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What HP should this combo be making?

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how69ss

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Discussion starter · #1 ·
I have a 427 with 9.2:1 cr, Comp cam hydraulic xtreme energy cam 230/236 @50, 552/555, 110 LSA. Edl air gap, ported and polished GM closed chamber heads, valve job, roller rockers, 750 DP, milled choke horn, etc. Headers and flowmasters. It's balanced and blue printed, forged crank and rods, total seal rings, hyper pistons. Motor has maybe 3,000 miles on it, and only 1,000 on the cam. Maybe 100 runs.

I know that it hasn't been running near its potential. I know that I need to jet up and also advance the timing. It was tuned on a chasis dyno for the street. I pulled out the old print out and it looks like the guy just tuned it to run to 5,500 rpms. The cam is good for 6,000, and this is a 427.

I know that some of you think these cams are a dud and not as good as ultradyne and lunati stuff. But this is what I have, and I want to get some idea of what it SHOULD be capable of. I know that running 8.7 is way off. According to my MPH and ET that's only like 325 fwhp. I have a plan as far as the tuning goes, but please let me know what kind of expectations I should have. I want to tune this to the max before I change cams or do anything else, unless it's "hopeless," i.e. there's no way to tune another 50-75 hp from this combo. It just seems like it should be able to do 1 hp/ci. But I know the 427s need the rpms to make the hp, so I might just be stuck there. :(

Thanks in advance for your wisdom.
 
Discussion starter · #3 ·
I've been running 3.55s. 4 speed M20. 2.5 exhaust, not mandrel bent. Not sure about the headers, buy they are a smaller header, originally on the motor when it was a 396.
Will have 4.10s next season. Also switching to 90/10 front shocks for next year. Have edl adj/boxed lowers/poly bushings, air bags right now. Hotchkis type springs, 1" lowered/pro touring type design.

My clutch is pretty old, so I am wondering if I am getting a lot of slippage and that's throwing my ET off a bunch? Ran 1.78 60/8.08 with a 150 shot of nitrous. Overall, it just doesn't add up. Somethin' aint right.
 
#5 ·
I agree that you should expect the power to be in the 425-450 HP range with that combo. I'm very curious about what header size you have. You can take a dial caliper to one or two of the primary tubes and simple measure that outer diameter of the pipe. If you have a 2" primary tube diameter, that can be robbing you of a lot of midrange RPM torque, and that will sure slow you down. A lot of guys over-do it with header size, so that's why I'm suggesting you check that out.
 
#6 ·
how69ss said:
I've been running 3.55s. 4 speed M20. 2.5 exhaust, not mandrel bent. Not sure about the headers, buy they are a smaller header, originally on the motor when it was a 396.
Will have 4.10s next season. Also switching to 90/10 front shocks for next year. Have edl adj/boxed lowers/poly bushings, air bags right now. Hotchkis type springs, 1" lowered/pro touring type design.

My clutch is pretty old, so I am wondering if I am getting a lot of slippage and that's throwing my ET off a bunch? Ran 1.78 60/8.08 with a 150 shot of nitrous. Overall, it just doesn't add up. Somethin' aint right.
Click to expand...
i think your gearing is ok with the muncie, but your exhaust should be 3 inch IMO , your 60 foots should be in the 1.7 range without nitrous. Yah maybe you clutch is slippin? TOOOOO many variables.
 
#7 ·
Just thought of something else, and this might sound simple, but make sure that your seconday throttle plates are opening up. Sometimes they can get jammed and fail to open when you hit the accelerator.
 
Discussion starter · #8 ·
The throttle plates are opening. I checked that.

Jason, yes, there are TOOO many variables to figure everything out through just thinking about it/bench racing. I mainly just wanted to know what I can expect from the combo I have, so that I have a better idea of where I should be. I am making some changes, transmission (another manual) and gears, 90/10 shocks, so that will change things yet again.

Of course, come May when our track opens, then I can get tuning and see where I get. Just wanted a baseline.
 
#9 ·
I would think that combo would run right around what mine does on motor. What is your timing set at??? Whats the jetting in the carb???
 
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#11 ·
I know you don't want to hear this but I tried a comp cam almost the same size as yours way back when and it was a dog! I was going to guess 325-350 motor hp from that combo.

Think of finding a cam like finding a woman, your going to go through a few before you find the one that spins your wheels.:D
 
#12 ·
how69ss said:
But I know the 427s need the rpms to make the hp, so I might just be stuck there. :(
.
Click to expand...
A 427 is no different than any other engine, they also need rpm's to make horsepower because power is directly related to rpm's.
 
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Discussion starter · #13 ·
2cool said:
I know you don't want to hear this but I tried a comp cam almost the same size as yours way back when and it was a dog! I was going to guess 325-350 motor hp from that combo.

Think of finding a cam like finding a woman, your going to go through a few before you find the one that spins your wheels.:D
Click to expand...
Yes, I know. I kind of just had the cam thrown in there because I wasn't racing anymore and just wanted a street cruiser. Well, you know how long that lasted! (About 25 miles or so)

Thanks for the feedback. I have some work to do, obviously. I know that I need to tune with timing and jetting. I am hoping that it warms up past 40 today and I will check my total timing again. It's 38 deg total advance right now but I do want to double check that.

The carb is a 750 dp with sec. blocked and came with 72/80. I just bumped up the sec to 84 (go up 6-8 for blocked PV, right...) and the primaries to 76. (Would it be better to go 86 sec and 74 primary????) Do you want to keep the same stagger that the carb comes with stock???? (That would be 70/80 though I couldn't find any part numbers on the carb, so not sure which 750 it is--bought it used/new rebuild)

I plan to start with jetting and then at the track come down on the primaries until I hit my best MPH, and then work on the timing, and then the jetting again. . . . . Of course, that's 5 months away! It's friggin' cold in South Dakota!!!!

Now that I have some kind of baseline to work from, in terms of power expectations, I will have a better idea of what it's capable of. I am going to tune it to the max when the season starts, and if it comes up way short, get that cam out of there, angle cut the heads for more comp and throw in a lunati or UD cam.

Thanks guys. Any other comments on general track tuning and a good place to start (for timing and jetting) for next year are appreciated, though I know it's a matter of "test and tune." :)
 
Discussion starter · #16 ·
Chris,

I will start at 38* and work on the jetting. I don't expect to make a ton of hp with it. I would like something close to 400, get everything dialed in, and then I can add the 150 shot and that will get me to as fast as I can go without a roll bar at my home track. I am goig to tune NA to the max first, of course.

Thanks!
 
#19 ·
mr 4 speed said:
Scott,I run 74/84 in my Holley 750..motor (454) seems to like it.
Click to expand...

I run the same jetting in my 750 Holley 3310 vac sec and it seems to run great. There is also nothing wrong with that cam...its the same one I run in my mild 408. I do have the solid version though(XS274S). With the vac sec carb and 3.55's it runs 7.65 at 89.8mph in the 1/8 with O tuning. I bet your combo has a ton left in it. Did you degree the cam in???
 
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#20 ·
yes,no rear powervalve. This is a 3310 750 v/s
I also have a 750 double pumper that I use from time to time that has 73/83 jetting w/no rear powervalve.
Motor likes both carbs and for some reason the 3310 has a hair more MPH in it at the track but the double pumper "feels" like more fun on the street.
 
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