Compression ratio advise

There are other factors so it might help if you said what make and model the engine is.

You also need to take into account volumetric efficiency.

A 1 litre engine that only manages to draw in .3l of air can run a higher compression ratio than one that manages to draw in .5l of air. Obviously you can avoid detonation by altering ignition timing or adding a second head gasket to drop compression.

Also, what engine is it? I'm guessing it'd be a yank V8 as it'd be pretty horrific as a 4 cylinder and I can't think of any 6l straight sixes.

No, super is 97. Only the "special" fuels are higher octane, such as Optimax, v-max, Tesco, etc.

Things like fuel injection, electronic ignition and 3d mapable engine management can alter all this, and produce an engine that is high performance on 95ron but just as drivable around town as a super mini.

If you do it right, the days of non idling lumpy cammed monster carbed enines that would stall unless you stood on it from every dead stop are gone, unless you actually want that to happen and deliberatly build that way.

Thanks Doki. Sorry, I can't be specific here 'cos I don't know! It's going to breath pretty well though when I'm finished and be fitted with a 'warm' cam.

Obviously you

I've got the chance to get this right initially and with a combination of bits I can have just about and comp ratio I want off the shelf. If I can avoid having to do remedial work later then that would be great. I'm more interested in people's practical experiences here. One job Johnies and armchair internet experts need not apply!

The basic block is Mopar 440cid. But that's the only stock part, it's to be stroked to 500 or 512cid.

Julian

95 is normal, 97 is super, BP ultimate is 98 IIRC and Tesco's best fuel and Shell V-Power are 99. I glanced through a test in one of the comics and they reckoned that V-power was the best, testing by how far they could swing the timing on a Cosworth BDA. Didn't buy it as I'm not a Ford man.

Bah. Having built a grand total of zero engines, I'd say I'm not sure. But I can tell you that MK2 Golf GTIs run compression around 10:1 and do specify

98RON petrol as being required.

Abo might be the bloke to speak to then. He's likely to know people who know a bit about these engines in SCSA cars. I reckon the major problem you'll have is that a lot of the sites with data on the engine will be american and therefore a bit prone to bullshit and having funny ideas.

Mate, you've hit the nail on the head here, far too much BS, and at a guess American fuel won't easily compare to ours. Who's Abo? I just wondered if any serious or professional engine builders post on this (or any other) news group. Alt hi-po Mopars is very quite and mostly USA.

I've got a figure of 9.5:1 in mind, but that's based on one book and Google! We all know that a good 50% of stuff on 'tinternet is unreliable!

Julian.

Aye. I remember the Ultima in CCC which had an all singing all dancing engine from the US and was supposed to make 600 horsepower, but it turned out that the yanks had applied all sorts of funny fudge factor, IIRC "correcting" for internal engine friction from the figures among other things.

As for American fuel, they measure octane differently. How are you intending to get your air and fuel into the engine by the way? Airspeed will be very low at tickover on an engine that huge...

Bloke who posts here and helps out with a pick up team, who race at rockingham with the SCSA stuff (NASCAR alikes).

There's Dave Baker, but he's a) pretty infrequent and b) doesn't much like giving out free advice.

A quick glance at American Speed's website suggests CRs in the range of 10.5 to 11:1, and that compression ratio should be considered along with cam choice (hotter cam can handle higher CR, milder cam needs lower). I'd be tempted to go for 10.5 or 10:1 and skim a bit off if I wasn't happy. OTOH are you near a university? Most will give library access and lend books to non-students, and tend to have a pretty good selection.

My SD1 Rover has a compression of 9.75:1 and is fine on 97 octane, pinking wise. And it's a pretty low tech engine.

I've been running the Celsior on 95 (10:1). Has been fine with whizzy fuel injection, but since it got colder it has been sucking it down. Lex club guys suggested super might give better economy so I'm trying it for a couple of weeks.

I've rebuilt a few Chevy's and Ford 351C & 302 Windor

It really depends on the whole package & intended use, ie street, drag, track.

