2.4 vs 2.0 head ?

[ggl]

Hi all, been reading a lot of excellent posts since I found this forum a couple of weeks ago and I've picked up quite a few tips, but I didn't really find the answer to one thing I've been wondering about

I have a Mantzel built 2.7CIH with a modified 2.0 head. As far as I can remember (I've had this engine for 12 years now) it has 46mm (1.81) intake valves and 41mm (1,61) exhaust valves, I'll assume the head has a mild street port job (why else would a reputable engine builder put in valves that big) and it's running a mild street cam, 290 degrees (M15/H4 ?) and I'm running a stock LE-Jetronic injection setup. This is on a 86 Manta GSi/GTE. On a rolling road this engine was dynoed at 170hp at 4900 rpm, fuel starvation due to air meter bottoming out so I've no doubt that in it's day it delivered the 175hp at 5500 rpm Mantzel promised, which we overcame at the time by running it rich but never had the opp to do another test, and 265nm at 3500 rpm

All in all it was a very nice engine and I'm getting the itch to put it back into a car and have some fun again, so I guess my questions would be, is there any point in me hunting down a 2.4 head (they're fairly cheap here) and have that modified or am I just as well off sticking to my working 2.0 head, is there anything about a 2.4 head that makes it an obvious choice for a mild street head ?

Yes I'm looking for a wee bit more power, aren't we all, and breaking 200hp would be nice, but if I'm basically starting over again with a head that's only marginally better, I may as well stick with the 2.0 and spend the money elsewhere

Thx in advance for any advice and for the info I've already found just by browsing, man I thought it was difficult to to find good afordable Opel performance parts here in Norway but you guys really had to do some thinking to source parts

[RallyBob]

Welcome.

I posted quite a lot of flow test results in this thread here.

http://www.opelgt.com/forums/opel-en...alve-head.html

Another forum member, Hiro, made some very nice graphs which shows the airflow of the heads at various valve lifts. For maximum power, a 2.2 or 2.4 head generally flows about 20% more than a 2.0 head, if they have both been fitted with large valves and ported.

Bob

[Hiro]

Hi there!
I'm on my way too with the 2.7 version so maybe we can share infos.
As Bob said the 2.2/2.4 heads definitely flow better than the 1.9/2.0
Now I guess it also depends what you want to do with your 2.7?
This also depends what parts you have in it... & what max rpm you want to reach!
The main problems with the Mantzel 2.7 are the bad rod ratio & the piston quality:
If your version is equipped with the BMW M10 steel rods & the Kolbenschmidt cast pistons,
Then a 2.0 ported head will be more than enough as you are anyway restricted below 6000 max rpm.
Now if you have forged rods & forged pistons you will enjoy a nicely ported 2.2 or 2.4 head (I'm going this way),
But in any case remember that you have a 1.5 rod ratio,
So 7500rpm is the maximum you can get before blowing your cylinder bores & piston skirt!
HTH,
Hiro

[ggl]

Somehow it doesn't surprise me at all to find you guys to be the first to respond

@Bob, thx for providing those numbers. I had already looked at that thread and I'm sure they are invaluable to someone like Hiro who can make sense of them , I'm more of a practical hands on type of person. Don't get me wrong, I understand that higher flow numbers equates higher power potential, for a street engine, and I guess mine would be "mild" to "mild plus" or something, there's a point where there's "enough" air flow and you can look for other things besides air flow, like air velocity at lower rpms, fuel distribution....basically anything that will improve throttle response and torque at lower rpm, not to mention mpg as this will be a something of a daily driver, and it's here my knowledge falls short and I can't really interpret your numbers into anything useful other than as you say, a big valve ported 2.4 flows more than a 2.0, so I guess I'm trying to tap into your experience in evaluating my current head vs building a 2.4 head

@Hiro, I didn't know that about Mantzel's engines.....I had mine built in 1996 and didn't specify things like that, it was one of his "off the shelf" 2.7 conversions so I'll just assume I have the "low rpm configuration". I realize that piston speed is up quite a bit with the increased stroke, but compared to something like the old FIAT Twin Cam engines with it's 90mm stroke it's not *that* bad so I assume it's the rod ratio that's killing it ?

My goals, well, 200hp or thereabouts in a streetable engine, 6k rpm is plenty for me as the only track time it will see is on track days and I currently don't have the funds to do anything about the Getrag240 with the 3.44 diff I salvaged from my old Manta and 6k rpm in 5th gear means hard jail time here in Norway

I'll be quite happy to share whatever info I have with you Hiro, but reading your posts in this forums indicates that you already have any and all info I could possibly provide ....and then some

I guess you guys have answered my question, I'm probably better off spending my money on improving other parts of my setup, like the stock 2.0 injection manifold which seems to receive "less than favorable" reviews around here

[Hiro]

Yes piston speed is high but this is something we can overcome with lightweight design & forged material,
On the other hand the rod ratio dictate its law on the geometry & lateral stress,
So this is where this 2.7 version reaches the physical limits.
The funny thing is the Imotech company designed a 3.0 version so I'm very curious to see how they did this!

My understanding of the Mantzel strokers is that a special crankshaft was made for the late versions,
Looks like this crank had 8 counterweights instead of the 23D crank used for the early versions.
So if you plan to rebuild your engine please take some pictures & measurements of the parts,
You have a very rare CIH so it would be very usefull for us to know more about it!
Hiro

[ggl]

How badly do you want to see it, according to my GPS I can be in Paris in about 15-16 hours , does this mean you haven't yet completed your own 2.7 that I've been reading about in here ?

