V-12 Engine into 308 Build, over on Grassroots

Interesting on the SNJ5 car....I didn't do the heads on that, my buddy did....I have a few sim models for that engine as Russ, Vic, and I talked quite a bit while Russ was planning it. I have an extra set of the custom 31.25mm intake valve for that engine if you ever need them.

I've run a lot of sims and yes, the numbers are pretty close on the stock setup. Right now the usb key for the software is with another buddy, Wade who's piston vise I still have until I can clay my pistons, and who is lending me his line lapping bar so I can finish my engine so I can only give you estimates at the moment. The cam swap will give you...10hp. The pollution cams cost the carb cars 25ish hp. The CIS cost another 20. Going not quite 1/2 way back up on the cams will get you not quite 1/2 the lost hp....so 10ish is what I'd expect....air=hp, its just that simple. To me it does not seen other the expense or bother...if you are keeping the CIS and want hp you of all people should be thinking turbo

 

What about higher comp pistons and cams with CIS.

 

I’ve dyno’d a few different Ferrari’s on my Dynojet. Here’s some quick data (from memory)

81 308 GTSi 129whp. No idea what is so wrong with that one.
82 Mondial 8, no cats 157whp
79 308 in “average” state of tune 165whp
78 308 with carbs balanced and ignition timing as good as I could get it. Also no cats 182whp
82 Mondial 8 with 10:1 compression, no cats, Electromotive ignition 183whp
83 Mondial QV no cats 188whp
77 308 no cats, 10:1 comp, euro cams, ignition and carbs dialed in VERY well. 220whp (this car came in making 172whp, tuning is important)
87 328 no cats 216whp
1990 348 243whp

 

Hi Aaron,
Thinking about building a Frankenferrari myself. One question, did you reinforce the chassis at all? In a GTS, the chassis is already a little floppy...

 

I don’t have any chassis reinforcements. I’ve considered adding some of the Group 4 tally car braces, but haven’t bothered yet.

What spring rates do you have in yours? Mine is sprung pretty softly and doesn’t feel too floppy. It’s nothing like a modern car, but it’s more rigid than say a C4 Corvette. Are the rubber inserts and cone shaped things on your door latches in good shape? Those are a huge help because they make the doors into stressed members.

Aaron

 

Everything helps some. Compression is a diminishing return game but going from say 9 to 10 will gain you ...3-4%?, 9 to11 maybe 6-7%. It goes like that ASSUMING you have high enough octane fuel and don't need to retard the spark below optimal. Higher compression usually wants less timing as the combustion space is smaller and that's fine, but if you see hp going up as you add timing but can't add more because you've got detonation....well every degree you're short is around a 1-2% hp loss so you can loose all and more of the gain from the added compression quickly.

Then just add the cam gain to it, again assuming you have enough octane to tolerated the added cylinder pressure, more flow=more hp...because there is more air in the cylinder and that means higher cylinder pressure, higher octane requirement.

There are terms called Brake Mean effective Pressure (BMEP) and Volumetric Efficiency (VE). Porting heads, good cams, tuned intake and exhaust all increase the amount of air getting into the engine so the VE goes up, and that drives the BMEP up, cylinder pressure is what makes torque, torque at rpm is hp. There is an old rule of thumb for us pushrod engines...torque (ft-lb)=deployment (ci)....it just always works out because they always run around 85-90% VE and BMEP around...10-11bar? CIS 308 engine fall almost exactly at this same point...180ish ft-lbs, from 183ci. The highest numbers are up around 135%VE and 18bar, the FrankenFerrari should be right about 125%VE (over filled cylinders, so effectively 6-8pis boost giving around 500ft-lb from 330ci) and 16 bar, at its10.7CR but you could also be 10-11 bar at 10.7CR....its a system and everything works together. But my point is that anything you do to make more power makes more cylinder pressure and generally wants more octane so you need to keep that in mind.

 

We ran into exactly this yesterday on the dyno. Customer built his own motor, used off the shelf forged pistons for a different gen motor, a factory thin metal head gasket, a decked block and a resurfaced head, so compression is up from a factory 8.5:1 to about 10:1 on a turbo MR2 motor. On 93 pump gas it makes 300whp at 14psi of boost, but also makes 300whp at 17psi because we had to knock so much timing out of it to keep it from knocking. Switching to E85 today. Should be able to run the boost up until we run out of injector somewhere around 28psi and 450whp.

 

A little more on this topic, its worth says that a 308 uses a transaxle so there is no torque transmitted through the chassis......so 100hp or 1000hp the chassis acts about the same. I've dirven my cat at stock 235(maybe) hp, 380ish, and 600ish and very honestly didn't notice a difference it how it drove other than faster acceleration and generally using less rpm as hp/torque went up. I think with a 308 its pretty safe to talk about hp and handling in completely separate conversations.

 

Thanks Aaron. I run 350/300 - from what I've read, 400/350 seems to be the sweet spot for a GTB, so I cut it back a bit for the GTS. Roads can get pretty rough over here, and I wanted to lower the ride height (only for aesthetics), so wanted to increase the spring rate for safety. The car creaks over driveways, so I know the chassis is what it is, and all the rubbers need replacing, which will help with the creaks and rattles while driving. I just thought putting some triangulation and gusseting in the floor structure might lessen the scuttle shake a bit.

