Sigma-galant.com

Greetings all.

Thought some of you may be interested in this project. Basically I wanted to build a 1600cc-ish carby 4G32 with maximum possible output. Here's the project so far:

- modified 4G37 pistons
- 4G37 head with extensive port mods (inlet flowing to 175cfm from memory)
- 12.5:1 static compression (may need to run 102 RON?) - machined head and decked the block
- #5 camshaft adapted to fit belt drive engine
- lightened flywheel
- knife-edged and balanced crankshaft
- balanced conrods
- double valve springs
- 4G54 roller rockers modded to screw adjustment
- 45DCOE carburettors

Assembly is about to start. Hope to provide further updates a bit later. Pics:

http://s1200.photobucket.com/user/16LGS/slideshow/

Happy to take your feedback/suggestions! Cheers.

Yeah nice
I like the 4G54 roller rocker idea.

Dave...

So running an engine that hard....how much reliability u expecting from it??

What power u expecting? 120hp?, 130hp?

75wagon wrote:Yeah nice
I like the 4G54 roller rocker idea.

Dave...

+1..

Was it mutch of an issue to regrind the cam to suit the roller followers?




Cheers.

Who is doing the billet cam and what grind
And are the rockers the same ratio and length
And how much is the cam and postage costing roughly
Asking because im interested
Scorpma 120 is achievable and reliable
I just dont understand how a mechanical no.5 grind will work as a roller follower
As roller cams have completely different ramps and timing events
Cheers stealth

Bugger, I just wrote this big long reply, saved it as a draft, now I can't find it! Anyway, in short:
- don't have a power target. If I do everything I can reasonably do, and do it well, I ought to get more than my C2-ish chain drive 4G32
- current chain engine is very reliable in tarmac rallying, 4000-8000rpm for 10-15minute intervals. Time will tell re belt drive I guess!
- keeping current engine as a quick-change spare in case belt drive goes bang!
- biggest power restriction I can see in chain drive engine is valve diameters. Hence 4G37 head, hence belt drive block. That's how the circus started!
- Stealth, it's an unmolested factory #5 camshaft
- I considered how the rollers will operate on the profile and as the roller radius is very similar to the radius of the wiping face on the standard arm I'm hoping the motion paths won't change much, if at all. But I'm not 100% certain, so:
- Once I have the best fit timing belt (head and block machining plus different drive sprockets have made it an exercise in scouring Dayco and Gates catalogues) I'll map and compare the motion paths of the two rocker types and post the results up here. Here's a couple of pics comparing the arms: http://s1200.photobucket.com/user/16LGS/library/
- For me the whole build is about using up bits from my collection, seeing how much grunt I can extract out of one of these engines within the class rules, seeing if I can keep up with Pinto powered Escorts, and learning along the way!

Cheers, DRS

Would be a good idea to map the valve timting events , with pistons out
Do the std rockers , measure at valve
Then do the rollers
I think you may find some weird stuff starts to happen
But who knows
Cheers stealth

Thanks for that, I think I'll be fine to do it with pistons in situ - prior to machining the head and block I checked the piston-to-valve clearance with #5 cam and roller rockers (http://s1200.photobucket.com/user/16LGS/library/) and the opening and closing timing looked to be about right (although the purpose of that exercise was not to confirm valve timing maps, just to check clearance). It will be interesting to see how it all pans out!. DRS

The contact path for roller followers is vastly different to slippers.

The curve on the slipper is much larger than the roller,
therefore on the same cam,
Roller followers will open the valves slower and close the valves quicker than a slipper rocker.

This will lose you a lot of the gains the No:5 cam would normally give you.

Love the idea, but you will need to have a cam ground to take full advantage of the friction gains.

In theory, you can open the valves much quicker with a roller follower, due to the rolling properties rather than slipping, along with a smother closing curve to help reduce valve bounce.

The trouble is finding the right CAM company who are interested in going the extra mile..



Cheers.

To put it into perspective, this is a graphic example of the difference in diameters.





Cheers.

Yep, thanks, I'm aware of the difference in radii. I want to quantify what that means in terms of change in motion paths - so it'll be out with the dial indicator and degree wheel over the holidays. All part of the learning process, and any time spent in the shed is far preferable to the shite that's on TV!

Where's the like button
Love to see the numbers when your done
Cheers stealth

16LGS wrote:Yep, thanks, I'm aware of the difference in radii. I want to quantify what that means in terms of change in motion paths - so it'll be out with the dial indicator and degree wheel over the holidays.

Sounds great. Nothing like doing the hard work to get the correct information.

16LGS wrote:All part of the learning process, and any time spent in the shed is far preferable to the shite that's on TV!

Very true..




Cheers.

Howdy all.

Mapped the inlet valve motion paths today, comparing the standard rocker with the roller rocker - see chart in the Photobucket link above. Result was probably not anybody expected - especially not the reduced maximum lift. What's also interesting is that the maximum valve lift of this camshaft is different to that measured in my current engine (also a #5) a couple of years ago. But it also has non-standard rockers, it has aluminium rockers from a Colt 4G32 belt drive. Over the next couple of weeks I'll source some more 4G54 roller/hydraulic rockers and see if they can be modified to more closely match the shape of the standard 4G32 wiper-type follower. Interesting little project. Keep ya posted! Cheers, DRS.

G'day.
Having run 4G32's in GA/GB rally cars back in the 80's, may I ask why you're bothering with a belt drive?? They are universally known as 'boat anchors' - heavy and less than stunning performance (even when modified) - not to mention the buttery crank........
I truly don't wish to put a dampener on your project but I would suggest keeping with the chain drive 32' if you haven't gone too far down the track.
I'm just about to begin the process of building a 4G35 1750 chain drive for my GTO Group 2 'Works' GTO and have been discussing the details with Ron Masing (formerly of Coltspeed).
I'm happy to pass on any relevant info if that's any help?

Cheers, S

G'day.
Having run 4G32's in GA/GB rally cars back in the 80's, may I ask why why the belt drive?? I read through the thread and while there is some interesting angles to the project, belt drives are universally known as 'boat anchors' - heavy with less than stunning potential - plus the buttery crank........
Not wishing to sound negative at all but is it possible to stay with the chain drive 32' - if you haven't gone too far down the track?
We're about to build a fresh 4G35 1750 chain drive for my GTO Group 2 'Works' GTO replica and have been discussing the details with Ron Masing (whom I'm sure you would know?)
I'm happy to pass on any relevant info if that's any help?
If you're keen to forge ahead, I'll watch with interest and keep in mind V6 roller rockers - we had a play with some of those in a chain drive 32 with pretty good results after a little machining
Cheers, S