L71 L72 427 Running on Pump Gas

[Ted S.]

Re: L71 L72 427 Running on Pump Gas

GM dropped the SHP/FI CR half a point with an extra head gasket in '62-'63 to mitigate detonation, and it worked despite the increase in quench clearance.

Duke,

You keep quoting this. Do you have the engineering documentation as to why they did this? How do you know they did this to purely drop the SCR? How do you know there wasn't a problem in the machining process of the pistons used or the block? You keep quoting ancedotal information, poo poo everything else, and provide no real evidence of anything you're saying other that quoting Taylor whose studies on internal combustion engines ended over 45 years ago.

Please provide some evidence from your vast experience on big block engines. So far you have provided ZILCH!!!! and only made comments on how great your expertise is! Shall we all bow down to the DUKE or is it the KING!!!!!! Or maybe the all knowing ORACLE on internal combustion engines especially Cosworth Vegas!!!!

In consulting we used to use the terms of capacity and velocity to describe the effectivenesss of staff members. We always looked for a balance between the two. If an individual had capacity and no velocity they belonged in achedemia verses the real world. I think I've been corresponding with one of those.

The bottom line is the members of the board can utilize which ever approach they deem fits their situation. I'll keep waiting on those real world examples from you, but I don't think I'm going to hold my breath.

[Michael H.]

Re: L71 L72 427 Running on Pump Gas

Ted,
I was one of the guys who's engine will not run on 93 octane. The engine is on a stand now with heads off. I've measured deck clearance and CC'd one head. The CR values range from a low of 11.32 to a high of 11.59.
This is with a deck clearance that is basically zero and a head gasket compressed thickness of 0.035" My plan is to have Cometic make me a 0.070" head gasket which will bring the CR down to about 10.5. I may do a little chamber grinding to even up the cylinders. Pistons are standard 0.030 over. Engine was professionally built 10 years ago (15-20k miles) and looks great inside.
John McRae 30025

If you use head gaskets that are .070" thick, it's possible that you may run into a problem with intake gasket sealing. The thicker head gaskets spread out the dimension of the intake gasket surface from head to head. (been there)
I don't understand what kind of problem you may have had with the original 11.0-1 CR. Are you refering to pinging?
Were the heads surfaced a lot?
How did you establish the C/R? Were you using advertised piston dome/relief dimensions or did you actually measure the assembled engine chamber volume with a CC burrett?

[Michael H.]

Re: L71 L72 427 Running on Pump Gas

Did you make all the measurements to compute the true as-built SCR, or are you going by the factory advertised value?

Duke

I measured several chamber volumes but I didn't verify piston dome/relief volume. (original GM pistons)
Piston/deck averaged about .010-.015" down as I remember.

If I use 93 octane pump fuel, the engine runs very well but I can't get on it. If I'm going out to seriously play, I use race/aviation fuel.
However, I haven't done that for many years. Been using 93 for a LOT of years and driven that car ALL over this country with no pinging problems.

If someone wants to hot rod one of these cars today, (and I don't understand why they would) then they're going to have to use higher octane fuel. There's no getting around it.
However, for driving like an adult, there absolutely no need for racing fuel, CC burretts, double thick head gaskets or any of those other patches.

Chamber volume and measured C/R are only PART of what makes a few cyl's detonate before others.
Camshaft lobe placement/clocking on the cam itself is another item that raises/lowers C/R or, more accurately, cylinder pressure. Most cams have at least a few lobes that are not clocked correctly. (I have one0

Cyl to cyl efficiency is another. Some cyl's, especially in a big block, are more efficient than others. Long/short intake manifold runners and long/short intake ports do affect cyl filling at anything over about 2500 RPM. This directly affects the cyl pressure.

All cyl's don't operate at the same temp, for a few different reasons. That too can have an effect on the point where detonation begins. Some racing engines actually use different timing for a few cyl's.

Adjusting chamber volume/CR is only part of the issue. Adjusting these numbers so the measured C/R is down to 10.25-1 isn't going to eliminate pingine at heavy throttle with todays fuel.
Changing the vacuum advance isn't going to stop detonation during heavy throttle either. It has nothing to do with it.

If a 11.0-1 big block with a 143 cam can't run decently on todays fuel, it has some other issue.

[Duke W.]

Re: L71 L72 427 Running on Pump Gas

Duke,

You keep quoting this. Do you have the engineering documentation as to why they did this? How do you know they did this to purely drop the SCR? How do you know there wasn't a problem in the machining process of the pistons used or the block? You keep quoting ancedotal information, poo poo everything else, and provide no real evidence of anything you're saying other that quoting Taylor whose studies on internal combustion engines ended over 45 years ago.

Please provide some evidence from your vast experience on big block engines. So far you have provided ZILCH!!!! and only made comments on how great your expertise is! Shall we all bow down to the DUKE or is it the KING!!!!!! Or maybe the all knowing ORACLE on internal combustion engines especially Cosworth Vegas!!!!

