PRV turbo questions

[Michaltalbot]

Hello guys,

after some long time back here :-) after building the Horizon 2,2 Turbo II - the Shelby's GLH clone, reached 330 PS and 415 Nm, I'm starting the next project - the Super Tagora.

Yesterday I brought the carrosserie of Talbot Tagora 2,6 SX. The engine train is still there, but original 2 tripple Webers and all parts arround inlet and airbox are missing. But I don't mind, because I want to place there the V6 Turbo, or better bi-turbo. Our family house is finnished, all other cars are sold, so no time/money/wife problems :-) (the Tagora is exactly the same like Peugeot 505 - chassis and axles)

At this moment I'm sorting out what to use as the base. Few years ago I had the P505 2,2 Turbo 180PS and also Tagora 2,2 where the engines are nearly the same, but Turbo had some specific parts to be able to stand the boost pressures. So my first question is:

Which modifications are present inside the PRV turbo engine in comparison to non turbo PRV engine?

Second thing is the source for the PRV engine, I know about Renault 25 V6 Turbo which is easy to buy here in Europe, but it is 2,5 with cca 205 PS, does anybody have some experiences with placing this engine into Peugeot 505? Because I can make the silentblocs, but I heard that the bottom of the engine is completely different, is that true?

Does someone tried to modify the later version of PRV - 2849 ccm to turbo version?

Than there are the latest version of PRV engines, the 3,0 24v which are the most available, but I really don't think that will have the same connection points to screw it to the 505 gearbox, or am I wrong?

Thanks in advance to all who will reply!

Best regards, Michal

[boostin'euro89]

Looking forward to hearing some feedback on this one!

[andrethx]

short answer -- the early PRVs were odd firing; i've read that this is because peugeot originally planned to make it a v8 but lopped off two cylinders when the arab oil embargo hit in the early 70s when the engine was being designed. this version of the PRV was the so-called "odd firing" engine, and is the one that was used in the 604s, the renaults and the volvos -- as well as the delorean. only peugeot stuck with the engine, and the second generation had a split-crankshaft design (making it even-firing), this is the engine that was in the 505 v6.

the r25 v6 turbo is based on a lower-displacement version of the early PRV. delorean owners have come up with all kinds of mods for the early PRV, including programmable ECUs and turbo setups, so you should start with these engines in your research.

AFAIK, all of the PRVs have the same mount points, maybe someone else can comment on that...

andré

[SRDT]

The V8 and V6 where both planned as Audi and others did with their V8/V6 family, an engine bigger than 2.7 liters was heavily taxed in France at this time so the V8 needed a smaller V6 to lessen tooling costs and fill the gap. With the oil crisis they only kept the bread-an-butter V6.

The 2.5 turbo is the first evenfire engine but it's based on the 2.8 oddfire engine with a smaller stroke so for exemple intake manifold can't bolt on a 2.8 or 3.0 evenfire. Also cylinder sleeves from a 2.8 or 3.0 evenfire are too big to fit on the block so you can't make an easy 3.0 out of a 2.5.

Which modifications are present inside the PRV turbo engine in comparison to non turbo PRV engine?

Not so much, mostly pistons, rod bearings, camshafts and for the 3.0 sodium valves and solid rockers (the others 3.0 where hydraulics).

Second thing is the source for the PRV engine, I know about Renault 25 V6 Turbo which is easy to buy here in Europe, but it is 2,5 with cca 205 PS, does anybody have some experiences with placing this engine into Peugeot 505? Because I can make the silentblocs, but I heard that the bottom of the engine is completely different, is that true?

Not the same but not a problem, the specific "semelle" that you can see between the block and the oil pan can be swapped as the bearings arn't machined inside, the Alpine guys are doing this with Peugeot/Volvo engines or 3.0 transverse.

Does someone tried to modify the later version of PRV - 2849 ccm to turbo version?

The 2.8 Evenfire is really close to the 3.0 so why not, but the 2.8 turbo from back in the day (Alpine V6 turbo Pierangeli, Venturi 260) where 2.5 Turbo with 2.8 evenfire crank.

Than there are the latest version of PRV engines, the 3,0 24v which are the most available, but I really don't think that will have the same connection points to screw it to the 505 gearbox, or am I wrong?

