Bill, I didn't see an answer to your question about calculating dynamic compression ratio. If you don't know yet, you measure the remaining volume of a cylinder after the intake valve has closed. The captured volume is your usable compression ratio and the intake valve always closes after BDC. As for the drop gears, the 3.4L engines I build make 335 - 375HP and there have been no failures of any component in the driveline. When deciding on compression ratio, 10:1 is a good number because you wont feel the difference between 10 and 10.5:1 torque-wise but you might get detonation if you have a streetable cam in it while running the higher ratio. Run P6 cams and the 10.5 wont be an issue but that cam might not be what you like on the street.
Paul has described 'effective stroke' or 'static dynamic' compression. Actual dynamic cpr fluctuates based on the volumetric efficiency of the engine, which for purposes of this discussion are basically the head flow/cam selection. A static compression ratio is generally chosen based on what the known quantity of air volume the heads/cams are flowing and what fuel one is planning on running so to avoid detonation. If the engine is running at 100% volumetric efficiency at some point, then the dynamic ratio matches the static ratio. Peak torque rpm is when the heads/cams are flowing the most air. A stock 2v 308 head with carbs and the cams you plan on running is probably getting very close to 95-100% VE at peak torque. Naturally aspirated F1 engines make so much power at ridiculous rpm due to their heads/cams flowing well above 100% VE.
Hi hyenahf, The plan is to swap to a 328 trans, but so far, no candidates. I’ll expand my search to look at Mondials. I wonder if the gear ratios are the same as used in the 328. I sure miss those online, SPC’s and OM’s. Throughout the 308-328 family, I can only find two sets of trans ratios. The differences are in first, 13/42 or 13/40 and fifth gears, 28/24 or 29/24. First gear is machined into the input shaft, Ferrari input shaft 126843 is used for all 328’s. Fifth gear is determined by a replaceable main shaft gear and a replaceable layshaft, 4-5 cluster gear, so really any good 328 transaxle will work for me and 5th gear can be changed if desired. I prefer to stick with a clutch cable, but we will see. Hi Fabspeed, I had some welding done to what I think was a Larini muffler I bought slightly used on ebay. It was almost new and all stainless. I had to weld a support structure onto the muffler outlet pipes, to match up with the OEM chassis hangers. I also had to shorted the length of the front bank inlet pipe. In lieu of Ferrari studs and springs, I use stacks of stainless steel belleville (truncated cone) washers and by alternating their orientation one creates a variable length compression spring. This muffler is euro style, no cats, but 2 inlets and 2 outlets, plus double outlet tips. I have O2 bungs welded into the muffler inlet pipes for each bank. I use an LM1 with aux box to normally collect A/F (lambda), rpm, MAP (a pretty good measure of throttle opening), and g-forces in 2 axes, for a 44 minute period of time. Other/additional signals are possible. I plot and analyze the data in Excel. Hi Paul, I have to wrap my head around your dynamic compression ratio definition. If I understand correctly, as the piston starts upward, after BTDC, some of the stroke is considered wasted for compression purposes, because the intake valve is still open, so no compression yet. At some point, the intake valve closes and when this happens, we begin the theoretical compression which will be a little less than if we calculated compression from BDC. Did I get this correct? I’m using Cat Cams 1700402, so pretty good lift (Int 10.75 mm 0.423in; Exh 10.00 mm 0.394 in), but modest duration (at 1 mm, Int 254 deg, Exh 246 deg) . This cam should be a good street cam. No plugs in the exhaust and a bigger intake valve should help. I’m shooting for 10.3:1. My ignition system is stable, accurate, and semi smart in that it can be mapped to adjust to MAP. I’m looking for a noticeable torque increase throughout the usable rev range, which I hope will extend to 8 krpm, given the carb limitation. I think I will come in near the bottom of your results. I got 190 bhp from a 1.9 liter Lotus twin cam on 45 DCOE's. A 3.4 liter at an equal state of tune would be 340 bhp. I'm expecting about 320 from my 3.4, but very good torque. The lightweight 360 crank should be happy with the factory Ti rods and their bigger pins. When you are referring to CR in an engine discussion among knowledgeable people, are you more often than not thinking in terms of static or dynamic compression? Thanks especially for the feedback on your 3.4 liter engines and their drivetrains. John Henkel, MMC's service manager made me aware of the drop gear weakness saying he saw instances where the cover retaining studs were pulled out. I think his assessment is correct in. Frank at Modena Engineering acknowledges that his earlier semi helical drop gear sets, beat up the drop gear cover, but no specific findings were ever provided. I've talked about reducing the helix angle, the main trade off being additional gear noise. I wonder if this is a linear effect, the less the angel the more the noise or is it more of if the helix angle angle is reduced to some threshold, is there a step change in noise? It seems fair that if all is in order, a good 308 transaxle setup will work. Hi Ferraripilot, Thanks for jumping in. A big fat torque curve means an engine can run at near 100% VE for a good part of the rev range if desired. I think the carb induction with the low inertia crank and rods will be a good driving experience. So far, there are no 328 transaxle transplant candidates on the table. What do you think a new one would cost? What is a NOS 328 engine/transaxle worth? What is a NOS 328 engine worth? Bill
Bill are you going 3.4L with the build? John you're splitting hairs, in the real world you will just use a degree wheel and given the seat timing you can say X amount of volume is left in the cylinder after the intake valve closes. That will tell you the effective ratio. Its a street car not John Forces Top fuel car. Bill, with no heads on and knowing intake valve closing you can measure the piston position in the bore once the degree wheel tells you the valve would be closed and measure the volume at that time. Im sure there's software to accomplish this as well.
