The V8 Owners Forum -

On my never-ending RV8 spending (poet and i know it lol) I've found some Buick 300 heads. They are in generally good condition, but there are two issues with them. Firstly, they are not a matching pair; one is an early casting, the other a late casting - they are identical in terms of spec though. Water ways etc are all good with no corrosion.

Secondly the comdustion chambers are pitted, is this a problem, and if so, can it be fixed (and how much for) or could i get away without doing anything??

Olly

I think that you find it fairly normal for the chambers to be slightly pitted, mine were, and I just cleaned them up with a bit of fine grade wet & dry but not enough to increase the chamber size.

Do you have a picture of the chambers?

I'm still not sure why you want to go to the not insignificant cost of preparing these heads for a turbo engine, when your stage 3 heads would be fine and at most an upgrade on the exhaust valve would be all you'd need to do as it's more important to get the exhaust gasses out to drive the turbos.

What size valves are in the stage 3 heads?

Kevin.

Kevin,

Yeah there's not much on the internet about pitted combustion chambers, but from what i have read people just tidied them up like you suggested.

I do have some photos will sort them out in a bit.

The heads i have we modified to stage 3 apparently with TVR wasted stem large valves, other than that i am not sure without taking them off. They were done by you-know-who so everything is taken with a large dose of salt unfortunately.

As for why, well the way i see it, decent stage 4 heads are £1500, half that 2nd hand. Wildcat are out of the question, and Merlin have a silly long waiting list. For less than 1k i can buy and fully modify some buick 300 heads which flow better than all bar wildcat, then sell my stage 3 ones on.

I'm still waiting to hear back about the valve sizes on buick 300 heads and 3.5" bore. Looks like I'll be sticking with a 3.5 litre crank now anyway rather than the 5 litre, as apparantly that would send my C/R wat up past the 10:1 mark lol, not good!

Olly,

What pistons are you intending to use and what is the compression height, pin size and the volume of the bowl.

There is no point looking at components that will not work with each other, you need to have a stroke rod and piston combo that will work within the 3.5 block and give you the desired comp ratio.

The centreline of crank to deck height on all rover V8 engines is stated to be 8.96" so the dimensions are half the stroke + rod length + compression height of piston which is the dimension from the centre of the gudgeon pin to the top edge of the piston. and ideally you want those figure to add up to approx 20thou less than the 8.96"

The buick 300 heads have been used on 3.5 engines but they have mainly been the bigger 94mm bore with a short 63mm stroke to still achieve 3.5L Also ultra big valves do not work well in the smaller bore engine as they become very close to the cylinder walls.

Kevin.

Kevin, piston dish volume is 19cc.

As I said to Olly : for the same piston dish volume and the same combustion chamber volume, more you increase the stroke more you increase your CR. That why Omega pistons with 2.8'' stroke give an CR of 8:1 and with 3.510'' stroke an CR of +/-10.25-10.50 (according you use 37cc head combustion chamber and metallic head geaskets).
So if you intend to use 3.510'' stroke the only solution to have an suitable CR for turbo engine is to use Buick 300 heads with their 54cc head chamber volume.
Of course if you keep standard 2.8'' stroke crank, you don't need of Buick head. Rover heads with 37cc are ok.

There are several factors to determinate the good size for valve.

Valve size : square root of ((CV x RPM)/(Pi x GS X 90)).
CV = volume of one cylinder in Cubic inches
Pi = 3.142
GS = gas speed

Some GS figures for One port/valve head.
Full race : 230-240
Half race : 180-190
Road : 160-180

For N.A. engine : inlet to exhaust ratio 1-0.85.
With average boost pressures, 7-10lbs PSI, the inlet to exhaust ratio should go up about 0.05in on the previous figures.

Dimitri

I agree except I think you meant the more you increase the stroke the higher the compression ratio.

Kevin

LOLLLL , you are right. I confuse somethime word in english.

Please Olly don't .

More you increase stroke more you increase CR .

ok, I'm starting to get very annoyed because i'm getting confused all the time now. I started this project with the idea of getting a strong bottom end to turbocharge. I have zero knowledge of CR, stroke/bore ratios and all that shizzle. I've attempted to put plans on here, but evidently they aren't clear enough as I'm getting conflicting views, people giving me adivce one minute then saying i can't do something else because of this the next and that and so on and so on. I've been trying to look at all the options to give me the best combo/power for the money. I've got hold fo the major parts now for the short engine (except a crank) so i'm trying to determine head and camshaft/valvetrain suitability.

