Legoland951

I believe the car was running normal boost for a turbo in the NA motor. The car belonged to Danno back when he was running Guru Racing. If you look at his previous posts, maybe you can find some information. I remember having to go to Willow Springs to tow his car back to my house and he tore the motor apart in my garage before finding a crack in the cylinder bore.

I am pretty sure there is a table where compression vs boost is listed. If you want a super high compression (NA compression + boost), you will need aviation fuel to prevent pre-detonation. Basically, a 8.0 to 1 compression + turbo (at factory boost levels) effectively ups the actual compression ratio. If you use the factory boost level on a 9.5 to 1 ratio, the actual compression ratio is much higher than that of a turbo and the higher the effective compression, the higher octane fuel needed (think diesel level of compression where gas will detonate long before the spark ignites it)

The differential ring and pinion is not easy to change properly IMO. The pinion gear is machined into the output shaft and will require the complete disassembly of the gear box which will require special tools, heating to a certain temperature in the oven, and proper shimming (if required) to get the right spacing between the parts inside the tranny. The ring gear and pinion and how they mesh may need careful measuring and shimming for the specific case you are putting it in. Think changing the ring and pinion in your typical rear wheel drive axle assembly (where on the teeth on the ring and pinion contacts) requires proper shimming of bearings for preload and back lash.

It is MUCH easier to swap out the tranny. If you are trying to get a higher 5th gear for top speed or gas mileage, take the 5th gear out of the NA and put it in the turbo tranny and install the turbo tranny into your car. The 5th gear change is easy and requires only the rear of the transmission to be taken apart. You will need a new rubber "cap" in the rear of the transmission and the gasket.

I would put a LSx Chevy motor in it. It is much cheaper to do as there are conversion kits (and its been done many times compared to any other swap). 400HP with torque of a V8 and the reliability of a Chevy motor is hard to beat.

Somebody will buy the body from you and likely put it back on the road one day. The NA car will be relatively worthless compared to a turbo IMO.

Dwizle

Wasn't planning on running high boost. 12psi or less on E85 for the most part with a standalone running dual knock sensors and a flex fuel sensor. I want a quick daily driver car, not I'm making 500 hp trailer queen I can only drive on the weekend car

That's an option but would probably put a 6 speed from a Boxster S uses a shifter linkage similar to the 944 has a hole in the trans for the shift rod just like a 944 only that the slave cylinder for the clutch sit there so with a little shade tree engineering it can work just waiting for the prices to drop a little. also I was planning on doing the work off swapping the diff just wanted to know if it was an option and has it ever been tried?



Kits for the O7k are about the same as a LS and the 5 cylinder has a sweeter sound.
And I wouldn't say the NA is worthless cause 10/15 years ago the whole 944 family was worthless not even considered a real Porsche by many even if it was the car that saved Porsche as a brand. Now turbo's are worth something so give it time the NA's will be worth something even molested ones

Legoland951

I don't know how to calculate effective compression ratio at 12 PSI on a 9.5 to 1 compression motor. The compression ratio for forced induction is dynamic, not static and varies across the RPM range. I don't understand why you insist on using NA pistons when it is not the right part for boost. Why not put a set of used turbo pistons and rods and be done with it? If you are going through all the work anyways, it is a few hundred dollars more for much more power potential...

How much is a boxster 6 speed cost? I have been out of the 944 scene for more than a decade. Isn't a 951 box in the hundreds and the boxster box in the thousand $+? What is the cost difference between the conversion + boxster tranny compared to the cost of a bolt in 968 tranny if you really want a 6th speed? Also, does the gearing ideal for the 944 turbo torque curve compared to a 951 box?

IMO, very few engines sound better than a V8 with a good muffler. Maybe some V12 from Ferraris and some other exotic cars.

The 944 is relatively worthless compared to the turbo. It has been that way from new and into the future if you ask me.

odurandina

Yup. The some/many/most turbo cars have killed/will kill their owners though.
Been that way from new, recent past, and into the future.

Dwizle

I guess you didn't read the part where I just pulled the whole turbo motor out of the turbo body and stuck it in the NA body no MOD other than the S2 flywheel and clutch to run my standalone ECU.
Why does every one think the NA parts can't handle boost. a 12:1 stock Honda can handle boost as long as it's tuned properly and running good gas. So can a 944 na it's been proven it can be done you said you have been out of the 944 scene for a decade in that decade there have been mistakes made and improvements and discoveries made and I've taken what I've learned from them and will apply it to what ever I decide to do. a stock turbo is pretty gutless until boost kicks in the higher compression pistons will fill in the bottom end until boost kicks in properly tuned and knock managed and engine should live a happy life until it eats a #2 rod bearing.

In 2021 you can control boost electronically to fit the individual gear ratio of a car. a Boxster tranny is about the same as Turbo tranny but there are more of them readily available. find me a listing for a 968 transmission south of $4k. again you been out of the game do some research. It's not so much having a 6 speed but having a stronger gear box the 5 speed Boxster trans a just as weak as the 944 trans.

I guess that's you opinion and you are entitled to it. But I am sure a lot you people on this and any of the other car forums hosted be this site might disagree.
like the 944 is half a 928 engine the O7k is half of a Lambo Audi R8 V-10 engine

Legoland951

Never said the NA parts can't handle boost. The NA engine is identical to the turbo engine other than pistons, rods, ceramic coating and different valve material. The turbo engine is nothing special.

My friend (RIP) built 3000 HP dragsters supercharging motors that had more than 12 to 1 ratio before insane amounts of boost is applied. It can be done and it is done. But it cannot run on street gas. This is something I stated a few times already.

