Home » Public Forums » GMCnet » Big increase in power in my 1977 403ci engine (A mechanic increased my engine power, significantly, in 2 simple ways)
| Big increase in power in my 1977 403ci engine [message #318327] |
Thu, 01 June 2017 13:27  |
DavidJForjan
Messages: 65
Registered: August 2016
Location: Tularosa New Mexico
Karma: 2
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Hey everyone. This is an FYI post only. No questions. This info may be very helpful to others because a genius mechanic increased my horsepower considerably; very considerably. And he did this without any new parts. It's quite amazing actually. But it's true. I now have ALOT more power from my 403ci engine. Here's what he did (keep in mind this guy restores and services race cars). First he changed the arrangement/hookup of the vacuum hoses. He didn't add any, he just rerouted them. He said "Dave I want to connect the vacuum hoses the way we used to connect them. The other mechanic connected them the way people do nowadays. If you want I'll re-route them and you'll get more horsepower". And I did, just by him hooking up the vacuum hoses differently. I don't know how he changed them, but maybe one of you reading this post will understand and explain.
The second thing he did is adjust my timing differently. This was a wild experience. He had me start the engine, with the emergency brake on, and told me to hold down tight on the foot brakes, and put the transmission in drive. Then HE revved the engine with the throttle in the engine compartment, and revved it really really high. I had all I could handle just standing on the brakes to keep the motorhome from lunging forward. Picture this, he's revving the engine all the way up, while it's in Drive, the emergency brake on, me all but standing on the foot brakes, so the motorhome is trying so hard to lunge forward, but it can't, and with all these opposing forces fighting each other, the motorhome started shaking - violently. I almost lost it once and the motorhome almost got away from me the thing was trying so hard to go forward. And at this point of maximum forces, THAT'S when he set the timing.
I'm not a mechanic so I don't understand all that's involved. The mechanic before him was a young guy and he tuned and timed the engine when he put in new plugs and wires. Rick, the genius (he's about 55), changed the vacuum hoses and set the timing as I described above - and sure enough I have alot more power from that 403ci engine now.
Maybe all this is common knowledge and you all will understand what I've said. But this was all new to me and I have alot alot more power now. Even sounds different. Almost like a jet engine.
FYI to those who understand or want to understand. I look forward to comments from all you experienced folks out there.
Be well. Thanks for listening
david
David J. Forjan, 1977 403 26' Palm Beach, glad to have the 3.70 Final Drive and pork chop for level front end, Tularosa New Mexico
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| Re: Big increase in power in my 1977 403ci engine [message #318329 is a reply to message #318327] |
Thu, 01 June 2017 14:07  |
Chris Tyler
Messages: 458
Registered: September 2013
Location: Odessa FL
Karma: 7
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What he was doing was a version of power timing- an other words advsncing the timing under load until it pings or power drops.
Ive seen it done this way. However, its VERY dangerous to do- and there is no way Id try it on a 12k# vehicle with marginal brakes.
A much better method involve setting the timing based on driving performance- which is sometimes difficult to quantify.
Not sure how he routed the vac advance, but probably bypassed the TCS switch. Vac advance is more about cruising and idle.Personnaly, I prefer spark ported vac advance rather than full time, and an adjustable cannister to see what it likes under cruise
If he advanced the distributor, he increased both the initial and total timing. Unless you limit the centifigul advance mechanism.
What I have found is that most engines like more initial advance while limiting the total, and quickening the advance curve with lighter springs.But it is VERY easy to get lost if you dont know what you are doing
There are more than one ways to skin a cat {11 per Mr Spock, as I recall] and the bottom line is, if the setting work for you great. But you should probably use a dail back to zero type timing light and record the inital and total with the vac advance disconected so that you can get back to those settings in the future. However, my prediction is that when you drive it on a hot day uphill, its going to ping if not detonate after setting it this way.
What most will recomend is a patterson distributor and his settings, and call it a day.
76 Glenbrook
[Updated on: Thu, 01 June 2017 14:08] Report message to a moderator |
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| Re: Big increase in power in my 1977 403ci engine [message #318348 is a reply to message #318327] |
Thu, 01 June 2017 21:38 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Both things he did had to do with timing. Vacuum and initial. I hope you don't need new engine mounts now. You may also experience "hot start" issues if he over did it. Better to set on a road course, adjust and drive more etc til you narrow the tuning window until you are just bellow ping threshold in ALL conditions. If he set at WOT where vac drops, you will have pinging at part throttle tip in where loads are high along with still having vac signal to the advance pot adding advance.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Big increase in power in my 1977 403ci engine [message #318377 is a reply to message #318327] |
Fri, 02 June 2017 16:08 |
kingd
Messages: 592
Registered: June 2004
Karma: 2
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I wonder how much Manny cringed when he heard what this guy did. I'd bet the tranny fluid
temps were sky high. If Manny reads this would you choose to comment?
