based on factual numbers - not some opinion I've pulled out of a dark hole... I think you guys will find the upcoming Holley versus Q-Jet results interesting: The numbers tend to be very surprising under 3500 rpm.

We're going to see if I can get the dyno on the 16th: I should be healed up enough by then that I can at least run an impact wrench to get it zipped up to the water brake. The engine owner stopped by last night and heard the engine run for the first time - I'll see if i can get a copy of the video he shot. Hopefully by the 16th I won't be drinking beer from a straw...

Here are some recent engines I built and tested:

First one is an engine I actually built for myself, for a change. 407 small block Chevy for my '64 Vette. Engine made 500 horse and 500 ft/lbs under 6000 rpm with a solid roller and a big set of headers:











Here's a "little" 383 stroker Chevy that I built for a friend. We actually took this one back to the dyno twice after the numbers indicated that the intake manifold just wasn't up to the task. Swapping from a "Performer" to a Performer RPM Airgap bumped the power almost 20 hp, and forced me to build him a big-block hood to get it all to fit... We also found that the "big" (1-3/4")headers beat the little 1-5/8" headers by a solid 15 horse margin across the rpm scale - it's nice to have factual data and not this bench-racing crap:










I also build engines for enthusiasts in Europe. Here's an engine that I shipped over to Norway. 420 cubic inch small block that put out no less than 530 horse under 6000 rpm. As far as customs was concerned, it was a 270-horse 327...:












Lars


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## geeteeohguy (Feb 2, 2008)

Lars, I also was not aware of your current medical issues and wish you as speedy and pain free a recovery as is possible. As Mr. Bear said, _real _information such as yours is a breath of fresh air and rare indeed. Objective testing is the only way to come up with actual fact. It takes a lot of hard, unappreciated and unrecognized work. I for one thank you for your intensive efforts, and your willingness to share them with us. Please keep these posts coming: we love this stuff!!
Jeff


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## jetstang (Nov 5, 2008)

Happy to hear you are recovering, and love it you are going back quick. They gave me 3 months before I am 100% and can lift over 10 lbs, my work requires 50 lbs, so I'm out of work til I'm cleared. Love to know how you blew a second disk and why, don't want this ever again. No pain for me, awesome surgeon. 
How radical was the cam in the 530 tq, 500 hp smallblock? Sounds like a perfect fast street motor.


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## Eric Animal (Oct 28, 2007)

Lars, Speedy recovery...I have some lower back problems, but nothing like what you have. Get well!!!!!!!! Eric :cheers


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## lars (Sep 28, 2004)

jetstang said:


> How radical was the cam in the 530 tq, 500 hp smallblock? Sounds like a perfect fast street motor.


I assume you are referring to the engine that made 530 hp, since I don't make reference to a 530 ft/lb engine with 500 hp.

The small block 420 (400-based Chevy with an Eagle 3-7/8" stroker crank) shown with the two grinning customers behind it made 530 hp at 5900 rpm and 528.5 ft./lbs at 4800 rpm. Once again, the cam was a custom designed hydraulic roller that I developed with CompCams, ground on their 12-000-9 XFI billet with a cast gear pressed on it for the distributor. Lift was just short of .600 with durations @ .050 of 242/248 (292/300 @ .006). Intake was ground on a 106 centerline. The key was in the heads and getting some good flow. Since the engine was being exported, I used cast iron heads for brutal reliability. The graph below is the actual dyno run data from the first dyno pull. The numbers got a little better through the day with some tuning refinements. Yes, the car is very quick:


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## lars (Sep 28, 2004)

Eric Animal said:


> Lars, Speedy recovery...I have some lower back problems, but nothing like what you have. Get well!!!!!!!! Eric :cheers


I sincerely appreciate all the kind words and well wishes from everyone here on the Forum - I've received personal e-mails as well as thoughful posts here in my topic threads, and it's very much appreciated to have people take the time to express a kind thought. Thank you very much to all of you: I think I'm on the road to recovery, and just need to get to the point that I can start wrestling engines onto the dyno again...

Lars Grimsrud
Denver


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