|10/04/2005 16:34:14||paul||Hey guys
when building a high torque v4, what breaks first? head gasket? crank? melted pistons? im trying to work out where the weaknesses are so i know where the limits are. Im not too worried about the con rod bolts as im not going to rev the engine any higher than standard. Has anyone dyno'd their cars? what kind of torque (at the crank) do you reckon the gearbox can handle before it becomes unreliable? What kind of torque can you get out of the engine before IT becomes unreliable? If anyone knows the answers to any of these questions id be really gratefull.
|10/04/2005 21:04:42||paul||oh, and does anyone know the compression height for standard 1.5 pistons?
|11/04/2005 11:52:19||Alistair||All depends how well you build it! If you follow the Saab S&R tuning instructions you can't go too far wrong, but it would depend on how far you intend to go. Gearbox is by far the weakest link, followed by balance shaft gear. Boxes are often unreliable with standard power & torque. Expect that to break before the engine. Fibre-toothed balance shaft gear will shear if you rev over 6300 ona regular basis.
If you're not planning to rev beyond standard (5500 or so) then you won't get a whole lot more power out of this engine. Most of the accepted routes to mod your V4 will involve steel timing gears and stronger valve springs to allow it to reliably rev.
As for the components you list, it will depend on what types of each you use and the overall level of mods you make. Standard bottom end & head gaskets are good for 90bhp+
|11/04/2005 12:08:11||paul||hmmm... im gona put in a 1700 crank, with 93mm pistons (take it to 1815cc), drop the compression ratio to (hopefully) 6:1 using thicker head gasket and lower compresion height pistons, and fit a super charger running a bit over a bar of boost. I havnt finalized my calculations yet but this should keep peak pressures in the combustion chamber below those seen in a motor putting out 130bhp at 6000 rpm (thats a guess of what a na engine can make reliably but i need to check that out). Hopefully this should mean the loading on the bearings should actually be a bit less than those on a tuned engine. How can the bottom end be strengthened? the saab manual seems to talk about grinding imperfections off but are any different parts used apart from stronger rods/bolts? Again calculations not finalized but im hoping for ~100bhp&100lbft @4700 rpm, should make a nice little road motor (apart from the fuel economy)as the torque increase should be ~proportional through the whole range :)|
|11/04/2005 12:17:50||paul||oh yeah... how much torque do you reckon a standard box can actually take and still not need regular rebuilds?
|12/04/2005 08:01:33||Richard||If you are using the box for road use then you will get numerous years use out of it if it has been rebuilt correctly before hand. I recommend you set the pinion to the full -ve tolerence ie closest to the ring gear and from memory 2 thou backlash. All the bearings need to be good and most are available new bar the pinion bearing which is hard to get.
Basically work on a std Reniz head gasket being ok to 10.5:1. The timing gears are weak and so are the std 1500cc rods and bolts, go for v6 and arp bolts, if you are rebuilding it you may as well do this. Crank is strong, cross drill version better for higher revs. Your pistons will only be safe to 10.5:1 in cast form, so you may want to go to forged v6 which have a lower crown height and lower compression ratio. You will probably get 6:1 with some chamber removal from a unskimmed head and v6 pistons.
|12/04/2005 17:08:07||Alistair||A novel approach! Sounds like a good project.
6:1 seems very low for a blown engine these days. Why not keep the compression higher for better low speed performance but reduce the boost? That said, with a wardrobe full of Saab anoraks I know more about turbos than I do about superchargers...
You'll probably get over 100 lb ft as the standard 1500 engine gives 85 at about 2500 rpm. A 1700 high compression engine (ie not the LC US Saab engine) on a standard cam will give 100 lb ft on a decent carb, the long throw crank really helps the torque.