Hi Paul, Yes, 3.4L by virtue of 79 mm stroke 360 crank and 83 mm bore 328 sleeves. The cam spec sheet shows 22/52 for the intake cam at 1 mm for spec duration of 254 degrees. At a start flow lift of 0.1 mm, duration increases to 291 degrees for the intake cam, 37 degrees more duration. So half of this is 18.5 degrees either side of the ramp. We can say the intake valve closes at 52+18.5=70.5 degrees ABDC. That's a lot of wasted compression stroke based upon the geometry. I calculate 26.37 mm of 79 mm is wasted. The effective stroke for CR calculation is the difference, 52.63 mm. Bill
Yes a lot is wasted! And when you take into consideration the engine really only has just over 8:1 compression when you measure it you can see why the cars lack torque but pull well in the upper RPM range. The bump in displacement and a real world 10:1 engine (or a tad more) makes a dramatic difference and the first thought that comes to mind is this is how the car should've been originally. The car will then be a well balanced combo of power and handling. Certainly not overpowering the chassis.
hi bill im not 308 expert but i believe the mondial 3.2 and 328s are different. then there are the euro market cars that typically have longer gears with the taller final drive. some say the swiss market ones are a hybrid of usa and euro gears? mondials were often shorter than 328 or 308s. i reckon its to offset their weight penalty. perhaps the some of the historians can chime in here with gear ratios, drop gears and final drive combos. personally i like the tighter ratio boxes because im addicted to revs and still drive like a teenager. it helps a tad since found the usa's power with my 2 old 308s underwhelming. if memory serves, i find the short usa 1st gear nearly useless but i prefer the 4 afterwards. the euro qv i drove, the 1st gear seemed much better or the car was was significantly lighter with more power. for me it would be nice to stack a taller first to the usa 4 remaining gears/final drive.
Hi Paul, Thanks for the kind words. I too think the new package is balanced and was doable in the day. Hi hyenahf, I'm still looking at a Mondial 3.2 engine/trany combination plus extras. It's the right model, but Mondials use a hydraulic clutch. Maybe a Mondial pedal box with MC could be retrofitted to my 308? A 328 package is a better choice if available. I also have little information on Mondial 3.2 gear sets. The key is the right layshaft /CW which controls overall gear ratio, and there are at least 3 possible ratios. I think USA variants got the shortest gears. Bill
i reckon there will be a lot more gearset combination than 3 when you factor in the 208 tighter gear clusters along with 2 or 3 other transfer drop gears couple with the 208 tighter gear clusters. i dont think you need to monkey with the entire pedal box assembly; https://www.ferrarichat.com/forum/threads/formula-gt-308-hydraulic-clutch-conversion.563804/
Hi hyenahf, I want my car to be a well balanced grand touring car, with enhanced torque and long legs. There was real progress over the last week when I learned of a low mileage 328 donor candidate that could supply everything I need for the 328 transaxle conversion, from my go to supplier, GTCP. I await pricing. My QV/328 WSM says all 328 gearboxes had the same ratios as the euro 308’s, but differed in drop gear and differential ratios. US versions are very short geared. The QV/328 WSM shows all 328’s used the taller euro version 308 gear ratios, but with the 328 input shaft. The drop gear and differential ratios varied, depending on market. ..................................................... My spec US ver. std/base ver CH ver Drop gear teeth ratio (I/O):..............27/29.............27/29...................27/30..................27/29 Drop gear numerical ratio (I/O).......0.931.............0.931...................0.900...................0.931 Differential teeth ratio (I/O):............17/61............16/65...................17/63..................17/61 Differential ratio (O/I):......................3.588...........4.063...................3.706..................3.588 Overall ratio includes 5th (29/24):...3.190............3.611...................3.408..................3.190 The differential ratio makes a big difference. I want the 3.588 differential for low rpm cruising. The U SA drop gear ratio also helps. I was considering a Mondial engine/tranny/rear suspension package, on a pallet in Scotland, for an asking price of 3000 GBP, but it went down. I really needed someone to put eyes on it and I also started to feel uncomfortable when the seller insisted on a bank-to-bank transaction, with no justification. He claimed to be able to ship the pallet lot to my door for 600 GBP, but would provide no details. Too bad, cost appeared low enough to take a chance, as he said he had it running after his purchase, with the parts lot to be provided. The Mondials of interest all used a hydraulic clutch. I have little information on the gear ratios. I visited my engine builder in Long Island and got a few shots of my