When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I have a 1979 Euro with the M28/01 motor in it that I'm currently rebuilding. I figure that while the engine is out of the car I may as well do some upgrades to increase the hp a little bit. Ive recently thought about installing the Euro S heads (from the M28/11-12 or M28/21-22). Im aware of the minor differences between the chamber design of these heads but I'm curious as to what the diameter is of the heads combustion chamber (distance going across both valves). I hope this makes sense but I want to put the bigger valve heads on my engine knowing the bore of my engine is 2mm smaller than that of the 4.7, but maybe its possible to fit the big valve head without too much trouble? If anything I said doesn't makes sense let me know!
The larger intake valve, of the 4.7 Euro, will definitely slow down the velocity of the air, at lower engine speeds.
This will reduce cylinder filling efficiency. (Even the high compression Euro 4.7 engines run very inefficiently at lower rpms, resulting in "very dirty" tailpipe emissions.)
My guess is that you will lose torque below 4,000 rpms and perhaps gain a bit a the higher rpms.
In my experience, most 928 owners spend 98% of their time below 3,000 rpms.
You might want to consider the rpm ranges that you do most of your driving in, before doing this.
Interesting, so even though the high compression 4.7 euro engine has more power, you don’t really feel until after 3000 rpm? Well that kind of changes things. I suppose the set up I was going for would work much better if I used forced induction as well but that’s not really the route I want to take. I suppose for now I’ll stick to easier mods such as headers and try to get a feel for how the car is and how I want to drive it. And depending on how that goes I might end up just buying another 928 with a later engine. Thanks for the input!
Interesting, so even though the high compression 4.7 euro engine has more power, you don’t really feel until after 3000 rpm? Well that kind of changes things. I suppose the set up I was going for would work much better if I used forced induction as well but that’s not really the route I want to take. I suppose for now I’ll stick to easier mods such as headers and try to get a feel for how the car is and how I want to drive it. And depending on how that goes I might end up just buying another 928 with a later engine. Thanks for the input!
Or find a 310hp 4.7 Euro S with CIS, like your '79 has. (Not just the heads.)
With forced induction you don't see the same losses. I can tell you from driving my stock 84 Euro S that there is a noticeable power bump on a 4.7L as it crosses 3,000 rpm.
With forced induction you don't see the same losses. I can tell you from driving my stock 84 Euro S that there is a noticeable power bump on a 4.7L as it crosses 3,000 rpm.
Will totally agree on this, same on my 1983 euro 928s. Over 3500 it really wakes up. To be frank, I was a bit surprised by the powerbump, almost the feel of a vintage small turbo-bump. Very fun indeed..
Will totally agree on this, same on my 1983 euro 928s. Over 3500 it really wakes up. To be frank, I was a bit surprised by the powerbump, almost the feel of a vintage small turbo-bump. Very fun indeed..
So with that being said, what kind of options are available for increasing the low end power, before 3000rpm?
In my experience, most 928 owners spend 98% of their time below 3,000 rpms.
I'll never understand this. Who buys a high performance European supercar only to lug it around like a '67 Chevelle with a 2-speed power glide?
My 87 has the tallest gears of all my 928's (and every car I own except the Denali).
Here is my morning commute today. Speed limit is 70mph and if you are not doing at least 80mph in the hammer lane you're getting run over by dump trucks (they drive way too fast with a full load around here).
My speedo isn't off either.
I'm environmentally conscious so I car-pool. My passenger took the photo.
Do the same drive in my 78-81 with the shorter R&P - I'm well into the 3,000's. Where's my 87 going to be when I install the 89 transmission with a shorter R&P?
These cars has 4 or 5 forward gears, why are we lugging them around in top gear? Downshift, use the full powerband. This isn't a classic muscle car where RPM's are the kiss of death.
The only time my 928's are under 3,000 rpm is on the highway when I cannot travel at this speed. Even driving through down, drop a gear, keep the RPM's up. The way every other European car I've even owned likes to be driven.
I'll never understand this. Who buys a high performance European supercar only to lug it around like a '67 Chevelle with a 2-speed power glide?
My 87 has the tallest gears of all my 928's (and every car I own except the Denali).
Here is my morning commute today. Speed limit is 70mph and if you are not doing at least 80mph in the hammer lane you're getting run over by dump trucks (they drive way too fast with a full load around here).
My speedo isn't off either.
I'm environmentally conscious so I car-pool. My passenger took the photo.
Do the same drive in my 78-81 with the shorter R&P - I'm well into the 3,000's. Where's my 87 going to be when I install the 89 transmission with a shorter R&P?
These cars has 4 or 5 forward gears, why are we lugging them around in top gear? Downshift, use the full powerband. This isn't a classic muscle car where RPM's are the kiss of death.
The only time my 928's are under 3,000 rpm is on the highway when I cannot travel at this speed. Even driving through down, drop a gear, keep the RPM's up. The way every other European car I've even owned likes to be driven.
Interesting. My 84 Euro S 4-speed is only turning 2,800 rpms in the high 80s. Think it's 3,000 rpm at 90 mph. Final drive ratio must be a little different. Most of the fun in this car is above 3k rpm anyway, so even with the auto trans I have the kick-down relay mod so I can downshift a gear even with less throttle.