What fuel & ignition are you planning to use? What cam? What head work apart from opening the combustion chambers? Presume you will flow the heads to get the best from the blower & go for bigger valves? You might need to think about the valve material on a blown engine.
|12/04/2005 17:36:15||paul||The compression ratio should be ok as roughly the same boost is applied at all rpm, the plan was to use everything as standard apart from the pistons and rods and bolts. The main reason is simply to keep cost down, cams are expensive, require steel gears etc and to get the most out of them you have to get everything balanced, the price seems to add up...
My torque figures were based on the peak power, not actually peak torque, but based on standard peak torque vs torque at peak power, i should get ~130lbft ish at 2500 rpm... maybe thats a bit too much for the gearbox? The temperature of the exhaust gasses should be up about 20%, but the engine will need alot more cooling as overall heat dissaption will be up about 12%. Im not convinced by my model yet as it predicts best power for quite late ignition timing, less than 10°btdc at ~5000rpm, think i need to do a bit more research into burn rates of the mixture. As far as the fuel/ignition goes im thinking standard ignition with a good coil (maybe go electronic), and a single carb (i havnt done any somes yet but im guessing something designed to fuel a 3L shoud be ok) although i might need two. Im thinking about fiting an injector to richen it up when off the throttle to help cool things down a bit under braking. Im gona put in an intercooler, but not hook it up yet, and a bypass valve on the supercharger. Does anyone know if the torque and power figures in the haynes manual are on the road or at the crank? I guess some homebrew porting would be ok, but nothing too drastic, ill probably just match the manifolds to the ports.
|12/04/2005 17:48:08||paul||oh yeah, based on your figure of 100lbft(im presuming on the road), my peak shaft power/torque are 135bhp/151lbft torque... although the peak torque the crank is subjected to arent any higher than on the 140bhp@6700rpm engine, my torque curve is just fatter (same torque applied for longer, like going from a single cylinder engine to a twin cylinder engine). I really need to check those figures though, they seem unfeasibly high...|
|12/04/2005 17:52:49||paul||peak power still 110bhp, used 151lbft@4700 whih is cheating... thats better :)|
|12/04/2005 18:11:03||Senor Burt||Get steel timing gears. It's the balance shaft gear that usually goes and there's not much force on it. I've also had the camshaft gear strip. They're a major weak point.
Carb for a standard engine is usually Weber 28/36 DCD (I think). Probably a bit weedy for your purposes. 38 DGMS would probably be better (Simultaneous opening throttles). SAAB used 40 DFI on some rally cars, but they're not easy to get. I assume you have a 4-bolt manifold to fit a twin-choke carb. If not, get one now.
The heads are quite restricted. It's probably worth opening them out as much as you can.
Check out my site www.crumplezone.co.uk/project95v4 . There's a link to the 70's SAAB Sport and Rally mods manual on there.
|12/04/2005 19:24:11||paul||cheers, ill give that link a look. Im gona use a sidedraught carb, fitted upstream of the supercharger, with the supercharger attached to the standard manifold. Ill give the timing gears a look if my budget stretches that far. Does anyone have any recomendations for people to rebuild gearboxes? how much do you reckon for the parts to rebuild one?|
|12/04/2005 23:59:50||Alistair||Good luck getting a standard inlet manifold that will flow enough for a single side-draught carb on this engine of yours ;-), if you have to go that route you would do best with a 4-stud inlet manifold and some sort of custom swan-neck thing between carb & manifold.
If you have the know-how do some calcs on valve temps as I suspect you will struggle with standard exhaust valve material.
28/36DCD won't be up to this job. A twin choke carb from a late-ish Ford like an XR2/XR3, or even a 2.0 Pinto might be a reasonable start, but think also about the R5 turbo as that had a carb...but only a 1.4 engine.
Agree with Burt about going for steel timing gears. Pain in the arse to replace the fibre ones after all this work, and could be costly if you lose the cam gear.
Haynes figures will be flywheel.
Timing will be somethign you have to set up on a rolling road for summat this bespoke, but my old 1500 with SAH cam (roughly like Saab 7.2mm S&R cam) timed at 16 deg BTDC at 1000 rpm with vac disconnected.