I didn't realize it was *that* rare as I figured Mantzel must have done hundreds of these conversions over the years but I suppose most people chose the 2.2 or 2.4 conversions as the 2.7 was kinda expensive and you didn't really get a lot of extra hp for your money

I actually asked Mr Mantzel about the 3.0 conversions when I had my car in his shop, he was a very pleasant person to deal with, and he claimed they weren't that good as he felt they had taken it one step too far and that the 2.7 was a better compromise (he would say that wouldn't he)

[Hiro]

Yes my 2.7 project was stopped for a very long time,
Because I could not find new rod bolts for my Mantzel forged rods.
This year I reluctantly started preparing a set of M10 steel rods,
Then found the correct missing bolts by pure luck,
So I hope I will fire this engine quite fast now on next spring.

I've spent much more time on various versions of the 2.5
This one I use in my KadettC for vintage GP racing here in France.
Actually the 2.7 is a kind of side-project for me because of its rpm limitation,
It will probably end up in my "400 replica" for road/fun track days!

If I were to build a serious 2.7/2.8 for racing I would probably start from the 23D block,
I've posted a few pics of this one on this forum section.
This project is appealing but much more expensive of course,
So it will be launched only if I can't get what I want from the current 2.5
Too many projects maybe...

BTW now I remember another 2.8 in northern europe,
I think the owner's name is Are Lev but I've lost his webpage,
Maybe you know him?
Hiro

[AZManta]

Be aware that your 2.0 LE manifold will not work with the 2.4 head (intake ports are higher)

[ggl]

Originally Posted by AZManta Be aware that your 2.0 LE manifold will not work with the 2.4 head (intake ports are higher)

So I've gathered

Further reading on the subject has led me to believe that it's not the manifold itself that is too small, bit of a misunderstanding on my part I guess, it's the throttle body and this can easily be rectified with a 3.0 throttle body, or something from a BMW "big six" , which only leaves me with my old problem with the air flow meter bottoming out and the fuel to air mixture leaning out (drastically) above 4500 rpm, which I should be able to fix (temporarily) using the tricks from this site

About Opel fuel injection systems

which I found after following links in a couple of other posts in here, man this place is a wealth of information, almost oo much to keep track of

[ggl]

Originally Posted by Hiro Yes my 2.7 project was stopped for a very long time, Because I could not find new rod bolts for my Mantzel forged rods. This year I reluctantly started preparing a set of M10 steel rods, Then found the correct missing bolts by pure luck, So I hope I will fire this engine quite fast now on next spring. I've spent much more time on various versions of the 2.5 This one I use in my KadettC for vintage GP racing here in France. Actually the 2.7 is a kind of side-project for me because of its rpm limitation, It will probably end up in my "400 replica" for road/fun track days! If I were to build a serious 2.7/2.8 for racing I would probably start from the 23D block, I've posted a few pics of this one on this forum section. This project is appealing but much more expensive of course, So it will be launched only if I can't get what I want from the current 2.5 Too many projects maybe... BTW now I remember another 2.8 in northern europe, I think the owner's name is Are Lev but I've lost his webpage, Maybe you know him? Hiro

Nope, that first name could easily be Norwegian but there are no people with that name combination listed in the phone directory here

I've never been part of a large Opel community, it's just been a couple of friends and me working on our projects and figuring stuff out, so the stuff you guys have been doing around here is pretty amazing to someone like me who's pretty much been used to mixing and matching various Opel bits and leaving it at that

I'd be insterested to see your 400 project, a friend of mine shares workshop space with me, so right next to my Manta project is his Manta project, a genuine 400 . Unfortunately the body shell is rusted beyond the point of being salvageable, theoretically it could still be restored I suppose but it would need professional help as the floor is basically gone, all of it, including the trunk, the inner fenders (front and rear), sills....but at least it's 100% complete and mechanically sound so it will be rebuilt around a GSi body shell. As far as we can tell it was sold new in Denmark back in it's day, which explains the rust as the salty sea air there will kill just about anything, let alone an 80's Opel

[Hiro]

Originally Posted by ggl I'd be insterested to see your 400 project, a friend of mine shares workshop space with me, so right next to my Manta project is his Manta project, a genuine 400 . Unfortunately the body shell is rusted beyond the point of being salvageable, theoretically it could still be restored I suppose but it would need professional help as the floor is basically gone, all of it, including the trunk, the inner fenders (front and rear), sills....but at least it's 100% complete and mechanically sound so it will be rebuilt around a GSi body shell. As far as we can tell it was sold new in Denmark back in it's day, which explains the rust as the salty sea air there will kill just about anything, let alone an 80's Opel

my "400 replica" is a GSI with the Irmscher widebody kit,
it currently runs with a near-stock 2.4
upgraded brakes/springs/shocks & 3.67 diff,
8x13 & 10x13 rims with race slicks,
it's not a race car it's just a "streetable race-for-fun car" I was using for club events.
plans are to put the 2.7 in it if it checks OK on my "engine test race car" (= KadettC City),
if not I can still upgrade it using last year's 2.5 version from my "real race car" (= KadettC GTE),
either way should be fun!
Hiro

[ggl]

I'd love to see some pics of either

[Hiro]

Originally Posted by ggl I'd love to see some pics of either

some pics of my cars here:
the KadettC is my GP racer,
the CommodoreB is a genuine FIA spec group1,
the MantaB is my "fun racer",
no pics of my City (to trashy to show!)
Hiro

[ggl]

Nice looking cars Hiro.....I approve

[markandson]

Came across this link to a Gary/RallyBob thread that applies to this thread.