engine build in progress. We’re still waiting on the pistons from JE. Image Unavailable, Please Login One of my replacement heads with valves and seats ready to go. The intakes are oversized. Retainers are Ti, The inner/outer springs rub together lightly for damping. These springs are wound opposite handed. Image Unavailable, Please Login The exhaust ports look like they were just cleaned up with a flapper wheel. Image Unavailable, Please Login The oversized intake valves are clearly bigger than the exhausts. The rough seat for the intake is on the very outer edge of the valve. Image Unavailable, Please Login Sleeves are fitted and held in place with the studs. Image Unavailable, Please Login The 360 crank spins freely in the block. Image Unavailable, Please Login This is an overhead view of the 360 crank in the 308 block with a note to change the thrust bearings. Image Unavailable, Please Login This is the bottom of the 308 block bore, with a 328 sleeve fitted. Image Unavailable, Please Login Overhead close up of the 360 crank in the machined 308 block. Note the X and A markings on the crankshaft. I’m told the 360 crankshaft is very light weight. It appears to be a forging. Any idea what the markings mean? The rods will be Ti. Image Unavailable, Please Login This is the nose of the 360 crankshaft.where a spacer needs to be fitted. Bill
New pistons came and were fitted. Bore clearance was good, but deck height was not. Delivery time for the new pistons was about 3 weeks. With the new pistons installed, it was possible to check valve clearances and calculate actual static compression. In the beginning I was thinking 10.2-10.5 CR. Peter Morcovicci, my engine builder, was recommending 10.0-10.3 CR. In the end, we wound up at 10.5:1 CR. The valves were lashed up, mounted to the block, and the cams were timed. The round tooth pulley set, I bought from derekW, was fitted with Gates Blue belts. Thanks Derek. I elected to purchase the 328 drive train from Bill Young at GT car parts. Bill supplied the following photos. The US specification ratios are good except for the CWP. New Swiss specification CWP’s are available but pricey. I could not find euro spec CWP, my second choice. The gear train assembly was shipped to John Henkel, at Miller Motor Cars in Greenwich, CT. As a teenager growing up in Southport, Ct, I had visited Luigi Chinetti’s (NART) show room, a short distance from the current MMC dealerships, as a teenager in 1965 time frame. I remember seeing two, black GT40’s in the parking lot. Over the years I have run across folks who were involved with Ferrari in the day. Lee Slaton, of MMC, oversaw the tear down and assessed the condition as nearly new. Lee is the technical guru and from what I have seen, really knows his stuff. I feel pretty good knowing he’s going to supervise the rebuild where we are replacing all bearings, seals, synchros, synchro rings and springs and pads. Even though all pieces look perfect, including the LSD plates, I elected to reset the cycle number clock, to as close to zero as possible. The other thing is they are using my transmission pieces as an internal, refresher/training course, for their legacy cars. The other interesting thing is my engine builder, Marcovicci Wenz Engineering, does the vintage engine rebuilds for MMC. They recently rebuilt and inside plug V-12 for a PF Coupe. The owner is reportedly very pleased. The insides of the new gearbox are pristine. The gear teeth and shifter fork faces show no wear upon disassembly. Image Unavailable, Please Login This is a really good shot of the transfer gear system, which looks great in the photo. One can clearly see the outboard bearings and other features that distinguish a 328 gear train. I don’s see the outboard bearing for the tranny input shaft, in this photo and indeed they were apparently lost some time after these photos were taken. Bill supplied a replacement 328 input shaft and offered to supply the two missing lower drop gear bearings. Thanks Bill. I elected to go with new bearings for replacements. Image Unavailable, Please Login As shipped. Nice crate. Image Unavailable, Please Login I contacted Frank, at Modena Engineering, asking if he could supply a tall, quick change, helical drop gear system, giving 80 mph at 3000 rpm using: 5th gear: 24/29 (0.8276) CWP: 65/16 (4.0625) Rear tire 225/50 R16 Frank recently replied that he could provide an appropriate gear set, so I asked him to go ahead and build me a tall ratio and a USA spec equivalent, as a second ratio. I expect to select another ratio or two, after break in and on-road experience. This upgrade will be made when hardware is available. Until then, I will be running just the USA spec assembly, so more revs than desired but acceptable until the fall time period. Bill
Glad to see some progress Bill. Fancy swapping your used bearings and synchros for those cam pulleys? I know where to get more pulleys, bearings and synchros... not so much With the work you’ve put into the engine I think there’ll be enough torque and rpms to be fun and fast with any ratios.
