2.4 Engine build advice

[lamchop77]

Hi all

Need some advice with building a 2.4 CIH. Quick bit of history first. I race in Autograss in the uk (basically 1/4 mile dirt oval racing). Been running a 2.2, stock pistons, Bill Blydenstein race head (2.0 with 46mm(1.81) in 41mm(1.61) ex valves), Kent 244 cam, lightened/balenced running 48 Dellortos,stock cast exhaust to a home buit 2.5" exhaust system. This engine puts out 180bhp with good torque.

Good motor but i need more power to keep with the big boys. Stick with what i'm familiar with and never follow the herd when it comes to engines.

Decided to go the 2.4 route with some advice from a guy Dave Jackson who i think has been in touch with Bob L.

This is what i have got at the present time.

96mm Wossner Forged pistons 12.1 comp
Forged H section con rods/ ARP rod bolts
Std 2.4 crank
Lightened flywheel (8 kg) Manta 400 Rally paddle clutch

Got lots of bits lying around at home, 5 - 2.0 motors at varying stages of tune, 3 - 2.2 motors and the 2 - 2.4 motors.

Reading through the forum i can see theres alot of knowledge here that i hope you will share with me. Picked up some good tips already.

Really need to know what head to use. Dave Jackson suggests the 2.2/2.4 as they flow better than the 2.0 ported head as std. Valves i will be using are the 46/41 set up, got the correct 2.2/2.4 48 inlet manifolds. Would also like advice on cam profiles etc. Looking to get 230-250bhp if possible with high low down torque. As you guys know with oval racing you need a good spread of power.

The gearing is for 80 mph @7600 rpm so thats the max revs at the moment, but i can change this quite easily. Bob L seem to be the man in the know so your advice would be greatly appreciated, as would any of you guys that have done similar engines.

Thanks

Chris (Lamchop77)

[opelnut10]

Originally Posted by lamchop77 Hi all Need some advice with building a 2.4 CIH. Quick bit of history first. I race in Autograss in the uk (basically 1/4 mile dirt oval racing). Been running a 2.2, stock pistons, Bill Blydenstein race head (2.0 with 46mm(1.81) in 41mm(1.61) ex valves), Kent 244 cam, lightened/balenced running 48 Dellortos,stock cast exhaust to a home buit 2.5" exhaust system. This engine puts out 180bhp with good torque. Good motor but i need more power to keep with the big boys. Stick with what i'm familiar with and never follow the herd when it comes to engines. Decided to go the 2.4 route with some advice from a guy Dave Jackson who i think has been in touch with Bob L. This is what i have got at the present time. 96mm Wossner Forged pistons 12.1 comp Forged H section con rods/ ARP rod bolts Std 2.4 crank Lightened flywheel (8 kg) Manta 400 Rally paddle clutch Got lots of bits lying around at home, 5 - 2.0 motors at varying stages of tune, 3 - 2.2 motors and the 2 - 2.4 motors. Reading through the forum i can see theres alot of knowledge here that i hope you will share with me. Picked up some good tips already. Really need to know what head to use. Dave Jackson suggests the 2.2/2.4 as they flow better than the 2.0 ported head as std. Valves i will be using are the 46/41 set up, got the correct 2.2/2.4 48 inlet manifolds. Would also like advice on cam profiles etc. Looking to get 230-250bhp if possible with high low down torque. As you guys know with oval racing you need a good spread of power. The gearing is for 80 mph @7600 rpm so thats the max revs at the moment, but i can change this quite easily. Bob L seem to be the man in the know so your advice would be greatly appreciated, as would any of you guys that have done similar engines. Thanks Chris (Lamchop77)

The first place I would start is cutting down the counter weights on the crank while you are doing the balance on it. If you can get 3 or 4 pounds (1.5-1.8 kilos) that will help it rev quicker and higher and get it up out of the oil basin somemore. Bob L is the man to consult on the head work and camshaft, also inlet manifold mods. A good tuned length header with low restriction exhaust system will also help. With an engine that size I would not run header tubes smaller than 1 5/8", You need a good flange to make up the header from, there are some available on this site (Gumby) I think.

