Did anyone do this and what are the problems?

I went the other way around to gain compression. Putting 117 heads on a 116 would cost you about 50HP I'd guess, and probably a 6.0:1 compression ratio. On the bright side you could probably run on 70 octane.

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

I believe the K-jet M117 heads have a smaller combustion chamber than the D-jet M117 heads. The K-jet heads are 45cc. Not sure what the d-jet heads are but just looking at pictures the combustion chamber is recessed instead of flush with the mating surface like the K-jet heads.

__________________
Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT

Thanks Tomguy.
Is there some math behind this? I mean does someone have numbers
Volume the piston is moving and volume of combustion chamber?
If the original ratio is 9.5 :1 for the 3.5 liter
The ratio of the 4.5 is 9:1
the ratio of a 3.5 with 4.5 heads would be 9:1 * 3.5 / 4.5 = 7?

Or coming from your experience: Did you experience much more HP on your 4.5?

Martin

It would depend on the combustion chamber volume. The 3.5 heads apparently have smaller combustion chambers-not sure exactly what. The various 4.5 heads have larger combustion chambers. so you would lose some CR due to the larger combustion chamber. To get the CR simply divide the cylinder volume by the combustion chamber volume for instance a 500cc cylinder with a 50 cc combustion chamber would have 10:1 cr. You have to consider deck height, head gasket thickness, valve reliefs etc to get the correct combustion chamber volume. You could cc one of you old heads to see what the combustion chamber volume is.

__________________
Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT

Just running some very simple calculations I cam up with 3.5 cylinder volume=437cc. Using the 4.5 K-jet combustion chamber volume of 45cc I come up with a CR of 9.7:1. The 3.5 has a positive deck height of about .75mm so there is very little head gasket volume. Not sure if the 3.5 pistons have a recess or valve notches. Am I missing something?

__________________
Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT

I think you are correct. The 3.5l cylinder has 437ccm!
However the compression of the 4.5 is 8:1.

Here are my calcs so far. The information missing is the colume of the heads themselves. I'll cc the 2 heads.

Best, Martin

Compression rates 116 and 117 engine according data I gathered
Compression rate = VP( volume of piston area xstroke) plus + VR (rest volume:volume above cylinder head at TDC)/ VR (rest volume:volume above cylinder head at TDC)
Definitions:
C= compression rate
VP= volume displaced by piston
VR= rest volume in cylinder head = minimal volume
VP + VP = max volume
Formulas: C= (VP +VR)/ VR
VP= VR (C-1)
VR = VP/ (C-1)

117 engine:
Compression rate C117: 8.0:1 (information I received, needs to be confirmed)
Bore: 92mm
Stroke: 85mm
VP117= 3.14 (9.2cm) (9.2cm) /4 * 8.5cm = 565.046ccm [8 x 565 = 4520ccm] correct

116 engine:
Compression rate C116: 9.5 (assumption, needs to be confirmed)
Bore: 92mm
Stroke: 65.8mm
VP116= 3.14 (9.2cm) (9.2cm) /4 * 6.58cm = 437.412ccm [8 x437 = 3496] correct

VR116 = 437.41ccm/ 9.5 -1 = 51.46ccm
VR 117 = 565.046ccm/ 8.0 -1 = 80.72ccm
Difference VR is 29.26ccm
VR is the rest volume in the head which is split in a part within the steel cylinder and then the parts in the head including volume in gasket . It is not 100% sure if the part in the steel cylinder is the same in the 117 and 116. I guess by looking at the 2 pistons that this part of VR is not the same. Therefore my upcoming calcs might not be a 100% match.

However in principle a bigger volume engine needs a bigger volume cylinder head for the same compression rate(It is a linear function).
If I calculate 117 head on a 116 engine ….
Compression 116 w/ 117 head= (VP116 + VR 117)/ VR 117 = (437ccm + 80.72ccm)/ 80.72ccm = 6.413:1

The other way around
Compression 117 w/ 116 head= = (VP117 + VR 116)/ VR 116 = (565.ccm + 51.46ccm)/51.46ccm = 11.98:1

Hi Martin,
A lot of the difference in CR between the M116 3.5 and M117 is in the piston-not the head. The M117 pistons are deeply dished (K-jet) or have a negative deck height (D-jet) to add up to a much larger combustion chamber volume. Using the K-jet 4.5 with it's 45cc combuston chamber as an example it would have well over 10:1 CR with flat top pistons instead of the 9mm dished pistons.

__________________
Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT

Just an FWIW, 12:1 is about what I got with my 4.5 after the swap to 116 heads, so I think this math may be right. I say that based off of my before and after compression PSI measurements, plus other math I did... I put my theories, measurements, etc into a thread long ago - but 4.5 heads on a 3.5 will net you much worse performance and is never a recommended step if your 3.5 needs heads.

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

Tony, do you have a picture of the 2 type heads?
Martin

Tony, you are correct.
Assuming the 117 K-jet has a 45cc head and compression is 8:1
resulting in VR 117 = 565.046ccm/ 8.0 -1 = 80.72ccm (this is the volume of the final burning chamber)

The recessed pistons plus gasket must make a volume of 80.72cc - 45cc = 35.72cc
3.14 (9.2cm) (9.2cm) /4 * x cm = 35.72cc.... x= 0.53cm = 5.3mm
This means: 35.72cc are the part volume (of the 80.72cc total burning chamber) with the piston ending about 5.3mm below the head surface. This includes head gasket and dished surfaces on the piston.
Do you agree?

For any further speculations I need more precise and confirmed data: like the compression rate of the 450 engine this head came from. Is it very likely that the compression rate was 8:1?
Is it very likely that the compression rate for my 3.5 is 9.5:1?
Martin

I found this data on the forum
117: 52.6cc combustion chambers (measured
using a non-medical syringe).
The 3.5 116 heads are ~38.4cc (this data could be from Tomguy?)
And I guess both are D-jet.

I am not sure how this data goes along with Tony's 45cc for the K-jet 117 head.
But obviously there are differences in the types of 4.5heads? Are there D-jet and K-jet type heads and what is the differences exactly? Was the Compression rate the same on both versions of the 4.5?

Is there a way to gain compression when I am using these 4.5 heads?
Can I use a thinner head gasket?
Can the head be changed in a what to gain volume...Planed once again, about 2.5mm making a 16.6cc smaller chamber per cylinder?
Of course I need big time offset keys in order to make up for the 'chain stretch'?
Did someone do this?

Martin, are your heads too far gone for a shop in Oman to redo them? It is hard to kill these in my experience. There were 2 4.5 compression ratios in the USA - 8.0:1 and 8.8:1 - hence the two numbers. Some areas, like Africa, got 7.0:1 from what I understand as well.

The head gasket is already too thin to make that much of a difference really, even if you halved it (which would be too thin to seal) you would only gain maybe 0.5 at most I imagine.

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

Hi Tomguy,
thanks, you'd be depressed to see the quality of mechanical work around here. Maybe there is genius somewhere but I haven't found him yet.
I don't think there is a chance to redo a head here in Oman.
At least some mechanic must get the right valve guides and should install them correctly. Same with valve seats. I doubt it to be honest.
Even in the US I'd need to know the shop in order to have faith in their work. But the US is a total different league to start with.

So no, I don't see a chance to get these heads repaired. I also don't want another nightmare.
Increasing compression rate seems to be not possible how I understand.
So I don't have an answer.
Maybe I'd be crazy to install 117 heads on a 116. Maybe. I don't think I'll do it unless I find someone who would support me.
Best, Martin