Interesting. My 84 Euro S 4-speed is only turning 2,800 rpms in the high 80s. Think it's 3,000 rpm at 90 mph. Final drive ratio must be a little different. Most of the fun in this car is above 3k rpm anyway, so even with the auto trans I have the kick-down relay mod so I can downshift a gear even with less throttle.
What size rear tires? Mine are "stock" 25". If you are running a bit taller tire the RPM's will drop (Or is it the other way around? I've only had one cup of coffee....)
My Turbo S Beetle with a 1.8 liter turbo flashed to 250hp is spinning at 3,400rpm at this speed.
The idea that the 928 engine is so poorly designed that we need to lug them around under 3k is completely asinine to me.
What size rear tires? Mine are "stock" 25". If you are running a bit taller tire the RPM's will drop (Or is it the other way around? I've only had one cup of coffee....)
My Turbo S Beetle with a 1.8 liter turbo flashed to 250hp is spinning at 3,400rpm at this speed.
The idea that the 928 engine is so poorly designed that we need to lug them around under 3k is completely asinine to me.
Yep, you nailed it - 25.55" on my chosen tire - Nitto Invo
Those are paired with a 235 front that's very close in diameter.
I'll never understand this. Who buys a high performance European supercar only to lug it around like a '67 Chevelle with a 2-speed power glide?
My 87 has the tallest gears of all my 928's (and every car I own except the Denali).
Here is my morning commute today. Speed limit is 70mph and if you are not doing at least 80mph in the hammer lane you're getting run over by dump trucks (they drive way too fast with a full load around here).
My speedo isn't off either.
I'm environmentally conscious so I car-pool. My passenger took the photo.
Do the same drive in my 78-81 with the shorter R&P - I'm well into the 3,000's. Where's my 87 going to be when I install the 89 transmission with a shorter R&P?
These cars has 4 or 5 forward gears, why are we lugging them around in top gear? Downshift, use the full powerband. This isn't a classic muscle car where RPM's are the kiss of death.
The only time my 928's are under 3,000 rpm is on the highway when I cannot travel at this speed. Even driving through down, drop a gear, keep the RPM's up. The way every other European car I've even owned likes to be driven.
If you drive your 928 automatic, not doing "jack rabbit" starts, it will shift below 2,500 rpms. And by the time you are doing 80 in 4th, it's doing 3,000 rpms.
And if one is driving a 5 speed, the "light throttle tone change" occurs way before 3,.000 rpms, so most people shift to the next higher gear, before that.
That's the way almost all of my clients that use their 928's for daily driving, use their cars.
Certainly, the clients who drive their cars on Saturday and Sundays use the higher rpm ranges more.
My point to the OP was for him to figure out how he intends to drive the car and design the engine around that.
How someone else drives does not change that point.
(Someone should probably tell the OP what fuel mileage he can expect from a CIS 928....they were not/are not "fuel efficient".
12mpg cruising around town? 8mpg hot rodding around town?)
If you drive your 928 automatic, not doing "jack rabbit" starts, it will shift below 2,500 rpms. And by the time you are doing 80 in 4th, it's doing 3,000 rpms.
And if one is driving a 5 speed, the "light throttle tone change" occurs way before 3,.000 rpms, so most people shift to the next higher gear, before that.
That's the way almost all of my clients that use their 928's for daily driving, use their cars.
Certainly, the clients who drive their cars on Saturday and Sundays use the higher rpm ranges more.
My point to the OP was for him to figure out how he intends to drive the car and design the engine around that.
Still the same point.
I get your point, it just seems crazy to me.
I don't know what "jack rabbit" starts are but going down an on-ramp, driving in such a way to keep the RPM's at 2,500 rpm, I'll get run over by a Prius who's trying to accelerate faster to 80mph than I'll be going.
Looking at the transmission diagram for my manual 1980, shifting at 2,500rpm equates to:
1st Gear - 19mph
2nd Gear - 27mph
3rd Gear - 37mph
4th Gear - 49mph
I cannot fathom driving any car, much less a 928 this way.
Then again I don't live in Los Angeles. I live 1/2 mile off the main highway to town and the only gridlock we see is after a Packers game, if the neighbors cow got loose again and is wandering down the road, or it's harvesting time and there are combines everywhere.
(Someone should probably tell the OP what fuel mileage he can expect from a CIS 928....they were not/are not "fuel efficient".
12mpg cruising around town? 8mpg hot rodding around town?)[/QUOTE]
I’m well aware of the fuel mileage on this car. I was really only planning on using it as a weekend car. Currently I drive very conservatively in terms of fuel mileage but to that same point, I have no reason to drive hard with my daily. This 928 I have will most likely be used for fun driving, but once again, it all depends on how I feel with it once I get it going.
Will totally agree on this, same on my 1983 euro 928s. Over 3500 it really wakes up. To be frank, I was a bit surprised by the powerbump, almost the feel of a vintage small turbo-bump. Very fun indeed..
This is exactly what it feels like, a turbo! Not enough people describe it accurately.
08-21-2023, 04:03 PM
16V cylinder head size