[jeff denton]

I can't say I know much about building the 2.4, but do recall that the rods aren't the greatest. You weren't specific on which rods you'll use, but you got the right bolts apparently.
Study up on the Total Seal gapless rings, I'm convinced they're the way to go!
Fellow racing member Hiro would have good advice for you.
Your 7600 rpm range is pushing the stock rockers' luck, isn't it?

Since you won't be needing the 2.2 cranks, please feel free to send one to Montana. We pay good money for them around here!

[lamchop77]

Jeff

The rods i'm using are specials from America somewhere through a company called Autosprint in the uk. They will take up to 10000rpm in bursts. Knew the std rods would be pushed at the 7600 limit so got some decent ones instead. Can't get ARP bolts to fit the std rods here anyway tried and failed!!

One thing i'm really interested in is the different rod and piston combinations you guys use. 2.2 pistons are now really scarce over here, if you can get them there £175 EACH, converted to dollars thats about $340 a piece. A bit too rich for my wallet!!!!

I can get pistons made up over here through the wossner rep, for 8 or more it works out about £80 a piece but i need to get numbers up for that.

Not had any problems with the rockers up to now but the time spent at 7500/7600 is a very, very short space of time. Not heard of any problems or cures for that matter.. would you care to enlighten me???

Thanks

Chris

[RallyBob]

A few things stand out in my eyes.

*I'd lighten the crankshaft for sure. 2.0 crank weighs 36-36.25 lbs, a 2.2 crank weighs about 34 lbs, and a 2.4 cranks (8-cwt) weighs about 43 lbs! That's a lot of mass to accelerate off the turns.

*I'd use the 2.2 head. It has better inlet flow, and slightly less exhaust flow than the 2.4 head. More importantly the exhaust ports are smaller. As a result, it has better throttle response than the 2.4 head (although similar power figures). Again, important for accelerating from the turns.

*If at all possible, use smaller stemmed valves. 8 mm - 5/16" at least, but 7 mm would be nice! Allows for more rpms and less spring pressure. Parts last longer in fact and the reduction of forces on the standard rocker arms is substantial. You can run 8500 rpms reliably if you match components carefully. You'd only need approximately 105-110 lbs of seated spring pressure and 255-270 lbs of open pressure if using 8 mm valves. With 9 mm valves you'd have to run well over 300 lbs of open spring pressure.

I'd also 'prefer' to see 1.88" inlet valves to allow those ports to breathe! The exhaust valve size is adequate however. Porting work on this head needs to be concentrated on the exhaust ports. Not just via massive enlargement, but rather careful reshaping. If done right, you can retain the high velocities needed but you can improve the exhaust port flow by about 40-45%...quite a lot! I barely enlarge the port size at the head face, all my work is concentrated near the valve guides and the seats. I'm not sure if the Wossner pistons have adequate valve reliefs in them to fit such a cam/valve combination however.

*Even with the exhaust parity someone cured by valve sizes and porting, the 2.2 head responds nicely to a split-profile camshaft favoring exhaust flow. And those heads also flow very well at higher valve lifts. More lift will get you more torque. I'd usually recommend something on the order of .525" inlet lift and .550" exhaust lift, with about 260° inlet duration @ .050" tappet rise and 265-ish° exhaust duration @ .050". Advertised duration specs wouldn't help here, as every manufacturer uses different opening and closing ramps so they only hint at the cam's true profile.

IIRC, Kent's numbering system roughly indicates the duration @ .050" numbers...so the '244' cam should be 244° @ .050" duration...a fast road cam for a 2.0 litre engine actually! A larger 2.4 engine with big compression can tolerate and needs far more cam to make decent power.

Normally on a road version of a 2.4 I'd use 110-112° lobe separation, but for 'roundy-round' racing 106° to 108° lobe separation angle and about 102° to 104° intake centerline is more appropriate. This should net you a strong powerband from 4500-7800 rpms. A wider lobe separation angle will widen the power spread a bit, but you won't have the 'sharpness' and response.

