Jr. Corvette

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Hey guys,

So there was a local car show here in Calgary and there was a shop with a dyno machine setup. I decided to dyno my car to see what I was making but I can't seem to believe these results.

To start off my engine is a short block ZZ4 350 that I built up with AFR 210 heads, comp cam, retro hydraulic lifters, stainless steel rockers with magnesium pushrods, double roller chain, edelbrock rpm performer intake manifold, flame thrower 3 module and coil and MSD rotor and cap, and a FiTech EFI fuel injection. The car has 36 degrees total timing with 17 degrees initial and 19 degrees mechanical. Engine has 8.5:1 Cr (for plans of adding a supercharger in the future). Behind it is a T56 6 speed that I built with gear ratios 2.66, 1.78, 1.30, 1.0, 0.78, 0.5. lastly I have 3.90's in the rear.

Factory an extremely similar engine the ZZ6 makes 405hp and 403FtLb. I know one guy with an identical setup except he has 10.5:1 compression ratio is making 506hp. So I estimate mine is around 450hp and honestly it feels that way on the street. The car goes. So on the dyno it made 268rwhp and 272FtLbs... A lot of other cars ran on the dyno and everyone was getting oddly low numbers. A factory (it my not have been totally factory because it sounded meaner) 370Z made 240rwhp which is about 50rwhp low of where others have dyno'd. A swapped LS 240SX made 227rwhp.

Some things that seem odd to me is that the dyno run was done in fifth even though I told him to pull in it 4th. Horsepower and torque crossed at 5420 but it should have crossed at 5252. The page that printed off didn't even include the entire rpm spectrum that the pull occured up too. It was pulled to 6100rpm and the graph stops at about 5800ish. Another thing that strikes me as odd is I have done all of this tuning off feel and I've gotten the car to perform as well as I believe it can. However, the shop criticized my tune (I can build an entire car but apparently I'm an idiot at tuning... I think not) then they said I could bring it by there shop and they could sort it out. I'm thinking they are scewing the results to try and drum up business. I know a lot of the people around the dyno were very sceptical of the results, especially after the 370Z dyno'd so low.

I personally don't care. I know how fast my car is and I know the HP of cars I've beaten. I'm more just annoyed I wasted $100 on this dyno pull and got these result. I also know that I should assume a 15% drivetrain loss but even with that factored in there seems to be missing power. I also don't understand that big dip in the curve. What do you guys think about this? Do you think it was fair or a rip off?

I've attached pictures of my cam card and dyno sheet at the bottom. That's my writing on the dyno sheet so apologies. I was just trying to make some notes of things that didn't make sense.
 

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Jr. Corvette

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I think you gave the answer.... low numbers to get you in their shop. Lots of us have seen your car and met you so we know better than 268 hp. You could take it to another dyno to confirm but that may be a waste of your mods money. :thumbs:
Thanks for confirming my suspicions. Another thing that was odd is he said he checked the dyno with their Corvette that he said is extremely consistant. However, when my car was on the dyno he said he had to calibrate the dyno. Do they normally calibrate the dyno everytime they dyno a car? I know they correct for air temp, and density but that's a fairly easy calibration I thought. This guy kept taking his keyboard in the car and it would take him like 5 minutes to 'calibrate' the dyno before the run. Just as a side note, he had already entered in my name and vehicle information before he got in the car so he wasn't doing that. Anyone know if that's normal or just another indicator of a shady dyno?
 

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Seems relatively reasonable for a 8.5:1 build. A CR that low (even with heads and cam) is going to be significantly lower in power than a comparable build with a higher compression ratio. A ZZ4 crate runs around 355HP / 425TQ at a CR of 10:1. This factors in no drivetrain at all, this is BHP at the crank. Now drop the compression by 1.5 points and that number drops drastically. You gain a tiny bit back with heads and cam, but your major gains would come from boost (effectively increasing the compression ratio).

At any rate, a dyno is great tool for measuring gains to compare before and after mods. Most numbers do differ from dyno to dyno by at least a certain percentage. Also varies by dyno manufacturer. A mustang dyno will always read lower than a comparable dynojet.

Hard to tell from your pictures, but that appears to possibly be a Dyno Dynamics brand machine. They usually fall somewhere in the middle based on my experiences.

Hope that helps..........
 
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Jr. Corvette

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Seems relatively reasonable for a 8.5:1 build. A CR that low (even with heads and cam) is going to be significantly lower in power than a comparable build with a higher compression ratio. A ZZ4 crate runs around 355HP / 425TQ at a CR of 10:1. This factors in no drivetrain at all, this is BHP at the crank. Now drop the compression by 1.5 points and that number drops drastically. You gain a tiny bit back with heads and cam, but your major gains would come from boost (effectively increasing the compression ratio).

At any rate, a dyno is great tool for measuring gains to compare before and after mods. Most numbers do differ from dyno to dyno by at least a certain percentage. Also varies by dyno manufacturer. A mustang dyno will always read lower than a comparable dynojet.

