Forged Setup Advice

FarnhamStag · Post by **FarnhamStag** » Thu Jul 16, 2015 8:54 pm

I have exactly the same issue as you on my 4.3, I planned around 8psi of boost with the Rotrex and got around 13psi on standard pistons (10:1) in a non cross bolted 3.5 block .. just made 440hp and torques at the Dyno yesterday but that was retarding the top end timing somewhat to keep things vaguely sensible....490 hp popped up once!
I just wish I had prepared for that first, but I just didn't expect that sort of power!
Dorian

Post by **Coops** » Thu Jul 16, 2015 9:29 pm

Hi Dorian.
glad to see im not the only one caught out with the rotrex setup giving more than asked for,

Whats your spec as that's good numbers

r2d2hp · Post by **r2d2hp** » Fri Jul 17, 2015 6:10 am

What size top and bottom pulleys are you guys using

Post by **Coops** » Fri Jul 17, 2015 6:31 am

Stock serp bottom pulley as per tvr and scpower use who supply the kits.

JP. · Post by **JP.** » Fri Jul 17, 2015 10:38 am

Coops wrote:JP don't want to sound rude,
but how does that help with parts needed to go forged setup which this post is about??????
had all this already like I said in other post,

Its even a lot for a forged setup. With these high final cr ratios you have to run it on very high octane rocket fuel.

You might consider lowering your cr to more sensible levels while going down the forged route.

Horsepower aint worth sh.t if the components aint up to it. Been there, done that & did cost me a lot of money.

kiwicar · Post by **kiwicar** » Fri Jul 17, 2015 1:18 pm

Hi
I am not sure of the maths being used here but 14 psi boost on an 11.5:1 cr is not an equivalent CR of 22.something :1 but closer to an equivalent 13.5:1 static CR. The pressure ratio of 14 psi boost is 1.95:1 and you add this to the compression ratio of the engine. This is still far to high, you still need to take into account when the inlet valve closes and the actual pressure ratio seen by the cylinder (not at the inlet manifold) is dependent on volumetric efficiency of the engine (ultimately the cylinder heads) but it isn't 22.something:1.
As for bottom end I would get a fresh brand new large journal block, not one second hand in any way, get it bored out for the thickest wall top hat liners you can persuade turner engineering to fit, get main caps like Perry's made up and fitted by a top line machine shop. Get a 1" thick aluminium bottom end brace made up and fitted to the block and main caps. rods need to be eagle 2.1 small block chevy with 7/16 ARP bolts or better bushed to take 3.7" ford mod pistons. Find a forged steel chrome molly crank blank, for a rover, get the mains turned down for the rover size, get the gig ends turned down for the 2.1" SBC big end size and to take SBC clevite bearings. your final choice of stroke and choice of rod length will be dictated by the deck height of the block and the piston compression height but I would start with pistons at zero deck, find the compression height of the pistons work on 6" rods to start with and from that work out the stroke, if the final displacement of this comes out at more than about 4.4 litres try again using 6.125" rods, work out the stroke from there and see if that works. The reason for doing it this way is that you will not get the right CR and squish band for a blown engine if you go to a higher displacement. I am assuming that you will be buying proper aftermarket heads with a modern combustion chamber (probably tomcat) and not wasting more time and money with ported rover castings. You want to have a static CR of 9.25:1 for what should end up with manifold boost of about 10-12psi. run an external high volume oil pump so you can run a second oil gallery just to spray oil inder the pistons, run a crank scraper. Convert to roller cam because when you have bolted this lot together you will need to stick it all on an engine dyno and select camshaft and it gets too expensive in flat tappets to do it any other way.
It is obvious to me this is not the original Paxton blower you had a few years ago as that would never have sustained 14 psi. And that this new one was intended for an engine of over 5 litres and heads that flowed over 220 cu ft/min.
If you think this sounds too complicated too expensive and too much maths for you I would unload the blower on ebay and find a blower of a better match like the one Reg has.
It would be a mistake to "pick and choose" from the list above because to get the engine to last any time you need the whole lot as a package. you will need to strip and inspect it annually. By the way I recon your bill by the end of all this will be the far side of £12k as you will probably be in for about 80 hours on the engine dyno just sorting out cams, blower pulleys and fuel/ignition maps. You will need a better gearbox. Personally for that money I would buy a crate LS3 and an electronic auto get a 7 speed controller and have a warranty with it. But you have said you don't want the hassel

You asked for input so here it is
I don't really have anything else I wish to add.
Best regards
Mike

JP. · Post by **JP.** » Fri Jul 17, 2015 2:39 pm

kiwicar wrote:Hi
I am not sure of the maths being used here but 14 psi boost on an 11.5:1 cr is not an equivalent CR of 22.something :

The formula for calculating your exact final compression ratio is as follows:
Final Compression Ratio (FCR) = [ (Boost÷14.7) + 1 ] x CR

Source : http://www.blowerdriveservice.com/technical-charts.html

Ever considered a custom made drive pulley to slow that blower down. UKblowers can make those as he did for mine ( blower drive & custom made V groove pulleys).