HTH,

Bob

[lamchop77]

Bob

Thanks for the reply and info. Lots to take in there!!. Not well up on Cam theory so i'll have to brush up. Theres not a lot of choice over here for different cams unless your prepared to spend big bucks. Would if i could but i can't!!!!!! Was thinking of using the kent 264

4000-8000 power band
12.52mm(0.493") in lift
12.47mm(0.491) ex lift
310 duration
timing figures 52/78 88/42
Inlet exhaust @full lift 103

Guys over here have got 250bhp using these which is more than enough for me at the moment. The class is limited at the moment and racers are switching to 16v motors limited to 2050cc.

The 2.2 has the edge out of the corners but is losing out a little at the end of the straights. Was looking to get more grunt out of the corners and beef up the mid range to keep ahead.

Jeff Denton meioned a weakness with the rockers, what is the major problem with them?

Thanks

Chris

[jeff denton]

I haven't had a valvetrain failure yet, but my cam is legal at .430 lift and my tach hasn't seen 7500 yet that I know of. But taking Bob's advice of running the 2.2 head with .525 lift and going to that RPM would worry me unless you're listening real close to his explanation of lightweight valvetrain parts.
Look at Dan's thread about "small stem valves". I think he's on the right track there.
Then of course there's the option to go with the "roller rockers" but all I can say is Good Luck.
Custom pistons are the way to go, you can get lighter weight and skinny rings and the pin placement correct for the longest rod possible.
You hint that cost will be a factor here, kind of typical amongst us racers, but sending 2.2 cranks to Montana should pretty well offset the price of the right pistons...
And Welcome to the Opel Racers Club

[Hiro]

I've built several race 2.4/2.5 so here is my recipe:
pistons: Wossner's 96mm or 97mm
rods: std 2.4 reworked
crankshaft: std 2.4 reworked (std -2.5kg = 17kg)
flywheel: std 2.0 reworked (228mm & 5.7kg)
clutch: 228mm Sachs 6 bolt cover
head: ported 2.2 with race valves (45mm & 41mm)
camshaft: D. Bilas DB32C (310° @ 0.3mm & 12mm lift) with Bob Legere's roller rockers
intake: short 30E manifold with Megasquirt EFI.

This combo is OK up to 8200-8500rpm with a nice 4000-8000rpm powerband,
But the cylinder bores wear quite fast because of the bad rod ratio (1.58),
Therefore I've set my rev limiter at a safer 7500rpm this year.

Next 2.5 version will have longer forged rods,
Shorter forged pistons (cd28mm instead of 31.5mm),
Bigger intake valves (Chevy SB or Imotec 49mm),
A Martelius race header,
And an alu flywheel to keep my legs on the safe side too.
HTH,
Hiro

CIH 25E 1

http://www.martelius.com/index.php?m...product=330022

http://www.imotecgmbh.com/Leistungst...el-cih4-t.html

[tekenaar]

. . . DAMN!, you do nice work, Hiro!!!

[Hiro]

Originally Posted by tekenaar . . . DAMN!, you do nice work, Hiro!!!

thanks Otto!
I'm doing my best which is hum... slow amateur work,
but I have a very good & patient teacher named Bob!
cheers,
Hiro

[lamchop77]

Cheers guys for all the info up to now, its a great help.

Hiro thanks for the info, been reading through other threads of yours and noticed that you have had problems with the clearances on the Wossner pistons. Is this only with the 97mm or does it apply to the 96mm pistons as well? Very interested in what your planning for the next 2.5/2.7. Got a bloke here in england that supplied me with H section chrome alloy shot peened forged rods with ARP bolts for £375 (469 euros) a set delivered to my door, from what he was telling me they are the same manufacturer that supply Eagle rods, Farndon etc and if i give him measurements he should be able to get them manufactured ( will double check this next time i speak to him).

Also spoke to the Wossner supplier here in the uk and he reckons that they can manufacture any piston to supplied drawings. He quoted about £85 (106 euros )a piece for pistons if 2 sets were made (8 total). Thought that this could be useful info to you.

Where do you get the manifolds from, is there a supplier in France?
Are you ordering aa alloy flywheel or having on made up specially? I'm looking at doing the same but making a High Tensile Steel one, just struggling to find the correct dimensions for mounting the ring gear and also the ring gear itself. Have you any info on dimensions or suppliers?

