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Old 07-03-2019, 07:25 AM
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How Much HP?

My engine is finally going together and Id like to hear from some of you more knowledgeable guys what you think the hp is going to be. Here's what Ive got:

94 351W with a stock deck height of 9.503. Squish/quench is .066. ProMaxx aluminum heads with 60cc chambers, 2.02/1.60 valves and a 175 runner. Static compression is 9.5:1. Howards hydraulic roller cam with .225/.231 at .050 with .533/.544 lift. LSA is 108 and centerline is 104. Typhoon intake with a Holley vacuum secondary 750. I havent decided on headers yet but considering long tube Hookers with 1-5/8 tubes 28 long into 3 collectors.

So, what do you folks think I'll be looking at for hp? Also, how much difference will shorty or mid length headers make?

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Old 07-03-2019, 08:28 AM
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Should do 425-435 HP, around 420 Ft.lbs. HP peak up near 6500 rpm, torque peak at 4500-4600 RPM. Might be as good as 440-450 HP, heads are pretty good.

Long tube headers promote more torque below the torque peak, with not loss of higher rpm power. Mid and short headers give up that lower rpm torque but don't add any HP at high rpm to offset that loss, so long tubes are always the better way to go if you can. 25-40+ft lbs lost down low, with the worst loss lowest in the rpm band 2500rpm-ish.
Only reason mid and shorty's exist is ease of installation and/or connection to factory exhaust.

Curious as to why you didn't source a thinner head gasket to tighten up the quench clearance to something closer to ,035-.040"??
Especially with aluminum heads, as the increase in compression ratio that would also result could have added another 25 Hp between both the added comp and the quench factor with no risk of increasing detonation tendency.

Other than the wide quench it seems like a really good build. Match it with a manual trans or a tight 3000 stall 9.5-10" converter'd automatic and at least 3.50 rear gear and it ought to be a blast.
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Old 07-03-2019, 07:24 PM
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Eric,

Thanks, you were one of the guys I was hoping would chime in. I wasn't thinking 425 hp. I thought it was going to make around 350 hp. I went with a .041" gasket for two reasons; I was trying to keep the static compression below 9.5:1 and I was keeping an eye on piston to valve clearance. For what it's worth, it's also going to have Scorpion 1.6 roller rockers.

If it's going to make 425 hp then I'm on thin ice. It'll be backed up by a T-5 and an 8" rear. They'll both be challenged with that much power. It's not going to pounded super hard but it'll be "exercised" occasionally. So, I guess it's going to have "enough."
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Old 07-03-2019, 09:57 PM
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I think you're looking well into the plus 400 mark. Everything looks pretty good, the heads probably biased toward the needs of a 302 with pretty tight chambers and smallish ports.

The squish/quench is pretty wide. On one hand aluminum heads are more tolerant of this since they move heat faster than iron, but on the other hand at the same time a tighter clearance results in greater mixture agitation. If this is a slow turning highway cruiser keeping the agitation up by mechanical means is more important than for a fast turning race motor where frequent WOT operation uses the high dynamic of the mixture flow to do that function. To some extent the 175cc port will bring that kind of action on sooner in the rev band than a larger port.

Bogie
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Old 07-03-2019, 11:45 PM
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Quote:
Originally Posted by Molon Labe View Post
Eric,

Thanks, you were one of the guys I was hoping would chime in. I wasn't thinking 425 hp. I thought it was going to make around 350 hp. I went with a .041" gasket for two reasons; I was trying to keep the static compression below 9.5:1 and I was keeping an eye on piston to valve clearance. For what it's worth, it's also going to have Scorpion 1.6 roller rockers.

If it's going to make 425 hp then I'm on thin ice. It'll be backed up by a T-5 and an 8" rear. They'll both be challenged with that much power. It's not going to pounded super hard but it'll be "exercised" occasionally. So, I guess it's going to have "enough."
Keep the T-5 away from 1st gear holeshots along with 2nd and 3rd gear tire chirp "power shifts" and it will live a decent lifespan. Get a good aftermarket shifter, not that crap mounted in rubber stock piece.
You might look into a ClutchTamer to soften the clutch hit if you feel the spirit of the moment might overpower your good sense. Original universal version.
CLUTCHTAMER.COM
8" is much the same, it will live if not hammered....but to me the fact you can put 8" axles and brakes into a 9" means you really ought to get a 9" housing and put the money you would spend on gears, carrier, and posi in it that rather than an 8". Do the housing with the correct bearing ends and the 8" brakes and axles bolt right in.
Otherwise, and 8.8" conversion might be a better idea. than the 8" on strength
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Old 07-04-2019, 06:17 AM
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Glad to hear from you too Bogie. Thanks. My intention with this build was not to make maximum hp but to make about 350 hp without sacrificing driveability, reliability or requiring constant tuning. I made the decision not to increase compression by decking the block for the same reasons as I chose the .041" gasket. Besides, the decks were dead flat. Other than not obtaining maximizing mixture agitation at cruising speeds are there any other implications to having a wider squish/quench?