Post by **Coops** » Fri Jul 17, 2015 4:30 pm

Cheers Mike,
after reading that essay I think its time to sell up as yes as you said I will not be able to afford that little lot,
seems a lot of money for an occasional RWYB car and road car,
I will start working out what all my parts are now worth when the block comes back from V8D as just about had enough of it all,

Also anybody want to take over the forum and its domain???, as may also chuck that in too that's how fed up I am.......

kiwicar · Post by **kiwicar** » Fri Jul 17, 2015 4:32 pm

Hi
Ratio (FCR) = [ (Boost÷14.7) + 1 ] x CR
is wrong it should be
FCR = ((boost/14.7)+1)+CR
the chart is silly it effectively says you cant run a bar of boost with a CR above 6.5:1, this is plainly not the case (ask any Scooby owner!) you can run a bar of boost with 9:1 CR easily and many engines run 2 bar of boost which by the logic of the chart would require a CR or 4.2:1 such an engine would not run because the fuel would not disassociate. A basic principle when cascading ratios is that you add them that is why people like them.
best regards
Mike

kiwicar · Post by **kiwicar** » Fri Jul 17, 2015 5:10 pm

Hi Tony
I am afraid the reality of life is that "power costs money how big is your wallet" what your current blower set up says is "I want 620 to 680 bhp, your base engine, displacement, state of tune and cam spec says base engine of about 320 bhp and you have shoved a bar of boost on top, therefor your spec is for an engine producing about 650bhp give or take. That means a bottom end that will take around 700 bhp (remember the blower takes power out of the engine to drive it but the bottom end still has to hold together with the blower power going through it. Look at the bottom end of Perry's motor, and that was running around 580 to 620 through it and the crank failed when starved of oil for about 1/5th of a second you want 80 bhp more, well for that you need to build a bottom end that will take it! You also need a valve train and heads that will flow enough air to handle it, otherwise you just create pressure and heat in the inlet and overload the supercharger.
If you came down to 6 to 8 psi boost then it is a different game, a stock rover block with ported rover heads will work, I beam forged small journal chevy rods are fine at £220+£100 machining a set you cn use 305 pistons in a bored out block, cast rover crank is fine, cam choice is less fussy and flat tappet is fine the list goes on, 420 to 430 real solid bhp at the wheels is yours for a reasonable budget.
I know what a 700 bhp motor costs, in my case about 14.5k so far and I recon that is cheap, the money goes into the development and the fact at that level of tune you can have no compromises, everything has to match everything else one week spot and the power finds it.
If I were you I would put together a speck around a 430bhp motor, stock crank stock block bored to 3.736" chevy forged pistons and chevy small journal rods and get pressure map for the blower and reduce the drive ratio down so you get 7 or 8 psi, it may cost a couple of hundred quid in custom pulleys but it is cheaper than 8k in bottom end development.
The guys who help me when I race know how often I feel like chucking it all in, I would strongly advise not doing so as in the long run the hobby is too much fun, just compromise on your spec a bit, 650bhp in just over a ton of car is a lot to handle, you would have to have a very good cage in with you otherwise the shell would unstitch itself in about 2 seasons, think it through. . .
best regards
Mike

bigaldart · Post by **bigaldart** » Fri Jul 17, 2015 6:19 pm

Tony,

I have to second what Mike said, not sure of the spec for your blower as it's Rootes style blowers I am familiar with. It is purely a matter of matching things up and you will be pleasantly surprised at the results. We went through a lot of parts to get a combination that survives what we do to it. But the information is all available. tbh we only went to forged pistons because we couldn't get any more Volvo ones and we never broke one of them. We did melt plenty especially when trying an alky carb set up

The volvo pistons are cast but incredibly strong. The Rover pistons are among the weakest I have ever seen. Take a step back, come up with a plan and you have much more success with the Capri in the future. Best wishes mate and anything you need to know just ask, I will get back to you as soon as I can.

Alan

mgbv8 · Post by **mgbv8** » Fri Jul 17, 2015 7:30 pm

Coops!
I agree with Mike and Big Al mate. Sometimes less is more as they say ??