A 12 to 1 Honda with any kind of boost cannot run on street gas. Pre detonation is determined by laws of physics. Nothing more, nothing less. Running race fuel IMO is impractical on the streets.


How much are boxster S trannys going for and how much are the turbo trannys? Serious question.

Dwizle

Dude you have no idea what you are talking about plain and simple.
http://www.roguetuning.com/944na_internals_-_the_limit

While I was doing the engine swap I helped a younger guy 2 stalls over install twin turbos on a stock V-8 2018 ford mustang
Came in a kit engine wasn't opened up just headers and injectors removed and turbo system and larger injectors and fuel regulator installed with a intercooler plumbed the oil system for the turbos reflashed the ECU n drove away the tune was good enough to run pump gas out the box at 6psi. no exotic race gas or aircraft fuel.
93 octane pump gas the car will run better on E85 which is available locally at several gas stations.
https://www.hellionpowersystems.com/...-turbo-system/

V2Rocket

stock Honda (Ford/GM/etc) engines with 11:1+ take boost fine on pump gas - it's all about timing and not getting greedy with it.

yes the 4V head gives you a lot more leeway with timing than the ancient bucket the 944 calls a combustion chamber but the rules still apply.

speedjw

We've been racing our stock NA 944 motor now with boost on 93 octane for the last 3 years (6x 14hr long endurance races).

https://rennlist.com/forums/924-931-...ons-944-a.html

Dwizle

Thanks so much for chiming in
Where were you 2yrs ago lol Nice set up BTW

Legoland951

A 9.5:1 compression ratio engine of a 944 NA with 12 PSI boost will give you an effective compression ratio of 17.31 to 1. The conversion chart showing this is here: https://www.rpmoutlet.com/boost-comp...atio-chart.htm. To quote the article:

"Experience has shown that if you attempt to run more than about a 12:1 effective compression ratio on a street engine with 92 octane pump gas, you will have detonation problems. To some degree, this can be controlled with boost retard devices, but we do not recommend that you set up your engine and supercharger to provide more than a 12:1 effective compression ratio.... Table 1 shows that you obviously can't try to run 10 pounds of boost on a 9.0:1 compression ratio engine. This gives you an effective compression ratio of 15.1:1, way beyond our 12:1 figure. If you are building your engine from scratch, it is a good idea to try to build it with a relatively low compression ratio, such as 7.5 or 8.0:1"

If you are telling me it is OK to run pump gas on 17.31 to 1 ratio without pre detonation, I don't have anything else to add to this conversation.

I stand by what I said. Your example of a Honda with static compression ratio of 12 to 1 with any kind of significant boost should not be run on pump gas. Will it run on 87 octane? Yes it will. For how long? Your guess is good as mine. A Honda with 10 PSI of boost will yield over 19 to 1 dynamic compression ratio. This is reaching diesel territory.

Pre detonation is exactly what kills engines like the broken piston ring in the link you provided. The turbo piston ring is nothing magical and the NA piston ring didn't break due to excess power.

Legoland951

Nice car. 4 to 5 PSI boost yields an effective compression ratio of 12.1 to 1 to 13 to 1, which is consistent with the top end of compression ratio on pump gas.

What kind of power are you getting?

Dwizle

where did I say how much boost I was planning to run? Guess you are stuck on your high horse and still can comprehend I put the stock 2.5l turbo motor in my car.
Stock mean original turbo pistons ring rods crank block balance shafts water pump turbo and associated plumbing
But you made an assumption of what my plans were. But if I do go thru with it I plan on building as much boost as the engine will take until I detect knock or pinging then back it off whether it's 6 psi or 15 psi who knows same with timing run it as high as I can go until I detect knock or ping then back it of a couple degrees. but I will have a better ECU than Bosch and Porsche had in 1988 controlling the entire thing. Not Say I am smarter that Porsche or Bosch just that I have access to better equipment and experience in 2021.
Rouge tuning ran a stock engine to 350 hp before a piston ring failed the engine didn't explode into a million pieces the ring broke into 4 pieces when the
ends kissed due to heat expansion not knock or detonation. the ring gap is a bit larger on a turbo to account for that scientific tidbit the engine failed because of thermal expansion of the ring not detonation or knock
https://rennlist.com/forums/924-931-...ons-944-a.html he's been running a turboed NA 3 yrs guess he's breaking your laws of physics and thermodynamics

Zirconocene

I can't speak to the conversation on compression, but holy S#!+ do I want to see if you can make that Boxster transmission work.

I have a beater 968 that I'm planning on putting an 07k into. I don't think that the car will need a transmission but...it's in rough shape, so I'm at least collecting ideas for contingencies and that sounds like an incredible idea.

Cheers

Legoland951

This is where I got the 12 PSI from. I ain't going to get into a pissing match with you as it was not intended to be.

The compression parameters are what they are. Not my rules.

Read a couple posts up about the lemons 944. In his post, he stated he is running 4 to 5 PSI, which yields effective compression ratio of 12.1 to 1 to 13:1, which is exactly what I was saying to be the upper bracket for using pump gas.

Thinking I am on any kind of a high horse is incorrect. I am only stating what is. Again, not my rules. Pre detonation on pump gas will happen at excessive compression, static or dynamic. I think it would be quite silly to argue against it. One doesn't need to take thermodynamics to utilize that concept to their advantage.

My opinion is what it is. I would go one step further and change the pistons out to turbo pistons to realize the full potential of forced induction on pump gas and not cripple a forced induction motor by having high compression pistons to start with.