You can bolt it, again the Alpine guys are doing it. A modified 24v with twin turbo was the engine inside the Venturi 400 GT and trophy, the engine is deemed reliable: the Venturi trophy was an all inclusive challenge for gentlemen drivers so Venturi needed an engine that doesn't blow or need half his parts replaced after each race. They also raced it at LeMans with the stock crank.

In Europe you can use the 2.5 turbo for an easy swap with stock parts or go for a turbo conversion on a 3.0 with pistons, camshafts and maybe exhaust valves. You can ask Techniprofil for a camshaft suited to your build:

http://www.techniprofil.com/

And you can also order Alpine engine parts from Simon-auto.de:

http://www.simon-auto.de/

You will find a lot of documents here but all in French:

http://club.acm13.free.fr/Documentation/

And here are some pictures from a 2.5 v6 turbo 505:

[Michaltalbot]

Great! Thank You very much! I will go through that web links. I know Simon-Auto because I had several Matra Murena (all models).

Very important info is that 2,8 is the 2,5 with longer crank, is the same way how Chrysler-Simca made the 2,2 (Tagora/Murena/P505 Turbo) out of the 2,0 (Chrysler-Simca 2 Litres). So if I will use the PRV 2,5 Turbo from R25 which is constructed to stand the boost and will use the 2,8 crank, I will get the 2,8 turbo.

Anyway I'd like to play with the cams because Tagora SX had a special cams, that was one of reasons (except of 2 triple Webers and 3-1 exhausts) why Tagora had 170PS and not just pure 136-145 as Renault/Peugeot had. From my experiences from Tagora, the PRV is a brilliant engine, but all people who know PRV just from Peug/Renault speak about it not nicely.

[SRDT]

The Tagora is closer to the Alpine A310 150hp engine, probably same pistons ; I have seen drawings from the Talbot engine with tubular exhaust manifolds and not the ugly cast iron log type, can't tell if they kept them on the production engine.

Talking about the 2.5 and 2.8 it is the 2.5 that is an evolution of the 2.8, they reduced the stroke to have more overlap on the split crankpins. The oddfire crank is cast iron but the split ones are forged and nitrided with bigger crankpins.

On this document you can see what changed between the old 2.8 Z7W 720 that is probaby the same as in the Delorean and the slightly updated Renault/Alpine 2.5 (Z7U) and 2.8 (Z6W)

http://club.acm13.free.fr/Documentation/Alpine%20GTA/MR-MOT-Z-%28E%29.pdf

When looking for Renault/Alpine parts the ones starting by 60 are specific to Alpine, talking about that the A610 engine used "60" parts at first but then Renault released the Safrane Biturbo with a really close engine and so "new" parts replaced the "60" parts from the A610.

[PeugeotPilot]

SRDT, this is exactly the sort of information I need for my eventual Turbo PRV project! I did not realize that the odd-fire PRV cranks were cast - the ones I've seen looked forged but I only assumed this based on the fact that they lacked the thin ridge that indicates a cast part. Two questions then: How hard is it to find Alpine 2.5 internals (the crank and cams at the very least, but hopefully the pistons, sleeves, and con rods as well) and secondly, as far as you know did the later even-fire 2.8 Peugeot engines use a forged or a cast crankshaft?

Hugh

[SRDT]

You will be wasting your time looking for 2.5 turbo parts and importing them, start directly with your 2.8 or a 3.0 Eagle and buy forged pistons.

The evenfire 2.8 and 3.0 have forged rods and cranks and if you look at Safrane parts you will see that a lot are identical between the 3.0 170hp and the Biturbo.

The only thing is that it seems american 3.0 from Eagle Premier arn't exactly the same as the european transverse units, probably a mix between the 2.8 and the later 3.0 but anyway those two are pretty close so not a big deal.

[Bean]

It hasn't been mentioned yet but I'd say John Lane in the US would be the guy to talk too or to do some research on.

John has pioneered the turbo PRV even fire engines (in the US) since his Volvo rally car was powered by a boosted even-fire engine that was rumoured to be 500HP. 4 SP Jehrico manual tranny and a Ford 9" diff were the only parts that could live behind it.