Also was interested in the article about using the 2.3 diesel unit. Is that the current model as fitted to Frontera, Omega models?

Also what is the problem witht the rod ratio and how is this calculated?

Did you have clearence problems when fitting the 2.4 crank into 2.0 opr 2.2 blocks?

Lots of questions i know sorry, just trying to gather as much info as possible.

Thanks again everyone

Chris

[opelnut10]

First you have to make up your mind how light you want to go with your choice of flywheels. There are postings on this site for both aluminum and steel flywheels,with the aluminum wheel (With alloy insert) you can get down to about 9-10 lbs. and the steel wheel in the 14-15 lbs. range. A stock flywheel is 24 lbs. or so. Lighter wheel will rev quicker but requires higher RPM to launch the car from the start and keep the engine in the power band. As far as starter ring gears, the one used on the stock flywheel works very well when building a new flywheel. Heat the stock flywheel ring gear and drive it off the step while heating it, allow the flywheel to cool back down and take your measurments form the stock wheel ring gear step and the inside diameter of the start ring you are going to use and machine the new flywheel to those measurments. Put the new flywheel in the freezer for 24 hours taking it out and then turn the ring gear over (to get new teeth configuration) and tap it on the flywheel then heat the flyweel to expand it back to size and allow it to room cool after installing. That is the way the manufacturers do it and it works very well.

[lamchop77]

Thanks Opelnut10 will give it a go next week.

Flywheel i have at the moment is 7.58kg (16.68 lb) but is cast. Value my ankles and feet so want a steel / ally one.

Thanks again for the info

Chris

[opelnut10]

I am with you there, I had a 1/4 steel plate formed into a scattershield around the bellhousing and a 18 lb. billet flywheel in the Drag Car (Bodacious) but I layed the tach on 7000 RPM and side-stepped the clutch with drag slicks on the rear on the launch. This is the only pair of feet and legs I ownand I wanted to take very careful care of them. One thing about Drag racing you only need to witness one cluth-flywheel explosion to make you want all the safety equipment that you can have in those areas. In this country auto racing is big business and there are a lot of Manafacturers making a lot of good scattershields, flywheels and clutches for the most popular engine combinations. But if you race an Opel you have two choices, adapt their products or make your own

[Hiro]

Originally Posted by lamchop77 Cheers guys for all the info up to now, its a great help. Hiro thanks for the info, been reading through other threads of yours and noticed that you have had problems with the clearances on the Wossner pistons. Is this only with the 97mm or does it apply to the 96mm pistons as well? Very interested in what your planning for the next 2.5/2.7. Got a bloke here in england that supplied me with H section chrome alloy shot peened forged rods with ARP bolts for £375 (469 euros) a set delivered to my door, from what he was telling me they are the same manufacturer that supply Eagle rods, Farndon etc and if i give him measurements he should be able to get them manufactured ( will double check this next time i speak to him). Also spoke to the Wossner supplier here in the uk and he reckons that they can manufacture any piston to supplied drawings. He quoted about £85 (106 euros )a piece for pistons if 2 sets were made (8 total). Thought that this could be useful info to you. Where do you get the manifolds from, is there a supplier in France? Are you ordering aa alloy flywheel or having on made up specially? I'm looking at doing the same but making a High Tensile Steel one, just struggling to find the correct dimensions for mounting the ring gear and also the ring gear itself. Have you any info on dimensions or suppliers? Also was interested in the article about using the 2.3 diesel unit. Is that the current model as fitted to Frontera, Omega models? Also what is the problem witht the rod ratio and how is this calculated? Did you have clearence problems when fitting the 2.4 crank into 2.0 opr 2.2 blocks? Lots of questions i know sorry, just trying to gather as much info as possible. Thanks again everyone Chris

Thanks for the price infos Chris,
I guess the Wossner price is for a bare piston without pin & rings?

Dome clearance problem:
Is the same for 96mm or 97mm Wossner 2.4 piston,
Easy cure by grinding the combustion chamber (this I do) or grinding the dome itself (didn't try yet).