I've read that really HOT tranny fluid has a VERY short life, like in minutes
DAVE KING
lurker, wannabe
Toronto, Ontario, Canada
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| Re: Big increase in power in my 1977 403ci engine [message #318390 is a reply to message #318327] |
Sat, 03 June 2017 07:27 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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This is the equivalent of using "Locked Rotor Amp Draw" to determine how many Amps a running air conditioner compressor actually draws. A range of driving conditions is way more accurate. The final setting should be just a slight hint of ping in maybe one of the RPM/load conditions and not the others.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] Big increase in power in my 1977 403ci engine [message #318417 is a reply to message #318377] |
Sat, 03 June 2017 18:14 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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The Chevrolet P-30 Chassis Owners' Manual says in its transmission appendix
that stalled torque converter will heat the ATF at a rate of 1*F per
second. It also recommends a maximum temperature of ATF at the torque
converter output of 350*F, and states that at 300*F, parts begin to warp
and seals to melt.
Considering that the ATF was probably at 150*F at the start of the
exercise, 200 seconds of mistreatment should reach the maximum outlet
temperature. Since the coach was not moving, the ATF cooler probably
wasn't reducing the temperature much before returning the fluid to the
transmission, meaning the limit should be 300*F, reducing that to 150
seconds.
At 300*, ATF has a service life of about 1500 miles.
I think I'll use another method.
Ken H.
On Fri, Jun 2, 2017 at 5:08 PM, Dave King wrote:
> I wonder how much Manny cringed when he heard what this guy did. I'd bet
> the tranny fluid
> temps were sky high. If Manny reads this would you choose to comment?
> I've read that really HOT tranny fluid has a VERY short life, like in
> minutes
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: Big increase in power in my 1977 403ci engine [message #318497 is a reply to message #318327] |
Mon, 05 June 2017 06:49 |
Mike S
Messages: 82
Registered: February 2017
Location: Vero Beach, FL
Karma: 3
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I too tuned my engine that way. The shuttering was probably the trans plates slipping.
Mine ran great after the power tune!
And after the 120 miles that the trans lived, the new trans that my wife picked up at Ken's works great also.
Mike
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| Re: [GMCnet] Big increase in power in my 1977 403ci engine [message #318538 is a reply to message #318521] |
Mon, 05 June 2017 15:06 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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David,
Frequently posts here receive a lot of feedback that's not necessarily
critical, but could easily be taken as such. Yours is one of those.
Some, perhaps many, or even most, of us here understand the procedure that
Rick used to set your timing. But just telling how he did it doesn't really
"cover all the bases". I'm sure that in the back of Rick's mind were a
number of factors to consider that were not obvious to many of the
readers. Among them was probably the dramatic ATF temperature rise being
generated (he may have been "watching the clock" without telling anyone).
And the potential for disaster if brakes slipped (he may have even
positioned you in a clear area without mentioning why). And perhaps other
factors no one among us has thought of.
Frequently someone of us will try to divulge such background information
for the benefit of those who may not recognize it. That is, without meaning
to be critical, many of us sometimes make comments just to be sure that
everyone's aware of non-obvious considerations. Hopefully, doing so will
prevent bad consequences for the uninitiated.
I know of people who refuse to post here because they've been "insulted" by
such comments, even though they're really a part of the extreme value of
this forum: Broad knowledge and experience are shared freely without
"finger pointing". It's rare that anyone is really chastised here, 'tho'
it may sometimes seem so.
Ken "Learning something new every day" H.
On Mon, Jun 5, 2017 at 12:41 PM, David J. Forjan
wrote:
> ...
> Maybe, just maybe, Rick, who builds and restores and repairs show cars
> and race cars in El Paso TX, knows what he's doing. Have to
>
> consider that.
>
>
...
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Big increase in power in my 1977 403ci engine [message #318548 is a reply to message #318538] |
Mon, 05 June 2017 17:28 |
DavidJForjan
Messages: 65
Registered: August 2016
Location: Tularosa New Mexico
Karma: 2
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Thanks Ken, I appreciate your point and I live by it. My previous post was not meant to be sarcastic, although now I can see it could have been taken that way. My point was that, despite people's concerns and opinions, valid ones to be sure, that somehow Rick made this work, and for the benefit of everyone, to point out maybe it's possible, and as such, there's a tremendous benefit. I have lots more horse power now. Lots. And from a 403ci. And it was worth making my point, helpfully not to offend anyone. I don't take criticism or advice negatively, not for a long time. I posted this topic for the benefit of discussion and education, for me and others if they can learn too. I also try to learn every day, being open to everyone's opinions and advice, otherwise I would have remained as stupid as the day I was born. 
Thank you for your wisdom in raising this issue. And if you follow my posts you'll see I am always grateful for people taking the time and educating me and others with their experience.
