951 block as NA engine?
 

Wondering if anyone has taken a 951 short/long block and run it in an NA944 with NA manifolds/DME etc. I figure it'd be down about 10hp vs standard na engine due to lower compression...

Down more like 20-30bhp. There's some online engine-calculators somewhere that can model this change for you. I just extrapolate in reverse the difference between U.S. 944 NA vs. later Euro 944 NA with the higher-comp pistons.

You think? My guess was based on the 87 vs 88 motors. Upped CR by 0.7 and gained 5 HP. So going down roughly double that from 9.5-8.0 should be double or more that change down...

The euro na had higher cr but a hotter tune for higher octane gas, even accounting for the euro/us octane ratings, and no catalyst.

Online calculators show-5 or so HP for that cr drop.

In that case, 10bhp, sounds about right, not sure how linear that function is.

The 944-spec guys were seeing +10bhp from increasing compression to max, about 11:1 I think. Also 3-5bhp from removing balance-shafts. Full-time 93-octane chip another 5bhp. Paul Bloomberg in AZ's the one to consult on this.

Might get the 8.0:1 NA back up to same as the 9.6.

944 Spec rules limit compression ratio to 10.5 and no balance shaft removal.

My interest is relating to making power with cam timing, ignition advance, and perhaps added displacement later but with more margin for knock protection on crappy pump gas like we get here in California.

Basically an old school big, low compression, super street friendly pump gas motor

Why not swap in a 16v head if you want to make more power? I have a local friend who has one for sale. I know that isn't the answer you're looking for, but a 2.5 8v motor with 8:1 compression isn't going anywhere fast unless you're running E85 or something lol.

I had a16v head and sold it because I didn't want to deal with added complexity and it'd be questionable at smog testing time.

I want a meaty torque monster engine that will run on California pump water... Building it bigger with cam timing and tuning for power.

Spencer, why don't you upgrade to an S or S2 if you are looking for a "meaty torque monster engine?"

Please don't say you won't because of the 16V cam tensior and gear train; you replace the chain and tensioner blocks and you're good for 100K or more miles of torque. And they are very easy to do.

Because the S could never be considered torquey. The s is hopeless below 4000rpm.

The S2 is better by a long margin but pricey, and like I just said there's the problem of (visual) smogging the car if the tech is by any means Porsche savvy, which they sometimes are around here.

A big displacement, sohc is what I want. Even if it's down on power versus say an s2. And I want it to require 89 octane max for some knock headroom since ca gas is so bad. Which throws the s/s2 out anyways.

The point of this thread is seeing about people's experiences driving a low cr 944 around daily.

An 8.0:1 NA engine just sounds depressing. I can't really think of any reason to build a low-compression engine except to add some kind of forced induction. At least not from a performance standpoint, anyway.

I'm no expert in engine building, but wouldn't you want a higher CR for a torquey NA motor? I just don't see you being able to get all the power back with a cam and ignition timing, let alone end up making more than the original would with the same mods.

Also - I run my S on 89 octane with no problems. The manual calls for 90 RON, and around here I can either get 89 octane midgrade or 93 octane premium. The car doesn't mind the 89, so that's what I run. No issues with knocking even on hard runs on hot days, and I get slightly better mileage with the 89. It's an S with an S2 intake swap and a freer-flowing exhaust but otherwise stock. It's definitely not very torquey below 4000rpm, but then I wouldn't call the 8V a torque monster at low RPM either.

Compression is only a small factor of power production. Yes high cr will make it snappier and make more torque. But the "91 octane" out here won't support a very high static cr. So I'd want to make the most of what I can with the gas I have. Cr will give better mileage too, but that's not really a concern of mine. 944 vs 951 is 1mpg difference in epa mpg ratings.

By adjusting cam and ignition timing, my US spec 9.5:1 cr car is currently 3 HP shy (160vs163) of the 10.6:1 2.5L euro cars power rating, and I still have a catalyst installed when they didn't, and I can still adjust the cam a good bit more. And the car makes as much or more torque (165lbft) than the 2.7L 10.9:1 cr motor of 1989. This is cataloged with many successive dyno runs after each individual change versus factory stock setup.


If I build this kind of engine the cr would end up 8.5-9:1 or so, at 2.8-3.1 litres displacement, depending on some other factors. Yes, boost is planned down the road which plays into this... I could build an 11:1 3.0l 8v without much trouble but I'd have to run a100 octane/91 mix or e85 (which I'm OK doing but these fuels are pretty hard to come by reliably around here)... So pump 89/91 is more realistic.

Makes sense. I wouldn't have assumed that there was that much left on the table in terms of cam and ignition timing, but there's no arguing with the dyno. :D

I have seen other engine builds where the CR was the main thing changed and created significant power increases, but I guess that's not so much the case with the 944 engine, then.

Like I said up above.. From 1987 to 88 the 944cr was upped from 9.5-10.2 and they netted +5hp (147 to 152) while requiring 89/91 fuel.

Then from 88-89, they added another 0.7 cr (10.2 to 10.9) plus an extra 0.2l displacement and got 10-11 more HP (163 vs 152)

So cr does definitely make power but it's not as much as you might think. And the higher you keep going the less the returns you get. (Not linear)

How much ignition advance would you be able to get away with? With ****ty gas it's probably going to limit options, unless detonation isn't likely with the low compression.

dont see any need to go crazy with the ign advance, the factory maps and the NA-tune stuff is pretty good as-is. and there's a point at which (based on the individual engine's characteristics like bore size and chamber shape) there's no point advancing the spark beyond a certain point. when i have a good ign. profile set up that might be the time to switch over to the COP/EDIS setup and open the plugs up a bit

one thing to keep in mind is that even though this motor would be built with low static CR, the advanced cam timing would bump up the running CR a fair bit, so an 8:1 engine runs like an 8.5:1 or so.

i did just see there are a few more E85 stations near me than i had known about which is nice. but still...cranking out power on 89 octane would be cool by me.

A local friend (Dougs951S) with a 951 (also has Megasquirt) did a test a while back where he ran it as an NA just to see, and raced it against a stock 86 NA. He says it embarrassed the NA...

So with the right tuning it will probably work out - he had LSx COPs and a other significant mods too though. He has a lot of 951 maps...if you want to get a good tune going for a NA 951 motor, send a PM to Dougs951S on rennlist.

by "ran it as an NA" did he have all the NA manifolds or was he just driving a 951 set at 0 boost?

Hmmm, I have some 106mm JE pistons in 9.0:1 for 2.5L block. Would give you 2.8L displacement for low-end torque and still some immediate snappiness.

I was thinking of using it with Nikasil-coated bores to avoid sleeving. Two thin metal-layers are actually weaker than a single one of same thickness. Although I haven't had any issues with flanged chromoly sleeves.

ive got a 4" sleeved block already that i can take to 4.030 and fit with a stroker crank up to ~3.1L = any CR i want.
or an alusil-bore 2.8 taking a different block to 101mm w/ 3l crank = 8.4 cr or so :)

or an alusil-bore, high CR 3.0 with 2.7 pistons, short rods and a 3L crank...11:1 cr :)