How much does average guy leave on the table vs. pro in mundane build?

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Calypso
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Re: How much does average guy leave on the table vs. pro in mundane build?

Post by Calypso »

Not takin away from meticulous home builds and experiments I’m partial too. How about stuff like valve and seat angles which have been optimized with serious testing? That’s a challenge for home builder. Carb is easier but with dual plane there may be reasonable differences. Ignition is easier for wot, but more involved for wider range of operation. Cam of course...
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Re: How much does average guy leave on the table vs. pro in mundane build?

Post by CGT »

Calypso wrote: Thu Jul 05, 2018 2:30 pm That’s a challenge for home builder.
Depending on the situation, the engine shop can have a much harder time doing testing. They have due dates, deadlines and customers to keep happy. That sometimes doesn't leave much time for R&D. A dedicated hobbyist "can" have an advantage here, but not always for sure.
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Re: How much does average guy leave on the table vs. pro in mundane build?

Post by BigBlockMopar »

I don't think the intend of the topic was shop(time) vs hobbyist.
IMO it's more like what would be the difference in engine-output when a pro engine-builder would build an engine for himself during his off-hours, vs when a hobbyist is putting an engine together in his garage.

I think there are many levels of 'hobbyists'. What is average?
Like; would an hobbyist try to (pocket) port heads?
Gasketmatch intake/heads/exhaust?
Polish ports?
CC and equalize head chambers?
Backcut valves?
Think about valve seat angles?
Check rocker-tip alignments?
Installed springheights?
Decide to either or not leave a texture on heads ports if ported?
Use 1.5 to 1.7 rocker ratios on a cam to fine-tune it ot even go for a properly ground custom cam with self-chosen lobes?
Use thinner rings?
Tune bearingplay to be used with a certain oilweight?
Consider max. usuable SCR for the fuel used, or even consider port flow?
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Re: How much does average guy leave on the table vs. pro in mundane build?

Post by Brian P »

I suspect the bigger difference will be that a "professional" (who actually knows what they are doing ... not all who claim that, actually are, but let's leave that whole issue aside) should know which parts to pick in order for the whole package to work together, while the average home mechanic won't have enough experience to know which cam, which head, which valves, which intake manifold, etc.
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Re: How much does average guy leave on the table vs. pro in mundane build?

Post by rfoll »

I want to say that decking is something the average guy will not do, but a pro would always at least check. I recently did a quickie rebuild with some more serious work to follow later this year. The deck on the left bank only varied about .003" from front to back, but the right side averaged .015" taller than the left, and about .005 front to back. That's enough to make a measurable difference.
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Re: How much does average guy leave on the table vs. pro in mundane build?

Post by steve316 »

If you don't have the labor cost on the hobbyist; with the same budget. The pro may not have as large of gain over the hobbyist.
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Re: How much does average guy leave on the table vs. pro in mundane build?

Post by andyf »

The answer could be most any number. I've seen a lot of junk that came out of professional shops. Just because someone owns a machine shop doesn't mean they actually take any care when building the engines. There are a huge number of "recently rebuilt" engines that come in the doors of the shop I hang out at. So I give the average pro zero advantage over a home builder who actually pays attention.

Best case scenario is the engine lands at a shop where someone has a bunch of experience with the same combination and has a collection of tools, fixtures and parts for that build. In that case the pro can build the engine in a faction of the time that a home guy would take and the pro engine will probably run smoother, last longer, leak less, and maybe make a tickle more power even if the same parts are used.
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Re: How much does average guy leave on the table vs. pro in mundane build?

Post by jeff swisher »

I had a few friends that work at different machine shops and one said to me do not bring your stuff here as you are too picky on clearances and we can't get you there as well as another machine shop that he mentioned.

I used to check everything after I got my block and heads back from the machine shop until I went to the one that buddy suggested and I checked his work 3 times and it was spot on.

I am maybe an over the top home hobbyist.

I do have the block square decked and rods and crank equalized and clearances ground into the crank that I feel is what I need.
Torque plates are a must and many times a bit of overbalance I like 7000+ rpm.
Valve angles are played with along with some fancy rounded back cuts and regular angle back cuts.

Everything mentioned is done along with other stuff like polished beams and using a stretch gauge to torque the rod bolts.
Yes file fit rings and certain cylinder wall finishes are used.

If the machine shop uses one of those hand held bore machines that references or sits on the deck I will pass.

I am very picky as to what I want.
I have built enough to know what I want and all were built for me or buddies.

One 355" was built with TQ plates balanced and all the other good stuff ..indexed and all.
It got a set of $65 cast flat tops 345NP and some 1978 2 barrel 305 heads with 1.72-1.50 valves that i did a rounded back cut and lapped the stock valve job.
110 seat pressure springs and a 280H magnum cam and tunnel-ram and 2 600 cfm carbs
The tunnel-ram had that very large plenum TR1YX 12" tall.

TH350 and 456 gears the converter stalled to 2200-2400. that stupid junker headed thing went 12.51 @ 111 MPH.
3300 LB 1978 Nova. Shift at 6700rpm.