THE gearbox expert is Chris Partington, dunno about cost but Richard Simpson on here (Rich rallies a V4) knows lots about them so over to you Rich...
|13/04/2005 07:53:17||Richard||Well Chris has had to do the work through dealers and this has bumped up the cost. This is due to Chris having closed his bussiness and therefore his insurance. To get insurance he has to go through specialists and quite correcltly they want something in return for this.
You need to contact Highgate, Saab Restoration company, Graham McDonald.
Due to the fact I need plenty of gearbox rebuilds, it had doubled my cost and I have machined up a set of set up tools. All you need is a false diff that is set at a known position. We then have a metal pointer that fits on the end of the pinion in the cone machining and we smear this with thin grease to hld it in position. This then sits near the false diff so we can use feeler gauges between the two to set the pinion. The backlash can be set with a bracket and dial gauge off the top casing.
|13/04/2005 07:56:27||paul||I dont really know enough about the four stud manifold, is it the same casting as the two stud manifold with a bigger hole in the top, or are the actual passageways different inside? The plan is to put the supercharger inbetween the carb and the manifold, so that i dont have to put the carb in an airbox, thinking about it im going to be drawing enough air to power a 3~4L engine so youre right, i probably will need two carbs. The timing gear does sound wise, it would indeed be a pain in the arse to pull the front off the engine again. As far as exhaust valves go youre right it may be a problem, its a tricky one to work out though as the temperature of the gas is not equal to the temperature of the valve. The valve material has a greater specific heat capacity so the gas has to cool down more than the valve heats up. I might try and come up with some figures, didnt they make a turbo v6? or did i imagine that, maybe those valves would do. The S&R manual mentions a cast iron housing for the box, ive never heard of these, do they still exist? Im guessing they arent exactly lying around by the shed load. Will post revised power and torque figures when i work them out. does anyone know if you can run an engine in by letting it run at fast idle for a hudred hours or so, or does it have to be done under load?
Thanks for all the help by the way everyone, all this advice is proving incredibly usefull...
|13/04/2005 08:28:05||paul||hmmm... that doesnt sound too bad richard, dont suppose thered be any chance of some photos of your tools in use, i cant really visuallize what you mean? I havt rebuilt a gearbox before, but im not in a hurry so i guess if i just take my time and follow the instructions carefully it should be ok... btw now presuming the 100lbft on a standard 1.8 is at the flywheel im looking at 133lbft peak torque, nicer figure i think
|13/04/2005 17:43:09||Alistair||Here's some info I've posted elsewhere on the 96 turbo that Mike Woolfe built in the 80s, not all relevant for you but some of the issues will be the same and you can see the extent of the mods Mike & Barry made:
OK some more info on the Mike Woolfe/Barry Marsden car:
1500 crank, +30 thou overbore (so not quite +1mm, ~ 1520cc)
Heads ported & gasflowed, combustion chamber opened up to lower the CR (doesn't say to what), bigger exhaust valves, std size inlet, all in 214N stainless.
Asymmetric Burton cam, timed to standard. Polished & lightened rockers, standard pushrods, all blue printed & equalised.
Baffled sump, additional rocker cover breathers & oil return for the turbo.
Weber 32/34 DMTT carb on modified manifold.
T3 turbo, fabricated exhaust, fabricated intercooler to LHS of slightly relocated rad, oil cooler in front valance. Early V4/long-nose 2 stroke round lamp grille.
All flexible fuel & brake lines in proper Aeroquip, solid lines in Kunifer 10 brake piping.
Pukka Saab 5x15 minilites, 185/65 tyres (IIRC he had BF Goodrich on when I saw the car) S&R front springs, I know from speaking to Mike at the time that they tried S&R rears but didn't like the progressive nature as "the car kept swapping ends" and ended up with custom static rate rears. I believe they fitted billies all round too. 1 deg -ve camber up front with 4.5deg castor. Custom strut brace in 18/80 stainless.