You have the bare bones of what could be a great motor for the cappa on boost. I've been through the mill on nitrous and now boost + nitrous. I have worked my poop out on the safe side all the way with lowering CR and keeping timing knocked back as I still run pump gas from the local BP or Shell garage. I know the MGB is a track slag and not road car. But the Rover V8 I now have does the business as long as I dont pull the front wheels 5 feet in the air on a stock oiling system

FFS sake dont go throwing in the towel Dude! We have all been there many times during a race season. When I knacked my crank last September it was MY FAULT. I should have had the wheelie bars fitted and I didnt. I beat myself up over it for a while and then covered the car and ignored it for 3 months until my head was in the right place to get back on the horse and see what was required. My choice was simple. Rebuild the Rover to original or better spec and then fit wheelie bars. That would give me safer running at low 9's on track. But I want 8's now so the best thing for me is to still rebuild the Rover to a slightly better spec and sell it to fund the SBC engine which when its done should almost run the mid 9's or at least sub 10's nasp. Then i can add nitrous and eventually boost when I can afford an 8/71 blower.. Which may not happen before I hit 60 in a few years time

Sorry for rambling dude!! I wont be much longer in spitting out my thoughts

To be honest I am somewhat embarrassed about how much money I have put into the Rover over the last 4 years to get it to where it is now. This was simply me being pig headed about keeping a Rover V8 in the MGB because it left the factory with a Rover V8 in it. That has cost me a lot of money. But hey! I did what I wanted to do Coops. I built a Rover V8 that runs mid 9's in my MGB all day long. And that is something I'm proud of. And I was faced with a big dilemma about continuing with the Rover because after checking data logs we could see that the Rover was driving through the converter and losing me shed loads of power. Step in uncle Mike with a 4000-5000 stall converter to bolt in so we could get the best from the engine at launch with a converter that would not slip on me. And thats when the big wheelie happened. Its all history now mate.

I woke up eventually to realise that I had put more money into developing the tweaked 3.9 got get 600hp than my mate spent on his 1000hp crate big block for his Capri which runs mid 8's like Mike rail all day long? So the Rover is going up for sale and I'm fitting the SBC now because I want more as always.....

What you need to do is decide what you want from the Cappa in the next 2 years. And with your engine control setup you no doubt have the choice to dial in a Road map and a 1/4 mile map to control boost, fuel and ign. So either build and tune for Drag Racing with a knocked back map to say 300hp for road use. Or just build for your existing 400hp for the road and see how she does on the 1/4 mile. ?

Ramble over mate... Just my thoughts

Pel x

DaviesDJ · Post by **DaviesDJ** » Fri Jul 17, 2015 9:24 pm

Coops mate - going to give you some tough love!

Pretty much all of us at the moment have been on our arse!! Some financially - some physically - and some emotionally! I am not going to list anybody at all.

A grass roots racer is not just somebody who shows and shines, or buys parts as you know. It's about the package- and the package involves destroying parts once in a while. If a broken piston puts you off then it was never meant to be, but we all know you will be back!:-)

There are lots of options open to you! Just be sensible and don't go off on tangents about sequential ignition and ceramic coated headers and you will be back stronger than ever.

And don't throw away comments like "I'm giving up; I'm giving up the forum etc" without thinking first - it does you discredit. Think for a few days before posting things like that.

All the best

mgbv8 · Post by **mgbv8** » Fri Jul 17, 2015 9:38 pm

DaviesDJ wrote:Coops mate - going to give you some tough love!

Pretty much all of us at the moment have been on our arse!! Some financially - some physically - and some emotionally! I am not going to list anybody at all.

A grass roots racer is not just somebody who shows and shines, or buys parts as you know. It's about the package- and the package involves destroying parts once in a while. If a broken piston puts you off then it was never meant to be, but we all know you will be back!:-)

There are lots of options open to you! Just be sensible and don't go off on tangents about sequential ignition and ceramic coated headers and you will be back stronger than ever.

And don't throw away comments like "I'm giving up; I'm giving up the forum etc" without thinking first - it does you discredit. Think for a few days before posting things like that.

All the best

Post by **Coops** » Fri Jul 17, 2015 9:40 pm

I know what your saying mate but your not the one who has been at the end of constant abuse and snide remarks via PM on facebook
and im afraid to say it, a couple of them were members from this exact forum, (note WERE)
I was not going to say anything about the remarks but It getting beyond a joke now and really pissing me off,
now can you see why im at my end with it all, im trying to get an engine sorted, (would of been done a year ago if the parts shop had started) then get poop thrown at me, if it discredits me then so be it, the persons sending me comments on facebook should also realise what its doing, f***** good confidence builder, and I thought they were classed as friends how wrong I was,

And yes the forum domain is up for renewal soon if it carries yes I will step down, and call it quits, as don't real deserve it,
I have no one local to me who I can pop round to and go have little issue need some advice, hence why mistakes have been made yes expensive ones, like others have made but to keep getting it thrown at me is now wearing thin,
Lets see what turns up once the block has been looked at as that could be the deciding factor.........