No tricks. but I do feel that was decent.
Later I stuck some 601 heads on it 1.94-1.50 valves and 292H and it went 11.94 @ 115 MPH.
If my buddy would have played with shift points it may have went quicker .. but he just shifted all gears at 7400rpm.

We beat up on a bunch of vehicles that had way more and built by good shops.
Does not prove anything except maybe the other guy can't drive or tune or maybe the exhaust was choked off.
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Re: How much does average guy leave on the table vs. pro in mundane build?

Post by paulzig »

CGT wrote: Thu Jul 05, 2018 2:47 pm
Depending on the situation, the engine shop can have a much harder time doing testing. They have due dates, deadlines and customers to keep happy. That sometimes doesn't leave much time for R&D. A dedicated hobbyist "can" have an advantage here, but not always for sure.
A hobby DIY guy could try stupid stuff, the pro builder cant experiment with a customer build they need something safe and proven.

Would a pro shop give a guy 50° seats and 20 degrees exhaust split on the cam without having tried it before? Even if they did, the customer would might be hesitant because they see something they havent before.
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Re: How much does average guy leave on the table vs. pro in mundane build?

Post by David Vizard »

Calypso,

Bit of a difficult question to put in precise terms but I think I see where you are going with this. Would it be fair to say the you are looking for some kind of output number that would qualify a pro build versus a an enthusiast just doing a good assembly job of the parts involved. If so I have some real live examples I can relate as during my 50 plus years I have had to fix quite a few decently built but insufficiently detailed and with a few parts spec error motors (mostly in the cam and carb department).

With small block Chevy's and Fords that I have had on the dyno and subsequently gone through because the builder (some pro) was disappointed we are talking 30 - to as much as 100 hp. With BB Chevy's the gap was much bigger. 50 to 125 is about the average in such situations but on a couple of occasions I have seen near 300 hp on a well assembled but poorly speced BBC build.

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Re: How much does average guy leave on the table vs. pro in mundane build?

Post by KnightEngines »

I did one last year, 355 chev, professionally machined & put together at home - nothing wrong with it, was a good enough motor, made around 420-430hp.

I went through it & re-used almost all of the parts, only things I changed other than stuff like rings & bearings were camshaft, intake manifold, intake valves, intake rockers, valve springs & sump.

I ported the edelbrock heads & upped the intake valve size a little, switched out the 1.5 ratio intake rockers for 1.6, had a cam sft ground for it & swapped the performer rpm air gap intake for a strip dominator.
Milled the block to zero deck, milled the heads a little to bump comp & put it back together set up nice.

It picked up a solid 70hp, idled rougher but drove better (tighter lobe centres + more duration), turned 1000rpm more before it fell over - owner was giddy, turned the car from sorta quickish to genuinely quick.
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Re: How much does average guy leave on the table vs. pro in mundane build?

Post by ProPower engines »

I was asking about bore and stroke options such as a 4.125 bore 3.330 stroke combo.
The OP never clarified any parameters but 350ish displacement.
That is in the 350ish range but the average quality head would do better on a larger bore then a 4.030 bore.
There is other variables like cam and LSA rpm range etc that was not clear.
But I don't thing a larger gain could not be had with the given parameters mentioned above.

Even at 10.5-1 the potential is better then a common 4" bore 3.480 stroke and 5.7 rod with any head.\

And a higher RPM potential to make power in with the larger bore
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Re: How much does average guy leave on the table vs. pro in mundane build?

Post by FuelieNova »

Just thinking out loud... maybe the better question would be which would last longer. I have seen a lot of home builds that make power initially but the engine doesn't last as long as expected due to assembly technics, accurate blue printing etc.
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Re: How much does average guy leave on the table vs. pro in mundane build?

Post by oldjohnno »

What about the tune? I suspect there may be just as much if not more variation in power output due to differences in the quality of the tune. How many home-built engines never quite reach their potential simply because the jetting and spark curve etc. was never fully optimised. How many cars have you seen and heard that were plainly over/under fueled and or had other other problems like timing, gearing, convertor choice. I think tuning may have more effect on output than say chambers that weren't exactly equal in capacity. One disadvantage most home builders have is the lack of easy access to a dyno.
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Re: How much does average guy leave on the table vs. pro in mundane build?

Post by CGT »

paulzig wrote: Thu Jul 05, 2018 11:58 pm
CGT wrote: Thu Jul 05, 2018 2:47 pm
Depending on the situation, the engine shop can have a much harder time doing testing. They have due dates, deadlines and customers to keep happy. That sometimes doesn't leave much time for R&D. A dedicated hobbyist "can" have an advantage here, but not always for sure.
A hobby DIY guy could try stupid stuff, the pro builder cant experiment with a customer build they need something safe and proven.

Would a pro shop give a guy 50° seats and 20 degrees exhaust split on the cam without having tried it before? Even if they did, the customer would might be hesitant because they see something they havent before.
Exactly, or a street short block that rolls over at 6lbs of torque(special needs)? More freedom, less consequence.
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