Most Chevy's dropped CR from 10-11 in the 70's down as low as 7.8 IIRC in the 400 . My '95 Camaro is about 10.8 with ally heads.

If it's for the street, keep it lower. If your racing 12-13 not unusual, and i've read of motors running 15+ on alcohol.

I'd suggest the usual advise if you've not built much before, copy something similar built by somebody else.

Chevy's motors and I suspect Mopar are similar have a large range of heads available with vastly different characteristics, so it depends on what your using.

Also a higher winding motor will have a bigger cam and can bleed off compression.

A street motor would be OK between 9 & 10.5. If you are using computer ignition and Electronic Fuel Injection running nearer 11 shouldn't be a problem.

HTH

. How are you intending

I haven't firmed up the details but probably something like a 750 or 950 cfm Holley and dual plane manifold. The idle has a bit of a 'lope' to it with anything bigger than stock cam, but I'ts easy enough to live with.

I'd be

I'm actually starting to think along these lines too. 10:1 is doable with alloy heads and a 'warm' cam.

Julian.

How does it get on with regular (95RON) unleaded?

Thanks, that's a big help. I've almost decided on around 10:1

The last Mopar big blocks (like the Chevys) that fell foul of the emission regs had low compressions and very poor outputs compared with (say) the earlier Max Wedge and Hemi engines. I want power and torque for street use without having to buy toluene or octane booster etc :-( As I see it, more compression = free power, but if you have to start retarding the timing then the process is self defeating!

Julian.

Egads man. Fuel inject it. It'll cost the same, use less juice and if you get a decent ECU you can even swap maps in case you can't get 98 RON and need to retard the timing.

Accompanied by the sound of a chisel on slate Doki, managed to produce the following words of wisdom

I put a 750 cfm Edelbrock on the Jensen lump and it was fine. Ok, not exactly fuel efficient - a 7.2 V8 isn't likely to be, but easy peasy to set up.

The carb, new, cost around £300.

Accompanied by the sound of a chisel on slate Pete M, managed to produce the following words of wisdom

As I've just dug a bit deeper into this post and discovered the OP is using the same engine, a 440 Mopar, all I can say is that the 750 Edelbrock is more than enough for almost anything you'll be using on the road. The Jensen I fitted one to has a well-tuned motor, non-standard cam, breathed on heads (standard headers), and a few other bits and the 750 was still on the "rich" side of things.

As the Jensen is doing a happy 360 bhp @ wheels with oodles of torque (it's on its second gearbox rebuild) I'm just interested as to what you're planning on putting a 500 cube motor into.

Also Jensen. That sounds a highish figure for the spec, I don't think the Interceptor SP with the 6 pack engine (over 1000cfm) made that much power, but I'll not argue!

I'm actually looking at a 512cid motor. But keeping it quite lazy for longevity and torque, so say about 500(ish)bhp/ftlbs. Gearboxes ain't a problem. The standard torqueflite box can handle over 900bhp with some mods, (and with lightened parts too) mine is being rebuilt as we speak by a Mopar transmission drag specialist, but due to age related internal seal problems. The diff is a bit of an unknown though, but there's only one way to find out :-) Hopefully I'll have the block next week so I can order bits when I've checked it over.

With the exchange rate as it is there's no better time to get cracking!

Julian.

Accompanied by the sound of a chisel on slate Julian, managed to produce the following words of wisdom

The 6 pack SP produced 330 bhp at the flywheel, but I don't know exactly what's been done to this one, when the Edelbrock was first fitted I had a few issues with jetting and advance curves so I took it to the local rolling road place where the 360 (well, 357) bhp figure was produced. I was more than a bit surprised at this as it doesn't feel /quite/ that powerful. The Jensen does appear to have had a huge amount of money spent on it at some time, most of the traditional Interceptor III mods have been done and the radiator is possibly the largest I've ever seen with two rather huge fans.

This one managed to turn most of its roller bearings into square section lumps of steel last time it killed it.

Indeed.