308 Engine Rebuild & CIS to TWM Throttle Bodies Conversion Thread!

Is all this work worth the trouble/expense for 6 HP? That's the most you will get above stock for the compression change assuming the standard compression ratio is 9.2:1. A one point change is worth around 2% assuming the gas/timing can support the compression increase. If you have to retard the timing then you lose most of the gain.

It takes around a 30HP increase on a 3000lb car to make a clearly noticeable and consistent difference in actual performance. All 6 HP will do is to allow you to claim that instead of having say 270 HP, you now have 276! In the world of engine building, increasing compression on it's own by one point is not worth the trouble. Compression increases are useful because they increase power throughout the rev range, not just at the top end but they are usually accompanied by a lot of other mods and are usually 2 or even 3 point increases. But this requires very careful attention to timing and fuel quality.

 

Super excellent - exhaust looks nice.

You, sir, have things well in hand for a supremo Ferrari.

 

With the bigger cams and the bump from 8.8:1 (I think that's what our cars were) you are going to see a massive improvement .. . (edit: I'd consider going higher than 10:1 though especially if you're doing a programmable ignition curve) in spite of the carbs . . .. the guy should remove the sleeves and bore them out of the block (if they need boring . . . ball honing is fine if there's no wear) . . . if he can't do that Artvonne mentioned cycle guys doing it which makes sense . . . the Wiseco's have been working for me and cost less than J&E although they left some details off that I think are important . . just me I guess.

Get your guy to CC your heads . . piston guys want that # . .. I think mine were 41/42 cc but I've seen different numbers posted here so better to get your own IMO . .. also if you want to get every bit of power change the compression height of the piston so they come flush with the deck . .you'll still have the gasket thickness for clearance . . . again I have these numbers but would hate to find out there were variations in the blocks.

Or you can just order them from Norwood and pay a little more but they'll make sure they're right for you.

You mind posting a pic of the other side of your heads? . . . love to see the freshly machined surface . . and there's hardly any meat under there . . take a close up of the intake valve seat if you don't mind.

Thanks,

Sean

 

keep in mind my experience is only with the injected cars . . hate for you to find out Mike's right 'cause of the carbs . . . I'm a little over 11.5:1 compression with stock low lift injected cams (.300 lift) and made 210 rwhp . . . my recent spark plug experimentation has got me thinking I'm making more now but maybe 10 hp I'd say at the absolute most.

Mike our cars 2Vi stock were real dogs . . like 205 at the flywheel and I've heard that's optimistic .

cheers

 

If you are really getting into tuning this engine it is definitely in your best interest to have the cams reprofiled to take advantage of all that extra compression. Your current cams will certainly respond very well to it, but to take full advantage of it then a little more lift and duration is in order.

This opens up a whole new can of worms of course: How much more lift/duration? how should the cam timing be set one they are reground? should the heads be matched etc blah blah blah.

If you dont want to mess with all of that and are just in the compression for a little more of a bump I completely understand. It can turn into a never ending project if you decide to go as far as to change everything because of all the second guessing regarding cam timing etc.

Good luck!

 

I was led to believe you need to be near some "standard" size for rings . . . it was my understanding filing the ends of the rings is only to compensate for a few thou . . so you really can't just randomly pick a bore diameter 'cause you're getting pistons custom made ... . the "available" ring sets define it . .. I heard this from very very reputable engine builders and layed it out in CAD to see how much (or how little) the curvature of the ring made contact with the bore when just filing the ends of the ring to compensate . . . it looked like a real concern to me.

cheers

 

Wiseco made my pistons, didnt need to send a sample. You do have to specify compression ratio such as 10 to 1 but I would bump it higher still such as 10.5:1 and you need to specify the over-size you want. My car for example had fresh liners in it, fresh ferrari pistons etc so a standard 81mm piston did the trick and I simply deglazed the cylinder wall with a hone. The new pistons came with rings (3 ring design unlike the originals), pins and clips for $1400, awesome deal. If your cylinder walls are not tapered and measure out standard then you can run the same size piston again with a quick hone for the rings to seat and to assure correct piston to wall clearance.

 

some guys use a honing machine to remove material that other guys use a boring machine for . . it all depends how much is being removed.

having cross hatch lines doesn't mean **** . .. someone could've been in your motor before . .you need to have someone measure 'em

 

Wiseco calls for .0035" clearance which is more than the standard cast pistons call for . . . do not run the same clearance as the standard cast pistons . . . run what the manufacturer specifies which can be achieved by a little honing.