Hi Derek, Thanks for the encouragement and the offer. I'm inclined to do the swap but let's see what the pieces look like after tear down. While the shaft assemblies are out of the trans, they are not yet disassembled. Should I have synchro gaps checked? I think I now have all the pieces I need for the rebuild. Quality of individual replacement pieces should be challenged. Many of the pieces are unmarked, like the needle bearings on each of the shafts. I need to spend some time identifying about half the pieces. Bill
New synchros should have a 1.2mm gap and limit is 0.4 so you can estimate how much is left if you re-use any of them. Hope all the bits look good and fit together nicely. The diff spider gears are known to wear (and hard to find) so hope yours are ok. You can switch around the LSD clutch plates if they are worn-- I think there is info here on Fchat somewhere.
Hi derekw, Am I correct in assuming the gaps can be measured in their current state, shafts assembled, but out of the case and on the bench. I estimate about 1 hour to align and measure the the 5-gaps, say measure 3--places, for each synchro, then average for that synchro (ex. (1.2 + 1.1 + 1.0) / 3 = 1.1 mm average gap, nearly new?. LSD was stripped down and all appears perfect but build up requires 8, expensive, one use nuts and bolts. I found spider gears available from a Dino specialist in Germany, along with all the other fixings. All my LSD stuff, except for the output bearings, CW nuts and bolts, will be reused, as is. I thought you already acquired synchros for your rebuild? Bill
I had ARP make new diff bolts for the race car I worked on some years ago. ARP has made many special bolts, & studs for me over the years. The quality is unreal, torquing a set of there studs is an unbelievable experience compared to original Ferrari studs, not even close. Far superior.
For rare metric bolts try Misumi-ec.com and Accu.co.uk. Latter seems to do custom stuff and more expensive/slower. I can order for you if they won't ship to US. ARP are works of art but I never had replies to several requests for custom fasteners over the years.
Hi MerlinTech and derekw, I contacted ARP weeks ago, but they couldn't offer anything off the shelf (about 180 ksi tensile). Although ARP do make a few flywheel bolts, they were too short and had inadequate heat treating for the CW application, according the representative I talked to. He also said that Ferrari normally has very good metallurgy. I declined to evaluate having custom bolts made. Ferrari replacement nuts and bolts are now in hand. Bill
Good to know, I have never had issues with ARP not getting back or getting it done. They are not fast or inexpressive but they are nice. Next time I need something I may go a different way.
Hi Wade, Best ARP rod bolts are heat treated to deliver 180 ksi, maintains enough ductility to withstand cyclic, tensile loading. I think ARP said their CW bolts (2 for VW and one other application IIRC) were heat treated to 190 ksi, by increased hardening (likely the same material). These attributes might be better to a a more constant tension application like a flywheel or CW bolt. Bolted joints are really difficult to analyze structurally. Bill
I have never used them for rod bolts on Ferrari engines, but I have had them make studs for old engines that would just have old replacement studs. Head studs & main cap studs, some trans axle stuff. I just love the repeat ability of there stuff. When re-machining stuff I tend to assemble and measure a lot. They are dead on start to finish. I do agree, I wouldn't want to put in there rod bolts. I usually just put in an aftermarket rod and that takes care of any rod issues. I haven't had the need to have the old original rods in one yet, but I would imagine I'll face that at some point and will have to have a solution then. ARP is probably not it for rod bolts.
I have put their rod bolts into lots of engines (incl my 308.) Beautifully made and checking torque vs. stretch they are always very consistent.
Great information, I didn't think they made the rod bolts for a Ferrari. I have used there rod bolts many times, just never in a Ferrari.
ARP 126-6101. These are for a 4-cyl Alfa so you'll need two sets. They are tighter in the rods so you will need to hone a touch or re-size the big ends (which you'll probably do anyway-- none of mine were round within spec.)
