Dyno Numbers - I am pissed.

[JJRJR]

OK guys, well don't I feel like a fool. Dyno says 392 HP @ 5500 and 407 TQ @ 4500. I am beside myself with anger right now. A bone stock 383 pulls 335 HP. I picked up 57 HP and spent $8,000??

Guys, what are your thoughts here. The builder MUST have done something wrong.

383 bored .030 over;
9.8:1 CR (according to the builder)
Eddy Performer RPM intake
Holley 750 Double Pumper
Eddy Performer RPM aluminum heads (hand ported)
1.6 ratio rockers
Comp Cams XE275HL (275/287 duration, .525 valve lift, 231/237 duration @ .050 lift)
TTI BB Headers
Fully balanced rotation assembly

The dyno guy said "maybe the combination of parts isn't right." Everyone I spoke to that I thought knew about these engines said this is a great combination.

What do you guys recommend or think??

Thanks.

John

 

[metalstorm]

can you post the dyno sheet?
the true test is on the road/track not the dyno.

 

[bigmanjbmopar]

get rid of the Holley 750 and put on a 1050 you are restricting the hp with that 750. What rotating assembly is it? Is it stroked? Pistons? domed or dished? I would think dished to get that low of compression. Mine are dished 24cc to get 9.6:1 all we can get is 91 gas out here.

 

[JJRJR]

The dyno shop did recommend to get a bigger carb he also said the 750 isn't big enough. He recommended an 850?? With regard to rotating assembly, it is not stroked. Flat top pistons with what I think are called valve reliefs?

Do you think a bigger carb will get me more power?

John

 

[69hemibeep]

The dyno shop did recommend to get a bigger carb he also said the 750 isn't big enough. He recommended an 850?? With regard to rotating assembly, it is not stroked. Flat top pistons with what I think are called valve reliefs?

Do you think a bigger carb will get me more power?

John

Yes :yesnod: 850 would help for sure

 

[metalstorm]

it takes 1.5 cfm to make 1 hp.what do your heads flow?how much tuning was done on the dyno to max the hp?results?
edit:i have to check my formula for correctness.i cant think streight today.

 

[JJRJR]

From the flow bench: .200/145cfm, .300/213cfm, .400/248cfm, .500/287cfm, .600/309cfm, .700/317cfm, .750/318. The guy that ported them said just under .750 lift the spring was bottomed out. I'm wondering if I should have gone with the Comp Cams XE285HL instead of the 275 and used an 850 carb? Probably not getting everything I should from those heads with the 275 cam and the 750 carb.

 

[JJRJR]

While I know it's not the gospel, the Mopar Muscle guys did a 383 with stock heads; but used an 850 Demon carb and the XE285HL cam and got 455HP/457TQ.

 

[3BIRDS1X]

The dyno results might be S.A.E. corrected which would make your comparison to the 335 hp number wrong.

 

[sixgunrunner68]

my thoughts, carb will help, although I'm not sure it's going to give you the numbers you're expecting. :cents:
Compression could be better. I would have shot for 10.5:1 myself.
Just curious, did you deck the block, how deep are the slugs in the hole at TDC?

 

[JJRJR]

Sixgunrunner68, those are questions I'll have to ask my builder. At this point, I'm leaving the engine with the Dyno Shop as they are a very reputable racing engine facility down here in Florida. I think I may go with an 850 and maybe even go with a bigger cam; but I'll wait to see what the carb does. If I can get into the 420 to 425 range, I may be happy.

 

[sixgunrunner68]

Your cam sounds pretty healthy to me but see what the shop says.
Good luck bud.

 

[A31PKG]

Just curious, to what extent are they "tuning"? Are they messing with the advance curve? Cam timing? Plug heat range? Carb jet sizes?

 

[JJRJR]

Good question. I know he said they worked on the timing and said 35 advance was as much as I want to go with pump gas. Said air/fuel mixture is good, but thought it needed a slightly bigger carb. Not sure about cam timing or plugs, etc. I plan to discuss with him tomorrow to see what the next step is.

 

[mcmopar]

I've not dyno'd mine but the results in the car are more than pleasing. The thing is a beast and pulls like mad. Before you get all upset do what you can to get the most out of it but don't just go by the numbers. Put it in the car with some good gears and see how it runs. You may be pleasantly surprised.

