How much compression is safe for the street?

Just for fun, I'll guess you're about 8-9 degrees advanced.

Ken

 

Noe you know that the number your talking about is advance at idle right? The engine will be around 35 total (for a 2V) above about 3000 rpm, and that is the important number.

 

Of course. "Static" advance is at about 950 RPMs on my car.

You have total advance at 3000 RPMs? That sounds very low for a higher revving engine. Mine tops out at about 5000 with a 6750 red line, with about 37 degrees (12 from static and 25 from the dizzy). What does the owners manual (or whatever) say about how many RPMs should have total advance?

Ken

 

I worked with a guy that ice raced a Lotus Europa with the Renault R-15 engine, uprated to the Gordini 807 engine with DCOE carbs. He bought an R-17 ice racer from Archer Racing that had been built to the gills, to put the motor in the Lotus. Structurally its not a lot different than a 308 2V motor, except it operates with push rods. Same 45 degree valve angle, aluminum block, wet liners, aluminum head, 1565 cc's displacement, so like about half a 308. I spoke to the guy who built it, and I forget now a lot more than I remember, but there would really have been no way to drive that motor on the street. Freeway maybe, but in town it would have been literally rediculous. IIRC it had around 12:1 compression and some very extensive porting, the cam had been reworked, shot peen and polished rods, polished crank throws with knife edge's, 45 DCOE's, tuned header, etc.. Power was in the 225-250 HP range at around 9-10.5 K RPM. It was an animal. It really would not run below 1500 rpm, and at that speed was very loud with a chopping sound, like it was whooping. Best idle was more like 1800. RPM's would bounce all around at idle, it just didnt like running slow. Give it gas and it would explode. Let the clutch out without giving a large jab of gas and pumping the throttle to slip it to get it moving, and it would flame out. You basically had to just rev it and dump it if you wanted to take off. Tach would momentarily drop a few hundred RPM if you punched it, and then it would be past 6K before you could catch it. It would pin you in the seat real hard once it lit though.

I have to believe that 450 HP NA in a 308 would be one wild animal. Being its got twice the internal reciprocating mass, it would be able to idle down a lot lower, but it would still be quite the animal. And running like that, any engines life will be remarkably shorter. Thats a race engine, pure and simple. And honestly, from whats been shown with blowers on here, and what Mark has shown us, a blower is far far easier on these engines. I think if you start pushing very much above 350 HP you may not be real happy with it at low speed IMHO.

 

I'm amazed at both the redline and HP of the Gordini! That guy must really know his stuff; that's a full race engine spec for sure. The "stock" Gordini (which was never offered on an S2 but lots of them have been swapped in) is 10.5:1 and makes 95-100 HP on a good day. Swapping for duel Webers is common. People have claimed 120 HP but the dynos don't bear that out.

My engine is the Lotus head, Ford block DOHC 1.6L with twin Strombergs which is mostly stock. With emissions crap it makes 117 HP; mine without the crap, plus SS headers and electronic ignition probably is about 125. It has nice low end torque but comes into its own 30-80 MPH and over 3000 RPMs. I've been told it's also similar to 1/2 a 308 engine but I do have a steel block, not aluminum. The engine only weighs 30 Lbs more than the Gordini.

As your post indicates, a full race engine for street use is stupid. The wear and tear alone makes for an expensive and difficult trip to the store with it! I question if the ancillary parts of a 308 could take 400+ HP for any length of time. My Europa would fly apart!

Ken

 

I have no doubt the 308 would hang togther as good or better than any engine around. Its really over built. You cant really compare it to many other engines. Mark had his pumping out great gobs of power, no trouble. Norwood had built many motors developing well above 325-350 HP NA with no troubles, and the gearbox might even be tougher than a TR/Boxer gearbox. 900 HP is a figure I have heard a few times that the 308 gearbox can withstand.

IIRC, the early Europa came with a Renault motor and gearbox. But the engine was the basic 807 block with an L head and a two bbl down draft Weber. The US carbed version was about 95 HP IIRC, but the 17's came with an injected Hemi head version that made really good power. The problem was the breathing and the camshaft. Fix that and it would probably hang with a twin cam? Lots lighter too. That motor all assembled, and with all the accessories hanging on it and ready to run, only wieghs about 220 pounds. Your twin cam is cast iron IIRC?

 

Mine's was up at 500+ for 2 seasons with stock internals and no problems. I'm working on it now to see how it deals with 700

Russ's 3.2 should be about 340 or so when it roll out again and I think my 3.0 will be about the same pre-boost. The hp is in the head flow


A stock 4v is 32 degrees full timing at 3500 rpm I think the 2v is 36 degrees at 3500, but I'd need to double check that.