Hard to tell from your pictures, but that appears to possibly be a Dyno Dynamics brand machine. They usually fall somewhere in the middle based on my experiences.

Hope that helps..........
Hi Cable guy,

Ya, that helps a bit. However the reason I use the ZZ6 specs is because all GM changed from the ZZ4 to the ZZ6 was the heads and cam and even then they still weren't top of the line. I've also read that 1 point of compression ratio generally increases HP by 3-4%. So let's assume even though I put all these improved parts on the engine I still only managed to get 405hp and 403torque if I was running 10.5:1. Now let's factory in the compression ratio by taking 8% off those numbers. So 372hp and 370FtLb. Now factoring in a 15% drivetrain loss. So it would be 316rwhp and 314rwFtLbs. That's still a 48rwhp discrepancy and that's assuming everything I did was practically useless and I wasted ten grand on parts I didn't have too. I will say there are guys running ZZ4's with just bigger heads and 8.5:1 running 7lbs of boost making around 610hp. I know it's hard to compare builds and who's really to say what's going on but even that dyno graph doesn't match how the car feels and I had a different engine in the car before and I know how much faster it is. Given all the discrepancy's and issues I've pointed out and the poor results from everybody there today while they keep telling people to come see them to fix all of these problems it just seems wrong. I think I will get another dyno done just because of how wrong I felt this was just to see if the shop was being honest or not. I appreciate all the opinions never the less. I just can't believe those numbers to how the car performs.
 
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Dyno runs should be done in 4th or the closest to 1.0 ratio to be accurate...
If they do in 3rd or 5th, the results will be offsets by the transmission ratio up or down multiplication and will be way off!
That would make a part of your low numbers story, but every dyno is different and calibrated by the owner to say what he wants you to believe... 🤷‍♂️
 

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I would also be suspicious of chassis dyno results provided by the shop's that perform mods! It's in their interest to provide a rosier result than might be accurate. I have a 2010 Challenger R/T (5.7 Hemi) that was supercharged and more by a speedshop in Canada which their chassis dyno result graphs at 480 rwhp. For reasons which make for a long story I had to contact the supercharger tuner at Magnuson who too seemed suspicious about the dyno result. It doesn't feel like a 550 crank hp car to me (adding 15% to the rwhp #) even accounting for the fact it weighs over 4k lbs. On another note: AM I WASTING MY TIME WAITING FOR THE PRICE OF A C6 ZR1 TO DROP SIGNIFICANTLY?
 

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I would also be suspicious of chassis dyno results provided by the shop's that perform mods! It's in their interest to provide a rosier result than might be accurate. I have a 2010 Challenger R/T (5.7 Hemi) that was supercharged and more by a speedshop in Canada which their chassis dyno result graphs at 480 rwhp. For reasons which make for a long story I had to contact the supercharger tuner at Magnuson who too seemed suspicious about the dyno result. It doesn't feel like a 550 crank hp car to me (adding 15% to the rwhp #) even accounting for the fact it weighs over 4k lbs. On another note: AM I WASTING MY TIME WAITING FOR THE PRICE OF A C6 ZR1 TO DROP SIGNIFICANTLY?

Brian,

I completely agree. You know the more I keep looking into things the more dyno results are absolutely useless because they vary so much. Super Chevy did a test with an engine dyno'd 750 HP engine. They went to 5 dynos and 3 of the dynos were between 620-660rwhp however one of the other dynos was 540rwhp and the other was like 520rwhp. I honestly can't remember the numbers and I can't seem to find the article but I remember results between these dynos have a difference of as much as 140rwhp.

From the people I've talked to they say that dyno result seems weird for my build. Super Chevy actually built almost my exact engine with the exact same cam and cast iron 200CC heads with a 9:0cr and they made 406hp and around 400ftlbs of torque. Then when they bolted the supercharger on they made 550hp and 550ftlbs and that was with cast iron heads.

I've book in another dyno session with Dale Adam's just to compare. I'm not as concerned with the numbers although it better be more than 268 and 270. I'm more concerned with a smooth power curve and then I can work with the dyno and do some tuning to try and improve my car. I don't think I would even be as concerned if my dyno would have been a smooth curve but my curve looks like a have an inline 4 with a turbo. Plus the 5th gear pull is annoying.

I will update you guys on the 21st after my dyno (as long as it hasn't snowed and I can't make it). I appreciate all of the input!
 

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I didn't mention earlier that it was Davenport in Calgary that did the performance work (and dyno once completed) on the Challenger I own. The original owner spent 18k there for the mods when it was months old. I have another bill from his return there years later for a spark plug change at $16 a pop (not including labor) and there are 16 of them in the Dodge hemi's (ouch)! I've always been fond of the look of the 74-77 (like what you've done with yours visually and you've said your pleased with it's performance), don't see many in BC that have been improved upon. Just sold my C4 to a 72 yr. old guy on the island.
 

