DCR. What to aim for?

[DangerousDerek]

I am putting together a tasty 5.0 Rover V8 for my TVR.

Most of the spec is set but before I decide on head gaskets and maybe a little further head work I was wondering where I should aim for dynamic compression ratio.

Spec
ACR top hat block
96mm forged pistons with 20cc bowls
Offset ground crank to 86mm
6 inch Chevy I beam rods
a solid 50304 crower cam. Inlet closes 47 ABDC.
Deck height is 7.5 thou
I have Elring gaskets which are 1.28mm but thicker MLS are an option.
The will be measured this Friday. I believe they are 28cc for now.

So looking for advice on DCR in order to aim for a suitable static CR.

The car is mostly used for drag racing but will be used on the road also.
I intend to never put less than Vpower in the tank.
I also plan a 2nd fuel system to run VP racing fuel when adding 150 shot of nitrous.

[DangerousDerek]

Pumaracing said:

DangerousDerek said:

a solid 50304 crower cam. Inlet closes 47 ABDC.

74 ABDC.

spec sheet saya 47



I am just trying to establish where i need to be CR wise guys.
All advice taken thankfully.

[DangerousDerek]

Stan Weiss said:

One is talking advertised duration 108 ICL and one is talking 0.050" lifter raise duration 104 ICL.

If you check the 0.050" numbers the ICL is @ 104. Which it also states on that sheet.

As far as DCR / CR what cranking compression / cycle pressure are you looking for?

Just a simulation -- Bore = 3.5" Stroke = 2.8" Rod = 5.66" CR = 10.5 DCR = 7.9 Cranking Compression 196 PSI

Stan

Then maybe i should rephrase the thread title... What cranking compression to aim for?
On a learning curve here. Help me out.

[DangerousDerek]

There are very few that would stick their necks out when it comes to nitrous in general.
Maybe i should not have mentioned it. I used to use 170 in a 2 stage that worked well but will be winding the substance abuse down on this build (I promise).
I was thinking to getting the static CR to around 11:1.
Any thoughts on that number i plucked out the air?

[DangerousDerek]

In a 1100kg TVR with a lightish flywheel (19lb) i think it should have acceptable enough road manners.
The aim is for a useable road car that can run 11's NA on the strip.

[DangerousDerek]

Measured the heads today and they were pretty much bang on 28cc as i suspected.
So ive calculated CR will be at 11.3:1

Check my maths
bore 96, stroke 86.3 = 624.66cc
piston bowls 20cc, top ringland 2cc, 7,5 thou deck clearance 1.38cc, gasket (1.28mm) 9.26cc, head chambers 28cc = 60.64cc

624.66 + 60.64 = 685.3 / 60.64 = 11.3

60 thou MLS gaskets would give me an extra 1.89cc which would drop the CR to 10.99

Decisions?
Any thoughts?

[DangerousDerek]

Pumaracing said:

Your top ringland volume is almost certainly wrong and should be close to zero anyway when the engine is hot as was discussed on here a while back. Your CR is 11.3 with the thicker gaskets by my calcs.

I must admit I thought less than 0.5cc for the top ring land but my engine guy said 2cc. Maybe another chat needed.
Now I am at 96mm bore maybe I have room to gain a cc or 2 from the chambers also.

[DangerousDerek]

Roland said the 2cc he listed for the top ring land was to include the valve cut outs which makes sense.
So I am at 11.3:1 with the Elrings.
I will take a little out of the chambers and remeasure but think I will be using 60 thou MLS gaskets and bring the CR down into the 10's.

[DangerousDerek]

I think I got 28 thou in the top with the piston pushed to one side.

After talks with Roland at ACR he has offered to build the motor free of labour charge for me. Then the engine will be run up and tuned on his dyno. It also looks like I will be swapping over to an Omex 710. The MS2 has served me well the last few years but I want the best reliability and performance I can afford at this stage.

[DangerousDerek]

We were talking about the clearance at the top of the piston to the bore. I saw 28 thou and 5 thou at the skirt.

Deck height does average 7.5 thou as Roland designed but there is still the issue with a slight tilt along the pin line on the nearside pistons. I can't figure it out so it's going back for a proper inspection.

[DangerousDerek]

Pumaracing said:

Are you talking about piston crown to top of bore or piston land to side of bore? You don't measure the piston land to side of bore with the piston in the engine. You measure the top land diameter with a micrometer or vernier.

Bore to bore. I know it was not measured properly. I was just commenting a crude dimension check I made to show the piston is probably specced to the figures you quoted in the previous post. I think it was 95.3.

Anyway all will be sorted soon I am sure when it's back in the hands of a professional and out of my clumsy mitts.

[DangerousDerek]

Pumaracing said:

If you could get the loan of a computer connected to the internet for a bit you could go onto something called Ebay that we have nowadays and buy a digital electronic 6" vernier for a tenner which would save you an inordinate amount of buggering about with feeler gauges.

http://www.ebay.co.uk/itm/6-150mm-Digital-LCD-Vern...

Don't buy the cheap five quid ones from China that only measure to 0.1mm You want 0.01mm resolution ideally. I paid 80 quid for my Mitutoyo back in the early 90s but they're pennies now.

Maybe I do deserve the attitude.
I have a vernier but it's knacked. Promise i will replace forthwith.

[DangerousDerek]

Just measured a piston with a digital vernier.
Skirt is 95.85 diameter and top ringland 95.0

Edited by DangerousDerek on Thursday 3rd September 20:45