Thanks. David
David J. Forjan, 1977 403 26' Palm Beach, glad to have the 3.70 Final Drive and pork chop for level front end, Tularosa New Mexico
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| Re: [GMCnet] Big increase in power in my 1977 403ci engine [message #318567 is a reply to message #318564] |
Tue, 06 June 2017 12:08 |
Keith V
Messages: 2337
Registered: March 2008
Location: Mounds View,MN
Karma: 0
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I'm glad you got your timing better.
Just to be my usual doubtful self I'm of the thought that your increase is getting the engine back to where it should be. It's unlikely that your engine is performing significantly above design and likely that is used to be poorly tuned and running significantly below design. The change from below design to par or slightly above design definitely does occur , but it's very hard to exceed design by much.
a good total timing / distributor recurve would also get you there. It's 6 of one 1/2 dozen of the other. with the total timing being the more deterministic of the two.
nothing beats a well running engine.
________________________________
From: Gmclist on behalf of David J.Forjan
Sent: Tuesday, June 6, 2017 10:39:38 AM
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Big increase in power in my 1977 403ci engine
Just one point of reference about horsepower. If anyone has driven over St. Augustin pass, going from White Sands Missile Base over the Organ
Mountains to Organ and Las Cruces, NM you can appreciate this. Before Rick set the timing his way, I had to go over that pass in 1st gear. Now I can
climb that pass and go over in 2nd gear. A rise of 1800 ft. in
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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| Re: [GMCnet] Big increase in power in my 1977 403ci engine [message #318588 is a reply to message #318567] |
Tue, 06 June 2017 16:40 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Keith,
I was thinking the same thing. Being the pedantic bugger that I am I would
have liked Rick to set up the engine as per the MM, let Dave drive it and
assess the HP. THEN work his magic.
Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808
-----Original Message-----
From: Gmclist [mailto:gmclist-bounces@list.gmcnet.org] On Behalf Of Keith V
Sent: Wednesday, June 7, 2017 3:08 AM
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Big increase in power in my 1977 403ci engine
I'm glad you got your timing better.
Just to be my usual doubtful self I'm of the thought that your increase is
getting the engine back to where it should be. It's unlikely that your
engine is performing significantly above design and likely that is used to
be poorly tuned and running significantly below design. The change from
below design to par or slightly above design definitely does occur , but
it's very hard to exceed design by much.
a good total timing / distributor recurve would also get you there. It's 6
of one 1/2 dozen of the other. with the total timing being the more
deterministic of the two.
nothing beats a well running engine.
________________________________
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Big increase in power in my 1977 403ci engine [message #318596 is a reply to message #318567] |
Tue, 06 June 2017 19:07 |
DavidJForjan
Messages: 65
Registered: August 2016
Location: Tularosa New Mexico
Karma: 2
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You're right Keith, nothing beats a well running engine. I must also add, belatedly, that I had the engine tuned and timed (new plugs and wires and distributor) by a professional mechanic before Rick performed his magic (and drove it that way for a couple thousand miles). As for getting more out of a design, doesn't dual exhaust or quad exhaust or headers or turbocharging get more out of the original design? Significantly more too? Granted that those are new parts added on, but also keep in mind that Rick makes race cars perform better, getting more out of those engines. As for just changing the timing, even I can see conceptually what Rick did. He made the engine run best at the point of higher performance; higher RPMs. So when the RPMs are higher, that's the sweet spot of the timing setting (excuse my layman's description). Surprisingly to me, the engine still performs just fine at lower RPMs. And I also get better gas mileage, as he said I would (~11mpg vs.~10mpg - 10% savings on my gasoline bills). As for the proof of the pudding, going up a big mountain in 2nd gear vs. 1st gear is a significant improvement no? With no additional parts.
Personally, I think what Rick did is stunning. And I don't say that because of any ego-trip.
thanks to all of you for your opinions. Be well.
david
David J. Forjan, 1977 403 26' Palm Beach, glad to have the 3.70 Final Drive and pork chop for level front end, Tularosa New Mexico
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| Re: Big increase in power in my 1977 403ci engine [message #318600 is a reply to message #318327] |
Tue, 06 June 2017 19:41 |
Mike S
Messages: 82
Registered: February 2017
Location: Vero Beach, FL
Karma: 3
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One of the coolest things I got to do was build a spark curve for a new motor on a dyno. Hours of holding the motor at an RPM while timing was adjusted at 500 rpm intervals Cool stuff!
I set my timing by the light, and I could tell it wasn't right. Wrong pointer, slipped balancer don't know. I have power timed 100's of boat motors and a whole bunch of car motors. That's easy to do in a boat, under load lift the hatch and have at it. Boat motors run on a linear load curve like dynos do to engines. Motors at light load can take a lot more timing and should have it for mileage.
My point was most have no idea of the condition of there transmissions, and as others said, it can be tough on them.
Mike
Ken, I love your response!
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