Fly off handbrake. Totally refitted interior with custom dash using Sport gauges, 900 seats incl rear head rests, leather/ally s/wheel. Electric mirrors, modified rear wings to move the swage line up giving more space for the tyres, 96GL DRLs, 96L rubber bumpers.
116bhp at the wheels...
Without doubt this was/is??? one of the best 96s I have ever seen and beautifully engineered by Mike & Barry. Just wish I knew where it was now...
|13/04/2005 19:05:22||paul||wow! that sounds pretty amazing! goes to show how strong the internals really are... I think im probably just going to build the engine as strong as i can, run it in not using the supercharger, and then take it to a dyno and turn the boost up until i get to the kind of torque figures im looking for, i think its the safest way i can do it hopefully without braking anything... Its gona be a while in the building but ill keep you all updated as it comes together.
Thanks again for all the help everyone, in sure ill need more before too long :)
|14/04/2005 07:56:24||Richard||I will try to get a photo sent in and may do a little article for Al.|
|15/04/2005 08:57:40||paul||Ive got one more nice easy question for you guys, If i wanted to move peak torque up to about 3000rpm is there a cam that would do it? the rally cams seem to give peak torque at ~4700rpm which is a bit high for my needs.|
|15/04/2005 09:40:34||Alistair||The SAH cam I had in my 1500 would be fine - it was really a fast road cam, and I believe very similar to the Saab 7.2.
Don't know the exact details but timing (measured with schoolboy protractor) were approx:
Inlet opens @ 32 BTDC
Inlet closes @ 65 ABDC
Exhaust opens @ 65 BBDC
Exh closes @ 15ATDC
Piper & Kent used to offer similar cams so you might get some joy there. We had one 1500 engine in an ex-grass track car which was supposedly bog standard but with a Piper Stage 3 cam, even ran on a std car. No idea what it would have been like on the road but it ran fine round the field behind our house & wouldn't have revved any higher than standard (valve springs would limit that) but certainly flew. Of course, it might not have had that cam at all, we never took it apart...
|15/04/2005 12:19:34||Richard||Kent are very helpfull. Tell them what you are wanting to do and they will advise what cam profile you should use.
Kent do cams from mild to race, we have one that is between a std cam and a 7.2 for road use.
|15/04/2005 12:30:16||Richard||Just make sure your drive is up to the job. I would take the drive direct off the crank and not the balance shaft. So there will be a bit of engineering there. I think you would kill the timing gears and the balance shaft bearings otherwise powering a compressor.
Failing that a low pressure turbo could be used (I know not as nice as a supercharger). The 96 was turbo'd as a test bed for the 99 in rallycross before production of the 99T started. One of the Roadstar cars was up for sale in Sweden a few months back.
I have seen a turbo mounted where the heater is positioned. The exhausts were flowed together round the back of the engine and a turbo mounted in the pipe after that point. The exhaust then went through the floor at the back of the engine bay a la works exhaust.
|15/04/2005 13:00:20||paul||I did consider a turbo, but decided against it in the end as it would have been even more of an engineering job than a supercharger, which will be no small task in itself! Im planning to mount it sitting quite high and forward in the V of the engine, but im gona have to play with bonnet clearences to be sure. I may have to make a fibreglass bonnet with i higher central section but ill see how it goes. Im going to mount a drive pulley on the front of the crank pulley, with a wide belt just to drive the sc. The problem is what to do with the radiator... im considering mounting it where the heater is now ala the v6 in the gallery, or possibly fitting a lower wider radiator as i have a round headlight grill on. The thermostat may have to be removed to a remote location, but other than that im hoping it will be ok. The other drive possibility is to mount the sc behind the engine above the gearbox and engineer a gear drive off the flywheel, although im reluctant to do this as lubrication would be a nightmare coz you cant get oil on the clutch, and the length of the total induction tract would be huge.|