 

now I remember specifically when I was 'splained on this . .. the motor that's in my car is 1mm over . . one of the sleeves did not completely clean up . . discussing this on the tele with one of the Fchat sponsors here the next size that was available with a decent selection of rings was .06 over . . not .05 . . so I ran 'er at .04 over 'cause the pits weren't where the rings run anyway

 

J&E calls outs the same

 

I'm really surprised they are looking for that much clearance. I ran JE pistons in my race bike with an 81mm bore (iron liners), 9200 redline at .0015" clearance and threw them away at .003" clearance because the rocking would cause all kinds of problems. I'll need to look into this before I get to that point with my engine....could be the air cooled casue the cylinders to expand more, but I'd expect the pistons to expand even more then...hmmmm.

 

I think it's the expansion 'cause the Porsche guys were telling me they were running .0015" with billet air cooled jugs and J&E . . . plus aluminum jugs that expand more probably true on your bike? I had a scuffing problem at .003-.0035 but I am running the hell out of my motor . .. you might be doing that

 

I thought about this a lot . ..you guys experiment with less and report back . . . this was one tolerance I tried to stick to

 

I bet we're running the pistons near peak/same temp with air cooled or water cooled . . makes for more efficient combustion . .just a thought.

 

If you were running a single or a pair of rings that might explain it as would the skirt length.

 

JE says:
.0022-.0028 for the 4032 pistons which is what I've always run
.0030-.0035 for the 2618 pisons

It's been my finding that scuffing is offen casued at break-in by to much rmp or heat too soon. I've had good luck over the years runnign the clearance tight and doing a nice slow breaking.

 

as always . . the more I learn . . the less I know . . so this go kart guy was telling me I should run JE 'cause tighter bore tolerance and they were the only forged piston that you could run that tight . . then I get this set of J&E pistons and it calls out for .0035 and I'm thinking "no wonder I had scuffing if other forged pistons grow even more" . . but . .sounds like there's couple different alloys and I got the alloy with typical growth characterisitics like the Wiseco forged . . .

thanks for peeling another layer of the onion . . . next time somewhat talks about J&E I'll ask "which alloy mate?" .. luv doing that.

cheers

 

I was told.... The guys that bored the liners said they wanted the piston paperwork before they would touch them. If you bore first and the pistons come back under or over, well, you cant very well unbore the liners.

I dont know why, but Brian at Wiseco wanted to keep sizes to the mm, so instead of 81mm +.010", or 81.5, we just bumped them to 82mm. Once I had the pistons I took the liners, pistons and the paperwork over and they bored the liners to the proper size.

But as stated in another thread, Wiseco wanted a lot of measurments. They have 308 data on file, but as we all know, these cars are not always identical and after 30 years you never know if someone changed something. And the piston manufacturer wont be liable if you didnt give them the right information. Its also best to do it yourself and see it with your own eyes so you know how to discuss it as well as what you want. Its easily worth the price of the measuring tools and the time and effort to figure it out.

Measurements I recall they wanted;

deck height, compression height, stroke, rod length, cylinder head volume, gasket volume, dome volume, valve lift during overlap phase at 10 before, TDC, and 10 after, plus valve head edge to bore clearance at same points. Once you do all this you can calculate your actual CR you have now, and I believe you will find its not the 8.8:1 ratio the books say it is. More like 7.5:1. And if thats what you find, a set of real 10:1 CR pistons will really wake it up.

 

I just went to 10:1 in my car and YES, the machine shop wanted the pistons before they bored. I went with Weisco's and they were great to deal with. You need to CC the heads so they can get the compression correct.

 

JE USED to be the "tighter" piston manufacturer years ago but that is just not true today. Most good piston companies have their stuff together enough and all run about the same clearances according to the alloy used and design of the piston. Wiseco, Ross, JE all seem to have good recommendations from people on here.

 

I looked at the spec's on a couple of boxes of pistons I have this a.m.:

Wiseco: . .. .0035" clearance . . bought in 2006
J&E: . .. .003" clearance . . bought in 2007

Mark mentioned the other J&E alloy that can be run tighter . . so what are you saying? . . . new Wiseco and Ross you can run this tight . . as in new being after 2006?

Just as another side note I had scuffing on bores that I might have been closer .0032 not .0035 with the Wisecos and it was on the front bank that I thought ran hotter which I thought might of contributed to the scuffing . .. not the .0002/.0003 less clearance . .. however, I think this bank runs cooler than the rear which had no scuffing and a little more clearance 'cause those sleeves were more f'd up from the fire/rust . . basing this hot/cold on how plugs look when I've been looking at 'em (edit: hot bank had plating burnt off like 3-4 threads . . front "cold" bank only 1-2 threads)

cheers.