The T-5 has an MDL shifter on it. The Clutch Tamer sounds like a good idea also. I recently completed a total rebuild of the 8" including a new aftermarket posi but I hear what you're saying about stepping up to a 9". If I thought I was going to end up with 425 hp I wouldn't have wasted my time on the 8".

Thanks again for feedback guys. You've been very helpful.
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Old 07-04-2019, 05:56 PM
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Mixture agitation has a lot to do with detonation resistance, in the industry this is called mechanical octane. Getting to a .040 to .035 squish\quench clearance makes the burning fuel act like it has about 5 octane numbers more than it tests for. Ford built some very detonation sensitive engines like the M400 with about .080, these engines are difficult to tame for modern fuels under street use let alone high performance, which is too bad as otherwise they bring a lot to the table.


Agitation also has a lot to do with efficiency in terms of power produced for fuel consumed. A highly active chamber is a more efficient chamber getting not only more power but getting lower fuel consumption.


As I said earlier you get kind of stuck with a 351 using heads with chambers really sized for 302's as this drives the compression up on a 351 which then needs to be solved with piston crown shape such as a D dish or stepped crown otherwise you get into trying to control compression with increasing the squish\quench clearance which brings on increased sensitivity to detonation and higher fuel consumption for the power produced. A place hot rodders get into trouble is aftermarket heads are much more honest about their volumes, OEM production heads are mostly larger in volume than advertised as are piston reliefs which results in the very common finding that factory compression ratios are considerable less than advertised, this is done mostly to protect their warranty account from lead foot drivers detonating the engine to death.



None of this is say this engine won't work well, it will. It just won't be as good as it could have been but to really know that you would have to have built one of each way and ran them against each other. Something to keep in mind if you're ever invited to build a motor for Engine Masters.

Last edited by BogiesAnnex1; 07-04-2019 at 06:15 PM.
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Old 07-04-2019, 06:49 PM
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I love it I'm trying to tag on an edit and it blows me out, don't know if it's HRF or my suped up Dell doing weird things.


I was going to comment about the T5 and the 8 inch. The killer of gears is torque not horsepower. To that end a slipper clutch will help both as it prevents sudden shock loads, kind of like having a high stall converter in that regard. I have a friend that runs a Chevy 4.3 through an old 80's era Mazda pickup's original T5 he uses an oil which I think he gets at Ford that he claims is made with golden unicorn tears based on its cost. The stuff does work at minimizing torque shock loads. He drives with a mighty heavy foot, scares the crap out of me to ride with him. I met him when he was 14 or 15 and I was 40, he was crazy then and that hasn't changed much in the intervening 40 years.


Bogie
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Old 07-04-2019, 07:03 PM
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Quote:
Originally Posted by BogiesAnnex1 View Post
I was going to comment about the T5 and the 8 inch. The killer of gears is torque not horsepower. To that end a slipper clutch will help both as it prevents sudden shock loads, kind of like having a high stall converter in that regard....

Bogie
We're on the same page....that's why I recommended the original ClutchTamer, as it allows you to turn any clutch into an adjustable slipper clutch, with the added big plus you can do it right from the drivers seat, in 3 seconds, just be turning a knob!!

It is an ingenious product that really need a lot more exposure across the hot rod and racer ranks. Brilliantly simple idea!!
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Old 07-04-2019, 07:09 PM
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Thanks again Bogie and Eric,

You've got me thinking of going with a thinner gasket for efficiency and detonation resistance rather than additional hp. Easy enough to swap them out if they don't work for me. Getting down to a compressed thickness of .020" or .025" is pretty thin. Is this a laminated gasket? Recommendations? I'm in for the slipper clutch for sure.
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