The V8 Owners Forum -

Ah yes, just saw your additional info... the spreadsheet would be good ta. I'll pm my email add now, thanks.

Fitted the new rods/jets over the weekend, only managed to get out for a very short drive but it's clearly running a lot better now, the low speed hesitation/driveability with re-accel is virtually gone (thinking the remaining hesitation could be the vac advance - still yet to find time to look at the ign timing/adv etc yet).

Fitted the 86 primaries, 83 secondaries, 67-55 rods (Jim didn't have any 68-52 rods and wanted to at least get a bit closer to a decent set-up in the short term) and silver springs... basically the 3.5l set-up as a going in point.

Next step is the timing and we'll go from there!

mk1storm wrote:Fitted the new rods/jets over the weekend, only managed to get out for a very short drive but it's clearly running a lot better now, the low speed hesitation/driveability with re-accel is virtually gone (thinking the remaining hesitation could be the vac advance - still yet to find time to look at the ign timing/adv etc yet).

Fitted the 86 primaries, 83 secondaries, 67-55 rods (Jim didn't have any 68-52 rods and wanted to at least get a bit closer to a decent set-up in the short term) and silver springs... basically the 3.5l set-up as a going in point.

Next step is the timing and we'll go from there!

Cheers for the update!

Like you said the 3.5 setup is better than what you had before but it may well a little too rich on cruise and a lttle too lean during medium to hard acceleration. (Not so lean as to do any harm but if it is lean it won't pull as hard as it could do!).

Your hesitation could be that the pilots need tweaking, I've had good results just doing this by 'ear'

If the the hesitation is at fairly high revs where all of the mechanical advance is in and it happens just as you crack the throttle open (so there is a lot of vacuum) then it will be due to the vac canister dumping in a load more timing on top of the all ready in mechanical timing.

I've not had chance to test a 3.9 yet with regards to jetting as we still have not built the engine for my mate (We are waiting for the heads to come back from machining). I'll post up the jet and rod combo that we settle on once we have sorted it out. (Don't hold your breath though!)

I would still quite like to get the 68-52 rods, initially just to try out myself, but ultimately to have them available should I get a RR session sorted as I’m sure this rod combo with the 86 primary jets would be one to test.

Yeah would be good to hear about what rods/jets you end up with on that 3.9. What’s the rest of the spec of the engine out of interest (cam etc)?

mk1storm wrote:I would still quite like to get the 68-52 rods, initially just to try out myself, but ultimately to have them available should I get a RR session sorted as I’m sure this rod combo with the 86 primary jets would be one to test.

Yeah would be good to hear about what rods/jets you end up with on that 3.9. What’s the rest of the spec of the engine out of interest (cam etc)?

The 3.9 that we are building is based round a nice short motor that we got from V8Dev, its running Arp main studs.

We've buretted the pistons in the block along with the heads, 50 thou is now comming off the heads in order to run a CR of 10:1. (The heads must have already had around 20 thou off them earlier in their life). They are 14 bolt jobbies. The pistons may well need eye-browse cutting into them to give some valve clearance.

The heads have been gas flowed by V8 Dev but they were actually purchased from RPI. RPI call them stage 1, they only do stage 1 and stage 3. I think really any other tuner would call them stage II as they have had a lot more done over and above say a clean up and a 3 angle seat cut. The valves are standard size but with the wasted stems.
The springs are V8 Dev dual jobbies.
The cam is V8Dev's MC1 held in place with a cam plate, the timing gears and chain are Cloyes. The followers are Crane 'high rev' and the pushrods are adjustables with the smaller lower ball end fitted. The pushrods all need to be shortened by 2.5mm. We will run 20-25 thou pre-load.
Other stuff includes a 1mm skim off the rocker pedestal bosses to improve the valve train geometry, a 0.5mm skim off the inlet faces of the heads so that the manifold will fit. The thinner comp head gaskets will be used along with 10 Arp studs per head.
The inlet will be the Eddy Performer 180 with and Eddy 500 sat on top.
The front cover will be SD1 along with a cam driven oil pump.
I can't remember what the dizzy is but its electronic at least. (not points!). we will run 12-14 static, around 32 all in at 2700-3000 RPM with the vac system not fitted at all.