In consulting we used to use the terms of capacity and velocity to describe the effectivenesss of staff members. We always looked for a balance between the two. If an individual had capacity and no velocity they belonged in achedemia verses the real world. I think I've been corresponding with one of those.

The bottom line is the members of the board can utilize which ever approach they deem fits their situation. I'll keep waiting on those real world examples from you, but I don't think I'm going to hold my breath.

Take a chill pill, Ted. The double gasketing including the reasons are documented in a TSB, which has been discussed a number of times before.

I've consulted with a number of big block owners on engine restoration and detonation including John McRae's current L-71. I try to get as much technical information on the configuations as possible, but it's tough. Most engines get thrown togther without measuring anything!

I'm sure John will follow up with the results of the thicker gasket, and I would wager that they eliminate the detonation.

Where did you find the picture of me in the Cosworth Vega at Willow Springs and what discipline did you consult in? Engine system engineering?

Most CV owners used to sound just like you quoting various "race engine builders" and hot rod magazine articles and messed up their cars with big cams and Weber carburetors, but they finally figured out after a few dyno tests that I know what I'm talking about when it comes to responsive and elastic road engines. No one has ever shown more torque bandwidth than mine and the few that made more top end power would barely run below 3000 revs. Mine will easily pull from 1000 revs in fifth gear. My engine internals are all OE, as is the Bendix EFI but the cams are reindexed and the spark advance is remapped. CVs also need a low restriction exhaust system. The OE system generates about 15 psi backpressure, which just kills the top end!

I used to kill a lot of name brand sports cars - Ferraris, Porsches, Mustangs, and even Corvettes with the CV at Riverside, The Streets of Willow Springs, and the big Willow Springs track. Most of them took it in stride except the Ferrari drivers! Most of these cars were faster on the straights, but the CV has superb brakes and handling, and the driver might have had a little bit to do with it, too - black car, black helmet, #48 - gotta be Dan Gurney!

Duke

[Michael H.]

Re: L71 L72 427 Running on Pump Gas

(Micheael - I don't think John will have a problem with gasket fit because the block has been decked probably at least .020" and the heads may have been cut, too>0

Where did you find the picture of me in the Cosworth Vega at Willow Springs?

Duke

Ok, that's a different deal if there has been that much material removed from the block and heads. He's going to have to fit the intake anyway.

I dunno on the picture. I was searching around on the net one night and there ya were, at some Vega club meeting.

[Duke W.]

Re: L71 L72 427 Running on Pump Gas

Adjusting chamber volume/CR is only part of the issue. Adjusting these numbers so the measured C/R is down to 10.25-1 isn't going to eliminate pingine at heavy throttle with todays fuel.
Changing the vacuum advance isn't going to stop detonation during heavy throttle either. It has nothing to do with it.

If a 11.0-1 big block with a 143 cam can't run decently on todays fuel, it has some other issue.

We'll see what John McRae reports with the thicker gasket. Changing to full time vacuum advance can elinimate transient detonation because it lowers cylinder boundary temperatures - especially if you demand high load after a period of idling or low speed driving.

Do you know what the nominal deck clearance of a big block is if the crank throw radius, rod length, and piston compression height are all nominal? SBs are .025". I don't have all the data to calculate nominal BB deck clearance. I've asked for the data before, but no one responded.

Duke

[Duke W.]

Re: L71 L72 427 Running on Pump Gas

I dunno on the picture. I was searching around on the net one night and there ya were, at some Vega club meeting.

That photo was taken about 15-20 years ago at a Willow Springs track time event sponsored by the Ferrari Owners' Club/Pantera Club. It was probably taken on the warm up lap of the day's first session because there's no brake dust on the front wheels. The FOC/Pantera Club formerly did two annual events at Riverside, but moved to Willow when Riverside closed down, and the Cobra Owner's Club of America has had two Willow Springs events per year for decades. So I would run two Riverside events and two Willow Springs events per year, plus one or two with the Porsche Owner's Club at Riverside and then The Streets of Willow Springs after Riverside closed.

The photo was published in the November 2007 Hemmings Muscle Machines magazine along with a brief article about my 15 years of running the CV in track events.

I'd like to know and bookmark the URL where you found the photo.

Duke

[John M.]

Re: L71 L72 427 Running on Pump Gas

Michael, Ted, Duke and all,
The original and only problem with this engine is the pinging and the fact that I was just tired of mixing fuel. The car went like a rocket on the 96.5 mix but I never tried to fine tune that to see how low the number could go.
It has the correct pistons, 0.030 over. The block was decked and the heads were milled so I don't think the 0.070" gasket will cause a fitup problem. The deck clearance is basicaslly zero. I'm going to measure dome volume tonight and will report. My claculated SCRs were from about 11.4 to 11.6 on the odd side and I left the numbers at home for the even side but they must be close. If I try to come out at an even 11.0 to 1 and it still pings I won't be happy so the 0.070 was the proposed chioce. The domes look pretty smooth to me, no sharp edges. There are some very charp edges between the chamber and the quench area but how much will smoothing these help?
I'll have all the numbers tomorrow and will be looking for advice.
John

[John M.]