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I didn't mention earlier that it was Davenport in Calgary that did the performance work (and dyno once completed) on the Challenger I own. The original owner spent 18k there for the mods when it was months old. I have another bill from his return there years later for a spark plug change at $16 a pop (not including labor) and there are 16 of them in the Dodge hemi's (ouch)! I've always been fond of the look of the 74-77 (like what you've done with yours visually and you've said your pleased with it's performance), don't see many in BC that have been improved upon. Just sold my C4 to a 72 yr. old guy on the island.
Wow! That's an expensive spark plug change. That's too bad you sold yours. Do you have another Corvette or are you replacing yours?

Thanks, I'm very happy with it. Going to be some big changes this winter. I've finally decided to get it painted but I'll be doing all the body work and priming the car. Once it's ready for the color and clear my buddy and I are going to load it up in his new enclosed trailer and take it to the paint shop. I'm really excited and I'll be doing some unique body work on it with a design I made up that keeps the soft tail but eliminates the bumperettes. Here's a teaser photo of the design. Factory is on the left and my design is on the right. Some people have done something similar but not quiet the same and as far as I know no soft tails have been done this way.
 

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Wow! That's an expensive spark plug change. That's too bad you sold yours. Do you have another Corvette or are you replacing yours?

Thanks, I'm very happy with it. Going to be some big changes this winter. I've finally decided to get it painted but I'll be doing all the body work and priming the car. Once it's ready for the color and clear my buddy and I are going to load it up in his new enclosed trailer and take it to the paint shop. I'm really excited and I'll be doing some unique body work on it with a design I made up that keeps the soft tail but eliminates the bumperettes. Here's a teaser photo of the design. Factory is on the left and my design is on the right. Some people have done something similar but not quiet the same and as far as I know no soft tails have been done this way.


Nice!!

Look forward to seeing it done on the next cruise opportunity. (Fingers crossed for 21)
 
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I have a good feeling about your 2nd dyno. I agree with the others that it should be dyno'd in the closest 1:1 gears, makes mechanical sense. I am looking forward to see all the body mods and see it in the final paint. Having seen the past work you have done on it, she is going to be a looker!
 
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Jr. Corvette

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Hey guys. Just got my car dyno'd again today and there's quite the difference. On my baseline dyno it made 340ftlbs and 300hp at the rear wheels. That's 70ftlbs more torque at the wheels than the other dyno.

More importantly though we sorted out a big issue. We were getting a lean pocket at 3500 rpm which made a similar dip like my first dyno. After trying a few things, Tim from Dale Adam's suggested my inline filter could be causing the problem because it has a brass element. We removed the element from the filter and ran it again and low and behold that dip was gone and the car had an increase of 23rwhp at it's peak! There are still some little lean and rich pockets here and there but we believe that a single plane intake could sort that out and improve the car further. At the end of the day it made 338ftlbs and 325hp at the rear wheels. That equates to about 385hp and 400ftlbs at the crank which is right were it should be (just like the super Chevy build). That also confirms that this engine will really perform once I get a supercharger. Hopefully our dollar improves one of these days and I can. Maybe you guys can let me know if you hear of a used or broken V3 vortech that I could fix and bolt on:).

Here are some pictures of my first, fifth and sixth dyno pulls. We were still mucking with some settings on the sixth pull and it developed some rich and lean spots but 5th is the smoothest. I also forgot how to put my fuel injection setup into a closed loop while I was there so the unit kept changing numbers on us. However, the single plane should make it easier for the EFI to manage the fuel and those areas will improve.

Thanks again for all the input on this thread. I'm really happy that I could get those issues sorted out and find some more accurate numbers. It really goes to show that dyno tuning can help you find problems you didn't even know existed and help you improve upon your tune further.
 

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Well, I must admit that you are talking way (way way way) over my head. I just wanted to compliment you on what looks like an absolutely gorgeous C3! It appears to be in showroom condition. Very nice, brother.
 

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Can't find any info. as to why a brass element would have an effect. Are you able to provide an understanding? Wanted to share that for those gen 2 LT1 owners it doesn't require a great deal of time nor money (particularly if you're personally providing the labor) to bring crank hp from 300 to 430 (LS3 output).
 

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Well, I must admit that you are talking way (way way way) over my head. I just wanted to compliment you on what looks like an absolutely gorgeous C3! It appears to be in showroom condition. Very nice, brother.
Thank you sir! My paint's a little rough but I'll be painting the car this winter. It's a show car underneath though:).
 
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Jr. Corvette

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Can't find any info. as to why a brass element would have an effect. Are you able to provide an understanding? Wanted to share that for those gen 2 LT1 owners it doesn't require a great deal of time nor money (particularly if you're personally providing the labor) to bring crank hp from 300 to 430 (LS3 output).

He said that the brass elements are fine for carb where you have low pressure and flow. For fuel injection he said they just don't flow enough. I was skeptical at first to but thought, "what the heck, we're here, lets try it" and I couldn't believe it. I still can't believe it smoothed it out and the horsepower increased that much. He said the ones for fuel injection are typically longer and have an element inside. Sure enough if you go on summit and search fuel filters, there's an option for use with carburetor or injection.
 
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