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

[Calypso]

Hope I wont get shot down for too vague a question, but I'm curious with all the years of expertise available at this forum...

Consider a scenario where an average guy puts together a middle of the road 350:ish engine for a full exhaust street toy with 3.50 gears and regular headers. Average aftermarket heads, dual plane intake, roller rockers on studs, catalog cam "known" to be reasonable for the application (hydro roller or solid flat), off the shelf forged pistons, 4150 "performance" holley or some more colorful well marketed variant of it and aftermarket ignition & distributor.

Then a seasoned pro with prior, in depth, knowledge of the same heads, intake and surrounding parts builds the same engine to his specs. Setting the clearances & block prep, free choice of piston and rings as long as he can sell it at off the shelf price, his own proven hone job for the rings, his choice of valves (also sizes as long as new seat inserts are not needed) and seat & valve angles which have been well researched before, but now only done to the spec without porting, his carb or his choice of carburetor extensively tried before with distribution, calibration, atomization mods. Maximum 1 inch spacer of his choice that still allows hood clearance with a drop base filter. His choice of distributor calibrated on the machine to a known good curve. Custom cam for the application with springs. His choice of accompanying parts like rockers, damper, coil, ignition box etc.

Then a short dyno tune to break in, verify jetting and ignition, without playing with cam advance or lash loops etc.

How much difference in performance would you expect to see in a build like this, where you applied your hard earned knowledge in areas most average guys overlook and might even be disappointed seeing no pro-porting for bragging rights?

Edit: average guy engine was 10.5:1 and uses 93 pump gas. Same gas for both with compression open allowing for safe operation as long as the tune is not tampered with and everything properly maintained.

[ProPower engines]

Depending on who supply's all the required parts and if there is no limit to several things like compression rod length crank stroke and bore size header type top rpm limit etc for a sm blk to lets say 360 inches max could be 200 hp+ depending on intended purpose or just bragging rights

[Calypso]

Lets say the stroke and bore size would be the same and the valvetrain should be trouble free for 20k miles on the street. And the builder gets the parts he likes to use, but nothing "special" like Jesels, titanium parts, belt drives etc. Header would be the same "catalog" part for the chassis.

The idea being not an engine masters type all out, but something you could build rather easily leveraging knowledge from previous efforts using quality parts, but still staying reasonable with parts and hours (for yourself).

[AA Performance]

Depending on who supply's all the required parts and if there is no limit to several things like compression rod length crank stroke and bore size header type top rpm limit etc for a sm blk to lets say 360 inches max could be 200 hp+ depending on intended purpose or just bragging rights

I think he is referring to bolt on shelf parts with no port work. Just looking into the small detail that distinguishes the amateurs from the professionals. I doubt that it would come anywhere near the 200+ HP. Supplying parts should have no impact as they should be the same for both engine builders.

[midnightbluS10]

I wouldn't expect anymore than a 20-50hp difference. We're talking an average 350 built by your average car guy vs the same 350 built by David Vizard, for example, using all of his own preferred techniques, prep, etc... Or even someone following DV's guide step by step. Honestly, I wouldn't expect there to be that much of a difference. Especially not 200 hp worth on a estimated 400hp build.

[blykins]

I specialize in Ford FEs and Clevelands and have found that these engines are really responsive to the correct camshafts.

I sent a custom camshaft to a guy running a 408C. His builder had used a custom solid flat tappet camshaft combined with insufficient valvetrain parts. I picked him up .4 in the quarter with another solid flat tappet cam (and correct springs) and he still drove the car an hour each way to the track, running power brakes.

Another guy had a 428FE and was running a Comp 294S. I sent him a smaller custom camshaft and he picked up 27 hp and 35 lb-ft on the dyno. Peak hp rpm was 100 rpm lower with the new camshaft.

I think the majority of any horsepower left on the table is based on the experience level of who's picking the parts. It could be 80-100 hp in some cases. How many DIY'ers pick a cam by looking at the notes at the bottom of a cam catalog page?

[houser45]

50+\- And thats if the Diy picked a somewhat close camshaft, if they are off on the cam, which usually ends up with too much @.050 it could be close to 75-100

[Dragsinger]

Thoughts,

*I realize the question is just a "what if" situation because the variables are simply all over the map. The old "ask a 100 people"

*Then consider this, builders with knowledge gained that knowledge with experience and experimentation. All experts were beginners at some point.