 

[george68hemirr]

bigger carb /more compression...your guy did a compitition port/polish job on your heads...right.....was all the flow numbers close....when the guy did mine he said he had my heads flowed almost 100 times to get them correct..10.5 to 1 max compression for 93 pump gas....cast block/aluminum heads.....the dyno is just a tuning tool.....real numbers are at the dragstrip.....good luck....i am on my 4th motor and now i am happy...its all about HOW MUCH YOU WANT TO SPEND

 

[moparchris]

The dyno results might be S.A.E. corrected which would make your comparison to the 335 hp number wrong.

Bingo!!

I hate to hear of this JJRJR. Dynos have correction factors. The dyno operator enters in the correction factor manually. This is supposed to level the playing field so that engines can be compared to each other and to correct for differences in weather too. Unfortunately magazine articles usually are inaccurate. The correction factors can be manipulated to achieve certain results. This is unfortunate. Ever go to a show and watch the dyno shoot outs? There are lots of disappointments and broken dreams. Popular Hot Rodding recently has addressed this situation and show some of the truth in dynos. 392 HP is encouraging and can be bumped significantly by the right tuner. I would start by sitting down with the dyno operator and ask him to lay out each and every pull and what he did between pulls. Also you want all the dyno runs on paper. The reason for this is so you can check for certain things. If you want to pm me and send the sheets to me I can help you decipher what is going on. Also ask him what the atmospheric conditions were and what correction factor he used. Remember back when we originally talked about your combo and I warned you about how the Mopar Muscle test was "optimistic" well now you probably see what I meant, I remember you were really irritated with my stance. The good news is that by putting a bigger carb on it and some savvy tuning your motor will clear the 400 mark. When you bolt this engine in the car you will wonder why it is so fast but the dyno numbers were so crappy. Well you probably picked a shop that uses the proper correction factors for a more honest assessment. This also rings true for flow benches unfortunately. The flow numbers indicate that the heads will support over 500 hp, but you will have to up the compression a point and put a .600 plus lift solid in it to get there along with an 850 carb and a big single plane intake. My Dart Swinger made an honest 400 hp and at 3420 pounds it ran mid 11s at over 116 mph. That is no slouch ( well not as fast as a new boss 302 but) and your Road Runner will be the same way. So step away from the ledge and take a deep breath. Talk to the dyno guys and get the story, then go to your engine builder and talk it over with him. There is more in it if you are willing to get on to some more serious parts. Also your making more than 1 hp per cube and that is not too shabby.

 

[4spd69RR]

I have to agree with bigmanjbmopar, get rid of the Holley carb, however, it does take money to produce horse power. Sorry to here that you are not happy with the results.

 

[JJRJR]

UPDATE:

First of all, thanks to all of you guys for your honest opinions and sage advice. For me, hearing these dyno results is like waking up on Christmas as a kid and finding dog shit under the tree. LOL. BUT. . . we're still fine tuning and I wanted to let you guys know what I've learned since yesterday.

Dyno shop called me this morning and said that the motor is running great, no ring problems, etc. He said he has this thing called a whistler I think he called it and he can check the CR. He will also look at the cam timing. He asked me to send him the head flow numbers and the Mopar Muscle article and dyno sheets from their 383 build.

I also spoke to the engine builder. He says the slugs are .010 in the hole. He thinks there is another 30 to 40 HP in the motor with some minor mods. He can mill the heads .030 and use a thinner head gasket and acheive 10.3:1 CR, but is concerned with the pump gas. Is that too much? I was under the impression that you can run a bit higher CR with aluminum heads because of the way the heat disapates as opposed to cast iron.

He also thinks the motor/heads will benefit greatly by using the bigger Comp Cams XE285HL, as opposed to the XE275HL I have in their now, and topping it off with an 850 Carb.

Questions:

1) Will I have an issue with 10:3 CR using pump gas if I decide to go that route?

2) I'm going to call Comp Cams today, but will changing to the bigger cam (remember I have 1.6 ratio rockers) create any other clearance problems? Is it just a switching of the cam or does any machining need to happen? I am assuming I can use my existing pushrods, lifters and springs. The lifters and springs (double) came in the kit from Comp Cams for the XE275.

Finally, many of you have commented about the dyno being a "real" number. I have since learned that this guy is known for giving conservative numbers and not just trying to tell people what they want to hear.

Naturally, I will keep you all posted.

Thanks very much,

John

 

[metalstorm]

there was an article that changed head gaskets [stacked copper]changing the cr from 9/1 up to 11 /1 and the 1st 2 pints netted 20/15 more hp and went down from there the higher the cr went.[test engine was a 440 i believe]do a cranking cr test to see what the psi is to help decide is pump gas is on the borderline.