Re: L71 L72 427 Running on Pump Gas

Michael,
I missed the second half of your question. I cc'd the chambers with a burette. I have quite a bit of experience doing this and am fairly confident of the numbers although I have misread the thing a few times. What suprises me most is the variation in chamber volumes. I believe my measurements are within about 0.2 CC.
I'll post all that tomorrow.
John

[Ted S.]

Re: L71 L72 427 Running on Pump Gas

Duke,

My frustration with you is that for such a knowledgeable individual on internal combustion engines you come across very closed minded. You make statements like on the 143 cam intake closing event "I don't know how you came up with this closing point, but it's not even close." and provide no evidence to support your statments. If you had the data it would have been simple to have provided it but since you didn't it would appear you're just making self serving statements to support your ego.

One of your statements in a past post was to the effect that the only real advances that have been made in the last 30 years are the electronics that now are being utilized to control ignition and fuel injection. This simply isn't true. There have been alot of advances in head and more specifically combustion chamber design. Even with the advances in electronics I highly doubt that GM could run the compression levels they're running now without significant advances in their approach to the combustion process. If you'll notice all of the high compression engines being produced today are of a small chamber flat top piston design. This isn't by accident.

My research on high compression pump gas engines began in the late '80s when I started looking at motorcycles that were running significant compression in relationship to what auto manufacturers were putting out at the time. Later you started seeing the auto manufacturers beginning to pump up their compression but still use fairly short duration cams. The auto manufacturers seem to follow a common theme (with a few exceptions) in order to achieve this. Combustion chambers in the heads got smaller, quench area got larger, and domes on the pistons went away. I would venture that the 143 cam would support a higher compression ratio than 11:1 if it was paired with one of the current combustion chamber designs. There are steps that can be taken to move the existing piston and chamber closer to a current design however they're far from perfect.

In addition, you appear to immediately discount anything that comes out of the racing arena when it is convenient, but at times you will suggest something that comes from the racing community. This appears to primarily be done to support your point, which again indicates to me your unwilingness to admit there are other possibilites or it is self serving. Let's be honest, you and I both know that many of the advances in automotive technology came from the world of racing. You can see it incorporated in everything from suspension to engine technology to safety.

You asked about my background, I used to be an R&D engineer designing explosion proof electrical equipment for the petro-chemical industry. Much of the work was designing enclosures to contain the explosion. In that role I used to test my designs with Groups B, C, & D gases and did some testing with dust environments. You learn alot about flame propagation, pressures developed, containment, etc when testing with the most flamable mixtures of hydrogen, ethane, or propane and oxygen.

I know alot of individuals on the board don't have their master's in mechanical engineering but there are many of us that have engineering degrees and/or engineering backgrounds. Like you, I have played with cars, building engines, suspensions, etc since before I could legally drive. Unlike you, I couldn't afford a new vette when I was 16. I started with a '63 bug for $100 when I was 14 and rebuilt the engine with a Scat cam and headers, then a '68 camaro that I built a 327 for, then a V8 Vega with a 350, and on. All of them I wrenched on myself.

If you've read through it to this point that's a credit to you. All that I ask is give some creedence that some of us do know a little something about internal combustion engines either from a theory standpoint or reality standpoint.

Here's the book mark for the article/picture.

http://www.hemmings.com/mus/stories/2007/11/01/hmn_feature17.html

Best wishes,

Ted

[John M.]

Re: L71 L72 427 Running on Pump Gas

Michael, Duke, Ted,
Last night I cc'd one of the pistons to determine volume. The results are odd. I did it twice and the numbers are within 0.5cc. The bore is 4.280 the piston was 0.330 down in the bore. I got 29.5 and 30.0 CC. This volume is not listed anywhere that I've looked for dome volumes and the piston looks like it has never been machined?? The piston is an L2268F-30; stamped in the dome. Using these numbers I get SCRs that vary from 10.66 to 10.93, using the worst case both ways. What's the deal? I will check this once more. (I think I need a break from this excercise...)
John

[Ted S.]

Re: L71 L72 427 Running on Pump Gas

John,

Summit shows -35.5cc for the pistons.

http://store.summitracing.com/partdetail.asp?part=TRW%2DL2268F30&autoview=sku

Hope this helps, Ted

[Ted S.]

Re: L71 L72 427 Running on Pump Gas

John, What are the various numbers you're using to calculate the SCR? Thanks, Ted

[Duke W.]

Re: L71 L72 427 Running on Pump Gas

My old Speed Pro catalog lists the dome volume of the L2268F-30 as 35.5 cc and the dome height is .266".

I assume the SCR you computed is based on a .070" gasket. What would it be with the gasket you took off, and what was its thickness? Also, what would the SCR be with the two thickness gasket and nominal dome volume per the spec?

I can't think of any reason why your measurments are that far off from the spec.

The compression height is 1.765."

If someone knows, I'd like to know the BB center to center rod length so I can run some scenarios on the cgnet calculator.

Duke

[Ted S.]

Re: L71 L72 427 Running on Pump Gas

BBC rod length 6.135"