The rockershafts are new and Muscle Manta made up a decent set of rockers from ones that he had in a box! (We were going to use the ones off the 3.5 lump that the 3.9 lump will be replacing but the rockers were a bit worn and the shafts were bent!) RPI state that you can not use old rockers on new shafts and do give a reason explanation why but that's what we've done anyway!

The headers are from Pilgrim (the kit car manufacturer), they are not great but they will have to do for the mo. Hopefully the lump will push out 230 BHP with out having to be revved too hard.

Sounds like a nice build.

I'm not really sure what my exact spec is in terms of compression ratio etc. The engine is an early 3.9 conversion - the block is actually an SD1 3.5. Was converted to 3.9 by JE. Got 93.5mm Omega pistons in it with the 'eyebrow' recessess. The heads are 14bolt ones, but not sure how much has been taken off them. I did strip the engine down, but never checked the volume etc. It was running OK-ish when I first got it so didn't think at the time to mess about with it too much.

Knowing what (little more ) I know now I think I'd have investigated a bit more before rebuilding... Is there a way to check the CR without removing the heads? Will a compression test actually give you the CR or is it more a function of how well your piston rings, valves etc seal as well?

Hi
A compression test will not give anything more than a "relative" number, the result of such a test is as heavily dependent on the cam as it is on the volume of the combustion chamber. Have you checked to see of those pistons are cast or forged? just if they are forge then you have alot more posabilities in front of you tuning wise.
Best regards
Mike

Just a very quick update - Got the 68-55 rods off Jim, fitted and short test drive done, the car has now lost it's hesitation and generally seems to drive pretty well considering I've still not found the time to sort the ign timing/advance etc yet... That's the next mod to do.

A bit of a long delay before another update but got to check the ign advance this weekend.

I had the static at 12deg with about 750rpm idle, I then measured 25deg at 2000rpm and 30deg at 3000rpm (all with vac advance disconnected).

Didn't want to rev the engine higher in the garage, the neighbours will probably have got a bit pi55ed off but I guess it was high enough engine speed to prove that my advance needs tweaking.

According to the general advice on here I should be looking for around 32deg by around 2700-3000rpm. Sounds like my next step is to buy the advance spring kit from Real Steel....

Jaycar - and probably others - do a programmable ignition unit which allows you to make up the ideal curve for your engine. Normally with the dizzy advance locked - but it could be used to add/subtract with it still in operation.

Mechanical advance is extremely crude and was rarely the ideal even when new as there are limits to the shape of the curve it can achieve. Let alone on a 25 year old dizzy.

Cheers for the info Dave. Yes I may well give in and go down the programmable ignition route at some point but for the short term I just want to do a few fiddles to get it running 'relatively' well so I can just get out and enjoy the car. So far all I've done is swap the rods/jets with the advice from sidecar and it's already running miles better than I had it running initially.

I may give you guys a shout nearer the time regarding the best way for me to use programmable ignition, I have no experience whatsoever of setting one of these systems up, but I do like the idea of easily being able to play around with the timing.

Thanks.

Update for you....

Managed to get hold of a near new Mallory with Unilite conversion for a very good price off someone I know so now heading down this route.... Decided if possible I'd still like to keep the vac advance for mpg, but also for pick-up and not sure I could have done that with the Lucas (athough I appreciate from the comments that the differences without vac and the lucas set-up well might have been quite small).
So far just bolted it in and checked it fired up OK, which is did straight away... so roll on the better weather when I can spend a bit more time having a play with it

Mike - In a very very late reply to your question..... the Omega's are cast ones unfortunately so not forged but I understand that they're still supposed to be quite nice.