 

95 HP might be a factory quote but no stock US Renault powered S2 made that much. Most tweaked Renault enignes do however. Autocrossers tend to use the S2 as they are lighter and can be hopped up legal;ly in ASP to 125 HP; similar to my TC.

Yes, my TC block is iron; the Lotus head is aluminum and it all weighs 250 pounds. The extra weight is more than offset by the extra HP stock, and a TC engine can make 180 useable HP with porting, cam changes and Webers.

The Renault gearboxes were said to be fragile, but people use them up to 150 HP with no problems. Broken gearboxes are almost unheard of. Those who put Toyota 4-Age or Ford Zetec engines frequently swap them out however.

Ken

 

I doubt my engine at 1.6L could be modified to go much over 200 HP NA, and I'm pretty sure my stock crank would not be long for the world there.

I need a primer on advance I think; a 7500 redline engine has the advance top at 3500? Can anyone explain why this is preferred over a longer advance curve?

Ken

 

RPM is were most of the load comes from, increasing the power through flow improvements will maintaining stock redline adds very little additional load. 100-120 hp/liter is were a good naturally aspirated engine should be on pump gas.

You want to turn the advance up to were the hp peaks at any rpm....often that leads to detonation at lower rpm though. A more efficient combustion camber will require less total timing and allow more timing to be added sooner, the redline really doesn’t come into the equation. I have a programmable ignition curve and have found the 4v running 91+ octane premium will take full timing at 3000, the factory curve however works fine with 87 octane regular.

edit: I should add that most engines, including the 308 like the timing pulled back 1-2 degrees up past the torque peak.

 

The 2 valve peaks the ignition advance at 5000 rpm, at 34 degrees advance. However.... Mine, and I have read of others, BigTex I know for one IIRC, our flywheel marks were 3 degrees retarded from true TDC with the adjustable index plate moved over as far as it would go. Short of slotting the holes to slide it over farther I just magic markered mine temporarily until I can do a better fix.

Point being is that even if some of you reading this thread dont want to degree wheel your motors, it would be rather simple to put a piston stop in and "carefully" double check your true TDC. 3 degrees of advance can make a bit of difference.

 

My dizzy has a handy thumbwheel that gives me 4 degrees + or - advance. When I time the ignition, I have that at 0 and dial in about 11 degress static, then adjust it where it's as advanced as possible without kickback when I start the car, and no pinging. It's a lot easier than fractional movements of the dizzy to fine tune the advance before tightening it down. Do other people have this? It's one of the few good ideas Lucas ever came up with!

Ken

 

I cant recall seeing those on anyone elses distributors, I thought it was a good idea as well. But regardless of initial idle speed advance, full advance checked at the corresponding engine speed must be right on. So in the case of a 308 you need to rev the motor up while watching the timing advance on the flywheel to whatever point it stops advancing. It should top out at 5000, but you need to go higher just to see. Full advance 34 degrees should occur at that 5000 point and you need to time the distributor there and leave the idle timing alone. If your idle timing is to far off you need to service the distributor.

 

I would think the dinoplex is getting crankshaft position data from the magnetic pickup wheel or whatever they call the thing? Then it should in some way be possible to advance or retard the wheel to alter timing?

 

The sensor fixed to the bellhousing, is it possible to modify the sensor, or the bellhousing or both to get a slot so you can move it to and fro?

 

It's 36.5 degrees at 5000 on the 2v digiplex cars according to the manual

On the 4v, it's 32 at 4500, not 3500 as I stated earlier for stock.

Both the 2v and 4v car benifit from getting the timing in sooner, but there is no good or easy way to alter the timing on a digiplex car.....the only real options are to add a haltech E6x or similar in place on the digiplex boxes or switch to an electromotive set-up.

 

I'll be a whiped dog. I went back in and looked in both the GT4 service manual as well as the early carb owners manual. It shows 34 +/- 2 degrees at 5000, but it dont stop there. The curve shown in the shop manual stops advancing at 13 degrees total distributor advance at 3400 distributor RPM. That would push total advance to 38 +/- degrees at 6800 rpm. Unless of course the manual is wrong? The owners manual shows an entirely different curve that stops at 3000 distributor RPM with 16 degrees of distributor advance. Both graphs show 9 degrees at 2500, so they match for 34 at 5000, but they sure cant both be right. Its also interesting that the 2V injected take more advance than the carbed cars. They sure dont make it easy to understand thier cars thats for sure.