Last I heard he had the Volvo for sale, but I believe he can still supply custom PRV parts last I heard.

Rabin

[PeugeotPilot]

I have sort of an ulterior motive for wanting the 2.5 turbo internals. I'd like to build the most oversquare PRV I can, and in the process reduce the stroke to the point where the piston speed at 7000 rpm is the same as that of the 2.7s and 2.8s at 6000. Not sure if the Alpine crank will do it but it seems like just the ticket. I was going to ask what the bore and stroke on the 2.5 Turbo is, but then it occurred to me that if the bore is 91mm like the 2.8s then with a little calculation the stroke must be around 64mm. This puts the piston speed at 14.9 m/s @ 7000, while the standard 2664cc and 2849cc engines with their 73mm stroke have a piston speed of 14.6 m/s @ 6000. Jackpot. That crank is the solution.

[SRDT]

63mm, with 2458cc it's a small 2.5 ; using 93mm pistons you can reach 2567cc and even more with aftermarket oversized ones. Did you plan using 24v heads?

[Bean]

Hugh - May I ask why you want such a short stroke / lower piston speed for a boosted engine?

Years ago it was due to physical strength limits of components and lack of fine ECU control - but now days both are easily resolved.

Longer strokes usually have a favorable rod ratio, as well as a slightly longer dwell time at TDC for improved combustion.

For the N9TEA build I'd love to offset grind the stock crank and get even more stroke...

Now if you were building an all motor V6 with an 8k redline then the short stroke oversquare motor makes sense, but that old rule of thumb "No replacement for displacement..." is almost always true.

Rabin

[PeugeotPilot]

Rabin:

Fair question and I'll try to address it. I guess if I had to sum it up in one word, that would be "character." It has a lot to do with the type of car I want to build. To clarify, I'm not talking about the current STX project nor the Series I 505 V6 I'm going to create, but rather the V6 Turbo 505 I'm planning.

When I started driving the 604s, I was always intrigued by the somewhat schizophrenic nature of the car. It was an angular, fairly upright executive sedan that always handled and braked better than it looked like it ought to. The engine felt like it belonged in a sports car - not because of it's outright power but because it was so happy to rev and loved to operate at high RPM. Frankly I look at the numbers now and realize that the 604 needed a lot more power to be considered any sort of a sporting sedan, but the way the engine behaved made it feel and sound fast to me. That's viscerally exciting stuff. I love engines that like to be wound out and scream at high RPM. So part of the reason that I want to de-stroke the PRV is that I simply want a 7000 RPM redline in this particular 505. Reducing reciprocating and rotating mass will help accomplish that. So will reducing piston speed, not because I'm worried about failures, but because I want the same wear levels at the higher speeds. While reducing the stroke may affect dwell time at TDC, it also reduces the acceleration and deceleration forces on the con rod and wrist pin bearings at a given rpm, which should help longevity. Reducing the stroke does not automatically mean that the connecting rod needs to be shorter, and in any case the PRV engines have a con rod length to stroke ratio of roughly 2:1 which is excellent.

As for the role of the turbocharger, I'm only after about 200-220 HP because I don't want to have to re-engineer the entire drivetrain to handle the extra output. The turbo installation is as much about compensating for density altitude effects as it is about outright power. I'll run modest levels of boost and hopefully experience similar longevity to the normally-aspirated engines. But I want it to breathe well and rev freely and sound a bit like an F1 car. That will make me happy. Does that answer your question? Sometimes my reasons for wanting to do something are a bit less than purely practical.

SRDT:

I don't yet know which heads I will use. I need to figure out first if the engine can handle an increase in the redline RPM, and if that looks like it is workable then I'll calculate the flow rate I need to achieve and decide which head can deliver that. I've heard that the 24-valve heads can be problematic, so unless I need the extra air flow I will probably stick with the 12-valve heads. I have a lot of decisions yet to make. What is your opinion?

[SRDT]

Early 24v heads had problems but that was solved with the ceramic lifters. For 200-220 hp a turbo seems overkill unless you want a lot of torque, it's a 2.5 that must reach 7000 and be happy about it ; with ITB and good headers your engine will feel and sound fantastic.