*For me, gaining a lifetime of experience was a satisfying journey.

*I think the better question is, "what can I learn from this happening?"

[rfoll]

I never put a set of heads on an engine without some pocket porting and cleanup. There is a lot that can be done with a 30 minute investment of time. I'm sure any professional could do a much better job than me in 30 minutes, but when using stock castings its hard to not make some improvement. The quality of some of the newer and aftermarket stuff changes that picture in favor of the novice. I fully agree about cam selection, It can make or break the whole project. There's a pretty good chance that tuning what you built will have more impact than anything else.

[Calypso]

Apologies for the generalized type of question which would really need to be closely defined for accurate answers. The intent was not to troll the board into a meaningless speculation, but to get a ballpark idea what you're likely to miss, when you just don't have the experience that is hard to gain without being a pro in the business with years under the belt. I think hp in several tens is very impressive, especially when you could expect that to be combined with better reliability and driveability.
I got help from a very experienced pro in this forum picking cam and some other parts for two very mild resto type of builds. The other car is done and behaves and runs way better than I expected for what it is. The owner is seriously concerned about speeding tickets, because the combo loves to accelerate and run at 100mph and is enjoyable for everyday use in summer.

Just got me thinking what someone who really knows the combo and puts the effort in the details based on experience could rather easily gain in relatively small effort, once all that knowledge has been acquired through whatever it took. I'm not that guy, but I think there are many participating the board. Appreciate the responses I've got.

[Jim2527]

Care if I rephrase?

If a pro buys all the parts out of GM’s catalog for a ZZ6 or CT400 and does the works.... full blueprint porting etc... How much more HP would it make versus myself who would simply open the boxes and bolt it together?

[novadude]

So when you say "pro build", I assume you are talking about good practices like:

Equalizing deck heights and optimizing quench / squish clearances
Degree-in the cam
Optimizing pushrod length / valvetrain geometry
"blueprinted" clearances
etc
etc

Are we to assume that the home builder won't do any of this and will just bolt together parts with nothing more than a torque wrench?

[jeff swisher]

Before your last question was posted I wrote.

I am an average guy and I have experimented with a lot of small tweaks . the one that i found to make the most HP difference was piston to wall clearances.
My first 350" built many years ago i had it set up with cast pistons with .0015" clearances.I did not ask for that but the machine shop set it to that not knowing me or how I run my stuff.

I later went with .0045 clearance with cast pistons on the next build with the same cam and heads.
WOW I gained 1000 rpm on shift points and it ran cooler and drank less fuel.
I later built one at .0035" and it ran as well as the .0045"

But those were long skirt old school pistons and new short skirt may be different.
I have done things to my cylinder heads that a professional shop said was a big NO NO like port the venturi out of the ex port..But in my testing the car picked up power everywhere and lowered ET.

It is what it is.
The tune will net you a lot also.. never forget about that.
Buddy thought his 355" was spot on he had made maybe 12 passes one evening down the 1/4 mile track and came to me and said that is all there is in it .. that is as fast as she will go.

I took the top off his carb and rejetted it as he kept putting larger and larger jets in it.

I told him go make one more pass.
He came back and said it went 4 tenths quicker and asked what I did to the carb.

Lots of little things make a difference.
I have raced against "Professional" built stuff with way more cubes and cam than me and beat the pants off of them.
Was it the tune or was that professional built deal for longevity with .0015" piston to wall clearances.
Or could the other guy not drive?
Fun stuff for sure.

[CGT]

I'd throw 20hp the home guys way. Hobbyist's lives matter!

In all seriousness, their are large discrepancies between "professionals" and also large discrepancies between "diy'ers"

MOO

[PackardV8]

It's the old "speed costs money; how fast can you afford to go?"

If a pro square decks the block, equalizes rod lengths and big end diameters, line hones the mains to within .0005", hones cylinders with a torque plate to match each piston, file fits ring gaps, balances to 1 gram, then dyno tunes carb and ignition, how many hours of shop time will that 20-30 hp cost?

If the pro just specs his secret sauce cam, that's maybe some more, but then, who's to say our average guy didn't use a desktop dyno cam program or DV's system which led him to pretty much the same numbers? Easy to use examples of the average guy who guessed wrong, but that's not a given.