Ok. I am using 3.5 bore block, forged pistons with 19cc dish, steel rods, more than likely a 3.5 crank with 2.8" stroke because there seems to be too much hassle in using a 5litre crank.

I currently have stage 3 heads, comp gaskets. From what i can tell so far, if I use all my parts with the stage 3 heads and Metal gaskets, I'll get 8:1 CR and I'll have no issues with valve clearance with the pistons etc - is that right???

So, since it is possible to use Buick 300 heads on a 3.5litre 3.5" bore engine, can someone work out the compression ratio for me with metal head gaskets and also comp head gaskets so I can compare to the stage 3 heads??? Or at least tell me how to do it?

The whole point was I'm not going to just stick with the 6-8psi I'm running now, I want to run twice that, possibly more. Since it's a 3.5 now, it will rev more, so I am also trying to spec a cam to suit, potentially with roller rockers. arrrgh why is this so fecking hard


Also, what units are those valve sizes once the formula is worked out?? I'm basing a lot of my aims on the Le Mans TR7. The engine was a 3.6 litre, girdle, dry sump, and according to Dimitri used 1.7"/1.5" valves (i.e. ultra big/Buick size) for well over 500bhp. Can't be that hard to produce something along those lines given I have most of the engine parts, right?

Dimitri,

I think you do very well considering English is not your first langusge,

Would you agree that if Olly stays with the 2.8" stroke and bearing in mind the smaller bore, that he woulld be better off using his Stage 3 heads with an upgrade on the exhaust valve and having the throats futher opened up behind the exhaust valve heads?

He should easily achieve his optimum compression ratio and the rest is just a decent engine mangement system tailored to the boost he is going to run.

I think he has most of the parts to put together a very nice engine which will be very cost effective.

Kevin

Kev, what you said there about my stage 3 heads is the only other agreement with what Rob said at V8D. He said not necessarily best to run ultra big valve heads with massive ports on a turbo motor, but make the exhaust valve as big as possible to help things.

Theoretically I could run a 1.5" exhaust valve with the standard wasted stem inlet valves with minimal fuss I believe. Upgrade the springs to something meaty to match the roller rocker ratio of 1.75 and spec cam to suit that.

Roller rockers are a given now, they've been bought and I want rid of my Grp A stuff.

ok feeling a bit better about things now, still could do with knowing CR with the Bucik 300s just for comparison?

On a personal note, thanks for all the help with this I've learnt a fair bit (not that you'd notice ) hopefully on my way to 400bhp without nitrous with this build, that's the aim guys

Olly,

Buick 300 heads with 54cc chambers on a 3.5 engine with 19cc. dish pistons and tin gaskets will give 6.5/1 compression assuming the piston is approx 20 thou down the bore at TDC.

Get a price from V8 D to fit the 1.5" Ex. valves to your heads and machine the throats to match. The medium size inlets of 1.63" are probably what you have in the heads already and will be fine with a small bore engine.

Don't forget Torque that the important figure and how well it's maintained across the rev range, BHP is just a mathmatical calculation.



Kevin

CastleMGBV8 wrote:Dimitri,

I think you do very well considering English is not your first langusge,

All my aplogies again . I think it is better for me to stop to post rather than to say supidities in english .

Dimitri,

Don't stop posting, I'm sure we all enjoy your interesting contributions.

Kevin.

For my two pence worth I would have thought with a turbo engine there was an big advantage in having the larger part of the combustion chamber in the head as it will e with the buick 300 heads, as it gives you a bigger surface area to transfer heat to the cooling system. If you are going for big output I would start thinking seriously how you are going to get the heat out of this engine.
A 6.5 to 1 cr is quite low unless you are going for 25+ PSI.
On a high output forced induction motor inlet port flow gets to be very important as a more restrictive inlet port increases the heat of the inlet charge for a given boost pressure right where you can't do anything about it as it is after your intercooler. I think your aproach of 300 heads, although quite a bit more hassel than the stage 3 ones you have are a good route to go, they won't gain you much below 15 or so PSI but well worth it if you are going for more than that.
Mike

Wotland wrote:

CastleMGBV8 wrote:Dimitri,

I think you do very well considering English is not your first langusge,

All my aplogies again . I think it is better for me to stop to post rather than to say supidities in english .

Don't you dare Dimitri! You're one of the best contributors to this forum and the main contributor to my engine project, both via parts and advice!

I know torque is the thing to have, but i think that 400bhp is a good figure to aim for with a beefy 3.5, hopefully I should get that or near to it with 15psi. I should be getting over 300 with my current set up, i think the car can handle a bit more. I am planning to build on this engine in the future, water injection and the like, so who knows, but its fun finding out lol.