I understand quite well this "engine behavior" thing you're looking for, I have experiencied it with the mighty Alfa Romeo Boxer: the car was heavy, with the smallest engine aviable and no twin carbs but fuel injection with catalyst... so zero expectations. But just by firing it the stock exhaust sounded like a good aftermaket one, you're driving the lamest Alfa from all the range but the engine is incredibly happy to rev, it goes all the way to the max power then unlike others that immediatly came down and cut it keeps going and going right to the redline! You can just feel sorry for that brave little Alfa engine encased in this 1170kg Fiat body. Back in the day they said: "when you buy an Alfa you buy an engine, and all that is arond it is for free".

[Bean]

http://www.specialstage.com/forums/showthread.php?73402-The-Fire-Breathing-Monster-is-available-for-adoption

More info on John Lane's Volvo with boosted PRV in it... Legendary car in North America.

Rabin

[Bean]

One option for boost would be a Rotrex super charger.

It'd be a very linear power delivery, well suited for a fast revving v6, and it wouldn't be the same restriction in exhaust note.

Michal - I am not sure if the newer 24V PRV V6's fit, but they have been swapped in Australia so I would say they do bolt up to the transmission. North America never got the 24V engines - so there's no experience on this side of the pond.

Rabin

[SRDT]

The stock intake have been rotated by the aussies so I guess it doesn't fit the normal way in a 505, another reason to get ITBs.

[Guest glen]

I don't know anything of the 505, other then Alpine A310.

But I do know a great deal of the PRV, and of tuning them, specially with turbo. ......3,0 24v. If you want to go big power, you will need to change pistons and rods. Do some nice flowing work on the cylinder heads. Custom build the exhaust system and custom build the intake system. Other engine management system. Big injectors. Better water-cooling. Hard pressure plate for big torque, and cinder metal plate clutch. High end gearbox. Huge turbo, Precision turbo. And a hole lot of other stof, small bit and pieces. 550 bhp and 500 fpt. But most important, a lot of time and big money pile........

Have a nice day, Glen

[Guest glen]

[Bean]

Oh dear God Glen - that looks AMAZING!

Have you documented your build anywhere? I'd love to just pour over the details of that all went together. Your power results are staggering too!

May ask what ECU you're using?

Rabin

[SRDT]

Impressive, lots of mods and whe only see the top. Are you using a chargecooler built in the custom plenum?

[Stewart]

I've been toying with this for while myself. We are getting 200 hp NA easily from the 2850. I believe a new set of cams made with 240 inlet and 260 ex with lobe centre in correct position ( which is about 112) and a single Disco Potato would make your eyes pop. Although if it was easy enough more capacity plus cams and Disco and small charge cooler would freak a lot of V8s. 

[Stewart]

http://www.dmcnews.com/Techsection/performance.html and http://kutsumotors.free.fr/documents/manuel_PRV_Gastinne_Laliere_Wallman.pdf

[Stewart]

I just checked Garrett boost adviser for you. For 300hp and 50% intercooler efficiency a GT2871rs is a fine choice. The map here was generated for midrange at 2700rpm and max power at 6400rpm for a 2.9l engine and 300 hp peak. 50% intercooler efficiency. It tells me from here that in midrange at .6 bar the turbo is in it's 72% efficiency island. 75% appears to be the best area for this turbo so it should spool nicely here. Now add a little more boost to 0.8 bar and both red dots move closer to the best efficiency island. I close enough turbo number to explore for this option or one that is better. Notice at the 2.0 on the left, that means 2 bar absolute or 1 bar boost. At 1 bar boost the turbo runs nicely through the best efficiency  island. Not bad to start with. The Dynosim calculates a good projection. Looks good to start with.

[Stewart]

With a little closer real world intercooler at 50% efficiency, for street use in hot weather seee wher the dots sit on the map now. Bean is much better at this than me, but it might give you a place to start looking. If you can get 2850 Volvo injection cams they had 11mm or so valve lift which is spot on. Advance the cams 2 or 4 degrees and you have a pretty nice turbo cam profile! A duration of 260 or 270 with 220 at 0.050" I recall. I'll have to check for you. Maybe Mr John Lane has better info on that though.