 

That's a very good point! I was mainly thinking about scuttle shake and overall chassis stiffness. I'm putting 360 brakes on as part of the mod, and just wanted a stiffer overall structure. I have access to 348 heads, which Aaron tells me flow better, but I think some worked QV heads might be almost as good for a lot less stuffing around.

 

It has been a LONG time since I looked but I’m softer. Like 200-250 maybe. It’s really too soft because I have the shocks set to full firm. But on the rough roads around here it’s pretty nice. I have all new poly bushings too. I rarely have the roof on, so I don’t notice if it squeaks when I pull in the driveway. Haha.

 

My 308 is pretty extreme (678whp). The 3.2 Mondial was an easier to drive car with better low end and midrange and made 550whp. Mk e said he had a set of valves that fit those heads and he knows who ported them (it’s SNJ5’s old 3.2 Mondial, well documented on Fchat).

 

Once I got rid of the distributor (Tundra coils) I had room to fit a decent water to air intercooler in the engine bay.
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Very neat! I looked at the 928 supercharger, but it was more throttle response and mongrel I wanted, rather than outright hp.

 

That is an awful lot of power! I'm thinking about 400bhp from a 3.6 or a bit more NA motor would be the sweet spot for the chassis, which, let's face it, isn't much improved from the 50's.

 

I'm totally with Mk e, I don't think the extra power really had any negative effect on the chassis. If you're bored here is a video that shares a bunch of details about the turbo Mondial (and my 308).

 

I have F430 brake on now, haven't driven with them yet but they are on .

My car is also a GTS and I've been running 450/400 and its decent....proportionally stiff in the rear perhaps but kind of waiting to get it out with the new engine before making any changes, leaning toward 500/400 but may go a bit higher.

I need to do something with swaybar too, only running a front at the moment in an attempt to improve rear grip plus the stock bar didn't fit with the 550 wheel I was running when last it was running. I'm 3/4 planning to do cool hollow bars, they have lots of size option once I make ends for them.

The 308/328/348 head are all pretty much identical castings. The 348 is fitted with a bit larger valves and the port is larger at the intake flange. When I do 308QV heads I use a 348 manifold gasket as a template. Then you can use the 348 intakes valve or go a bit larger...31.25mm is about the biggest that will fit on the stock seat, I have 1 set left if you're interested. I flow at 10" and stock they are about 93, getting 105 or so is pretty easy, 115-120 is possible but pretty much a waste with a stock intake which flow...93

 

Come on man, the intercooler goes in the intake!

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Thanks Mark. I shouldn't be asking you this, because you probably find it no trouble to fabricate a space shuttle engine out of a Coke can and a Junior Mint, while half full of Chivas and cough syrup, but which way is more straight forward - QV heads with lots of porting and bigger valves, or 348 heads with somewhat less porting, but in need of modification to fit onto a 308 block?

 

Throttle response with a supercharger is indistinguishable from naturally aspirated other than the car actually RESPONDS when you push the throttle

Boost is by far the most cost effective way to add hp. I've built 3 setups over the years. 1 with an eaton mp112 I thijnk it was, it was good for 10si, 380 hp. Then I did 2 with a lysholm ax2300 and an intercooler in the intake that was good for 24psi and 600ish hp. 2 of them have popped up on ebay over the past 10 years so they are out there somewhere.....the 1 lysholm setup I didn't finish as the the guy buying it wanted to do the finish work but never did, it was still unfinish last I saw it. user Verell has or had the last, not sure he ever installed it but for sure it worked as I ran it about 15k miles on my car.

the down side to a blower is the engine sound.....blowers have a distinctive sound.

 

Yeah......I would say need porting is need porting so 308/348 are not much different to get flowing well. A little more grinding on the 308 but you just use the 348 gasket as a templet and have at it, it goes really quick to rough it out....an hour or 2 total then they are the sane work as 348 from there.

I have not personally fitted 348 heads to a 308 so I'm not sure or the steps. I now they will bolt on, studs, water, oil passages the same so the work would be cam belt sprockets....there is probably machining involved there. On the plus side the 348 cams are decent and putting them in the 308 heads would be the same machining.

I would use the heads I have because I have them I guess, no big reason to switch I can think of.

 

I would just port 308/328 heads over doing the 348 heads again. The 348 cams turn the opposite direction so unless you fit 308 cams (I don't know that you can) you have to run a weird firing order. I think that's why my 308 and 348 sound different.

 

Thanks guys - I'll stick with the QV heads. One less complication. Just need to find/fabricate a manifold that will fit with ITBs under the hood - lots of fun!

 

I know the lobes are symmetric so they don't care which direction they spin but I guess yeah, 2/3, 6/7 end up reversed in the firing order. He's going to need better cams than 308 to make hp thought....there are some aftermarket last I knew and Web can weld/grind to whatever spec for about $100/lobe, again last I knew.

 

that is the fun part!..Mmmmmm...welding.....

picked an ECU yet? literally sitting here changing stuff in mine so its on my mind. I THINK I just setup the CAN buss to read a MAP signal from each cylinder, calibrate it the primary MAP, then display it for TB syncing and use it to trim the fuel in each cylinder so TBs synced right or not it should still run good. I had it doing that sort of but using a massive amount of the ECU processor's time, like 30% and not working about about 3500 rpm. This change should drop that under 1% and work at all conditions.....If I did it right....I'll recheck it tomorrow one the influence of the force has worn off.....drink I must

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