Short 30E manifold:
Easy DIY just chop the two last runners from a std 30E manifold,
Some ready for use ones can be found on Ebay.de
Note that the short manifold will flow better if you remove the two front runners.

CIH race flywheels:
I've purchased my alu FW through a group buy here in this forum (thanks to coordinators for letting me join in!),
I've also found a billet steel FW in Germany made by Ronald Boltz (very nice part but heavier of course),
Also alu FW are available in Belgium from Lahouter Motorsport (CIH motorist, probably the best outside Germany).

23D block:
Yes this one was in Omega/Frontera & also RekordE/SenatorA etc,
There is a turbo version with oil sprayers & steel liners,
I don't know how far we can overbore these blocks.

Rod ratio:
Rod c-c length divided by crankshaft stroke,
ie for our 2.4 134mm/85mm = 1.576
Not good for any race engine below 1.6
Low rod ratio results in extra lateral stress during the power stroke,
May end up with piston/rod failure or excessive bore wear,
This prevents the 2.4 to reach high rpm safely.

2.4 crank clearance:
No problem in the 2.0 block (2.2 is the same block),
Not tried in the 1.9 block.
I think there is an issue with the brace that holds the oil succion tube,
The 2.0 brace will hit one of the 2.4 crank counterweight,
But if the counterweights are knife-edged this problem solves by itself,
And that's what we do when we remove material from the crank anyway.

Hiro

[lamchop77]

Hiro

Thanks for the info.

Concerning the piston price, this was for full sets with rings, pins etc but minimum order of 8. Got the quote a year or so ago so might be a bit more with the cost of steel / ally rising.

Pity about the rod ratio for the 2.4 but got the rods and pistons now. Looking to rev to 7500 so hopefully will be ok.

Looked at lahouter and the flywheels look good may have to invest in one!!

Couldn't find anything on Ronald Boltz, have you any contact details.

Thanks

Chris

[Hiro]

Originally Posted by lamchop77 Hiro Thanks for the info. Concerning the piston price, this was for full sets with rings, pins etc but minimum order of 8. Got the quote a year or so ago so might be a bit more with the cost of steel / ally rising. Pity about the rod ratio for the 2.4 but got the rods and pistons now. Looking to rev to 7500 so hopefully will be ok. Looked at lahouter and the flywheels look good may have to invest in one!! Couldn't find anything on Ronald Boltz, have you any contact details. Thanks Chris

I have Ronald's email somewhere,
will fetch it this evening.
Hiro

[Hiro]

Originally Posted by lamchop77 Hiro Thanks for the info. Concerning the piston price, this was for full sets with rings, pins etc but minimum order of 8. Got the quote a year or so ago so might be a bit more with the cost of steel / ally rising. Pity about the rod ratio for the 2.4 but got the rods and pistons now. Looking to rev to 7500 so hopefully will be ok. Looked at lahouter and the flywheels look good may have to invest in one!! Couldn't find anything on Ronald Boltz, have you any contact details. Thanks Chris

you have PM Chris,
Hiro

[lamchop77]

Hey all

Looking at the DBilas camshafts for the 2.5 motor. Does anyone know what the maximum lift on the cam that can be used with the 96mm Wossner pistons without modifying the pocket depth.

Any recommendations for the DBilas cams, looking to rev to 7500. They don't list the rev range that the cams work between like Kent do.

Cheers in advance

Chris

[Hiro]

Originally Posted by lamchop77 Hey all Looking at the DBilas camshafts for the 2.5 motor. Does anyone know what the maximum lift on the cam that can be used with the 96mm Wossner pistons without modifying the pocket depth. Any recommendations for the DBilas cams, looking to rev to 7500. They don't list the rev range that the cams work between like Kent do. Cheers in advance Chris

The Wossner valve pocket are 6mm deep,
That's OK with most of the current race cams we have in Europe.
Becareful if you plan to recarve the pockets because there is only about 2.5mm of metal left!
I'm using a DBilas DB32C cam for now:
http://www.opelgt.com/forums/139400-post3.html
This cam is more than enough for 7500rpm,
No need to modify the Wossner valve pockets.
Hiro